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Restoration of Damaged Peatlands - Biblioteca digital de CIREN

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Department <strong>of</strong> the Environment<strong>Restoration</strong> <strong>of</strong> <strong>Damaged</strong><strong>Peatlands</strong>


DEPARTMENT OF THE ENVIRONMENT<strong>Restoration</strong> oC <strong>Damaged</strong> <strong>Peatlands</strong>with particular reference to lowland raised bogs affected by peat extractionB. D. Wheeler and S. C. ShawUniversity o/SlteffieldLONDON: HMSO


© Crown copyright 1995Applicationsfor reproduction should be ma<strong>de</strong> to HMSOFirst published 1995ISBN 011 7529788Enquiries relating to this publication should be addressed to:Minerals DivisionDepartment <strong>of</strong>the Environment2 Marsham StreetLondonSWIP 3EBorEnvironmental Consultancy, University <strong>of</strong>Sheffield (ECUS)343 Fulwood RoadSheffieldSlO 3BQMain cover photograph: Solway Moss (Cumbria). [Air Images, Haltwistle, Northumberland(Tel: 034-320798), courtesy <strong>of</strong>B. Hen<strong>de</strong>rson & I. Richardson]Back caver, insets: Milled peat harvesting and revegetating block-peat cuttings at Thorne Waste(S. Yorkshire) [P.C. Roworth, ARPS]Photographs and figures presented in the report are by B.D. Wheeler or S.C. Shaw, unless otherwiseindicated.


AcknowledgementsThis report has been prepared by B.D. Wheeler (Department <strong>of</strong> Animal and Plant Sciences, University <strong>of</strong> Sheffield(APS» and S.C. Shaw (Environmental Consultancy, University <strong>of</strong> Sheffield (ECUS», based partly on contributionsfrom:T.R. BirkheadP. BradleyG. FosterA.L. HeathwaiteMiss L. BinnieMr D.M. Ellis(APS)(ECUS)(Balfour-Browne Club)(Department <strong>of</strong><strong>de</strong>ography,University <strong>of</strong>Sheffield)R.P. MoneyD.LJ. QuickeC. RouthR. Tratt(APS)(Imperial College, London)(ECUS) (Nominated Officer)(APS)With further assistance from: H. Morris, R. Houghton and J Clay (ECUS); R. Walker (Aca<strong>de</strong>rnic ComputingServices, University <strong>of</strong>Sheffield); S.Ball (Department <strong>of</strong>Law, University <strong>of</strong> Sheffield).The research was fun<strong>de</strong>d by the Department <strong>of</strong>the Environment (Minerals Division). We would particularly like tothank the nominated <strong>of</strong>ficer for this project, Dr Tom Simpson and Miss Ann Ward (Chair <strong>of</strong> the SteeringCornmittee) for consi<strong>de</strong>rable guidance and helpful comments throughout the duration <strong>of</strong>this project.We would like to express our thanks to all those people who have facilitated the progress <strong>of</strong> the project, in particularmembers <strong>of</strong>the project steering committee for helpful comments and advice on the draft project reports:Miss A. Ward (Minerals Division, DoE) Dr M. Meharg (Countrysi<strong>de</strong> and Wildlife Branch,Dr T. Simpson (Minerals Division, DoE) DoE (NI))Mr R. Sykes (Secretary) (DoE) Dr 1. Miles (The Scottish Office)Mr C. Bain (Royal Society for the Protection Dr T. Parr (Directorate <strong>of</strong> Rural Affairs)<strong>of</strong>Birds)Mr R.A. Robertson (Consultant to Peat ProducersDr W. FojtMrP. GordonMr S. GorrnanMrs J. HeapMr P. ImmirziMr R.A. Lindsay(Cumbria County Council)Association)(Doncaster Metropolitan Borough Dr 1. Smart (Plantlife)Council) Mr R. Stockdale (Peat Producers Association)(English Nature) Dr A. Stott (Directorate <strong>of</strong>Rural Affairs)(Cumbria County Council) Mr D. Stroud (Joint Nature Conservation(Cumbria County Council)Committee)(English Nature) Mr S.F. Shorthose (Humbersi<strong>de</strong> County Council)(Scottish Natural Heritage) Dr A.R.D. Taylor (Somerset County Council)(Scottish Natural Heritage) Dr c.P. Turner (Sinclair Horticulture & LeisureLtd)We are grateful to the staff <strong>of</strong> the Joint Nature Conservation Committee, English Nature, Countrysi<strong>de</strong> Council forWales, Scottish Natural Heritage, Countrysi<strong>de</strong> and Wildlife Branch <strong>of</strong> DOE-NI, and local Wildlife Trusts forwillingly providing inforrnation for the project and allowing access to unpublished <strong>de</strong>tails <strong>of</strong> sites, and especially tothose who gave up their time to sho~ us round sites and discuss the issues involved in restoration initiatives.Wewould Iike to thank all those who have found the time to comment on the draft reports, answer queries andprovi<strong>de</strong> inforrnative discussion and advice. We particularly thank 1. Blackie, 1. Bromley and M. Robinson (Institute<strong>of</strong>Hydrology), M. Cox (Gifford & Partners), H.A.P. Ingram (University <strong>of</strong>Dun<strong>de</strong>e), M.C.F. Proctor (University <strong>of</strong>Exeter), 1. Richardson (Richardson's Moss Litter Company), C.E. Wright (DoE), D. Wynne (Bord na Mona).We would Iike to thank colleagues in The Netherlands and Germany, who gave up their time to show us restorationsites and stimulated much thought and discussion; in particular, J. Schouwenaars, 1. Blankenburg, H. Kuntze, B.Bolscher and D. Maas. We are similarly grateful to 1. Feehan, G. O'Donovan, D. Wynne, 1. Ryan and C. Douglasfor providing inforrnation and showing us around sites in Ireland.We are particularly grateful to Dr Jos Schouwenaars (University <strong>of</strong> Groningen) and Dr Hans Joosten (StateUniversity <strong>of</strong>Utrecht) for many valuable insights and comm'ents on the draft project documents.We would also like to thank all those who kindly provi<strong>de</strong>d photographs for inclusion in the reporto


ContentsAcknowledgementsContentsSurnmaryBackground...111vXVIIXXXVPART l. ECOLOGICAL CHARACTERISTICS OF LOWLAND PEATLANDS USED FORPEAT EXTRACTION1. Lowland peatlands1.1 <strong>Peatlands</strong>: fens and bogs1.2 Origin and <strong>de</strong>velopment <strong>of</strong> peatlands1.3 Types <strong>of</strong>fens and bogs1.4 Some features <strong>of</strong> raised bogs1.5 Occurrence <strong>of</strong> raised bogs1.6 Current condition <strong>of</strong>British raised bogs1.7 Hydrology and morphology <strong>of</strong> raised bogs1.7.1 lntroduction1.7.2 The diplotelmic mire1.7.3 The water balance <strong>of</strong> a raised bog1.7.4 The shape and size <strong>of</strong>raised bogs1.8 Peat pr<strong>of</strong>iles and types <strong>of</strong> peat1.9 The vegetation <strong>of</strong>British raised bogs1.9.1 Plant species and vegetation-types1.9.2 Reproduction and spread <strong>of</strong>bog plant species1.9.3 Characteristics <strong>of</strong>bog plant species1.9.4 Habitat conditions and vegetation <strong>of</strong>raised bogsMicrotopography and water levelspH and base-richnessProductivity and nutrient availabilityAtmospheric pollution1.10 The invertebrates <strong>of</strong> raised bogs1.11 The birds <strong>of</strong> raised bogs1.12 Non-avian vertebrates <strong>of</strong> raised bogs1.13 Archaeology, palaeoecology and restoration1122681112121213141417172223232323252526282929


VIRESTORATlON OF DAMAGED PEATLANDS2. Characteristics <strong>of</strong>cut-over raised bogs 312.1 Introduction 312.2 Effects <strong>of</strong> peat extraction on bog rernnants and refugia 322.2.1 Introduction 322.2.2 Hydrological effects 32Introduction 32Effects <strong>of</strong>drainage upon chemical characteristics 34Effects <strong>of</strong>drainage on bog vegetation 34Effects <strong>of</strong>drainage on bog invertebrates and birds 352.2.3 Habitat fragmentation 36Introduction 36Size <strong>of</strong>remnants 36Shape <strong>of</strong>remnants 372.3 Peat extraction rnethods and habitat conditions 372.3.1 Peat extraction and residual topography 37Block cutting 38Milling (or rotavation) 39Extrusion ('Sausage') peat production 40Other production methods 412.3.2 The hydrological environment <strong>of</strong>cut-over bogs 41Water storage characteristics <strong>of</strong>residual peats 42Peat thickness and vertical water loss 422.3.3 The chemical environment <strong>of</strong>cut-over bogs 42Mineralisation 43Exposure <strong>of</strong>fen peat or un<strong>de</strong>rIying mineral ground 43Run<strong>of</strong>ffrom the surrounding catchment 442.3.4 The physical environment <strong>of</strong>cut-over bogs 442.3.5 The vegetation <strong>of</strong>cut-over bogs 442.3.6 The fauna <strong>of</strong>cut-over bogs 45Invertebrates 45B~ ~PART 11. PRINCIPLES OF RESTORATION3. Aims and general principies for peatland restoration13.1 Options for after-use <strong>of</strong> darnaged peatlands3.2 Airns <strong>of</strong> restoration3.2.1 The concept <strong>of</strong>restoration3.2.2 <strong>Restoration</strong> objectives3.2.3 Choice <strong>of</strong>options(i) Maintenance or recreation <strong>of</strong>wildlife interest not pertaining to bogs(ii) Maintenance or re-establishment <strong>of</strong>viable populations <strong>of</strong>typical bog species(iii) Maintenance or re-establishment <strong>of</strong>a regenerating, self-sustaining bog ecosystem3.2.4 Species-centred versus mire-centred restoration3.2.5 <strong>Restoration</strong> opportunities in current peat workings3.2.6 Constraints on restoration objectives3.3 Sorne principies <strong>of</strong> peatland restoration3.3.1 Scope <strong>of</strong>restoration3.3.2 Approaches to restoration515151515152525555565757575758


CONTENTSvii3.4 PrincipIes for restoration <strong>of</strong> raised bogs 583.4.1 lntroduction 583.4.2 Conditions required for the .establishment <strong>of</strong>bog species 603.4.3 Pathways <strong>of</strong>bog restoration 603.4.4 Starting conditions 603.4.5 Suitability <strong>of</strong>sites for restoration 604. Recolonisation oC peat workings 634.1 Introduction 634.2 RecoIonisation <strong>of</strong> peat workings by pIant propaguIes 634.2.1 Seed banks 634.2.2 Diaspores and dispersal distances 644.3 Effects <strong>of</strong>hydroIogicaI conditions on revegetation 654.3.1 Significance <strong>of</strong>water level 654.3.2 Colonisation mechanisms 67Introduction 67Rooting 67Rafting 674.4 PhysicaI and chemicaI influences on revegetation 694.4.1 Introduction 694.4.2 Physical factors 694.4.3 Chemical factors 70Base status 70Nutrient status 714.4.4 Peat-type 714.4.5 Depth <strong>of</strong>residual peat 714.5 ExternaI constraints on revegetation 724.5.1 Introduction 724.5.2 Effects <strong>of</strong>atmospheric pollution 72Introduction 72Possible implications for bog growth and restoration 724.5.3 Lowering <strong>of</strong>regional groundwater levels 724.5.4 Climatic constraints 724.6 RecoIonisation <strong>of</strong> peat workings by invertebrates 734.7 RecoIonisation <strong>of</strong> peat workings by birds 745. Rewetting damaged and cut-over peatlands 755.1 Introduction 755.2 Establishment <strong>of</strong>suitabIe hydroIogicaI conditions for raised-bog restoration 755.2.1 PrincipIes <strong>of</strong>rewetting damaged and cut-over bogs 755.2.2 Establishment <strong>of</strong>an acrotelm characteristic <strong>of</strong>little-damaged bog 765.2.3 Approaches to rewetting 765.3 Rewetting options for raised-bog massifs 775.3.1 Introduction 775.3.2 Methods 78(a) Elevation <strong>of</strong>water level by ditch blocking 78(b) Non-intervention - 'natural' reconformation <strong>of</strong>peat to position <strong>of</strong>perched water mound 79(c) Sculpting <strong>of</strong>the peat surface to the position <strong>of</strong>the perched water mound 82


viiiRESTORATION OF DAMAGED PEATLANDS(d) Elevation <strong>of</strong>the water level by containment within wall bunds(e) Elevation <strong>of</strong>the mire water level by increasing water levels in the surrounding area(f) Inundation using parapet bunds(g) Inundation by reduction <strong>of</strong>the level <strong>of</strong>the peat surface to fonn lagoons(h) Provision <strong>of</strong>supplementary water5.4 Rewetting options for extensive peat workings in bog peat5.4.1 IntroductionSituation, topography and rewettingWater levels5.4.2 Block cuttingsIntroductionEffects <strong>of</strong>topographyThe problem <strong>of</strong>baulksConclusion5.4.3 MilIed-peat workingsIntroduction(a) Ditch blocking(b) Impoundment <strong>of</strong>water in lagoons(c) Impoundment <strong>of</strong>water in sculpted hollowsConclusion5.4.4 Depth <strong>of</strong> inundation5.5 Rewetting extensive peat workings in fen peat5.5.1 Introduction5.5.2 Rewetting <strong>of</strong>flat fen peat surfaces(a) Ditch blocking(b) Irrigation by telluric water via ditches or by surface flooding(c) Impoundment <strong>of</strong>water in lagoons or sculpted hollows5.5.3 Rewetting <strong>of</strong>fen peat basins5.6 Integrated restoration <strong>of</strong> remnant massifs and commercial peat fields5.6.1 Introduction5.6.2 In<strong>de</strong>pen<strong>de</strong>nt water management <strong>of</strong>massifs and peat fields(a) Preservation <strong>of</strong>the peat massifby bunding5.6.3 Reduction <strong>of</strong>height <strong>of</strong>aH or part <strong>of</strong>remnant massif(a) Natural reconfonnation <strong>of</strong>the surface <strong>of</strong>the massif(b) Reduction <strong>of</strong>the height <strong>of</strong>the massifby peat removal5.6.4 Elevation <strong>of</strong>the water table around a remnant massif(a) Elevation <strong>of</strong>the water table in basins(b) Reconstruction <strong>of</strong>the water mound around a remnant massifon flat sites5.7 Maintenance <strong>of</strong>remnant massifs during peat-extraction operations5.7.1 Introduction5.7.2 Bunding5.7.3 Non intervention (except ditch blocking)5.7.4 Conclusion6. <strong>Restoration</strong> options and peat working practices6.1 Introduction6.2 <strong>Restoration</strong> options for ombrotrophic peat surfaces6.2.1 Climatic regimes and restoration options6.2.2 Assessment <strong>of</strong>restoration options6.3 <strong>Restoration</strong> options for minerotrophic peat surfaces8384858687888888898989909092929293939696979898999999100100100100101101101101102102102103104104105105106107107107107108119


CONTENTSix6.4 <strong>Restoration</strong>s options for mineral substrata 1206.5 Optimisation <strong>of</strong> peat- working practices and starting conditions for restoration 1216.5.11ntroduction 1216.5.2 General requirements 1216.5.3 Working practices for restoration during peat extraction operations 1216.5.4 Operations foIlowing abandonment 122Water management 122Topographical manipulation 122Control <strong>of</strong>vegetation invasion 1226.5.5 Maintenance 1226.6 Prospects for restoration 1236.6.1 Remnant peat massifs 1236.6.2 Cut-over ombrotrophic surfaces 1236.6.3 Cut-over minerotrophic surfaces 1246.7 Holistic approaches to raised-bog restoration 124PART 111. PRACTICAL ASPECTS OF RESTORATION7. Planning a restoration strategy7.1 Introduction7.2 Planning for restoration7.2.1 Approaches to restoration planning7.2.2 Feasibility study7.2.3 ConsuItation7.3 Financial consi<strong>de</strong>rations7.3.1 Introduction7.3.2 Land costs7.3.3 <strong>Restoration</strong> procedures and management(a) Personnel(b) Specialist advice(c) Management operations(d) Monitoring and maintenance7.3.4 Financial assistance7.4 Preliminary collation <strong>of</strong> information (<strong>de</strong>sk studies)7.4.1 Cartographic <strong>de</strong>tails7.4.2 Use <strong>of</strong>aerial photographs7.4.3 Ownerships and tenancies7.4.4 Current management regiines and general site history7.4.5 Hydrological information7.4.6 Wildlife conservation and archaeological interest7.4.7 Potential legal and land-use constraints on <strong>de</strong>velopmentPlanning legislationWildlife and conservation legislationLegislation relating to water resourcesMisceIlaneous legislation7.4.8 Summary7.5 Field investigations7.5.1 Introduction7.5.2 Site physical characteristicsGeneral size and shape; extent <strong>of</strong>site in relation to whole peat body129129129129130131132132134134134134134135135136136137137137137137137137138138139139139139139139


xRESTORATION OF DAMAGED PEATLANDSSurface and sub-surface topography; peat <strong>de</strong>pthsGeology and soils un<strong>de</strong>rlying and surrounding the siteAccess for machinery and equipmentLocation <strong>of</strong>existing features7.5.3 Land use7.5.4 Hydrology7.5.5 Substratum characteristics and water quality7.5.6 Survey and assessment <strong>of</strong> biological interest - flora and fauna7.5.7 Survey <strong>of</strong>archaeological and palaeoecological interest7.5.8 Potential for control <strong>of</strong> tire7.5.9 Engineering assessment7.5.10 Safety assessment7.5.11 Landscape assessment8. Water management8.1 Introduction8.2 Constructs for water retention8.2.1 Introduction8.2.2 Ditch blocking8.2.3 BundingPeatPlastic membranesMineral substrataGeneral comments8.2.4 Provision <strong>of</strong> supplementary water8.3 Buffer zones8.4 Practical implications <strong>of</strong> rewetting for adjoining land9. Facilitation oC revegetation9.1 Introduction9.2 Inoculation with Sphagnum species9.2.1 Introduction9.2.2 Sphagnum 'farming'9.2.3 Propagation <strong>of</strong>Sphagnum from small vegetative fragments9.2.4 Regeneration <strong>of</strong>Sphagnum from spores9.2.5 Facilitation <strong>of</strong>Sphagnum establishment and rafting9.3 Inoculation with vascular plants9.4 Legal aspects <strong>of</strong> transplantation9.5 Mitigation <strong>of</strong> adverse chemical effects9.5.1 Phosphorus fertilisation9.5.2 Base- or nutrient-enrichment9.6 Importance <strong>of</strong> 'bunker<strong>de</strong>' to revegetation10. Vegetation management and after-care10.1 Introduction10.2 Scrub control140140140140141141143143145146146146146149149149149149150150152152152155155156157157157157157157158158158159159159159159161161161


CONTENTSxi10.3 Mowing10.4 Grazing10.5 Fire10.6 Management and succession <strong>of</strong> herbaceous fen vegetation10.7 After-care <strong>of</strong>water control structures10.7.1 Ditches10.7.2 Dams10.7.3 Bunds11. Recording and monitoring11.1 Introduction11.2 Methods11.2.1 Hydrology11.2.2 Vegetation11.2.3 Invertebrates11.2.4 Birds11.2.5 Water chemistry11.3 Assessment <strong>of</strong> 'success'11.3.1 Hydrology11.3.2 Swelling and growth <strong>of</strong>peat11.3.3 VegetationInoculated plant materialRates <strong>of</strong>change11.3.4 Invertebrates11.3.5 Birds11.4 General comments163163163163164164164164165165166166166167168168168168168169169169169171171References173ApPENDICESAppendix 1Appendix 2Appendix3Appendix 4Appendix 5Appendix 6Appendix 7Glossary <strong>of</strong> termsLegislation relating to peat extraction and restorationoptionsSynopsis <strong>of</strong> characteristics <strong>of</strong> the main plant speciesassociated with lowland raised bogs in Britain.Plant species recor<strong>de</strong>d on raised bog sites in the UKBird species nomenclatureSummary <strong>of</strong> restoration measures implemented in selectedpeatland sites in lowland Britain and parts <strong>of</strong>NW EuropeUseful contact addresses181187194199203204210


XIIRESTORATION OF DAMAGED PEATLANDSList oC Figures1.1 Stratigraphical sections across Cors Caron (Dyfed), Bowness Common / Glasson Moss(Cumbria), Coalburn Moss (Cly<strong>de</strong>sdale) and Flan<strong>de</strong>rs Moss West (Stirlingshire).1.2 Diagrammatic pr<strong>of</strong>ile across a raised bog, ilIustrating sorne <strong>of</strong>the terms used in the texl.1.3 "Classic" topographical <strong>de</strong>velopment <strong>of</strong> raised bogo1.4 Hydroseral succession <strong>of</strong> ombrotrophic bog from various starting conditions.1.5 Distribution <strong>of</strong>soils i<strong>de</strong>ntified by the National Peatland Resource Inventory as associatedwith raised bogs in England, Scotland and Wales, by 10 km square.1.6 Main mechanisms leading to accumulation <strong>of</strong> peat and bog succession.1.7 Water budget <strong>of</strong>a raised bog and terms used in hydrological mo<strong>de</strong>lling <strong>of</strong>the'groundwater mound'.1.8 Stratigraphical section across Raheenmore Bog (Ireland).1.9 Typical zonation <strong>of</strong>plant communities across a raised bogo1.10 (a)Diagram <strong>of</strong>the succession <strong>of</strong>species forming the peat in a typical"hollow-hummockcycle (regeneration complex). (b) Niche zonation within the micro-topography <strong>of</strong> a bogo2.1 The concept <strong>of</strong>massifs & <strong>de</strong>pressions.2.2 Potential causes <strong>of</strong> <strong>de</strong>hydration <strong>of</strong> a raised bog massif.2.3 Conceptual ilIustration <strong>of</strong>the potential water drawdown <strong>of</strong>the perched water mound in araised bog as a result <strong>of</strong>marginal damage.5.1 The three main types <strong>of</strong> bund used in bog restoration projects.5.2 Approaches to rewetting badly-damaged remnant peat massifs based on resoaking.5.3 Suggested scenario for the Iikely changes in badly-damaged peat remnants subject tonatural processes <strong>of</strong>peat wastage.5.4 Approaches to rewetting badly-damaged remnant peat massifs based on reflooding.5.5 Revegetation <strong>of</strong>re-wetted block-cut peatland.5.6 Terraced casca<strong>de</strong> re-wetting <strong>of</strong>sloping cut-over peat surfaces.5.7 <strong>Restoration</strong> <strong>of</strong> peat excavations by inundation.5.8 Rewetting <strong>of</strong> remnant massifs and peat fields.5.9 Protection <strong>of</strong> massifs alongsi<strong>de</strong> peat extraction by bunding.8.1 Construction <strong>of</strong>shallow internal bunds using peal.5699lO121416212431323478798185909597103105152List oC TablesSIS2S3S41.11.21.31.4Summary <strong>of</strong>possible starting conditions on cut-over bogs.Summary <strong>of</strong>main factors affecting restoration options.Practical constraints and possible solutions in the restoration <strong>of</strong>cut-over mires.Factors which can be simply recor<strong>de</strong>d, measured or monitored.Sorne distinguishing features <strong>of</strong> fens and bogs.The current condition <strong>of</strong>raised bogs in Britain, as i<strong>de</strong>ntified by the National PeatlandResource Inventory.Modified version <strong>of</strong>the von Post scale for assessing the <strong>de</strong>gree <strong>of</strong><strong>de</strong>composition <strong>of</strong>peal.Main plant community-types <strong>of</strong>ombrogenous mires in Britain, as i<strong>de</strong>ntified by theNational Vegetation Classification.xxiXXIVxxxxxxii1111720


CONTENTSXlii1.51.62.13.13.24.16.17.17.27.37.47.57.611.111.211.311.4Informal physiognomic-habitat categories <strong>of</strong> raised bog vegetation in Britain.Invertebrate species for which raised bogs appear to have particular conservationimportance in the UK.Some chemical conditions in little-disturbed bogs compared with peat extraction sites.Occurrence <strong>of</strong> physiognomic categories <strong>of</strong> vegetation within cut-over peatlands.Summary <strong>of</strong>possible starting conditions on cut-over bogs.Recolonisation <strong>of</strong> cut-over surfaces by rooting or rafting.Summary <strong>of</strong>the likely outcomes <strong>of</strong>different options <strong>of</strong> raised bog restoration, from acontrasting range <strong>of</strong>starting conditioris.Potential scope <strong>of</strong> a feasibility study concerning the restoration <strong>of</strong>a cut-over or damagedpeatland site.Primary interested parties in the formulation <strong>of</strong> a restoration scheme.Useful consultees in the formulation <strong>of</strong>a restoration scheme.Approximate ranges <strong>of</strong>costs for selected restoration techniques.Possible sources <strong>of</strong>financial or practical assistance for restoration schemes.Standard survey methods applicable to survey <strong>of</strong> invertebr~teson cut-over peatlands.Suggested plant indicator species for monitoring progress towards a raised bog objective.Vegetational indicators <strong>of</strong>potential problems with respect to revegetation with bog species.Invertebrtlte species associated with little-damaged raised bogs, which may be useful in theassessment <strong>of</strong> 'success' <strong>of</strong> restoration initiatives.Invertebrate species associated with partly-damaged raised bogs, which may be useful inthe assessment <strong>of</strong> 'success' <strong>of</strong>restoration initiatives.222743526166109131132133135136144167167170170List <strong>of</strong>Boxes1.11.21.31.41.52.13.13.25.15.25.37.1Hydromorphological types <strong>of</strong>bog in Britain: the concept <strong>of</strong> 'raised bog'.Climate and the occurrence <strong>of</strong>raised bogs.Origins and <strong>de</strong>velopment <strong>of</strong>raised bogs.The acrotelm layer <strong>of</strong>raised bogs in relation to restoration.The 'Groundwater' Mound hypothesis.Main vegetation types occurring in cut-over bogs in the United Kingdom.Informal physiognomic vegetation categories in relation to restoration objectives.Hydrochemical constraints on bog restoration.Potential approaches to re~etting bog massifs.Efficacy <strong>of</strong>re-soaking approaches to rewetting.Approaches to rewetting based on surface inundation.Hydrological mo<strong>de</strong>lling.4681315465359788488142


xivRESTORATION OF DAMAGED PEATLANDSList oC PlatesNo/e /ha/ <strong>de</strong>/ails olmos/ al/he si/es iIlus/ra/ed are given in Appendix 6.1.1 Aerial view <strong>of</strong>the west bog, Cors Caron (Dyfed).1.21.31.41.51.61.72.12.22.32.42.52.62.72.82.92.102.112.122.132.142.153.13.23.34.14.24.34.4Distinctive microtopographical patteming <strong>of</strong>the bog surface (hummocks, lawns and bogpools), illustrated at Claish Moss, Argyll and Mongan Bog, Ireland.Section through raised bog peat (Solway Moss, Cumbria).Some species <strong>of</strong>Sphagnum found on ombrotrophic bogs.Sorne vascular plant species found on ombrotrophic bogs.Remains <strong>of</strong>a cow [c. 800-900 AD] found during peat extraction operations at Solway Moss(Cumbria).The Sweet Track - built in 3806 BC across a Phragmites reed swamp in the SomersetLevels.Vertical peat face between 'remnant' uncut peat block and cut-over area; Breitenmoos, S.Germany.Molinia-dominated surface <strong>of</strong>raised-bog 'remnant'; Holcr<strong>of</strong>t Moss (Cheshire)..Calluna-dominated vegetation on drained raised-bog surface at Moine-Mhor (Argyll).Birch and Rhodo<strong>de</strong>ndron invasion on raised-bog 'remnant'; Wreaks Moss (Cumbria).Sphagnum-dominated bog vegetation confined to cut-out pools, surroun<strong>de</strong>d by Callunadominatedbog surface; Bankhead Moss (Fife).Small-scale hand peat cutting at Glasson Moss (Cumbria) andMontiaghs Moss (Antrim).Block cutting at Solway Moss, Cumbria; Block-cut peat fields in the Somerset Levels.Mole drains in a milled peat field.Milled-peat fields, with temporary rail-track for removal <strong>of</strong> peat stockpiles; Bolton Fell(Cumbria).Peat extracted by the extrusion method; Montiaghs Moss (Antrim).Large-scale extraction <strong>of</strong>'fuel-peat', leaves trenches and 'islands'; Solway Moss(Cumbria).Peat extraction by the rotavating and ridging method (Somerset Levels).White marl <strong>de</strong>posit un<strong>de</strong>rlying peat, exposed in a drainage channel through cut-over bog;Turraun Bog (Offaly, Ireland)Eriophorum angustifolium growing in an excavated peat pit, surroun<strong>de</strong>d by Moliniadominatedvegetation on drained bog surface; Asíley Moss (Lancashire).Recolonised hand-peat cutting; ~illaun Bog (Ireland).Recolonisation <strong>of</strong>fen peat by herbaceous fen vegetation; Brackagh Bog (Armagh).Lake and reedbeds at Leighton Moss RSPB reserve (Lancashire).Lake with islands and reedbeds, created using clay bunds. Burtle, Somerset Levels.Recolonisation <strong>of</strong>block peat cuttings; Risley Moss (Cheshire).Sphagnum cuspida/um colonising forming a raft in a floo<strong>de</strong>d lagoon within worked-out peatcuttings; Amsterdamsche Veld (Bargerveen, The Netherlands).Bare peat surface created by surface milling, sparsely colonised by Nar/hecium ossifragum.Unstable and eroding sloping peat surface remaining after surface milling; Wendlinger Filz(S. Germany).37161819293033343535353839404040414144454554545565686969


CONTENTSxv4.5 Polygonum amphibium and Typha latifolia colonising peat cuttings in fen peat; SomersetLevels.4.6 Polygonum amphibium colonising refloo<strong>de</strong>d, marl-based peat workings at Turraun Bog(Ireland).5.1 Getty's Mire, Somerset Levels. Former peat workings mechanically contoured to thepredicted shape <strong>of</strong>the 'groundwater' mound.5.2 'Parapet' bund around an upstanding peat remnant; Engbertsdijksveen (Thé Netherlands).5.3 Revegetated block cuttings at Lichtenmoor (Germany).5.4 Block peat cuttings floo<strong>de</strong>d to the level <strong>of</strong>the top <strong>of</strong>the baulks; Fenns Moss (Clywd).5.5 Recolonisation <strong>of</strong>former block peat cuttings; <strong>Peatlands</strong> Park (Armagh).5.6 Extensive bunding around former peat cuttings; SE Bog, Cors Caron (Dyfed).5.7 Experimental restoration project in former milled peat workings; Gardrum Moss (Falkirk).5.8 An attempt to increase microtopographical variation by small-scale sculpting <strong>of</strong>the peatsurface as a series <strong>of</strong> <strong>de</strong>pressions and hummocks; Leegmoor (N. Germany).5.9 Tussocks <strong>of</strong>Molinia caerulea, killed by flooding; Fochteloerveen (The Netherlands).5.10 Extensive colonisation <strong>of</strong>former bare peat surfaces by Sphagnum cuspidatum and Moliniacaerulea, within shallowly-floo<strong>de</strong>d lagoon; Lichtenmoor (N. Germany).5.11 Floating rafts <strong>of</strong>vegetation <strong>de</strong>veloped in refloo<strong>de</strong>d, bun<strong>de</strong>d, block-peat cuttings;Meerstalblok (The Netherlands).8.1 Rewetting using damming and ditch-blocking techniques.8.2 Rewetting using bunding techniques.8.3 Scheme to protect an ancient woo<strong>de</strong>n trackway within a raised-bog remnant at Corlea (Co.Longford, Ireland).9.1 Storage <strong>of</strong>bunker<strong>de</strong>, alongsi<strong>de</strong> current peat extraction, for future use in bog restoration.Steinhu<strong>de</strong>r Moor (Lower Saxony, Germany).10.1 Scrub cutting at Roudsea Moss (Cumbria).10.2 Birch trees killed by <strong>de</strong>ep flooding; Neustadter Moor (Germany).10.3 Die-back <strong>of</strong>birch trees attributed to flooding; Thome Waste (S. Yorkshire).707083869191929294969898104151153154160162162162


Surnrnary51 Background and introduction<strong>Peatlands</strong> are wetland ecosystems in which thesubstratum is composed largely or entirely <strong>of</strong>peat. Peatis an organic soil formed primarily from the remains <strong>of</strong>plants that have accumulated in situ. Peat accumulatesin wetland habitats, largely because waterlogging andassociated anoxia retards the <strong>de</strong>composition <strong>of</strong> plantmaterial. <strong>Peatlands</strong> can be divi<strong>de</strong>d into two main types:ombrotrophic peatlands are mires irrigated directly andmore-or-less exclusively by precipitation inputs (rain,snow, fog etc.); minerotrophic peatlands areadditionally irrigated by groundwater. This report isconcemed largely with ombrotrophic peatlands, andparticularly with those known as 'raised bogs' (thepeatlands currently most utilised by the UK peatindustry), although sorne consi<strong>de</strong>ration is also given torestoration <strong>of</strong> fen peat workings.In Britain, as in much <strong>of</strong> north-west Europe, peatlandswere once very extensive and until recently, sorne <strong>of</strong>these areas were largely regar<strong>de</strong>d as unproductivewasteland. In consequence, in Britain as wi<strong>de</strong>lyelsewhere, a substantial proportion <strong>of</strong> former raisedbogs have been elaimed for agriculture and forestry.Others have been heavily damaged by commercial ordomestic peat extraction, or by drainage or repeatedbuming. The area <strong>of</strong> bog that has retained much <strong>of</strong> its(presumed) ,original character is undoubtedly small:figures collated for the National Peatland ResourceInventory (NPRI) suggest that in Britain the proportion<strong>of</strong> 'near-natural primary raised bog' which remains isonly about 6 % <strong>of</strong> the original extent <strong>of</strong> raised bog <strong>of</strong>sorne 70,000 ha (although any SUCh estimated figureshave to be treated with sorne caution, not least becausethe concept and compass <strong>of</strong> the category called'lowland raised bog' is itselfopen too <strong>de</strong>bate).In recent years there has been a growing recognition <strong>of</strong>the importance <strong>of</strong> lowland raised bogs for naturalhistory, science and conservation. Important featuresinelu<strong>de</strong>:• visual character <strong>of</strong>the peatland landscape;• peat archive (archaeology, palaeoecology);• biological resource (communities and species <strong>of</strong> flora andfauna).It is recognised that many UK peatlarids, ineludinglowland peat bogs, are amongst the country's mostimportant nature conservation habitats. However, thepeat industry also has a legitimate interest in sorne <strong>of</strong>these peatlands through mineral extraction activitiescarried out un<strong>de</strong>r valid planning consents. Many <strong>of</strong> theconsents lacked planning conditions controllingmethods <strong>of</strong>working, restoration and aftercare.This report, prepared for the Department <strong>of</strong> theEnvironment, provi<strong>de</strong>s guidance on the potential forthe restoration <strong>of</strong> worked-out or damaged bogs toregenerate, maintain or increase their natureconservation value and on the possible approaches,practicality, and requirements that may be appropriateto facilitate this process. It provi<strong>de</strong>s backgroundinformation and scientific advice for formulating andimplementing restoration strategies for the after-use <strong>of</strong>currently worked or abandoned cut-over bogs. It isinten<strong>de</strong>d for use by all parties with an interest inpeatland restoration, ineluding central and localgovernment, the peat industry and conservation bodies.The report addresses two rather different issues: (i)restoration <strong>of</strong> the abandoned peat fields; and (ji) themaintenance (if nee<strong>de</strong>d, restoration) <strong>of</strong> vegetated peatremnants.A separate report contains the results <strong>of</strong> a wi<strong>de</strong>-rangingcollation and review <strong>of</strong> relevant published andunpublished data, supplemented by consultation withappropriate individuals and organisations, and sitevisits in the UK, Ireland, The Netherlands andGermany.This summary should be used in conjunction with themain reports, which provi<strong>de</strong> background informationand the context and elaborate on the points ma<strong>de</strong> here.Two broad caveats un<strong>de</strong>rlie all <strong>of</strong> the information andobservations presented here:(1) Once any site has been damaged, be it a bog orother habitat, it is never possible to retum it exact/y toits former condition. However, in the case <strong>of</strong> a bogdamaged by peat extraction, it may be possible torepair or regenerate a bog by restoring conditionssimilar to those un<strong>de</strong>r Which it originally <strong>de</strong>velopedand hence to encourage the return <strong>of</strong> typical raised-bogspecies, both flora and fauna. In sorne instances thismay even <strong>of</strong>fer a 'value-ad<strong>de</strong>d' approach in terms <strong>of</strong>wildlife conservation, as in those sites which havelong-since been damaged by drainage, partial'agricultural conversion and burning as well as peatextraction. However, effective restoration is likely tobe a slow process, measured in terms <strong>of</strong> <strong>de</strong>ca<strong>de</strong>s;


XVIlIRESTORATION 01' DAMAGED PEATLANDSmoreover, given the present 'state <strong>of</strong> the art' it is notpossible to guarantee that a peat-accumulating systemwill subsequently re<strong>de</strong>velop. These gui<strong>de</strong>lines andobservations should not be used to provi<strong>de</strong> a justificationfor peat extraction on little-damaged bog sites.(2) Not all <strong>of</strong> the techniques outlined in this documentare well 'tried and tested', as bog restoration is arelatively new activity. There are strong reasons tosuppose that they have a good chance <strong>of</strong>success, but tohelp enhance knowledge and un<strong>de</strong>rstanding <strong>of</strong>effective restoration practices, it is suggested that allattempts at the restoration <strong>of</strong> damaged peatlands shouldbe regar<strong>de</strong>d as experimental, and the projects carefullyrecor<strong>de</strong>d and monitored. There is still much to learn.The advice given here is based upon currentexperience, knowledge and thought, but the gui<strong>de</strong>linesmay need to be amen<strong>de</strong>d or updated as new techniquesand results from existing studies become available.With respect to the main subject <strong>of</strong> this report, i.e. bogrestoration, the terminology proposed by R. Eggelsmannand co-workers has been followed in which:rewetting is the re-establishment <strong>of</strong> surface-wetconditions;renaturation is the re<strong>de</strong>velopment <strong>of</strong> anappropriate vegetation;regeneration is the renewed accumulation <strong>of</strong>peal.These concepts are here grouped un<strong>de</strong>r the generichead <strong>of</strong> restoration, but they are by no means discreteand separate: in<strong>de</strong>ed, the re<strong>de</strong>velopment or regeneration<strong>of</strong>a bog follows a continuum; there are no abruptdivisions or thresholds between each phase. Successfulbog regeneration must seek ultimately to re-establishthe self-regulatory mechanisms that ensure thatpermanently wet conditions are maintained.52 The raised-bog habitat52.1 IntroductionHydrologically, raised bogs can be consi<strong>de</strong>red as twolayered (diplotelmic) systems comprised <strong>of</strong> an uppermost'active layer' (or acrotelm) and a lower so-called'inert layer' 1 (or catotelm) [Figure 1.2]. The acrotelmis usually thin « 50 cm), is largely aerobic, and formsthe main functional horizon for plant growth,comprising the living plant cover, especially Sphagnumspecies, passing downwards into recently-<strong>de</strong>ad plantmaterial and thence to fresh peal. Water moves readilythrough the acrotelm, which both contains andregulates the water-Ievel fluctuations (caused byvariations in water inputs and outputs) and forms themain conduit <strong>of</strong> water discharge from the bogo1 The catotelm is not, strictly speaking, 'inert'.The catotelm is <strong>de</strong>fined as the zone <strong>of</strong> permanentsaturation, is largely anaerobic, and usually comprisesthe bulk <strong>of</strong> the peat <strong>of</strong> a raised bogo It is .built fromacrotelm peat which becomes incorporated into thecatotelm as the bog grows upwards. The catotelm peatis typically more consolidated and more-humified thanthe acrotelm, within which water moves exceedinglyslowly.Raised bogs may originate and <strong>de</strong>velop by a variety <strong>of</strong>pathways. The 'c1assic' <strong>de</strong>velopmental sequence showsinitiation <strong>of</strong> ombrotrophic peat from withinminerotrophic swamp or fen, which has <strong>de</strong>veloped overa pool or lake as part <strong>of</strong> a hydroseral or terrestrialisationprocess; however, raised bogs may also <strong>de</strong>velopover once relatively dry land, by paludification.Starting points for raised-bog <strong>de</strong>velopment inclu<strong>de</strong>such diverse habitats as reedswamp, floating vegetationmats, herbaceous fen, fen carr, woodland andsaltmarsh. The ombrotrophic peat may overlie a layer<strong>of</strong> fen peat or rest more-or-Iess directly on a mineralsubstratum. In the past, raised bogs have <strong>de</strong>velopedspontaneously in many parts <strong>of</strong> Britain. They arethought to represent climax ecosystems.Raised bogs provi<strong>de</strong> an acidic, waterlogged, lowfertility environment, associated with the <strong>de</strong>velopment<strong>of</strong>a characteristically species-poor flora and fauna.52.2 The vegetation <strong>of</strong>UK raised bogsThe vegetation <strong>of</strong> ornbrotrophic bogs in Britain israther species-poor and comparatively uniformo Mostplant species 'characteristic' <strong>of</strong> Iittle-darnaged raisedbogs also occur quite wi<strong>de</strong>ly in sorne other habitats.However, although the vegetation may be confined to alimited range <strong>of</strong> species, some combinations <strong>of</strong> plantspecies are apparently unique to bogs. The Ericatetralix-Sphagnum papillosum raised and blanket mirecommunity (NVC: MI 8) may be regar<strong>de</strong>d as the'natural' core community-type <strong>of</strong> rnany lowland raisedbogs, and hence its recreation can be seen as the mainfocus <strong>of</strong>the restoration <strong>of</strong> darnaged raised bogs.The vegetation cover, in particular the abundanc~ <strong>of</strong>some Sphagnum species, is <strong>of</strong> critical irnportance to the<strong>de</strong>velopment <strong>of</strong> the bogo This is because they provi<strong>de</strong>much <strong>of</strong> the physical basis <strong>of</strong> the bog itself and <strong>of</strong>some <strong>of</strong> its environmental conditions. In large measurethe vegetation <strong>de</strong>fines the habitat. This is because:• plant growth provi<strong>de</strong>s the basis for peat formation,water storage and impe<strong>de</strong>d drainage;• plant growth provi<strong>de</strong>s the basis for much <strong>of</strong> themicrotopography <strong>of</strong> the site and thus creates small-scalewater gradients;• the growth <strong>of</strong> Sphagnum species helps to create thestrongly acidic conditions <strong>of</strong> ombrotrophic peat andwater.


SUMMARYXIXWithin raised bogs, plant species show sorne microhabitat'preferences', particularly associated with theheterogeneous microtopography <strong>of</strong> the surfaces, whichis induced primarily by plant growth. Certain plantspecies tend to oc.cupy fairly distinct zones with respectto water level, either as part <strong>of</strong> the small-scale mosaic<strong>of</strong> a patterned bog surface [see Figure 1.10] or as part<strong>of</strong> a wi<strong>de</strong>r change in water level from the wet centre tothe drier margins <strong>of</strong> a bogo It is possible to recognise abroad pattern <strong>of</strong> vegetation zonation across the surface<strong>of</strong> at least sorne little-damaged raised bogs, from thecentral complex <strong>of</strong>shallow pools and hummocks to thedrier rand.Examination <strong>of</strong> sorne <strong>of</strong> the main characteristics <strong>of</strong>typical bog plant species enable the fol1owing general¡Joints to be ma<strong>de</strong>:• they are mostly <strong>of</strong>geographic wi<strong>de</strong> distribution;• they are not specific to ombrotrophic bogs;• most are long-lived perennials;• there is little evi<strong>de</strong>nce that seeds and spores are generallyimportant in maintaining populations in undisturbedbogs;• seeds <strong>of</strong> most species are light and may be readilydispersed;• they typically have slow relative growth rates;• they are apparently efficient at scavenging nutrients fromdilute solutions;• most have efficient internal conservation <strong>of</strong> nutrients;• ombrotrophic conditions seem generally sub-optimal forgrowth.A few species are uncommon or rare, and especial1y indamaged sites, for example Andromeda polifolia,Drosera anglica, D. intermedia, Rhynchospora fusca,Dicranum undulatum, Sphagnum fuscum, S. imbricatum.and S. pulchrum. Of these, Andromeda polifoliaand Dicranum undulatum are largely specific to raisedbogs in Britain.52.3 The invertebrates <strong>of</strong>raised bogsInvertebrates forro an important part <strong>of</strong> the animal life<strong>of</strong> peatlands, living in and on the water and plants. Ingeneral there are few bog 'specialists', perhapsretlecting the waterlogged, oxygen-poor, acidicenvironment with 'poor-quality' food sources.However, raised bog sites support populations <strong>of</strong> ahigh proportion <strong>of</strong> notable and rare insect and spi<strong>de</strong>rspecies both within the UK and on mainland Europe,and a number <strong>of</strong> species can be i<strong>de</strong>ntified for whichraised bogs appear to have particular conservationimportance. These inclu<strong>de</strong> the beetles Bembidionhumerale and Curimopsis nigrita, both known thus faronly from the Humberhead Levels in the UK.Areas which have revegetated following hand-cuttingor similar block-cutting peat-removal regimes may<strong>of</strong>fer a wi<strong>de</strong>r range <strong>of</strong> invertebrate habitats than little-damaged raised bogs, and consequently, may support awi<strong>de</strong>r species range than the latter, although the speciesconcerned are not necessarily characteristic <strong>of</strong> bogs.The extensive, bare surfaces created by mo<strong>de</strong>rnextraction methods may be far less amenable torecolonisation than the smal1-scale hand peat cuttings.52.4 The birds <strong>of</strong>raised bogsOpen areas <strong>of</strong> little-damaged bogs typically have lowbird <strong>de</strong>nsity and low species richness, and very fewbird species are consi<strong>de</strong>red to be particularlycharacteristic <strong>of</strong> raised bogs. The lack <strong>of</strong> trees andshrubs make such bogs largely unsuitable forpasserines, other than at the margins, as these birdsrequire perching posts and nesting sites aboye groundleve!. The vascular plants <strong>of</strong> bogs <strong>of</strong>fer a limited foodsupply to birds and sorne <strong>of</strong> the species which do breedare common and wi<strong>de</strong>spread breeding specieselsewhere in Britain. Species composition can bestrongly intluenced by the relative <strong>de</strong>gree <strong>of</strong> tloodingor <strong>de</strong>siccation and vegetation-types (e.g. scrub) <strong>de</strong>velopedon damaged sites. Both species richness and<strong>de</strong>nsity may be greater on partly-damaged sites, largelyowing to the increased variety <strong>of</strong>available habitats.Birds <strong>of</strong> particular conservation value which occur onlowland raised bogs in Britain inclu<strong>de</strong> " significantpopulations <strong>of</strong> breeding teal, red grouse, black grouse,dunlin, curlew, redshank, nightjar and twite, andwintering populations <strong>of</strong> pink-footed geese, Greenlandwhite-fronted geese, greylag geese, hen harrier andmerlin.53 Archaeology, palaeoecology andrestoration<strong>Peatlands</strong> are important for archaeology andpalaeoecology as they have the potential to provi<strong>de</strong><strong>de</strong>tailed evi<strong>de</strong>nce <strong>of</strong> post-glacial vegetational history,environmental change and human occupation inspecific areas (both for the site itself and itssurroundings), through preservation within the peatlayers <strong>of</strong> organic and inorganic artefacts, as well aspollen and plant and animal macr<strong>of</strong>ossil remains. Peatcutting is also consi<strong>de</strong>red to be part <strong>of</strong> the 'industrialheritage' and abandoned areas may have positive valueas a <strong>de</strong>relict industrial landscape. Archaeologicalaspects should therefore be consi<strong>de</strong>red in proposedrestoration schemes and there is a need for close cooperationbetween conservationists and archaeologists,to arrive at the optimum solutions for site restoration.


SUMMARYxxiextracts peat from below the surface, before it isextru<strong>de</strong>d as 'sausages' through nozzles onto the groundto dry. Where the vegetation has first been removed,the surface remaining after extraction is similar to thatleft by milling, but there will be more sub-surfacedrainage channels. Even where the vegetation is notremoved, consi<strong>de</strong>rable damage to the surfacevegetation and microtopography stiH occurs. Thetechnique is akin to mole-draining and <strong>of</strong>ten leads tosurface-dry conditions.54.3 Starling conditions forrestorationThe starting conditions for restoration that arepresented by cut-over bogs may thus varyconsi<strong>de</strong>rably. Table SI summarises sorne typicalstarting features <strong>of</strong>cut-over sites.55 General aims and principies forrestoration55.1 Aims <strong>of</strong>restorationRaised-bog sites that have been damaged by peatextraction or other land-uses have various possibleafter-uses. In the past, these have <strong>of</strong>ten inclu<strong>de</strong>dafforestation, conversion to agriculture, use as refusetips etc. However, changing attitu<strong>de</strong>s and circumstances,coupled with a recognition <strong>of</strong> the conservationvalue <strong>of</strong> sorne peatlands and their potential forregeneration have led to the view amongst conservationistsand others that the after-use presumption formany, if not aH, peat-cutting sites should be for natureconservation. There is accordingly a need for properplanning controls over workings which wiH inclu<strong>de</strong> arequirement on the peat industry to restore their sites,possibly to enable raised-bog conditions to re-establish.Table 51. Summary <strong>of</strong> possible starting conditions on cut-over bogs.TopographyTopography may be very variable across an abandoned peat extraction complex, <strong>de</strong>pending on the method and extent <strong>of</strong> peatextraction. Two situations can be distinguished, at several scales [2.1]:Massifsblocks with an overall convex or water shedding pr<strong>of</strong>ile.Depressionshollows wilh an overall concave or water holding pr<strong>of</strong>ile.Nole thal <strong>de</strong>pressions may occur within massifs.Block cutting <strong>of</strong>ten produces a regular system <strong>of</strong> baulks, flals and trenches, but can sometimes result in a largely flat surface.Mil/ing <strong>of</strong>ten produces a series <strong>of</strong> long peat fields, usually as cambered beds.Peat workings are <strong>of</strong>ten lower than adjoining refugium areas (which may be uncut remnants or revegetating cuttings).Water conditionsPeat extraction and drainage modify or <strong>de</strong>stroy typical bog vegetation and the charcterisitc bog acrotelm. They also typically inducedry conditions in cut-over areas and may also affect adjoining upstanding remnanls either directly or indirectly [Chapter 2]. Inconsequence:• water levels are generally too low for growth <strong>of</strong> peat-building Sphagnum species (except perhaps in some hollows);• water levels tend lo flucluate to a greater extent than in 'inlac!' bog;• waler storage capacily <strong>of</strong> lhe peat is typically lower than in 'intac!' bog;• water loss may be exacerbated if the lTlineral subsoil is exposed.Physical and chemical conditionsThe peat surface <strong>of</strong> a little-damaged bog is typically acidic and nutrient-poor. Peat extraction and drainage may lead to changes inthe physical and chemical characteristics <strong>of</strong> the peat available for recolonisalion [Chapter 2]. For example:• rewetting dried peat may lead to release <strong>of</strong> nutrients;• rewetting dried peat may lead to further acidificalion;• peat extraction may expose fen peat or mineral ground;• bare, dry peat provi<strong>de</strong>s an inhospitable physical environment for vegetation establishment.VegetationThe vegetation <strong>of</strong> remnant peat surfaces and <strong>of</strong> abandoned peat workings can be extremely variable, <strong>de</strong>pending upon suchconstraints as <strong>de</strong>gree <strong>of</strong> damage, <strong>de</strong>pth <strong>of</strong> extraction, topography, base status, nutrient status, water level (and source) and length<strong>of</strong> time since last worked [Chapter 41. Areas to be restored may thus inelu<strong>de</strong> the following [Box 3.1]:• bog-Sphagnum vegetation • non-wetland vegetation• para-bog-Sphagnum vegetation • completely bare surfaces• 'dry' bog vegetation • open water• fen vegetation


xxiiRESTORATION üF DAMAGED PEATLANDSIn addition to their potential for exploitation, theperceived 'values' <strong>of</strong> raised-bog sites inclu<strong>de</strong>:• plant and animal species and communítíes;• habitat-types;• mire system;• archaeological and palaeoecological archive;• 'peatland landscape'.Conservation priorities and restoration preferences\ forraised bogs wil1 be intluenced by the perceivedimportance <strong>of</strong> these various foci. The requirements forthe preservation or, where appropriate, restoration <strong>of</strong>these features are not i<strong>de</strong>ntical. For example, it may bepossible to preserve sorne <strong>of</strong> the features <strong>of</strong> a 'boglandscape', or the archival value <strong>of</strong> a raised-bog peat<strong>de</strong>posit, without necessarily retaining, or re<strong>de</strong>veloping,al1 <strong>of</strong> the characteristic biota <strong>of</strong> such an ecosystem.Conversely, in an extensively cut-over site it may bepossible to regenerate a typical bog surface, withcharacteristic biota, but the peat archive cannot bereplaced and the re<strong>de</strong>ve10pment <strong>of</strong> a 'bog 1andscape',whilst possible, is likely to be long-term and outwiththe foreseeable future. A further complication <strong>of</strong> choicearises in those raised-bog sites which have been badlydamaged but where the replacernent habitat has itself<strong>de</strong>veloped a high conservation value centred on speciesand habitat conditions that are essentially atypical <strong>of</strong>raised bogs. There is also a need to consi<strong>de</strong>r the currentcondition <strong>of</strong> a site when <strong>de</strong>termining most appropriateafter-use. It is recommen<strong>de</strong>d that the appropriateoptions for specific sites are discussed with natureconservation advisers, in the light <strong>of</strong> the informationcontained in this report [in particular Chapters 4, 6 and7].The following objectives are currently adopted in theconservation management <strong>of</strong> sorne raised-bog sites inthe UK:• the maintenance or re-establishment <strong>of</strong> wildlifeinterest not pertaining to bogsThis may inelu<strong>de</strong>: heath (wet and dry); rough grass;birch scrub and woodland; open water; reedbeds;herbaceous fen; fen meadow; fen woodland.• the maintenance or re-establishment <strong>of</strong> viablepopulations <strong>of</strong>typical bog speciesThis may inclu<strong>de</strong> bog species-populationsmaintained on badly-damaged bog surfaces orre<strong>de</strong>veloped within peat workings etc. Such sitesmay support, and be valued for, a range <strong>of</strong> species(sorne uncommon) other than bog species,including both tlora and fauna.• the maintenance or re-establishment <strong>of</strong> aregenerating, self-sustaining bog ecosystemThis inelu<strong>de</strong>s the maintenance <strong>of</strong> the on-going<strong>de</strong>velopment <strong>of</strong> an existing little-damaged bog; theregeneration <strong>of</strong> a damaged peat massif; andinitiation <strong>of</strong> 'new' raised bogs in peat workings. Invegetation terms, such sites have, or, it is hopedwill re<strong>de</strong>velop, vegetation referable to the MI 8 bogcornmunity over al1 or part <strong>of</strong>their surface.There are thus at least two rather different approachesto the conservation and restoration <strong>of</strong> damaged raisedbogs. One is essentially species-centred and aims tomaintain or re-establish viable populations <strong>of</strong> typicalbog (or other) species. The other is mire-centred, tomaintain or recreate a <strong>de</strong>veloping raised-bog ecosystem(with associated bog species). These two approachesare not necessarily mutually exclusive.It is possible to maintain or re-establish populations <strong>of</strong>many bog species on damaged bog surfaces (providingthey do not dry excessively). Such artificial situationsmay maintain numbers <strong>of</strong> typical bog species aseffectively as on a little-damaged or regenerating bog(although species will not necessarily be present in thecharacteristic proportions, or with the typical microtopography).Biodiversity may be increased relative toa little-damaged bog by the occurrence <strong>of</strong> supplementaryspecies on damaged sites with increaseddiversity <strong>of</strong> habitats (including those produced by pastpeat extraction activities and those atypical <strong>of</strong>bogs).In principIe the regeneration <strong>of</strong> a Sphagnum bog maybe expected to occur spontaneously in a variety <strong>of</strong>situations. However, SOrne starting conditions are moreimmediately suitable for raised-bog re<strong>de</strong>velopmentthan are others; and where the object <strong>of</strong> restorationinitiatives is to regenerate an ombrotrophic ecosystemwithin the foreseeable future, it is likely to be <strong>de</strong>sirableto consi<strong>de</strong>r active procedures that will optimise andfacilitate such a process, rather than to adopt a laissezfaire approach in which natural processes <strong>of</strong> mire<strong>de</strong>velopment are just left to sort themselves out.Where parts <strong>of</strong> cut-over raised-bog sites haveconsi<strong>de</strong>rable existing conservation interest, there is<strong>of</strong>ten an un<strong>de</strong>rstandable <strong>de</strong>sire amongst conservationiststo rnaintain or enhance the status qua. By contrast,there may be scope for a wi<strong>de</strong>r choice <strong>of</strong> objectives forcurrent workings where the existing biological interestis minima], but even in current peat workings therestoration opportunities may be constrained bypracticalities. For example, in sorne sites there may belittle option but to accept that wet restoration will, atleast in the first instance, be to a minerotrophic habitat(or, or course, sorne form <strong>of</strong> alternative 'dryland'habitat). However, even this does not necessari1ypreclu<strong>de</strong> the <strong>de</strong>velopment <strong>of</strong> raised bog in the longtermo


SUMMARYxxiii55.2 PrincipIes o(raised-bogrestorationAs different species and restoration objectives mayhave markedly different environmental requirements,the creation <strong>of</strong> appropriate habitat conditions can onlybe consi<strong>de</strong>red in terms <strong>of</strong> the specified objectives. Thepurpose <strong>of</strong> rewetting damaged peatlands is not just tomake thern wet, but to proví<strong>de</strong> condítíons appropríatefor the <strong>de</strong>sired renaturation and regeneration objectives.The <strong>de</strong>velopment <strong>of</strong>restoration strategies needs toconsi<strong>de</strong>r the conditions required to realise the specifiedobjectives, whilst recognising, for example, that theconditions nee<strong>de</strong>d to re-establish <strong>de</strong>sired types <strong>of</strong>vegetation may differ from those required to maintainexisting examples.Two broad approaches to peatland restoration can bedistinguished: repair and rebuilding. Repair usuallyentails relatively minor restorative operations (ditchblockíngetc.) and aíms at direct reinstaternent <strong>of</strong> the<strong>de</strong>sired objectives. It is particularly appropriate forsites with limited damage. Rebuilding involves there<strong>de</strong>veloprnent <strong>of</strong> the peatland and implies that the<strong>de</strong>sired endpoint cannot be produced directly butrequires phased construction, with a starting point <strong>of</strong>ienrather different from the final product. In Sorne cases,further 'damage' may be required to produce a securefoundation for rebuilding. Depending on the restorationobjective, the restoration <strong>of</strong> bogs extensively damagedby commercial peat extraction will usually requirerebuilding rather than repair.The aim <strong>of</strong> restoring cut-over peatlands to raised bogmay be achieved following four different paths:• direct colonisation <strong>of</strong> bog peat by plants associated withtypical bog vegetation (M 18);• colonisation <strong>of</strong> ombrotrophic water by plants and mossesassociated with bog pools followed by successionalinvasion <strong>of</strong>other bog species;• colonisation <strong>of</strong> fen peat (or wet mineral soils) by fenplants followed by successionaI <strong>de</strong>velopment to bog;• hydroseral colonisation <strong>of</strong> minerotrophic water to formfen and thence bogo<strong>Restoration</strong> initiatives must en<strong>de</strong>avour to createenvironmental conditions which ·are conducive·to the<strong>de</strong>velopment <strong>of</strong> acid mire vegetation and peataccumulation, and re-instatement <strong>of</strong> an acrotelm withproperties comparable to that <strong>of</strong> a little-damaged bog,with the intention <strong>of</strong> leading to the <strong>de</strong>velopment <strong>of</strong> aself-sustaining, ombrotrophic system. To halt orreverse hydrological effects <strong>of</strong> peat cutting anddrainage and their impacts on the flora and fauna, twomain objectives must be realised:• establishment and maintenance <strong>of</strong> consistently wetsurface conditions, maintained primarily by rainfalJ;• <strong>de</strong>velopment <strong>of</strong> a suitable peat-forming vegetation-type,dominated by Sphagnum species.In practice, these may be brought about by thefollowing measures:•••••increase in appropriate retention <strong>of</strong> nutrient-poorprecipitation input;prevention or reduction <strong>of</strong> water inputs from othersources;faci litation <strong>of</strong>waterlogging;facilitation <strong>of</strong> colonisation by bog specics, in particular,Sphagnum spccies;reduction <strong>of</strong>water-Ievel fluctuations.These aims will be mainly realised by on-sitemanagement, but with careful regard to activitieswithin the surrounding catchment which may affect thesite [Chapters 5 & 8].A summary <strong>of</strong> the main factors affecting restorationoptions is given in Table 82 [see also Chapters 3 & 4].86 Planning a restoration strategyS6.1 IntroductionThere are at least three broad approaches to peatlandrestoration: unplanned, empirical and measured.Although several important eonservation sites arelargely a produet <strong>of</strong> unplanned restoration, this cannotbe commen<strong>de</strong>d as a reliable approaeh to realise aspecific restoration goal. The 'empirieal approach' isone in which restoration is substantially based upon anintuitive appraisal <strong>of</strong> the requirements for habitatmanipulation, rather than upon the data acquisition andprediction, which forms the basis <strong>of</strong> a 'measuredapproaeh'. 80th <strong>of</strong> these approaches have merits andlimitations [see Chapter 7], and in practice, manyrestoration sehemes will rely on a sensitive interaetionbetween them. In most cases, empirical proceduresrequire some 'hard' data to heJp ensure (and monitor)their suecess, but equally, the empirical approach mayprovi<strong>de</strong> the only realist option when data acquisition isina<strong>de</strong>quate or <strong>of</strong> limited predictive reliability. To yieldmaximum benefits for restoration, data acquisitionshould be: (a) focused upon answering specifie,<strong>de</strong>fined questions that are critícai to particular aspects<strong>of</strong> restoration; (b) sufficiently well resourced to enSUrethat reliable and useable data are eollected; and (e)performed by experieneed practitioners who are aware<strong>of</strong> the inherent problems and likely limitations <strong>of</strong> theirstudies. Emphasis must be placed on the need forcollection <strong>of</strong> relevant and relíable data and for aconsi<strong>de</strong>red appraisal, at the outset <strong>of</strong> planning arestoration strategy, <strong>of</strong> the salient questions and datathat are likely to be required to answer them.Thus, in most damaged peatland sites, particularlythose subject to extensive commercial peat extraction,sorne form <strong>of</strong> plan will be required to optimiserestoration, particularly where it is <strong>de</strong>sired to restore


xxivRESTORATlON OFOAMAGED PEATLANDSTable 52. Summary <strong>of</strong> main factors affecting restoration optionsLegal consi<strong>de</strong>rationsNational, regional and local planninglegislation and policiesInternational and national conservationlegislation (including wildlife, archaeology,paJaeoecology etc.)Legislation relating to water resources(e.g. water impoundment, abstraction,discharge)Obligations to neighbouring land-ownersetc.Miscellaneous legal constraints (rights <strong>of</strong>way, grazing rights. public utilities etc.)Practical consi<strong>de</strong>rationsTopography (within site and in relation tosurrounding landscape) (inclu<strong>de</strong>s size andshape <strong>of</strong> site, and disposition <strong>of</strong> surface)HydrologyPeat <strong>de</strong>pths and types (or mineralsubstratum)ClimateFlora and faunaArchaeology I PalaeoecologyChemistryAccess by machineryPractical assistanceFinancial oonsi<strong>de</strong>rationsWil/ affect <strong>de</strong>cisions on most appropriate after-use (particularly with respect toplanning conditions and costs)Wil/ affect <strong>de</strong>cisions on most appropriate after-use and methods by which it can beachievedMay affect methods by which a particular after-use can be achievedMay constrain possibilities for after-use and methods by which they can beachievedMay constrain possibilities for after-use and methods by which they can beachievedDetermines the feasibility <strong>of</strong> retaining water on site, preventing minerotrophicinputs etc. and methods by which these can be achievedIt is important to establish causes <strong>of</strong>dryness, <strong>de</strong>gree <strong>of</strong>drainage, water inputs andoutputs. interactions with water in surrounding 'catchment' etc.; affects feasibility<strong>of</strong> potential options; provision <strong>of</strong>appropriate hydrological conditions <strong>de</strong>terminesrecolonist species and type <strong>of</strong>successionHydrological, physical and chemical implicationsAffects feasibility <strong>of</strong>potential options for water retention, and timescales forphasing <strong>of</strong> workPreservation <strong>of</strong> existing interest; availability <strong>of</strong>recolonist species (especial/ySphagna); availability orprovision <strong>of</strong>appropriate hydrological and chemicalconditions for individual species; possible conflicting conservation <strong>de</strong>mandsPreservation <strong>of</strong> existing interest; monitoring during extractionBase and nutrient status <strong>of</strong> substratum (peat or mineral) and irrigating water<strong>de</strong>termines recolonist species, and rates <strong>of</strong> recolonisation; air pol/ution mayinfluence recolonisation, especial/y by SphagnaMay affect feasibility <strong>of</strong>different management operations, particularly in relafion tophasing <strong>of</strong> workPossibilities may affect management options (inclu<strong>de</strong>s machinery, survey,monitoring, management etc.)May affect management and monitoring options (possibilities for compensationand grant-aid etc.; costs <strong>of</strong>surveys, feasibility studies, management operations,on-going maintenance etc.)the raised-bog habitat. A plan is required to ensure that,inter alia:• areas <strong>of</strong> existing natural history interest that will not besubject to further peat extraction are safeguar<strong>de</strong>d;• peat workings are left in a condition optimal forrestoration;• restoration practices and objectives for specific areas arewell phased and integrated with one another;• techniques appropriate to achieve specific restorationobjectives are i<strong>de</strong>ntified.Formulation <strong>of</strong> such a restoration plan for a raised-bogsite requires the acquisition <strong>of</strong> sorne information aboutthe site in question. Information (environmental andbiological) is particularly required (i) to help selectappropriate restoration options; (ii) to i<strong>de</strong>ntify theconstraints upon the chosen options and to enableinformed <strong>de</strong>cisions to be ma<strong>de</strong> on the most appropriateways to achieve specific objectives; and (iii) to provi<strong>de</strong>base-line data for monitoring purposes. Consultationwith various statutory and non-statutory bodies willform an important part <strong>of</strong> the planning stage. Theseinelu<strong>de</strong> the local mineral planning authority, heritage,conservation and water resources bodies. It is alsoIikely to be necessary to involve specialists in ar<strong>de</strong>r,for example, to carry out survey work; interpret theresults; assist in the preparation <strong>of</strong> an appropriaterestoration scheme with <strong>de</strong>tailed specifications andperhaps occasionally to provi<strong>de</strong> legal advice.


SUMMARYxxvThe variability <strong>of</strong> starting conditions amongst damagedlowland peatlands means that a universal statement <strong>of</strong>'information required' cannot be ma<strong>de</strong>, although it ispossible to i<strong>de</strong>ntify some <strong>of</strong> the main types <strong>of</strong>information that may be required.Assessments will be based on information <strong>de</strong>rived from(a) a preliminary '<strong>de</strong>sk study' by collation <strong>of</strong> existinginformation and (b) from on-site investigations. Thelatter, together with interpretation <strong>of</strong> the information,may require the expertise <strong>of</strong> specialists from severaldifferent disciplines. Collection <strong>of</strong> superfluous informationshould be minimised by careful scoping <strong>of</strong> thesite assessment programme (an example <strong>of</strong> the potentialscope <strong>of</strong>a feasibility study is given in Table 7.1).56.2 Potentiallegal and land-useconstraints on <strong>de</strong>velopmentThe relevant legislation (local, national andintemational) which may affect <strong>de</strong>velopnient[Appendix 2] should be investigated and itsimplications for restoration options i<strong>de</strong>ntified. Themost important areas to be consi<strong>de</strong>red concemlegislation relating to planning, conservation and waterresources. Consultations with the local planningauthority, conservation bodies and water resourcesbodies are therefore <strong>of</strong> particular importance. Searchesshould also be ma<strong>de</strong> for possible constraints such ascommon land, rights <strong>of</strong> turbary, rights <strong>of</strong> way, riparianrights, mineral rights, shooting rights, grazing rights,location <strong>of</strong> public utilities such as gas pipes, electricitypylons etc. The implications <strong>of</strong>any such constraints forthe project should be assessed.56.3 Financial consi<strong>de</strong>rationsUnless funding for restoration work has been agreed inadvance, the feasibility <strong>of</strong> restoration options may<strong>de</strong>pend on financial limitations, as well as practical andlegal constraints, and the potential for financial orpractical assistance from statutory and non-statutorybodies should be assessed.56.4 Field investigationsThe aim <strong>of</strong> the field investigations is to build on theinformation gathered in the preliminary <strong>de</strong>sk-study,enabling all the relevant options to be consi<strong>de</strong>red in theformulation <strong>of</strong> an appropriate restoration strategy. Sitesurveys must necessarily gather information on a wi<strong>de</strong>range <strong>of</strong> inter-related topics (topography, hydrology,peat <strong>de</strong>pths etc.), so it is <strong>de</strong>sirable to co-ordinate effortsfrom interested parties. Particular care should be takento ensure that data acquisition is well focused, sufficientlywell resourced and performed by experiencedpractitioners who, when appropriate, are aware <strong>of</strong> thelikely limitations <strong>of</strong>their studies.Site physical characteristicsA broad survey <strong>of</strong> the topography and physicalcharacteristics <strong>of</strong> the site should be carried out toobtain information on the following factors, if notalready available in sufficient <strong>de</strong>tail from existingdocumentation:• general size and shape; extent <strong>of</strong> sitc in rclation to wholcpeat body;• surfacc and subsurfacc topography; pcat <strong>de</strong>pths;• gcology and soils undcrlying and surrounding thc sitc;• acccss for machinery and cquipmcnt;• location <strong>of</strong> cxisting tracks, pathways, boundaries,buildings and other structures; 10cation <strong>of</strong> potentialhazards (e.g. rubbish tips).HydrologyThe major problem for the restoration <strong>of</strong> most damagedbog sites is the lack <strong>of</strong> sufficient water <strong>of</strong> appropriatequality at or near the surface <strong>of</strong> the bog to sustain thegrowth <strong>of</strong> peat-building Sphagna. lt is essential toi<strong>de</strong>ntify the causes <strong>of</strong> <strong>de</strong>hydration and the main waterinputs and outputs in different areas <strong>of</strong> the bogo Usefulinformation may be obtained while peat extraction ison-going, for example incorporating pump tests to gaininformation on water gradients and flows.lt is recommen<strong>de</strong>d that expert hydrological advice issought on the level <strong>of</strong> <strong>de</strong>tail required for an a<strong>de</strong>quatehydrological assessment <strong>of</strong> a site in relation to theproposed restoration objectives. Information whichmay be required could inclu<strong>de</strong> the following (at leastthose items marked * are likely to be nee<strong>de</strong>d):• climatic information*;• dctails <strong>of</strong>watcr courses* (type, distribution, slope, <strong>de</strong>gree<strong>of</strong> functioning);• water outputs*;• topographical disposition <strong>of</strong> peat fields* and remnants*;peat <strong>de</strong>pths* and sub-surface contours;• peat hydraulic conductivity;• vegetation characteristics;• distribution and stability <strong>of</strong>open water*;• potential for water supply;• local and regional context <strong>of</strong> the site.Substratum characteristics and water qualityThe chemical properties <strong>of</strong> water and peat will have apr<strong>of</strong>ound influence on the plants that will colonise agiven area <strong>of</strong> peatland, and on the likely course <strong>of</strong>subsequent succession [Chapters J. 2 & 4]. They mayalso affect the long-term preservation <strong>of</strong> some archaeo­IogicaI structures. Thus some basic chemical data may


xxviRESTORATION OF DAMAGED PEATLANDSbe nee<strong>de</strong>d to make <strong>de</strong>cisions on the most appropriatestrategies and outcomes.Knowledge <strong>of</strong> the type <strong>of</strong> peat present is veryimportant in assessing the potential and options forrestoration. One <strong>of</strong> the most important factors iswhether the peat is ombrotrophic (bog) peat or minerotrophic(fen) peat. Simple assessment <strong>of</strong> the <strong>de</strong>gree <strong>of</strong><strong>de</strong>composition <strong>of</strong> the peat (humification value) mayalso give insights into likely water storage capabilitiesand permeability <strong>of</strong> the peat, and its suitability for usein the construction <strong>of</strong>water-retaining structures.Biological interestA survey and assessment <strong>of</strong> the eXlstmg biologicalinterest <strong>of</strong> a site is an important component in theformulation <strong>of</strong> a restoration strategy. Where possible,field survey should build on the information collatedduring the initial <strong>de</strong>sk study [7.4]. The aims <strong>of</strong> thesurvey should i<strong>de</strong>ally inclu<strong>de</strong> the following:• i<strong>de</strong>ntification and assessrnent <strong>of</strong> any areas with existingbiological interest;• i<strong>de</strong>ntification <strong>of</strong> any species or cornrnunities with specialconservation status (e.g. statutory protection) eitherpresent on, or using the site; for the less cornrnon species,sorne assessrnent <strong>of</strong>population size should be assessed;• i<strong>de</strong>ntification <strong>of</strong> any potential conflicts between existingconservation interest and airns <strong>of</strong> restoration strategy;• assessrnent <strong>of</strong> the potential for 'natural' and 'assisted'recolonisation <strong>of</strong> damaged or rewetted areas (i.e. theavailability <strong>of</strong> inoculurn etc.);• i<strong>de</strong>ntification <strong>of</strong> areas with 'un<strong>de</strong>sirable' species orcornrnunities (e.g. scrub etc.);• i<strong>de</strong>ntification <strong>of</strong> potential 'threats' to the existing floraand fauna;• provision <strong>of</strong> base-line data for rnonitoring.Archaeological and palaeoecological interestA search should be un<strong>de</strong>rtaken for eXlstmgdocumentation or records and pr<strong>of</strong>essional advicesought on the potential archaeological interest <strong>of</strong> thesite. In addition to the palaeoecological record andartefacts, the historical and industrial landscape andbuildings on a cut-over site may be <strong>of</strong> interest, and maywarrant recording before remedial action is un<strong>de</strong>rtaken.Specific points which should be consi<strong>de</strong>red during anarchaeological investigation inclu<strong>de</strong>:• the 'value' <strong>of</strong> the site both in terrns <strong>of</strong> the individualstructures and artefacts and the site as a whole;• the irnportance <strong>of</strong> the site in the context <strong>of</strong> others in thearea;• the historical and industrial landscape;• the palaeoecological record contained in the peat;• the conservation needs <strong>of</strong> any finds and potential for~onf1ict with wildlife conservation airns (and restorationrnethods).Additional assessmentsAssessments should also be ma<strong>de</strong> <strong>of</strong>:• land use on and around the site;• potential for the control <strong>of</strong> tire (i<strong>de</strong>ntification andassessrnent <strong>of</strong> access routes for vehicles carrying firefightingequiprnent, potential water sources andfirebreaks etc.);• engineering assessrnent, particularly on sites whererestoration involves construction <strong>of</strong> bunds, rnovernent <strong>of</strong>consi<strong>de</strong>rable arnounts <strong>of</strong> peat etc., consi<strong>de</strong>ring the natureand properties <strong>of</strong> the rnaterials available on site, theexisting topography, the condition <strong>of</strong> structures, thepotential for building water-retaining constructs, thepotential for access by rnachinery and the rnovernent <strong>of</strong>water through the site;• safety assessrnent - e.g. consi<strong>de</strong>ration <strong>of</strong> physical andchernical hazards, and health and safety legislation;• assessrnent <strong>of</strong> potential irnplications <strong>of</strong> rewetting fornearby inhabitants - e.g. increase in biting insects.57 Options and procedures forrestoration57.1 IntroductionPractical experience <strong>of</strong>wetland restoration and creationsuggests that chances <strong>of</strong> success are likely to beimproved by <strong>de</strong>fining clear objectives [Chapters 4 & 6]and i<strong>de</strong>ntifying appropriate management strategies fortheir achievement [Chapters 5 & 8-JO]. In mostsituations, the procedures adopted and associatedoutcomes <strong>of</strong> raised-bog restoration are likely to be acombination <strong>of</strong> <strong>de</strong>sirability modified by feasibility. Thefeasibility <strong>of</strong> specific objectives will be <strong>de</strong>terminedprimarily by the starting conditions available forrestoration, viz. the environmental context <strong>of</strong> the siteand the particular conditions created by peat extractionor other forms <strong>of</strong> damage [see Table SI]. Tablessummarising the likely outcomes <strong>of</strong> resíorationprocedures from a contrasting range. <strong>of</strong> startingconditions are given in Chapter 6 [Table 6. J]. It isrecommen<strong>de</strong>d that these tables are used as the basis fordiscussions between regulatory and planningpr<strong>of</strong>essionals and pr<strong>of</strong>essional ecological advisorswhen i<strong>de</strong>ntifying options to follow for individual sites.57.2 <strong>Restoration</strong> options forombrotrophic peat surfacesIn a little-damaged bog, the character, integrity and ongoinggrowth <strong>of</strong> the system is in large measuremaintained by the functional characteristics <strong>of</strong> theacrotelm (see aboye). In a damaged bog, where there isno acrotelm (in its full, functional sense), the surface isessentially characterised by relative instability <strong>of</strong>various environmental variables, especially water leve\.


SUMMARYxxviiThe essential problem <strong>of</strong> restoratio~ <strong>of</strong> bog vegetationon a damaged surface is one <strong>of</strong> 'kicking' the systemfrom the 'damaged surface' stable state to a 'bogacrotelm-based'stable state. The difficulty <strong>of</strong> this isthat the conditions required to re<strong>de</strong>velop an acrotelmwith the properties typical <strong>of</strong> little-damaged bogsurface are in consi<strong>de</strong>rable measure provi<strong>de</strong>d by thissort <strong>of</strong> acrotelm itself. A solution to this problem is totry to construct <strong>de</strong>vices that mímic sorne <strong>of</strong> theproperties <strong>of</strong>the original acrotelm and which permit itsre<strong>de</strong>velopment by sustaining the growth <strong>of</strong> typical bogspecies. Many <strong>of</strong> the different approaches to bogrestoration essentially represent different ways <strong>of</strong>attempting to solve this problem.The re-instatement <strong>of</strong> a Sphagnum-based vegetation ona damaged ombrotrophic surface is wi<strong>de</strong>ly regar<strong>de</strong>d asa most <strong>de</strong>sirable aim <strong>of</strong>raised-bog restoration [Chapter3]. It requires the establishment and maintenance <strong>of</strong>consistently wet surface conditions. The extent towhich this is possible will be inf1uenced by theprevailing climatic conditions and regulated by themain water-balance terms <strong>of</strong> each bog, viz. rate <strong>of</strong>precipitation input, rate <strong>of</strong> water loss (lateral andvertical discharge and evapotranspiration) and waterstorage at the peat surface.Rewetting problems may be greater on massifs (whichhave a propensity to shed water) than in <strong>de</strong>pressions(which are typically water-holding areas) [see Chapter2]. Various approaches can be used to rewet massifs[Chapter 5; Table 6.1a], but particular difficulties canbe found with badly damaged remnants. Likewise, aseries <strong>of</strong> upstanding blocks, at different levels, whichare found in sorne (usually abandoned) peat extractioncomplexes can present particularly intractableproblems for restoration. In sorne situations it mayhave to be accepted that effective rewetting is notfeasible, in which case the remnants may be lefi tosupport sorne replacement habitat - which may inclu<strong>de</strong>sorne bog species - .though they are ultimately likely tobe wasting assets.Because <strong>of</strong> their situation, effective rewetting <strong>of</strong> peatfields (Chapter 5; Table 6.1b) may be technically lessdifficult to achieve than rewetting !Jf massifs. In manycases it will be necessary to have structures to impoundwater against lateral f10w and to increase storage,though this will <strong>de</strong>pend upon the topography anddisposition <strong>of</strong> the abandoned surfaces and the c1imaticcontext. The f1at or gently sloping surfaces <strong>of</strong> mo<strong>de</strong>mcommercial peat fields are <strong>of</strong>ien well suited torewetting over extensive areas. Nonetheless, therewetting <strong>of</strong>peat fields cannot be divorced from that <strong>of</strong>peat massifs, particularly if the aim is to regenerate abog across the whole site, integrating both peat fieldsand the massifs (see below).57.3 <strong>Restoration</strong> options forminerotrophic peat surfacesThe type <strong>of</strong> vegetation that <strong>de</strong>velops in abandoned peatworkings in fen peat is primarily a function <strong>of</strong> water<strong>de</strong>pth (and stability), water quality (particularly baserichnessand nutrient-richness) and managementregime (if any). Peat workings within fen peat canprovi<strong>de</strong> a variety <strong>of</strong> habitats, which are valued forconservation for various reasons and in sorne cases aremanaged to maintain or re<strong>de</strong>velop these interests:• open water (interest <strong>of</strong>ten mainly ornithological an<strong>de</strong>ntomological);• reedbeds (interest <strong>of</strong>ten mainly ornithological an<strong>de</strong>ntomological);• herbaceouslen (various types);• len woodland;• len meadow;• Sphagnum bogoProspects for restoration <strong>of</strong> minerotrophic surfaces will<strong>de</strong>pend critically upon the topography <strong>of</strong> the site, thewater level that can be maintained and the quality <strong>of</strong>the water used to achieve this (Table 6.1c). In SOrnecases revegetation within f100<strong>de</strong>d peat workings hasproduced sorne <strong>of</strong> the most important areas <strong>of</strong> fencurrently extant within the UK. Such hydroseralsituations are also susceptible to Sphagnumestablishment and in sorne locations consi<strong>de</strong>rablethicknesses <strong>of</strong>Sphagnum peat have accumulated (up to1 rn <strong>de</strong>pth in c. 100-150 years) and an ombrotrophicsurface has re-established. By contrast, Sphagnum reestablishmenton solid fen-peat surfaces is generallymuch more limited (except in high rainfall regions),probably on account <strong>of</strong> periodic dryness and irrigationwith base-rich water.The formulation <strong>of</strong> <strong>de</strong>sirable restoration options for fenpeat sites is <strong>of</strong>ien more difficult than for sites based onbog peat as there is <strong>of</strong>ien more scope for habitatmanipulation and <strong>of</strong> renaturation outcome. A primary<strong>de</strong>cision is whether to focus upon the recreation <strong>of</strong> bogor fen, though these options are not mutually exclusive,as sorne forms <strong>of</strong> fen can give rise to bog vegetation.With the fen option, the choice then becomes the type<strong>of</strong>fen <strong>de</strong>sired, as this can be inf1uenced by <strong>de</strong>terminingwater sources and water levels. The choice <strong>of</strong>objectives is Iikely to be <strong>de</strong>termined by topography,availability (and quality) <strong>of</strong> minerotrophic watersources and implications for on-going management andmaintenance as well as by conservational <strong>de</strong>sirability.Procedures adopted for rewetting fen peat will <strong>de</strong>pendstrongly on the surrounding topography <strong>of</strong> the peatworkings. In general, rewetting can be achieved mostreadily where the wórkings form a c10sed <strong>de</strong>pression(within bog peat, fen peat or mineral soil) or wherethey have been <strong>de</strong>liberately bun<strong>de</strong>d. In this situation it


xxviiiRESTORATION OF DAMAGED PEATLANDSmay be possible to inundate the <strong>de</strong>pressions. In othersituations cut-oYer fen surfaces are tlat and located atabout the same level as, or even higher than,surrounding farmland. In this case attempts to maintaina permanently high water table on the peat surface withminerotrophic water may bedifficult without causing(at least temporary) waterlogging <strong>of</strong> adjoining land.Bunding may be used to help hold water on the site,both to prevent tlooding <strong>of</strong> adjoining land and tomaintain a high water level in the fen peats. In sornesituations, it may be necessary to provi<strong>de</strong> a drain tocarry away water from the agricultural land, to helpprevent the bund from drying out, and occasional1y toprovi<strong>de</strong> 'top-up' water to the fen in dry summers.57.4 <strong>Restoration</strong> options for mineralsubstrataIn sorne sites peat has been extracted to expose largeareas <strong>of</strong> the un<strong>de</strong>rlying mineral substrata. Specification<strong>of</strong> restoration options for this situation may be subjectto the same problems as for fen peat with respect tovariation in the character <strong>of</strong> water sources and sinks. Itis further complicated by the great variability <strong>of</strong>physico-chemical characteristics <strong>of</strong> the substrata,which, for example, may vary from very acidic gravelsto base-rich clays. Growth <strong>of</strong> Sphagna and other bogspecies may be just as good (if not better) on acidic,nutrient-poor mineral substrata as it is on ombrotrophicpeats and may provi<strong>de</strong> the basis for the <strong>de</strong>velopment <strong>of</strong>boginthelongterm.57.5 Integration <strong>of</strong> the restoration <strong>of</strong>remnant massifs andcommercial peat fieldsIn sorne situations the restoration <strong>of</strong> damaged peatlandscan be approached piecemeal. This approach is likelyto be most satisfactory when it is possible to provi<strong>de</strong>in<strong>de</strong>pen<strong>de</strong>nt hydrological control <strong>of</strong> particular landparcels. For example, in the fen peat basins <strong>of</strong>individual holdings in the Somerset Levels it may <strong>of</strong>ienbe possible to renature each working in<strong>de</strong>pen<strong>de</strong>ntly <strong>of</strong>the others. Similarly, sorne sealed <strong>de</strong>pressions withinombrotrophic peat may be rewetted in<strong>de</strong>pen<strong>de</strong>ntly <strong>of</strong>their surroundings; in<strong>de</strong>ed, such an approach may bethe only practical possibility in sorne sites where cutoversurfaces have been lefi at wi<strong>de</strong>ly differing levels.This approach may be very effective in maintainingpopulations <strong>of</strong> bog species within the landscape (i.e.production <strong>of</strong> a series <strong>of</strong> 'bog-gar<strong>de</strong>ns') but it is lesssuited to the co-ordinated regeneration <strong>of</strong> an entiremire [see Chapter 5], for which a more holisticapproach to water management is likely to be <strong>de</strong>sirable.The options for the water management <strong>of</strong> compositesites, where the aim is to restore (or maintain) bogconditions in both the peat fields and the massif, areessentially:a) to treat the massifs and peat fields largely as separateobjects; this approach involves the artificial maintenance<strong>of</strong> high water levels in the massif and does not attempt torestore the bog as a single entity. The possibility <strong>of</strong> futureintegration, as accumulating peat over the peat fieldscoalesces with that on the massif, is not preclu<strong>de</strong>d but isunlikely to occur rapidly;b) to unify the massif and the extraction fields byencouraging or engineering a common water moundappropriate to maintain, or recreate, wet conditions in themassif. The possibilities for this will <strong>de</strong>pend upon thesalient characteristics <strong>of</strong> the water mound associated withthe remnant massif. Approaches which have beensuggested are (i) to reduce the height <strong>of</strong>the massif to thelevel <strong>of</strong> a sustainable water mound; (ji) to elevate thewater levels (over the peat fields) around the remnantmassif; (iii) grading <strong>of</strong>the peal surface up lo the massif.In sorne situations it may be necessary to treat the peatfields and massifs separately in the short or mediumterm, while aiming for integration as a whole in thelong termo It is important to avoid the situation wheretreating areas separately could lead to a contlict <strong>of</strong>conservation interests.In many instances, restoration <strong>of</strong> a raised bog does not<strong>de</strong>mand the rewetting <strong>of</strong> adjoining land, even in thosecases where it once formed part <strong>of</strong>the original peatlandarea. However, in sorne instances localised rewettingcould enhance the coherence <strong>of</strong> the bog or effectiverewetting <strong>of</strong> a bog may only be possible by sornemanipulation <strong>of</strong> the drainage in the surrounding land.This is likely to be the case where land-drainagesystems directly (a) drain the mire or (b) indirectlydrain it, in situations where the water table in fen peator an un<strong>de</strong>rlying aquifer would otherwise form theimpermeable base to the water mound. Rewetting <strong>of</strong>peat workings in fen peat may have greaterrepercussions upon the adjoining land as <strong>of</strong>ien theability to rewet the workings may <strong>de</strong>pend upon watersupply and retention that is <strong>de</strong>termined, directly orindirectly, by adjoining land drainage systems.57.6 Optimisation <strong>of</strong>peat workingpractices and startingcondítíons for restorationIt is not possible to set out universal gui<strong>de</strong>lines on<strong>de</strong>sirable working practices, as these will partly <strong>de</strong>pendupon site-specific features, incIuding:• conservation objectives;• character <strong>of</strong>the existing biological resource;• character and configuration <strong>of</strong> the remaining peat <strong>de</strong>posit(especially topography and peat properties);


SUMMARYXXIX• environmental context (especially c1imate, but alsocharacteristics and use <strong>of</strong>the adjoining landscape);• existing or future planning constraints.However, it is possible to i<strong>de</strong>ntify sorne <strong>of</strong> theun<strong>de</strong>rlying principIes and suggest working practiceswhich should facilitate the restoration process, andwhich should be taken into account, particularly ifplanning perrnissions and conditions are un<strong>de</strong>r review.General requirements inclu<strong>de</strong>:• a scientific assessment <strong>of</strong> the character <strong>of</strong> the site,possibly by in<strong>de</strong>pen<strong>de</strong>nt scientists, with particular regardto features important in <strong>de</strong>termining <strong>de</strong>sirable andfeasible restoration options, based on factors i<strong>de</strong>ntified inChapter 7;• a restoration strategy should be <strong>de</strong>vised and agreed forthe site, based on the scientific assessment andconservation objectives (Chapter 3];• where feasible, peat extractors should optimise and phaseworking operations to facilitate the agreed restorationstrategy;• working practices should aim to minimise further damageto abandoned areas and refugia, and, where feasible,enable restoration work to commence on sorne workingareas as soon as possible;• at cessation <strong>of</strong> operations (in parts or all <strong>of</strong> the site), peatfields should be configured into an (agreed) conditionthat will optimise restoration (i.e. to maximise use <strong>of</strong> insitu machinery, operators and infrastructure) (Chapters 5&~. -The following principIes should be taken into consi<strong>de</strong>ration,and irnplernented where possible:• Important refugia (which may inclu<strong>de</strong> Iittle-damagedareas <strong>of</strong> bog, as well as revegetated cuttings or damagedareas with an important biological resource) should bei<strong>de</strong>ntified and steps taken to preserve or enhance theirexisting conservation interesl.• If feasible and necessary a buffer zone (Chapter 8]should be <strong>de</strong>signated around the core part <strong>of</strong> anyrefugium areas, which should also remain uncul.• Work should start on the restoration <strong>of</strong> abandoned areasand maintenance <strong>of</strong> refugia as soon as possible, so that<strong>de</strong>hydration is minimised.• Peat should be extracted in such a way as to leaveupstanding baulks to a specified eventual height at agreedintervals. .• Iffeasible, operations should be phased such that:(i) Contiguous areas should be completed in sequence.(ii) Areas c10sest to refugia should be abandoned first,Ieaving agreed <strong>de</strong>pths <strong>of</strong>peal.• Ifthe aim is to regenerate ombrotrophic bog directly, it isrecomrnen<strong>de</strong>d that as a general rule a minimum <strong>of</strong> 50 cm<strong>of</strong> ombrotrophic peat be left in situ. Sufficient peatshould also be left to allow for constructs to impoundwater (bunds or a scalloped surface).• Drains should not be dug into mineral subsoil (unless thisis impermeable and unlikely to lead to downward waterloss). (Where minerotrophic conditions are produced, fenvegetation will resull. It is quite possible thatombrotrophic bog may <strong>de</strong>velop from this, by naturalsuccessional processes, but this may take longer thanwhen ombrotrophic conditions are retained in situ.]• Where possible, 'nursery' pools for the 'farming' <strong>of</strong>Sphagnum should be initiated, to provi<strong>de</strong> an inoculum forabandoned areas (Chapter 9].• Drainage operations should be assessed, and wherepossible re<strong>de</strong>signed to minimise impacts on remnants andareas un<strong>de</strong>rgoing restoration. In low rainfall areas it maybe <strong>de</strong>sirable to pump drainage water into abandoned peatworkings etc., although this will partly <strong>de</strong>pend on thequality <strong>of</strong>the pumped water (Chapter 5].57.7 Rewetting and revegetationOnce an area has been brought out <strong>of</strong> production,further operations should start as soon as practicable t<strong>of</strong>acilitate the creation <strong>of</strong> optimum conditions forrewetting and reyegetation, including the building <strong>of</strong>constructs, such as bunds where necessary [Chapters 5,8 and 10], though this should be planned to ensure thatrewetting initiatives do not preclu<strong>de</strong> subsequent accessor actions elsewhere on the site. In sites where peatextraction is ongoing in adjoining areas, it will usualIybe rnost cost-effective to make use <strong>of</strong> the rnachineryavailable on site for restoration work. Sorne <strong>of</strong> thernain constraints to be overcorne and potential solutionsare i<strong>de</strong>ntified in Table S3.RewettingApproaches consi<strong>de</strong>red for minirnising hydrologicalchange within upstanding peat rernnants and forrewetting cut-oyer sites inclu<strong>de</strong>:• elevation <strong>of</strong>the water level by ditch-blocking;• natural subsi<strong>de</strong>nce <strong>of</strong> peat to the position <strong>of</strong> the perchedwater mound;• sculpting <strong>of</strong> the peat surface to the position <strong>of</strong> theperched water mound;• elevation <strong>of</strong>the water level by containment within bunds;• elevation <strong>of</strong> the water level by increasing water levels inthe surrounding area;• inundation using bunds;• reduction <strong>of</strong>the level <strong>of</strong>the peat surface to form lagoons;• provision <strong>of</strong>supplementary water.The potential applications and limitations <strong>of</strong> theseprocedures in different situations are consi<strong>de</strong>red inChapter 5 and practical approaches in Chapter 8. Inmost situations, it will be necessary to utilise more thanone technique to optimise rewetting. Where possible,use should be rna<strong>de</strong> <strong>of</strong> the existing network <strong>of</strong>ernbankrnents etc., raising levels where necessary,although the permeability <strong>of</strong> the baulks should first be<strong>de</strong>termined to assesstheir efficacy. On milled surfaces,it rnay be necessary to subdivi<strong>de</strong> large peat fields tocreate lagoons to facilitate rewetting and renaturation.Conyersely, on block-cut surfaces, <strong>de</strong>pending on the


xxxRESTORATION 01' DAMAGED PEATLANDSTable 53. Practical constraints and possible solutions in the restoration <strong>of</strong> cut-over bogsConstraintSloping surfaces and culting fields atdifferent levelsUneven topographyLoss <strong>of</strong> bog basal area, withsteepened hydrological gradientsWater losses through drainageLack <strong>of</strong> water storageWi<strong>de</strong>ly fluctuating water levelsWater loss through base <strong>of</strong> bogInput <strong>of</strong> water <strong>of</strong> 'un<strong>de</strong>sirable' qualityLack <strong>of</strong> recolonist bog species,especially SphagnaPresence <strong>of</strong> 'un<strong>de</strong>sirable' plantspecies (e.g. birch and Molinia)Dry, bare surfacesShallow <strong>de</strong>pth <strong>of</strong> ombrotrophic peatOmbrotrophic peat cut away to exposefen peat or mineral substratumVery low base- or nutrient-statusPossible solutionReconform surface to create more level conditions; create lagoons, as a series <strong>of</strong>'paddy-fields' where necessaryReconform surface to create more level conditions; lower the height <strong>of</strong>some baulksPeripheral bunding; raise water le veIs in claimed areas surrounding site; provi<strong>de</strong>supplementary water; create lagoons; remove peatBlock all ditches and outfalls where possible; ditches cut through to mineral soilshould be sealed along the whole length unless shown to be water-tightProvi<strong>de</strong> permanent inundation; consi<strong>de</strong>r use <strong>of</strong>mulch (e.g. bunker<strong>de</strong> 1 ) if available.Increase control <strong>of</strong> water levels and increase water storageInvestigate nature <strong>of</strong>sub-peat mineral material and connectivity with regional waterleveIs - remedy ifpossible (a greater <strong>de</strong>pth <strong>of</strong>residual peat may help to reduce theamount <strong>of</strong>downward seepage)Block or re-route sources ifpossibleInoculation from elsewhere on site (or furlher afield); Sphagnum 'farming' andinoculationRemoval <strong>of</strong> vegetation, followed by raising <strong>of</strong> water leveIs to keep in check. Mayneed to consi<strong>de</strong>r chemical treatmentRaise water leveIs (inundate if necessary); inoculate with plant material; consi<strong>de</strong>r use<strong>of</strong>mulch (e.g. bunker<strong>de</strong>) if availableConsi<strong>de</strong>r using mineral material for bundingConsi<strong>de</strong>r alternative habitats as such or as precursor to bog <strong>de</strong>velopmentConsi<strong>de</strong>r use <strong>of</strong> lime or ferliliserPositive featuresBaulks and trackwaysLocalised <strong>de</strong>pressions or trenchesExisting conservation ¡nterestPresence <strong>of</strong> Sphagnum speciesUse to retain water, ifpossible, (check functioning first), although may be necessaryto reduce height <strong>of</strong>baulks to encourage rewetting; use for access and firebreaksUse to i<strong>de</strong>ntify where water naturally collects as a basis for <strong>de</strong>veloping rewettingstrategy; use for Sphagnum 'farming'Preserve and enhance where possible; use as 'core'Use as sources <strong>of</strong>inoculum (where abundant) or as nuclei from which to spreadconfiguration remaining, it may be <strong>de</strong>sirable to flattenbaulks to achieve a more level area for rewetting,(though keeping sorne <strong>of</strong> them to help retain water). Itshould be possible to use sorne <strong>of</strong>the material from the'redundant' baulks to fill the ditches. However, proceduresinvolving the rnovernent <strong>of</strong> peat and altering theconfiguration <strong>of</strong> the abandoned peat cutting mayrequire consultation with the statutory conservation andarchaeological bodies.Because the rewetting necessary to regenerate raisedbogs can only be achieved by retaining the incomingprecipitation, aH drains, trenches and outfalls must bedammed where possible. However, any rneasures usedfor reduction in outflow from ··.the bog must have thecapacity to <strong>de</strong>liver peak discharges from the bog,otherwise erosion <strong>of</strong> the regenerating peat surface, ordamage to the dams, bunds or recolonist vegetationmay occur.1 see glossaryAfter-care and vegetation managementCertain practices are used wi<strong>de</strong>ly in the management <strong>of</strong>vegetation <strong>of</strong> damaged bogs and bog remnants, fromwhich sorne common principies can be i<strong>de</strong>ntified[Chapters 3, 9 & JO]:• vegetation management is necessary to reduce theinvasion and spread <strong>of</strong> 'un<strong>de</strong>sirable' species, which arenormally checked by high water levels;• scrub invasion and its control can be a major problem;• there are few circumstances in which mowing or grazingare likely to be appropriate techniques if attempts arebeing ma<strong>de</strong> to restore raised bog, except as an interimmeasure;• it may be necessary to consi<strong>de</strong>r the use <strong>of</strong> herbici<strong>de</strong>s tocontrol 'un<strong>de</strong>sirable' species;• it may be necessary to consi<strong>de</strong>r encouraging revegetationby '<strong>de</strong>sirable' species, through inoculation <strong>of</strong> diasporesor whole plants, in particular, Sphagnum species;• a<strong>de</strong>quate provision for control <strong>of</strong>fire is essential;• ongoing maintenance <strong>of</strong> bunds and dams may berequired. .


SUMMARYXXXIConsi<strong>de</strong>ration should be given to implementingpractical management procedures as soon asproduction ceases, both to reduce the establishment <strong>of</strong>'un<strong>de</strong>sirable' plant species, especially if it is notpossible to raise water levels within a short time, and tostart encouraging establishment <strong>of</strong> '<strong>de</strong>sirable' plantspecies. Where 'abandoned' fields lie within the zone<strong>of</strong> ongoing peat extraction, and cannot be rewetted inthe near future, it may be possible to achieve theformer by running rotavating machinery over thesurface each year. Where this has not been done, it maybe necessary to remove sorne vegetation (e.g. birch andMolinia) from abandoned areas prior to rewetting(although small amounts <strong>of</strong>vegetation may be useful inacting as 'nurse' species for Sphagnum inoculum).Full renaturation and regeneration <strong>of</strong> rewetted peatfields is Iikely to be slow, partly on account <strong>of</strong> the'difficult' nature <strong>of</strong>the ombrotrophic environment (andthe intrinsically low relative growth rates <strong>of</strong> bogplants). As the cut-over areas regenerate into bog theymay be expected to become increasingly selfsustaining.However, sorne <strong>de</strong>gree <strong>of</strong> maintenance maybe nee<strong>de</strong>d in the early stages <strong>of</strong> rewetting andrenaturation, such as rémoval <strong>of</strong> scrub from dry siteswithin the peat fields. The condition <strong>of</strong> the peat bunds,especially the outer ones, will also require periodicinspection and, if nee<strong>de</strong>d, sorne maintenance. Theexpected intrinsically-slow renaturation <strong>of</strong> the peatfields is likely to mean that sorne (intermittent)maintenance may be required for much longer than anafter-care period <strong>of</strong> 5 years. The restoration schemeshould be <strong>de</strong>signed to minimise on-going managementrequirements\ but also to make it practicable for themto take place, ifnee<strong>de</strong>d.Natural recolonisation <strong>of</strong> cut-over bogs by plants maytake place quite readily where there are local refugia <strong>of</strong>typical bog species. However, where these do not exist,or have a sparse range <strong>of</strong> species, or where sites areparticularly large, it may be necessary 'to consi<strong>de</strong>r themerits <strong>of</strong> 'inoculating' the damaged sites with selectedspecies either by transplantation <strong>of</strong> plant material orseeding. Plans for inoculation <strong>of</strong> rewetted areas mustbe consi<strong>de</strong>red carefully with respect to the phasing <strong>of</strong>restoration operations, as the practi'cable options will<strong>de</strong>pend critically on the planned hydrological regime.Clearly, provision <strong>of</strong> the optimum water regime, bothin terms <strong>of</strong> quality and quantity, for the <strong>de</strong>siredvegetation-type will· be an important basic consi<strong>de</strong>ration[see Chapters 4 and 5]. Conversely, the restorationscheme <strong>de</strong>veloped should take into account the\ For example, by ensuring that the floors <strong>of</strong> lagoons can be keptinundated, to minimise opportunities for establishment <strong>of</strong>un<strong>de</strong>sirable species; a strongly undulating, or sloping, surface maycreate periodical1y dry areas that are susceptible to birchencroachment elc.availability <strong>of</strong> plant inoculum. Legislation conceminguprooting <strong>of</strong> plants and transplantations must be takeninto consi<strong>de</strong>ration [Chapter 9].The main feature <strong>of</strong> the vegetation <strong>of</strong> an undamagedraised bog is the extent <strong>of</strong> the Sphagnum cover, which,besi<strong>de</strong>s being characteristic, plays various importantróles in the functioning <strong>of</strong> the bog [Chapter 1]. Thus,one <strong>of</strong> the most important factors in the restoration <strong>of</strong> adamaged bog is the question <strong>of</strong> how to regain theSphagnum cover, particularly in sites which possessfew refugia with conditions suitable for the survival <strong>of</strong>Sphagnum species. A lack <strong>of</strong> appropriate, availablepropagules may hin<strong>de</strong>r recolonisation, and it may be<strong>de</strong>sirable to consi<strong>de</strong>r inoculation with plant material.Clearly, it will be necessary to wait for hydrologicalconditions to stabilise following any rewettingmeasures before un<strong>de</strong>rtaking any inoculation or transplantationwork. For large-scale restoration, removal <strong>of</strong>Sphagnum from donor sites is likely to be consi<strong>de</strong>redunsatisfactory, and the possibility <strong>of</strong> increasing theavailability <strong>of</strong> propagules by farming Sphagnum couldbe consi<strong>de</strong>red. This could be started in abandonedareas well in advance <strong>of</strong> complete cessation <strong>of</strong>extraction to provi<strong>de</strong> an ongoing source <strong>of</strong> inoculum.It may also be appropriate to consi<strong>de</strong>r inoculation withsuitable vascular plants. Where possible, it is recommen<strong>de</strong>dthat planting should be carried out in the autumnor early spring so that maximum establishment can beachieved before possible summer dry periods. Materialshould be transplanted as soon as possible aftercollection (preferably the same day), and drying out intransit must be avoi<strong>de</strong>d. It should be apparent afteronly one growing season whether transplanted materialis likely to become established. Reasons for failureshould be investigated and remedied where possible.It may be possible to encourage rafting <strong>of</strong> vegetation incertain situations. ,For example, there is evi<strong>de</strong>nce thatthe establishment and spread <strong>of</strong> Sphagnum withinembryonic bogs can be facilitated by the presence <strong>of</strong>'nurse species' such as Molinia caerulea, Eriophorumvaginatum and Juncus effusus, or the provision <strong>of</strong>'artificial'· constructs within the water such as birchbrashings. Rafting may also be encouraged by loosepeat fragments or particles floating in the pools, eitherwashed in from the si<strong>de</strong>s, or <strong>de</strong>tached and Iifted fromthe base <strong>of</strong>the cuttings.SS Recording and monitoringProcedures and progress <strong>of</strong> monitoring schemes shouldbe monitored, for the following reasons:• . all schemes must be regar<strong>de</strong>d as essentially experimental,and therefore recording is important in increasing theknowledge <strong>of</strong>techniques elc;


xxxiiRESTORATION OF DAMAGED PEATLANDS• provision <strong>of</strong> 'base-tine' data so that progress can beassessed and the restoration programme revised wherenecessary;• provision <strong>of</strong> 'hard' data so that current and futuremanagers (and other interested parties) know the startingconditions, exactly what has been done and can continueto assess the <strong>de</strong>gree <strong>of</strong> success, in or<strong>de</strong>r to formulateappropriate further management strategies;• provision <strong>of</strong> information that can be used to assess theapplicabitity and potential <strong>of</strong> similar schemes at othersites.As recolonisation may be rather slow, monitoring mayneed to be long-term, and projects should be <strong>de</strong>visedaccordingly.Monitoring procedures need to be set up with c1early<strong>de</strong>finedobjectives and with i<strong>de</strong>ntified yardsticks bywhich the direction and extent <strong>of</strong> change can bemeasured. It may be difficult to carry out and interpretin a meaningful way. It is recommen<strong>de</strong>d that amonitoring programme should be set up taking thefollowing aspects into account:• management operations (present and future);• base-tine data on flora, fauna and water levels (based onreconnaissance surveys, but with additional <strong>de</strong>tail ifpossible) will allow i<strong>de</strong>ntification <strong>of</strong> selected species orpriority areas (e.g. those i<strong>de</strong>ntified as refugia), plusspecies <strong>of</strong> special conservation status for regularmonitoring checks to assess response to managementoperations;• the hydrological and biological response within arepresentative selection <strong>of</strong> cut-over areas should beregularly monitored;• annual review <strong>of</strong> results to allow assessment <strong>of</strong> anychanges nee<strong>de</strong>d to the management programme.It may be <strong>de</strong>sirable to involve specialists in <strong>de</strong>tailedmonitoring periodically in or<strong>de</strong>r to assess progress in<strong>de</strong>tail, but it is possible to make sorne simple recordsand measurements which will provi<strong>de</strong> usefulinformation and give a good insight into progress[Table S4].Sorne hydrological measurements should be ma<strong>de</strong>before <strong>de</strong>ciding on the optimum surface configurations(e.g. where to put the bunds for lagoons), particularlywhere water-table fluctuations are known to be erraticor there is a possibility <strong>of</strong>vertical water loss. Similarly,once the lagoons are constructed, a further period <strong>of</strong> atleast ayear should elapse to ensure that water levelswill stabilise before making <strong>de</strong>cisions on plantingoperations, so that appropriate areas can be targeted,plant material is not wasted and any adjustments can bema<strong>de</strong> without fear <strong>of</strong> damage to the vegetation.As each restoration initiative should be regar<strong>de</strong>d as'experimental', it is <strong>de</strong>sirable that the <strong>de</strong>tails andoutcome should be disseminated through publicationsor accessible reports.59 Prospects and costsThere are numerous examples <strong>of</strong> spontaneousrevegetation <strong>of</strong> (mostly) small-scale peat workings andon sorne damaged mires revegetated peat cuttingsprovi<strong>de</strong> the 'best' examples <strong>of</strong> bog or fen habitat. Mostsuch workings on raised bogs are relatively old (i.e.abandoned sorne 60-80 years ago) so, whilst it ispossible to fix an upper time limit for effectiverevegetation, the absence <strong>of</strong> younger workings thathave been kept appropriately wet since abandonmentprevent specification <strong>of</strong> the lower time threshold. [Itcan, <strong>of</strong> course, also be argued that recolonisation <strong>of</strong>these workings has been favoured by specialcircumstances, such as their (usually) small size andpossible 'shoeing' <strong>of</strong>the cuttings.]<strong>Restoration</strong> initiatives on large commercial cut-overraised bogs are mostly still in their infancy, i.e. havebeen attempted for less than 10 years or so; moreoversorne <strong>of</strong> them have been in sites where problems <strong>of</strong>water management have been exacerbated by severalunusually dry summers and by vertical loss <strong>of</strong> waterinto a permeable subsoil. They have also mostly beencarried out as post-extraction procedures, rather than asTable 54. Factors which can be simply recor<strong>de</strong>d, measured or monitoredThese inclu<strong>de</strong>:• careful recording <strong>of</strong> management operations un<strong>de</strong>rtaken (including time taken and costs);• water level <strong>de</strong>pth and stability (using data from dipwells, WALRAG's and stage boards);• recolonisation <strong>of</strong> rewetted areas (and others), especially by Sphagnum species;• birch <strong>de</strong>ath;• Molinia <strong>de</strong>ath;• photographic record, including:• 'fixed point' photographic records, including 'before' and 'after' -type pictures and regularly thereafter;• management operations (such as bund and dam construction);• regular checks to be ma<strong>de</strong> on any water control structures (dams, bunds etc.) and remedial action taken as necessary;• records should be ma<strong>de</strong> <strong>of</strong> events beyond the control <strong>of</strong> site managers (e.g. heavy storms, fires, vandalism etc.) whichmay influence the future interpretation <strong>of</strong> 'success' <strong>of</strong> the project.


SUMMARYXXXIIIan integrated programme <strong>of</strong> extraction and restoration.It is nonetheless evi<strong>de</strong>nt (a) that a wi<strong>de</strong> range <strong>of</strong> bogplant species can inva<strong>de</strong> commercially-cut-oversurfaces (where there is a proximate inoculum source);and (b) that it ispossible to rewet the peat fields to theextent that (c) carpets <strong>of</strong> aquatic Sphagna can rapidlycolonise large areas. Sorne <strong>of</strong> the rewetting initiativesin NW Germany have shown a massive expansion <strong>of</strong>Sphagnum cuspidatum over extensive areas. This eventprovi<strong>de</strong>s much optimism for regeneration prospects asin both the natural <strong>de</strong>velopment <strong>of</strong> bogs and that <strong>of</strong>recolonised peat working's, a wet Sphagnumcuspidatum phase has provi<strong>de</strong>d a basis for spontaneoussuccessional <strong>de</strong>velópment <strong>of</strong> a more diverse vegetationcomposed <strong>of</strong> more important bog-building species suchas Sphagnum papillosum and S. magellanicum. It isdifficult to see why this process should not be repeatedon rewetted commercialIy-cut over sites, provi<strong>de</strong>d thattwo conditions are satisfied: (i) that the site isaccessible to potential recolonist species (if it is not,then re-introduction <strong>of</strong> species will need to beconsi<strong>de</strong>red); and (ii) that the chemical composition <strong>of</strong>precipitation inputs will support the growth <strong>of</strong>recolonist species. [It is possible (but by no meanscertain) that the growth <strong>of</strong>sorne bog species, especialIysorne species <strong>of</strong> Sphagnum, may be consi<strong>de</strong>rablyconstrained in sorne regions by atmosphericcontaminants, particularly NO x and NH 4 [Chapter 1].]However, if such conditions are not Iimiting, it seemsIikely that commercialIy-cut peat fields wilI re<strong>de</strong>velopa characteristic bog vegetation and that peataccumulation wilI recommence in time. It is difficult tospecify the likely time-scale involved, but known rates<strong>of</strong> spread and establishment <strong>of</strong> bog vegetation suggestthat, <strong>de</strong>pending on the starting conditions, effectiverevegetation may <strong>of</strong>ten be possible within the upperthreshold <strong>of</strong> 70 years known from the spontaneousrevegetation referred to aboye, and perhapsconsi<strong>de</strong>rably more quickly than this, especialIy if it ispossible to discover, by further research, the conditionsnee<strong>de</strong>d to optimise the establishment <strong>of</strong> the bogbuildingSphagna upon the lawns <strong>of</strong> Sphagnumcuspidatum.Effective renaturation does, <strong>of</strong> course, require effectiverewetting. It is important to note that sustainedrewetting <strong>of</strong> relatively flat, cut-over surfaces maysometimes be achieved more easily and effectivelythan that <strong>of</strong> residual massifs. These may show aten<strong>de</strong>ncy to remain 'high and dry', unless provi<strong>de</strong>dwith substantial bunds to help retain water. Moreover,the long-term stability <strong>of</strong> peripheral bunds is notknown. Such consi<strong>de</strong>rations are <strong>of</strong> great importance interms both <strong>of</strong> the optimal surface configurationrequired at the cessation <strong>of</strong> peat extraction and <strong>of</strong> thepossibility <strong>of</strong> premature termination <strong>of</strong> peat extraction.The <strong>de</strong>sirability <strong>of</strong>creating comparatively flat, uniformsurfaces for initiation <strong>of</strong> wi<strong>de</strong>-scale bog re<strong>de</strong>velopmentmust, <strong>of</strong> course, be balanced against the need to retainsorne residual massifs on account <strong>of</strong> their existingbiological value, which may be important not only inits own right, but also as an inoculum source for therewetted, cut-over surfaces.The costs <strong>of</strong> restoration are likely to <strong>de</strong>pend stronglyupon starting conditions and restoration objectives.They must be split between capital costs (such as landpurchase), surface preparation costs and maintenancecosts. Typical costs incurred in sorne projects aresummarised in Chapter 7. These show consi<strong>de</strong>rablevariation, reflecting specific site circumstances and,probably, the 'one-<strong>of</strong>f' nature <strong>of</strong> may initiatives. Sorne<strong>of</strong> the most reliable gui<strong>de</strong>s to costing come from NWGermany, where a number <strong>of</strong> bogs have now beenprepared for restoratioil. These suggest that preparationcosts <strong>of</strong> cut-over surfaces are in the region <strong>of</strong>noo - 400 ha'¡ when appropriate equipment exists onsite and f800 - 1250 ha'¡ when it has to be brought in.


BackgroundPeat and peat extraction<strong>Peatlands</strong> are wetland ecosystems in which the substratumis composed largely or entirely <strong>of</strong> peat. Peat isan organic soil formed mainly from the remains <strong>of</strong>plants that have accumulated in si/u. Peat accumulatesin wetland habitats, primarily because waterloggingand associated anoxia retards the <strong>de</strong>composition <strong>of</strong>plant material.GlobalIy, peatlands are very wi<strong>de</strong>spread and extensive,occurring in aH but the drier regions <strong>of</strong>the world, fromthe tropics to the tundra (Gore, 1983a, b; Lugo,Brinson & Brown, 1990). Estimates <strong>of</strong> the globalpeatland resource vary consi<strong>de</strong>rably and none areprobably very accurate. Values <strong>of</strong> over 40 millionhectares <strong>of</strong> the land area are sometimes suggested(Bather & Miller, 1991).The waterlogged conditions required for peat accumulationare provi<strong>de</strong>d by two broad circumstances. Thefirst is in situations where more-or-less permanentsaturation is provi<strong>de</strong>d by telIuric water (i.e. water<strong>de</strong>rived from the ground and which has had sornecontact with mineral substrata, such as those thatsurround or un<strong>de</strong>rly the peatland). Amongst otherfactors, this may be because <strong>of</strong> a high regionalgroundwater table, groundwater discharge or impe<strong>de</strong>ddrainage <strong>of</strong> various water sources (such as landdrainageor river floodwater). But in alI such cases, thewetness <strong>of</strong> the wetland is a product, at least in part, <strong>of</strong>water that has had sorne resi<strong>de</strong>nce within, or contactwith, mineral soils and substrata. <strong>Peatlands</strong> that<strong>de</strong>velop un<strong>de</strong>r the influence <strong>of</strong> telIuric water arereferred to as minerotrophic peatlands, to which thetermfen is <strong>of</strong>ten applied as a synonym.In sorne c1imatic regions peat is also able to accumulatebecause relatively high and consistent precipitation,coupled to comparatively low rates <strong>of</strong> evapotranspiration,permit the maintenance <strong>of</strong> permanently wetconditions perched aboye the level <strong>of</strong> the mineralground and groundwater table. Such conditions lead tothe formation <strong>of</strong> a peat <strong>de</strong>posit that is raised aboye theoriginal ground level and which is fed and formeddirectly and more-or-Iess exc1usively by precipitation.Such peatlands are known as ombrotrophic orombrogenous peatlands and the word bog is <strong>of</strong>tenapplied as a synonym. In many instances they have<strong>de</strong>ve10ped from fen.In Britain, as in much <strong>of</strong> north-west Europe, bothminerotrophic and ombrotrophic peatlands were oncevery extensive. The total area <strong>of</strong> fen in Britain, past orpresent, has not been quantified, but was undoubted1yonce great. The largest fen complex (The Fenland <strong>of</strong>East Anglia) was once a huge wetland basin, coveringan area <strong>of</strong> more than 1200 km 2 (a total which inc1u<strong>de</strong>ssorne ombrotrophic peatland). Ombrotrophic peatlandsoccupy extremely large areas (e.g. sorne 1.5 million hain the British Isles) but sorne lowland bogs were alsolarge, the biggest being Thome Waste (S Yorkshire)with an original area <strong>of</strong> over 2500 ha. On the oppositesi<strong>de</strong> <strong>of</strong> the North Sea, in The Netherlands and LowerSaxony, much greater lowland bogs once occurred.The biggest had an estimated area in excess <strong>of</strong>1000 km 2 (Barkman, 1992) (i.e. about 1Y2 times thearea <strong>of</strong>the island <strong>of</strong>Anglesey).Although sorne peatlands have long and intricatehistory <strong>of</strong> interaction with human societies (Coles,1990), given their once-huge area it is scarcelysurprising that over the last few centuries much <strong>of</strong> thefocus <strong>of</strong> human activity in peatlands has been to drainand c1aim them for a more remunerative use. Sorneminerotrophic peatlands have been particularly amenableto agricultural conversion, their <strong>de</strong>rivative soils<strong>of</strong>ten being both base-rich and nutrient-rich. The peats<strong>of</strong> the Fenland basin <strong>of</strong> East Anglia have been almostentirely converted to productive farmland (Darby,1983). By contrast, bog peat is typicalIy acidic andnutrient-poor. Nonetheless, large areas have beendrained and claimed for agriculture or forestry. Variousmethods have been· found to reduce the acidity an<strong>de</strong>nrich the bog peat. Sorne have involved the application<strong>of</strong> lime and fertiliser, sometimes using 'nightsoil'(sewage) as a source <strong>of</strong> nutrients; others haveentailed physical removal <strong>of</strong>the peat. At Thome Waste(S. Yorks.), the primary stimulus to drainage and peatremoval in the nineteenth century seems to have been a<strong>de</strong>sire to lower the altitu<strong>de</strong> <strong>of</strong> the bog surface so that itcould be 'warped' - that is, covered with silt by inundationwith estuarine water at high ti<strong>de</strong>s (Smart,Wheeler & Willis, 1986). In the Forth vaHey <strong>of</strong>CentralScotland, Ca<strong>de</strong>H (1913) reports how large areas <strong>of</strong> peatwere stripped to expose the un<strong>de</strong>rlying carse clays foragriculture. The unwanted peat was jettisoned into theriver to such an extent that fish stocks were damaged.Such pr<strong>of</strong>ligacy with the peat resource suggests that itwas not at aH in short supply, as peat is likely to havebeen <strong>of</strong> sorne value to the inhabitants <strong>of</strong> the ForthvaHey as a fue!.


xxxviRESTüRATlüN ür DAMAGED PEATLANDSPeat has a number <strong>of</strong> properties that make it a valuedresource and it has found a very wi<strong>de</strong> range <strong>of</strong> uses. InBritain, its principal usage has been for fuel, litter(bedding material for animals) and as a growingmedium for plants. Its use as a domestic fuel is <strong>of</strong> longstanding. Records indicate that various peatlands havebeen dug for fuel since Medieval times and, in sornecases, probably long before. Most <strong>of</strong> the accessiblelowland peat <strong>de</strong>posits, and various upland ones, showsigns <strong>of</strong> former domestic peat cutting, especiallyaround their margins. The effects <strong>of</strong> these 'domestic'activities should not be un<strong>de</strong>restimated. In the earlynineteenth century, peat was removed from up to 90%<strong>of</strong> the surface <strong>of</strong> sorne fens in the Norfolk Broadland(Giller & Wheeler, 1986; J. Parmenter, unpublisheddata), mainly to provi<strong>de</strong> fuel for the parish poor. Sorneindividual pits were more than 11 ha in area. Elsewherein East Anglia, at the about the same time, estimatedpeat extraction rates in Parish Fuel AlIotments approxirnateto the equivalent <strong>of</strong> removal <strong>of</strong> 1m <strong>de</strong>pth <strong>of</strong> peatfrom an area <strong>of</strong> 1 ha every 50 years (Wheeler & Shaw,1995). At Thome Waste, eighteenth century peatextraction was consi<strong>de</strong>rable and led to the agriculturalconversion <strong>of</strong> a sizeable portion <strong>of</strong> the south-west part<strong>of</strong> the bog, apparently starting in the seventeenthcentury (Lirnbert, 1987). However, more systematicattempts to drain and exploit peatlands, for fuel orlitter, generally date from the nineteenth centuryonwards.In Britain, peat is no longer harvested for litter, butdornestic extraction for fuel persists in sorne areas,rnainly in the north-west <strong>of</strong> Britain, and there is a smallamount <strong>of</strong>commercial fuel peat production. Elsewherethe fortunes <strong>of</strong> the peat industry may well have flaggedhad it not been for the wi<strong>de</strong>spread adoption <strong>of</strong> peat bythe horticultural industry as a base for growing media.Peat has long been an important ingredient <strong>of</strong> varioussoil-based composts, such as the John Innes composts<strong>de</strong>veloped in the 1930s, but it was not until the 1960sthat the potential benefits <strong>of</strong>composts based largely, orentirely, on peat were recognised and promoted,revitalising peat extraction.The properties <strong>of</strong> peat are largely a product <strong>of</strong> the plantspecies that produced it and the conáitions un<strong>de</strong>r whichit accumulated. Both fen peats ('sedge peat') and bogpeats ('moss peat') are harvested in Britain but theSphagnum-rich moss peats are <strong>of</strong> particular value tohorticulture, because <strong>of</strong> their structure, waterholdingcapacity, low fertility, sterility and consistent character.Most moss peats are extracted from lowland bogs,primarily from sites which contain thick <strong>de</strong>posits <strong>of</strong>suitable peat, which are in comparatively dry regions(to facilitate drying <strong>of</strong> the material) and which arerelatively close to the main markets. Most <strong>of</strong> these sitesare sometirnes referred to as 'lowland raised bogs'.In Britain as wi<strong>de</strong>ly elsewhere, a substantial proportion<strong>of</strong> former raised bogs have been claimed for agricultureand forestry; others have been heavily damaged bycommercial or domestic peat extraction; by drainage orrepeated burning. Figures collated for the NationalPeatland Resource Inventory (NPRI; Lindsay et al, inprep.) suggest that in Britain the proportion <strong>of</strong> 'primarynear-natural' raised-bog vegetation cover whichremains is only about 5 - 6 % <strong>of</strong> the original extent <strong>of</strong>raised bog <strong>of</strong>sorne 70,000 ha.AlI <strong>of</strong> these estimated figures have to be treated withsorne caution, not least because the concept andcompass <strong>of</strong> the category called 'Iowland raised bog' isitself open to <strong>de</strong>bate. Nonetheless, it is clear that inEngland, Wales, southem and central Scotland the area<strong>of</strong> lowland bog that has retained much <strong>of</strong> its(presumed) undamaged character is undoubtedly small.The 'peat <strong>de</strong>bate'In recent years there has been a growing recognition <strong>of</strong>the importance <strong>of</strong> lowland bogs for natural history,science and conservation. Features which are perceivedto be important inclu<strong>de</strong>:• visual character <strong>of</strong>the peatland landscape;• peat archive (archaeology, palaeoecology);• biological resource.The importance <strong>of</strong> lowland bogs as a biologicalresource is most obviously expressed in terms <strong>of</strong> theirpopulations <strong>of</strong> typical 'bog species'. However, theyalso have importance in supporting populations <strong>of</strong>species <strong>of</strong> wi<strong>de</strong>r habitat-range in landscapes frornwhich other semi-natural habitats have largelydisappeared. Sorne <strong>of</strong> these species may persist in parts<strong>of</strong> bogs that have been partly darnaged. <strong>Damaged</strong> sitesmay also support populations <strong>of</strong> sorne uncornmonspecies which are not really typical <strong>of</strong> lowland bogs butwhich have established upon them in response tochanges in habitat conditions, such as those induced bydrainage and peat extraction.The recognition <strong>of</strong> the irnportance <strong>of</strong> sorne lowlandbogs for wildlife etc. has led to sorne concem withregard to their continued exploitation. As, today, peatextraction is the principal form <strong>of</strong> on-going utilisation,there has been sorne suggestion that the operations <strong>of</strong>the peat industry should be curtailed or reduced.The response <strong>of</strong> the British Government to the <strong>de</strong>bateon peat in the House <strong>of</strong> Lords on 9 May 1990 was torecognise that many UK peatlands, including lowlandbogs, are amongst the country's most important natureconservation habitats. The response also recognisedthat the peat industry had legitirnate interests in sorne<strong>of</strong> these peatlands through mineral extraction activitiescarried out un<strong>de</strong>r valid planning permissions. However,it was also recognised.that many <strong>of</strong> those permissionswere granted in the early years after the passing <strong>of</strong> the


BACKGROUNDxxxviifirst Town and Country Planning Act in 1947. This wasbefore the nature conservation importance <strong>of</strong> peat areashad been fuIly appreciated. Many <strong>of</strong> the permissionslacked planning conditions controIling methods <strong>of</strong>working, restoration and aftercare. The Governmentconclu<strong>de</strong>d that there was a need for a full assessment <strong>of</strong>all the relevant issues which had been raised.Scope <strong>of</strong> the reportThis report is the outcome <strong>of</strong> a project commissionedby the Department <strong>of</strong> the Environment (MineralsDivision) in 1992. The main aims <strong>of</strong>this were to assessthe potential for and Iimitations <strong>of</strong> restoring workedoutand damaged lowland peat bogs in the UK and toprovi<strong>de</strong> the basis for guidance and options forappropriate working practices and methods to restorethese bogs, the main focus being on natureconservation requirements.The study has procee<strong>de</strong>d through two phases:(i) A coIlation and review <strong>of</strong> relevant published andunpublished data, supplemented by consultation withappropriate individuals and organisations, and sitevisits in the UK, Ireland, The Netherlands andGermany. A working document was prepared forconsi<strong>de</strong>ration by a Steering Group <strong>of</strong> the project and arevised version <strong>of</strong> this is available from theEnvironmental Consultancy, University <strong>of</strong>Sheffield.(ii) The information and experience collated for theinitial working document has been utilised to preparethis present document, which provi<strong>de</strong>s backgroundinformation and scientific advice on the practice <strong>of</strong>restoration <strong>of</strong>cut-over lowland peatlands. It is inten<strong>de</strong>dfor use by any parties with an interest in peatlandrestoration, including central and local government, thepeat industry, conservation bodies etc., in particularwith regard to formulating restoration strategies for theafter-use <strong>of</strong>currently worked or abandoned sites.This report is concerned with the restoration <strong>of</strong>peatlands that have been damaged by peat extraction,with particular regard to lowland bogs. It gives a wi<strong>de</strong>rangingreview <strong>of</strong> much <strong>of</strong> the available informationand experience relating to the science and art <strong>of</strong>restoration <strong>of</strong> peatlands subject to peat extraction,based on practical experience and currentun<strong>de</strong>rstanding <strong>of</strong> salient ecological processes whichoperate within peatlands; it i<strong>de</strong>ntifies sorne <strong>of</strong> thepotential opportunities provi<strong>de</strong>d by restorationinitiatives, and associated difficulties; it examinesvarious approaches to restoration that may be used andconsi<strong>de</strong>rs the requirements appropriate to successfulrestoration.The study has focused on lowland bogs, as these arethe peatlands currently most utilised by the peatindustry. The dwindling resource <strong>of</strong> lowland raisedbogs with conservation interest, makes it important thatefforts are ma<strong>de</strong> to active/y preserve extant areas toprevent further <strong>de</strong>gradation and, where possible, torestore damaged areas and attempt to recreate thehabitat conditions suitable for the <strong>de</strong>velopment <strong>of</strong> thecharacteristic flora and fauna <strong>of</strong>raised bogs.Cut-over peatlands can be broadly divi<strong>de</strong>d into twostructural components: the peat cutting fields and uncutbog remnants. The 'remnants' sometimes retainconsi<strong>de</strong>rable biological interest, even when adjacent toon-going peat extraction. This report thus addressestwo rather different, but related, main issues:(i) restoration <strong>of</strong>the abandoned peat fields; and(ii) the maintenance (and, if nee<strong>de</strong>d, restoration) <strong>of</strong>vegetated peat remnants, both during and after peatextraction <strong>of</strong>adjoining areas.This document is inten<strong>de</strong>d to be used for theformulation <strong>of</strong> future planning policy with regard topeat workings and restoration, but it is not itself apolicy document. Similarly, it is inten<strong>de</strong>d for use as agui<strong>de</strong> to best practices in the restoration <strong>of</strong> worked outor damaged peatlands, but is not inten<strong>de</strong>d to provi<strong>de</strong> aprescriptive 'management handbook'.StructureThe material presented in this document falls fairlyreadily into three main parts. The first part consi<strong>de</strong>rsvarious aspects <strong>of</strong> peatland ecology relevant torestoration and with particular reference to sorneeffects <strong>of</strong> peat extraction upon the characteristics <strong>of</strong>peatland sites. The second part builds on this to outlinesorne <strong>of</strong> the objectives <strong>of</strong> peatland restoration an<strong>de</strong>xamines relevant principIes and information to assesspossible approaches to restoration and sorne <strong>of</strong> theconstraints upon them. The final part is concemedmore with various practical aspects <strong>of</strong> restoration, suchas i<strong>de</strong>ntifying the sort <strong>of</strong> information that may berequired to un<strong>de</strong>rtake a restoration programme or sorne<strong>of</strong> the possible methods <strong>of</strong> facilitating the process.However, the overall focus <strong>of</strong> this report is not toprovi<strong>de</strong> <strong>de</strong>tailed technical guidance. Nor is it toprescribe universal restoration formulas for lowlandpeatlands. This is not least because the permutations <strong>of</strong>possible restoration objectives and site-specificconditions in which restoration takes place prevent anysimple recitation <strong>of</strong> a 'recipe' for restoration. Rather,an attempt has been ma<strong>de</strong> to i<strong>de</strong>ntify the salient issuesinvolved in peatland restoration initiatives and provi<strong>de</strong>an overall factual and conceptual basis which it ishoped will enable informed <strong>de</strong>cisio.ns to be ma<strong>de</strong> andstrategies <strong>de</strong>veloped that are applicable to the peculiarcircumstances <strong>of</strong>individual peatland sites.


xxxviiiRESTORATION OF OAMAGED PEATLANDSCitationsThis volume is. a much con<strong>de</strong>nsed version <strong>of</strong> theoriginal working document [see aboye]. Although itcontains numerous references to the sources <strong>of</strong>inforrnation upon which it is based, it is not practicableto inelu<strong>de</strong> all relevant citations, nor the <strong>de</strong>tails <strong>of</strong> otherpieces <strong>of</strong>evi<strong>de</strong>nce (field observations, discussions etc.)which have contributed to various comments andconclusions. Comprehensive citations and other <strong>de</strong>tailscan be found in the working document.Scope for restorationOne important component <strong>of</strong> this review was anevaluation <strong>of</strong> the potential for the restoration <strong>of</strong>worked-out 01' damaged bogs to regenerate, maintain 01'increase their nature conservation value; and to provi<strong>de</strong>guidance on the practicality <strong>of</strong> such procedures. This isbecause peat extraction does not 01 necessity <strong>de</strong>stroy,01' irreversibly change, the salient environmentalconditions and circumstances that perrnit the growthand reproduction <strong>of</strong> many typical bog species and theforrnation <strong>of</strong> bog peat. In principie, the effect <strong>of</strong> peatextraction is to remove sorne <strong>of</strong> the accumulated peatand to cut the surface <strong>of</strong> the bog back to an earlierstage in its <strong>de</strong>velopment so that, <strong>de</strong>pending upon thecondition and conforrnation <strong>of</strong> the 'new' surfaces, itmay be possible to encourage the regeneration <strong>of</strong> 'new'raised bogs within the worked-out ramparts <strong>of</strong>the 'old'ones. That potential exists for the re<strong>de</strong>velopment <strong>of</strong>bog vegetation is illustrated by the spontaneousrecolonisation <strong>of</strong> sorne abandoned peat workings andby sorne experimental attempts to regenerate bogvegetation. Nonetheless, many current commercialoperations are on a much larger scale than those <strong>of</strong> theearly workings which have spontaneously revegetatedand this may present sorne additional constraints torestoration. Moreover, it must also be recognised that,in cutting the peat back to a lower level, peat extractionalso removes any existing living surface, together withinci<strong>de</strong>ntal peat contents, such as the pollen grains etc.thatpreserve a palaeoecological record. The palaeoecologicalrecord cannot be restored and whilstrecolonisation by plants and animals typical <strong>of</strong> bogsmay be possible in the long-terrn, it will not onlyrequire the re<strong>de</strong>velopment <strong>of</strong>conditions appropriate fortheir growth but may also <strong>de</strong>pend upon the survival <strong>of</strong>these species in a refuge adjoining, 01' near to, the peatworkings whilst extraction is taking place.Two broad caveats un<strong>de</strong>rly aH <strong>of</strong> the inforrnation andobservations presented here:(i) Once any site has been damaged, be it a bog 01'other habitat, it is never possible to retum it exactly toits forrner condition. However, in the case <strong>of</strong> a bogdamaged by peat extraction, it may be possible torepair 01' regenerate a bog by restoring conditionssimilar to those un<strong>de</strong>r which it originaHy <strong>de</strong>velopedand hence to encourage the retum <strong>of</strong> typical raised-bogspecies, both flora and fauna. In sorne instances thismay even <strong>of</strong>fer a 'value-ad<strong>de</strong>d' approach in terrns <strong>of</strong>wildlife conservation, as in those sites which havelong-since been damaged by drainage, partialagricultural conversion and buming as well as peatextraction. However, effective restoration is likely tobe a slow process, measured in terrns <strong>of</strong> <strong>de</strong>ca<strong>de</strong>s;moreover, given the present 'state <strong>of</strong> the art' it is notpossible to guarantee that a peat-accumulating systemwill subsequently re<strong>de</strong>velop. It is therefore suggestedthat these gui<strong>de</strong>lines and observations should not beused to provi<strong>de</strong> a justification for peat extraction onlittle-damaged bog sites.(ii) Not aH <strong>of</strong>the techniques outlined in this documentare well 'tried and tested', as bog restoration is arelatively new activity. There are strong reasons tosuppose that they have a good chance <strong>of</strong>success, but tohelp enhance knowledge and un<strong>de</strong>rstanding <strong>of</strong>effective restoration practices, it is suggested that allattempts at the restoration <strong>of</strong> damaged peatlands shouldbe regar<strong>de</strong>d as experimental, and the projects carefullyrecor<strong>de</strong>d and monitored. There is still much to leam.The .advice given here is based upon currentexperience, knowledge and thought, but the gui<strong>de</strong>linesmay need to be amen<strong>de</strong>d 01' updated as new techniquesand results from existing studies become available.TerminologyA <strong>de</strong>liberate attempt has been ma<strong>de</strong> to reduce thenumber <strong>of</strong> technical terrns in this publication, usingcommonplace 01' colloquial words and expressions toconvey the appropriate idiom, where possible.However, for both brevity and clarity it has beennecessary to use sorne technical words. Sorne terrns are<strong>de</strong>fined in the text and a glossary (Appendix 1) is alsoprovi<strong>de</strong>d. With respect to the main subject <strong>of</strong> thisreport, i.e. bog restoration, the terrninology proposedby R. Eggelsmann and co-workers has been followed,in which:rewettingrenaturationregenerationis the re-establishment <strong>of</strong>surface-wetconditions;is the re<strong>de</strong>velopment <strong>of</strong>anappropriate vegetation;is the renewed accumulation <strong>of</strong>peat.These concepts are here grouped un<strong>de</strong>r the generichead <strong>of</strong> restoration. However, note that they are by nomeans discrete and separate: in<strong>de</strong>ed, the re<strong>de</strong>velopment01' regeneration <strong>of</strong>a bog foHows a continuum; there areno abrupt divisions 01' thresholds between each phase.Successful bog regeneration must seek ultimately to reestablishthe self-regulatory mechanisms that ensurethat perrnanently wet conditions are maintained.


PARTIEcological Characteristics <strong>of</strong> Lowland <strong>Peatlands</strong>used for Peat Extraction


Chapter 1Lowland peatlands1.1 <strong>Peatlands</strong>: fens and bogsDifferent types <strong>of</strong> peatland can be recognised based onvarious characteristics (Gore, 1983a). One <strong>of</strong> the mostwi<strong>de</strong>ly-used distinguishing features is the nature <strong>of</strong> thewater supply. Von Post & Granlund (1926) subdivi<strong>de</strong>dpeatIands into three main types - ombrogenous,topogenous and soligenous examples - reflecting thedifferent primary causes <strong>of</strong> surface wetness and peataccumulation. This e1assification is stilI wi<strong>de</strong>ly used.Ombrogenous peatlands are those where surfacewaterIogging is maintained primarily by precipitation;topogenous peatlands occur in basins, flood-plains etc.,where water accumulates on account <strong>of</strong> the topography<strong>of</strong> the landscape; whilst soligenous examples are thosewhere lateraIly mobile water maintains wet conditions,most typicaIly on sloping sites (Sjors, 1950).Although both topogenous and soligenous peatIandsare partly fed by precipitation, they also receive inputs<strong>of</strong> telluric water (i.e. water <strong>de</strong>rived from the groundand which has had sorne contact with mineral substrata,such as those that surround or un<strong>de</strong>rIy the peatIand)and they are <strong>of</strong>ien referred to as minerotrophic ('rockfed')peatlands (or fens). By contrast, ombrogenous('rain-ma<strong>de</strong>') peatIands (or bogs) are exelusivelyombrotrophic ('rain-fed'), with the supply <strong>of</strong> water totheir surface being <strong>de</strong>rived directIy and exelusivelyfrom precipitation. Various broad differences can beobserved [Table 1.1] but, nonetheless, certain types <strong>of</strong>fen can be very similar to bogs in many <strong>of</strong> theircharacteristics and it is difficuIt to provi<strong>de</strong> a simple,universal specification <strong>of</strong> how the two types can, inpractice, be consistentIy distinguished (Wheeler, 1993).Whilst (as in this account) ecologists <strong>of</strong>ien use theword 'bog' to refer to ombrotrophic peatlands and'fen' to mean minerotrophic examples, such usage isby no means universal. Sorne wetlands that are <strong>of</strong>iencalIed 'bogs' are actuaIly fens in that they areminerotrophic in character. For example, most <strong>of</strong> theSphagnum 'bogs' <strong>of</strong> the New Forest (Hampshire) arestrictIy-speaking 'poor fens', as they receive substantialinputs <strong>of</strong> groundwater (and this is reflected in theirvegetation composition). SimilarIy, entire peatlandsites are sometimes 100sely caIled 'bogs' Of' 'fens',even though they support (or once supported) bothombrotrophic and minerotrophic components. Here,the term 'bog' is used to refer specificaIly to theombrogenous component <strong>of</strong>a peatland site.The term 'mire' has received a variety <strong>of</strong> usage (e.g.Ratcliffe, 1964; Gore, 1983a,b). It is <strong>of</strong>ien used as asynonym for peatland (Gore, 1983a), but sorneworkers also inelu<strong>de</strong> sorne mineral-based wet landwithin the compass <strong>of</strong> 'mire'.In Britain, peat extraction currentIy takes place both infens and bogs, but commercial extraction <strong>of</strong>bog peat ismuch more wi<strong>de</strong>spread than is that <strong>of</strong> fen peat (whichis confined to the Somerset Levels). In consequence,most attention in this report is focused upon bogs.Table 1.1 Sorne distinguishing features <strong>of</strong> fens and bogsWater sourceNutrient statusCharacter <strong>of</strong>substratumPeat typesPeatpHSpecies diversity <strong>of</strong>vegetationFenPrecipitation plus telluric water (minerotrophic)Nutrient-poor to nutrient·rich (may be supplementedby enrichment <strong>of</strong> water supply from agriculture etc.)Usually peat but may have varying mineral content;some mineral soilsTypically various mixtures <strong>of</strong> sedges, grasses, herbs,woody species, mosses etc.Typically c. 4.0 - 6.0 (poor 'en) and c. 5.0 - 8.0 (rich'en)Low to high (Iargely <strong>de</strong>pen<strong>de</strong>nt on nutrient supply, pHand management)809Exclusively from precipitation (ombrotrophic)Nutrient-poor (nitrogen may besupplemented by atmospherically-<strong>de</strong>rive<strong>de</strong>nrichment)PeatTypically Sphagnum mosses with somesedges, herbs and woody (ericaceous)speciesTypically < 4.5Typ'ically low (unless damaged)


2RESTORATION OF DAMAGED PEATLANDS1.2 Origin and <strong>de</strong>velopment <strong>of</strong>peatlandsThe origin and <strong>de</strong>velopment <strong>of</strong> peatlands, both asindividual sites and as part <strong>of</strong> the broa<strong>de</strong>r landscape, is<strong>of</strong>ien complex and is beyond the scope <strong>of</strong> this volume(see, for example, KuIczynski, 1949; Heinselman,1963; Walker, 1970; Casparie, 1972; Tallis, 1983;Pons, 1992). In very broad terms peatlands form bytwo main mechanisms - by the infilling <strong>of</strong> open waterand by the waterIogging <strong>of</strong>once-dry land.The process by which water becomes wetland is <strong>of</strong>ienreferred to as terrestria/isation or hydrosera/succession (Weber, 1908; Tansley, 1939). It occursaround lakes and pools and can lead to the completereplacement <strong>of</strong> once open water by peatland. The<strong>de</strong>tails <strong>of</strong> terrestrialisation processes can be complex(Walker, 1970), but they usually proceed by one <strong>of</strong>twomain routes - rooting or rafting. Rooting (or lit/oral)successions occur when water bodies graduallyaccumulate <strong>de</strong>posits <strong>of</strong> silts, muds and peats. Theshallowing water becomes subject to centripetalinvasion by plants <strong>of</strong> swamp and fen, rooting on theaccumulating sediments. By contrast, in the rafiingprocess, vegetation grows across the surface <strong>of</strong> openwater to form a floating mat, composed <strong>of</strong> peat andplants. In its early stages, this rafi <strong>of</strong> precociouspeatland is <strong>of</strong>ien thin, unstable and quaking and well<strong>de</strong>servesthe name <strong>of</strong> schwingmoor ('floating mire')which is sometimes given to it. But later, it maybecome so thick and consolidated that the former existence<strong>of</strong> a floating rafi can only be <strong>de</strong>duced by peatstratigraphical studies. Rafting successions are particularIycharacteristic <strong>of</strong> small, sheltered and <strong>of</strong>ien <strong>de</strong>epwater bodies, and have occurred quite frequentIy inkettle-holes and similar basins.The processes associated with terrestrialisation havehad a pervasive influence upon the conceptual <strong>de</strong>velopment<strong>of</strong> paludology, to the extent that the term'hydrosere' is sometimes used loosely (and incorrectly)for all forms <strong>of</strong> <strong>de</strong>velopmental change in wetIands.However, many peatlands have not <strong>de</strong>veloped by theterrestrialisation <strong>of</strong>open water but by the swamping, orpa/udification, <strong>of</strong> once relatively-dry land (Cajan<strong>de</strong>r,1913). It is <strong>of</strong>ien not clear, just on superficial inspection,which mechanism has been instrumental in the<strong>de</strong>velopment <strong>of</strong> a particular. peatland and, in consequence,the past occurrence <strong>of</strong> the two processes inBritain is not really known. Nonetheless, there can belittle doubt that, in terms <strong>of</strong> the total area <strong>of</strong> peatIand,paludification has been a far more important processthan has terrestrialisation. For example, the extensivepeatlands (fens and bogs) that occupy, or onceoccupied, the flood-plains <strong>of</strong> many lowland rivers(such as The Fenland <strong>of</strong> East Anglia) have largelyformed by paludification. So have the huge areas <strong>of</strong>bog peat that blanket many upland landscapes. Suchcontrasting situations as these point to a variety <strong>of</strong>causes <strong>of</strong> paludification, inc1uding climatic change,land-sea level change and <strong>de</strong>forestation.The initial type <strong>of</strong> peatland that <strong>de</strong>velops byterrestrialisation <strong>of</strong> open water is usually a form <strong>of</strong> fen,but in suitable c1imatic regions [1.31, ombrogenouspeat may subsequently <strong>de</strong>velop within and upon this asimpe<strong>de</strong>d drainage <strong>of</strong> precipitation permits the gradualaccumulation <strong>of</strong> layers <strong>of</strong> ombrotrophic peat aboye thelevel <strong>of</strong> mineral soil water influence. Paludification <strong>of</strong>dry land also <strong>of</strong>ien leads, first <strong>of</strong>all, to the formation <strong>of</strong>minerotrophic mire, which again may sometimes besubject to progressive ombrotrophication. However, insorne circumstances paludification can resuIt in a moreor-lessdirect <strong>de</strong>velopment <strong>of</strong> ombrotrophic peat,without a significant intervening minerotrophic phase.Ombrogenous bogs are thought to be c1imax ecosystems,which have <strong>de</strong>veloped spontaneously from avariety <strong>of</strong> starting points and which are believed to bestable, at least when undamaged.1.3 Types <strong>of</strong> fens and bogsMinerotrophic peatlands occur in a very wi<strong>de</strong> variety<strong>of</strong> situations, wherever the water table is sufficientlyand consistently high to sustain peat accumulation. Thedistribution and occurrence <strong>of</strong> fens is largely <strong>de</strong>terminedby an interaction between landscape topographyand local or regional, hydrology. Likewise, the grossmorphology <strong>of</strong> a fen is <strong>of</strong>ien largely a reflection <strong>of</strong> thefeatures <strong>of</strong> the landscape in which it occurs. Deepaccumulations <strong>of</strong> fen peat are most characteristic <strong>of</strong>topogenous sites, e.g. ground hollows, basins and riverflood-plains. Various classifications <strong>of</strong> fens based ontheir situation, shape and water supply have been proposed(e.g. Succow & Lange, 1984). Schemes suggestedfor Britain (e.g. Ratcliffe, 1977; Wheeler, 1984) requirec1arification and revision (Wheeler, 1993).Ombrogenous peatlands occur over a similar range <strong>of</strong>topographical situations to minerotrophic examples butboth their geographical distribution and the range <strong>of</strong>topographical situations in which they can form isstrongly constrained by climate. This is because their<strong>de</strong>velopment requires a sufficiently high rate <strong>of</strong>precipitation input (<strong>of</strong>ien coupled with low rates <strong>of</strong>evapotranspiration) to permit peat to accumulate aboyethe level <strong>of</strong> the mineral ground or the influence <strong>of</strong>telluric water. Within suitable regions, ombrogenouspeatlands may be far more extensive than are fens(Goodwillie, 1980), but globally they have a morerestricted distribution. The exact climatic conditionsrequired for bog <strong>de</strong>velopment have yet to be established,but examples occur from the tropics to the


CHAPTER 1: LOWLANO PEATLANOS 3Plate 1.1 Aerial view <strong>of</strong> the west bog, Cors Caron (Dyfed). The drier margins <strong>of</strong> the raised bog are picked out by thelighter colour <strong>of</strong> the vegetation, with the River Teifi forming the 'Iagg' on one si<strong>de</strong> <strong>of</strong> the bogo [Photo: J. Davis]boreal regions. In temperate Eurasia, most ombrotrophicmires occur between the latitu<strong>de</strong>s 50-70° N(proctor, 1995).By their nature, ombrogenous mires form as a peat<strong>de</strong>posit raised aboye the level <strong>of</strong> the regional watertable, the un<strong>de</strong>rlying minerotrophic peat and mineralsoil. The shape and dimensions <strong>of</strong> bog-peat <strong>de</strong>positsvary very consi<strong>de</strong>rably, <strong>de</strong>pending primarily upon theirage, the un<strong>de</strong>rlying landforms and the climatic regimein which they have <strong>de</strong>veloped. In the drier regions <strong>of</strong>Britain, bog formation has been restricted to flattishsurfaces or very gentle slopes, whereas in the wetter,cooler regions <strong>of</strong> the north and west, it has also beenable to occur upon quite steeply sloping terrain. Thisdifference has provi<strong>de</strong>d the basis for the recognition <strong>of</strong>two, rather ill-<strong>de</strong>fined, main categories <strong>of</strong> bog inBritain - 'raised bog' and 'blanket bog' [Box 1.1].Raised bogs: These are primarily (but not exclusively)lowland peatlands which, in Britain, mostly occupy thebottoms <strong>of</strong> broad, flat valleys, the heads <strong>of</strong> estuaries orshallow basins [Plate 1.1]. In their most distinctive<strong>de</strong>velopment they form shallow domes <strong>of</strong> ombrogenouspeat <strong>de</strong>limited usually by mineral ground, fenor watercourses. They sometimes form large complexesin which tracts <strong>of</strong> bog are separated by watercoursesor fen. In Britain, sites that are usually called raisedbogs typically occur in regions with an annualprecipitation range <strong>of</strong> c. 800-1200 mm a- Iand with140-180 wet days a-) (Rodwell, 1991), though the fullrange is wi<strong>de</strong>r than this [BOx 1.2]. [See al so 1.5]Blanket bogs: These are ombrotrophic peatlands that'blanket' large areas <strong>of</strong> variable topography. Unlikeraised bogs, they can form on quite strongly slopingground (slopes typically up to c. 10° (Tansley, 1939),but sometimes steeper (Moare & Bellamy (1974)suggest 25°). This reflects the particularly wet, coolconditions in which they occur with an annual precipitationtypically in excess <strong>of</strong> c. 1200 mm a- 1 and morethan 160 wet days a- I(Ratcliffe, 1977). In much <strong>of</strong>England and Wales they are restricted to the higheraltitu<strong>de</strong>s (above c. 400m) but in westem and northemparts <strong>of</strong> Scotland and Ireland they <strong>de</strong>scend to near sealevel. The capacity <strong>of</strong> blanket bogs to form on slopesmeans that they <strong>of</strong>ien form much larger tracts <strong>of</strong>continuous ombrogenous peat than is the case withraised bogs. They are most usually <strong>de</strong>limited by atransition to mineral soil (<strong>of</strong>ien a peaty podsol). andsometimes form very large complexes in which areas<strong>of</strong> bog peat are separated by watercourses or fen. Theterm blanket mire can be used to refer to blanket peatecosystems in aggregate (i.e. including both ombrogenousand minerotrophic components), restricting


4RESTORATlON OF DAMAGED PEATLANDSBox 1.1 Hydromorphological types o,bog in Britain: the concept o, 'raised bog'Two t~pes ?f .ombrogenous bog have been generally recog­",sed In Bntaln: raised bog and blanket bog (e.g. Tansley,193~). Some workers have suggested that these are linked byan Intermedlate type, such as 'ridge-raised mire' (Moore &Bellamy, 1974). However, the characteristics <strong>of</strong> these bog'types' have not been critically or rigorously <strong>de</strong>fined and theterms have been applied loosely to sites, sometimes withoutexamination <strong>of</strong> their actual features.'Classic' raised bog in Britain, as <strong>de</strong>scribed by Tansley (1939),reflected the observations <strong>of</strong> Weber (1908). ft occupied adiscrete lowland site; it had <strong>de</strong>veloped by hydroseral successionfrom open water (open water ~ swamp ~ fen ~ bog);and it formed a shallow dome <strong>of</strong> ombrogenous peat, with aquite strongly sloping marginal rand leading down into aperipheral moat-like, minerotrophic lagg. However, manyraised bogs in Britain do not conform to this 'classic' mo<strong>de</strong>l, forexample, in mo<strong>de</strong> <strong>of</strong> origin, gross morphology or altitu<strong>de</strong>.In the 'c1assic' raised bog, ombrogenous peat, <strong>de</strong>veloped upona flat surface <strong>of</strong> fen, formed a dome in<strong>de</strong>pen<strong>de</strong>nt <strong>of</strong> theun<strong>de</strong>rlying base. Such 'in<strong>de</strong>pen<strong>de</strong>nt doming' is sometimesregar<strong>de</strong>d as part <strong>of</strong> the character <strong>of</strong> a raised bog, butexamination <strong>of</strong> stratigraphical sections reveals that thecharacteristics <strong>of</strong> domes <strong>of</strong> ombrogenous peat in sites that arenormally consi<strong>de</strong>red to be raised bogs can show muchvariability. The <strong>de</strong>gree <strong>of</strong> 'doming' appears to be a product <strong>of</strong>age, topographical situation, basal area and c1imate. It is <strong>of</strong>ienmost evi<strong>de</strong>nt in small bogs; larger examples <strong>of</strong>ien do notappear strongly domed, but may form an extensive plateau <strong>of</strong>peat with steep edges (Ratcliffe, 1964). The surface <strong>of</strong> the bogpeat may sometimes be strongly related to the un<strong>de</strong>rlyingtopography, as when the summit <strong>of</strong> the dome reflects anun<strong>de</strong>rlying mineral ridge. Such sites may have <strong>de</strong>veloped bythe coalescence <strong>of</strong> separate ombrogenous mires thatoriginated in and spread out from adjoining basins and arethus referable to the 'ridge-raised mires' recognised by Moare& Bellamy (1974). However, it is far from certain that thisrepresents a useful point <strong>of</strong> distinction as many <strong>of</strong> the sitesthat are normally called 'raised bogs' in the British Isles and onthe European mainland have <strong>de</strong>veloped by expansion acrossridges <strong>of</strong> mineral ground (for example, most <strong>of</strong> the Lancashiremosses (C.E. Wells, unpublished data).The range <strong>of</strong> hydromorphology <strong>of</strong> those British sites that are<strong>of</strong>ien referred to as being raised bogs can be i1lustrated by foursections [Figure 1.1]. Cors Caron [Plate 1.1] comes close tobeing a 'classic' raised bog, with a c1ear 'in<strong>de</strong>pen<strong>de</strong>nt' domeand a flat base, having originated by autogenic successionfrom preceding phases <strong>of</strong> fen and open water. The stratigraphy<strong>of</strong> Bowness Common-Glasson Moss points to a sitewhere peat initially <strong>de</strong>veloped, hydroserally, in <strong>de</strong>pressions,but grew out <strong>of</strong> these to coalesce across substantial ridges.Flan<strong>de</strong>rs Moss West seems to have <strong>de</strong>veloped largely bypaludification. Its section illustrates the manner in which the'doming' <strong>of</strong> some British raised bogs reflects the contours <strong>of</strong>the un<strong>de</strong>rlying mineral ground. The section <strong>of</strong> Coalburn Mosspoints to a gently sloping site without a c1ear dome; moreover,undulations in its surface show some parallel with theun<strong>de</strong>rlying relief. Such systems have strong hydromorphologicalaffinities with some examples <strong>of</strong> blanket bog, and theactual point <strong>of</strong> distinction is far from clear - a confusionexacerbated by the occurrence within some blanket boglandscapes <strong>of</strong> mires with strong affinities to many 'Iowlandraised bogs' (see below).Raised bogs may be surroun<strong>de</strong>d by a minerotrophic lagg,which is sometimes consi<strong>de</strong>red to form par! <strong>of</strong> the concept <strong>of</strong>raised bogo The actual character <strong>of</strong> the lagg <strong>of</strong> many Britishbogs is difficult to assess, as it has frequently been <strong>de</strong>stroyed,but a well-<strong>de</strong>veloped, or complete lagg, may not have been afeature <strong>of</strong> all examples (Ratcliffe, 1964) except in the sensethat, as with all ombrogenous peats, their lateral limits musthave been marked by a transition into some form <strong>of</strong> minerotrophicfen or mineral soil. Distinctive, moat-like laggs are<strong>of</strong>ien most evi<strong>de</strong>nt in basins where the lateral expansion <strong>of</strong> thebog has been constrained topographically. In other cases, aswhere a dome <strong>of</strong> ombrogenous peat has exten<strong>de</strong>d beyond theformer limits <strong>of</strong> a basin, the lagg, if present, may largely be aproduct <strong>of</strong>. t~e growth <strong>of</strong> the bogo Elsewhere, minerotrophicmires adJolnlng or surrounding a raised bog may predate thebog and be substantially in<strong>de</strong>pen<strong>de</strong>nt <strong>of</strong> il. In yet other sitesthe 'Iagg , has effectively been imposed upon the bog, aswhere water courses and regular f100ding has preventedfurther lateral expansion <strong>of</strong> ombrotrophic peat (Ratcliffe, 1964).Such consi<strong>de</strong>rations suggest that it may be best to exclu<strong>de</strong>the lagg from any general concept <strong>of</strong> raised bog and to restrictthis specifically to the <strong>de</strong>posit <strong>of</strong> ombrogenous peal.It ismore dimcult to i<strong>de</strong>ntify a 'classic' concept <strong>of</strong> blanket bog- It 15 <strong>of</strong>ien Informally consi<strong>de</strong>red to be ombrogenous peatlandwith a more upland and north-western distribution than raisedbog, which blankets large tracts <strong>of</strong> land, conformed by thetopography and restricted only by the steeper slopes and otherobstructions. There is a ten<strong>de</strong>ncy to regard all ombrogenouspeatlands within 'blanket bog regions' as blanket bog, irrespective<strong>of</strong> their actual character, and even to consi<strong>de</strong>r theirgreat extent, across a wi<strong>de</strong> variety <strong>of</strong> relief, as a diagnosticfeature. However, location is not a hydromorphological attributeand size alone seems a specious basis for a distinction <strong>of</strong>bog types - especially as, elsewhere in Europe, lowland'raised bogs' once covered areas <strong>of</strong> comparable magnitu<strong>de</strong> tosome tracts <strong>of</strong> blanket bog [1.4]. The key distinguishingfeature <strong>of</strong> blanket bog is the occurrence <strong>of</strong> ombrogenous peaton hillslopes and it is far from clear that the ombrogenouspeatlands <strong>of</strong> the basins, flats and gentle slopes <strong>of</strong> 'blanket bogregions' are necessarily fundamentally different - in terms <strong>of</strong>their origin, gross form and stratigraphy - from the 'raisedbogs' <strong>of</strong> drier c1imates. In<strong>de</strong>ed, various stratigraphical sectionssuggest that some units <strong>of</strong> bog embed<strong>de</strong>d within a 'blanketbog landscape' have greater similarity with 'raised bogs'elsewhere than they do with the blanket peats on adjoiningslopes (e.g. Department <strong>of</strong> Agriculture and Fisheries forScotland, 1962-8). If such units are inclu<strong>de</strong>d within a broadconcept <strong>of</strong> 'blanket bog', they expand this to encompass much<strong>of</strong> the hydromorphological range <strong>of</strong> raised bogs elsewhere,thus eroding any 'real' distinctions that there may be betweenthe two types. It seems probable that the most distinctivehydromorphological subdivision within ombrogenous peatlandsis that between sites in topogenous situations and those on hillslopes, as has been recognised in the categories <strong>of</strong> hill bogand topogenous bog used by the Scottish Peat Survey. Onthis basis, the 'blanket peatlands' <strong>of</strong> oceanic regions can beseen as a mosaic <strong>of</strong> hill bog, topogenous bog and varioustypes <strong>of</strong> fen, whilst 'Iowland raised bogs' <strong>of</strong> drier regions arereferable to topogenous bogoThe variability <strong>of</strong> ombrogenous mires in Britain undoubtedlymakes it difficult to formulate a clear and coherent concept <strong>of</strong>'raised bog'. We suggest the following tentative, working<strong>de</strong>finition <strong>of</strong> 'raised bog' in the UK: "Ombrogenous mires inwhich much <strong>of</strong> the vegetation is typically referable to, orclosely allied with, or <strong>de</strong>rivative from (e.g. as a result <strong>of</strong>damage), Erica tetralix-Sphagnum papillosum mire (Rodwell,1991); they may exhibit a dome (or domes) <strong>of</strong> peat in<strong>de</strong>pen<strong>de</strong>nt<strong>of</strong> the un<strong>de</strong>rlying subsoil contours, but this is not alwaysthe case; some (usually ol<strong>de</strong>r) examples contain <strong>de</strong>ep(sometimes > 5m) bog peat, which is frequently little-humifiedin the upper layers." Mires thus i<strong>de</strong>ntified typically occur intopogenous situations - in basins or on surfaces which are, inaggregate, more-or-Iess flat or very gently sloping (the surfacemay have undulations or <strong>de</strong>pressions and ridges, over whichthe bog has <strong>de</strong>veloped); in some instances they have<strong>de</strong>veloped by coalescence <strong>of</strong> adjoining mires (sometimesoriginating in separate basins). Such sites may be surroun<strong>de</strong>dby mineral ground, fen or an ombrotrophic 'hill peal'. Using this<strong>de</strong>finition, most sites <strong>of</strong> commercial peat extraction in Britainare (sometimes former) raised-bog sites.


C1IAPTER J: LOWLAND PEATLANDS 5(A)W.N.Wo 20 40 6() 80 100 200 300 400 5001~ Sphagnllrn peal H S1/::::::1 Sill.Mu<strong>de</strong>II Relardalion layer• Phragmites peal(B)~I121110,876s.w.Bowness CommonGlasson MossI =,==c:::C:;:::C::c:i:::I========I:DCCi:::I::I:i:I::i:::i~' =,=1='=,='='=,====:500 1000 1500 2000 2500 JOOO MmN.E.• Dislurbed <strong>de</strong>posits 11I1 Sphagnum peal HH ~=======~ um;naled sandy clay • Silty clay (I.warp) • Oay mud (u.warp)o Wood fragments Sphagnum peal H5-10 ~ Boul<strong>de</strong>rday U Coarse <strong>de</strong>tritus mud(C)Eriophonun/CltllunltSphaSrllH"8.tsa1 soil(D)2.1510N.W.6050>l5


6RESTORATION OF DAMAGED PEATLANDSDomeacrote/mcatote/mten pealminera/ sub-soilFigure 1.2 Diagrammatic pr<strong>of</strong>ile across a raised bog, illustrating some <strong>of</strong> the terms used in the text.blanket bog specifically to refer to the ombrogenouselements <strong>of</strong> this.In Britain, most commercial peat extraction concernslowland raised bogs and these are the focus <strong>of</strong> thisaccount.1.4 Sorne features <strong>of</strong> raised bogsOn casual inspection, little-damaged raised bogsfrequently appear to be rather featureless, uniformtracts <strong>of</strong> waterlogged ground, sometimes with a windswept<strong>de</strong>solation that may be perceived variously asdismal or <strong>de</strong>lightful. They vary very consi<strong>de</strong>rable intheir size. In Britain, embryonic 'raised bogs' (e.g.areas <strong>of</strong> ombrogenous peat within fens) may cover justa few square metres, whilst the largest raised bogs arein excess <strong>of</strong> 1000 ha, although the majority are quitesmall « 30 ha). Extremely large examples onceoccurred on the European mainland, the biggest complexhaving an estimated area in excess <strong>of</strong> 1000 km 2(Barkman, 1992). The <strong>de</strong>pth <strong>of</strong> peat in raised bogs isvery variable and <strong>de</strong>pends particularly upon the age <strong>of</strong>the <strong>de</strong>posito Thicknesses <strong>of</strong> bog peat reported fromBritain typically range between about 1 and 5 m.The overall topography <strong>of</strong> little-damaged raised bogsvaries consi<strong>de</strong>rably. Sorne (usually rather small)examples have a quite strongly domed appearance inwhich the pr<strong>of</strong>ile <strong>of</strong> the bog peat <strong>de</strong>posit approximatesto a half-ellipse. In others, the peat <strong>de</strong>posit is more likea plateau, dipping sharply around its margins [Box1.1]. In both cases the margins are usually steeper thanthe main bog expanse and are sometimes referred to asthe rand. In sorne situations the interface <strong>of</strong> the bogmargins with the adjoining mineral ground is markedby a moat-like lagg, normally supporting fenvegetation. [A diagrammatic pr<strong>of</strong>ile across a raised bogis shown in Figure 1.2]. However, the naturalmorphology <strong>of</strong> many raised bogs, especially the naturalstate <strong>of</strong> the margins, is not really known, as peatextraction and agricultural conversion has altered thetopography <strong>of</strong> most sites. Commercial peat extractionusually alters the configuration <strong>of</strong> the entire bog whilstdomestic extraction, or agricultural improvement,Box 1.2 e/imate and the occurrence <strong>of</strong> raised bogsThe formation <strong>of</strong> a <strong>de</strong>posit <strong>of</strong> ombrotrophic peat, and to some extent its dimensions, is <strong>de</strong>pen<strong>de</strong>nt upon the c1imatic regime inwhich it occurs, especially the ratio <strong>of</strong> precipitation to evaporation [see Box 1.5], but the precise range <strong>of</strong> c1imatic circumstances inwhich bog formation can occur is not well un<strong>de</strong>rstood, partly because some water balance terms have received but Iimited study.Water supply to bogs is frequently specified just in terms <strong>of</strong> precipitation input, but this has to be balanced against potentiallosses by evapotranspiration. (The amount <strong>of</strong> evapotranspiration is influenced by such factors as solar radiatiqn, air and surfacetemperatures, wind speed and relative humidity. Vegetation-type and mulching effect <strong>of</strong> the moss or Iitter layer also affect it.)Moreover, the annual mean values that are usually provi<strong>de</strong>d for these variables may not be as significant to the <strong>de</strong>velopment andmaintenance <strong>of</strong> bogs as are seasonal values, though the importance <strong>of</strong> these latter has been little-quantified. Factors such as thefrequency <strong>of</strong> rainfall (proportion <strong>of</strong> rain-days, i.e. days with 1 mm or more <strong>of</strong> precipitation), number <strong>of</strong> days with sunshine, relativehumidities, temperature, exposure etc. may be <strong>of</strong> consi<strong>de</strong>rable importance in maintaining some ombrotrophic systems. In regionswith smaller rates <strong>of</strong> evapotranspiration, raised bogs can form with lower precipitation input. Various notional figures have beensuggested as a minimum precipitation thresholds for the <strong>de</strong>velopment <strong>of</strong> raised bogs (e.g. 460 mm, S Swe<strong>de</strong>n; 600-700 mm, NGermany). In the UK, peatlands that are usually called raised bogs occupy a wi<strong>de</strong> range <strong>of</strong> mean annual precipitation: ThorneWaste (S. Yorks.): c. 570 mm; south Solway Mosses (Cumbria): c. 800 mm; Cors Caron (Dyfed): c. 1275 mm; Moine Mhor(Argyll): c. 2,000 mm. Such differences are likely to affect both the feasibility <strong>of</strong> restoration <strong>of</strong> damaged sites and the nature <strong>of</strong> therestoration procedures that can be used.


CHAPTER 1: LOWLAND PEATLA D 7Plate 1.2 Distinctive microtopographical patterning <strong>of</strong> the bog surface (hummocks, lawns and bog pools), illustratedat Claish Moss, Argyll (Ieff) and Mongan Bog, Ireland (righf).around the margins has obliterated the naturaltransition to drier ground (or fen). In consequence theoriginal character <strong>of</strong> presumed features such as therand and lagg is <strong>of</strong>ien not known. In some cases, bysharpening the edges, marginal damage may haveaccentuated the domed appearance <strong>of</strong> peat <strong>de</strong>posit.Direct and indirect drainage may also have causedsome changes in the topography <strong>of</strong> many sites,including little-damaged examples, but the nature an<strong>de</strong>xtent <strong>of</strong> this can scarcely even be guessed.In Britain, as in other regions <strong>of</strong> the Atlantic sea-board,little-damaged raised bogs are generaIly treeless; wheretree do occur this seems mainly to be in response tosorne surface damage (such as drainage). In this respectthe oceanic bogs differ from their counterparts in morecontinental regions <strong>of</strong> the European mainland, whereconifer species can be important components <strong>of</strong> at leastthe landward zones <strong>of</strong> bogs. lt is possible that, even inBritain, trees may once have been natural components<strong>of</strong> bog vegetation, at least towards the margins, andperhaps more wi<strong>de</strong>ly in exten<strong>de</strong>d dry periods (elCasparie, 1972), and that the role <strong>of</strong> grazing andbuming in preventing natural scrub encroachment hasbeen un<strong>de</strong>restimated (H. 1ngram, pers. eomm.).The vegetation <strong>of</strong> little-damaged bogs forms a miresurface with a characteristic appearance, based upon itsmain constituents <strong>of</strong>sub-shrubs, 'sedge-like' plants andbog mosses (Sphagnum species) [see PIates 1.4 and1.5]. The sub-shrubs are mostly members <strong>of</strong> the Ericacea(e.g. heather (Cal/una vulgaris) and cross-leavedheath (Eriea tetralbe)) together with similar plants fromre1ated families, such as crowberry (Empetrumnigrum). 'Sedge-like' plants (i.e. members <strong>of</strong> theCyperaceae) inc1u<strong>de</strong> the cotton grasses Eriophorumangustifolium and E. vaginatum. Sphagna are <strong>of</strong>ien keycomponents <strong>of</strong> the vegetation, in terms <strong>of</strong> their coverand their contribution to the surface processes and peatformation <strong>of</strong> the bog [1.7; 1.8; 1.9]. The vegetation <strong>of</strong>little-damaged raised bogs and blanket bogs has agenerally similar overall appearance, but there aresome broad differences between them in terms <strong>of</strong> theirspecies composition (Rodwell, 1991).Some parts <strong>of</strong> the surface <strong>of</strong> a little-damaged bog mayshow a distinctive patterning (m icrotopographicalheterogeneity), in which various components can berecognised (hummocks lawns, hollows, pools etc.)[Plate 1.2]. Ofien 'pools' are just shallow-tloo<strong>de</strong>dhollows with aquatic species <strong>of</strong> Sphagnum, but larger,<strong>de</strong>eper and more permanent areas <strong>of</strong> open water alsooccur in some bogs. These may range greatly in size,from a few metres to several tens <strong>of</strong> metres across.Larger examples are variously known as 'bog lakes','moor eyes', 'wells' and 'dubh lochans', the [atterretlecting the appearance <strong>of</strong> their black, peat-stained,water. Some are sufficiently large to be marked evenon quite small-scale (1 :50,000) maps and may evenhave acquired individual names. Despite a quite largeamount <strong>of</strong> research, the causes <strong>of</strong> surface pattern ing arenot at all well un<strong>de</strong>rstood, neither for the 'hummockhollow'pattem nor the more permanent pools.The surface <strong>of</strong> a little-damaged raised bog is typicallywaterlogged, <strong>de</strong>spite its elevation aboye the adjoiningland. The highest, more central, parts <strong>of</strong> the bog are<strong>of</strong>ien the wettest and typically show the mostpronounced <strong>de</strong>velopment <strong>of</strong> surface patterning andpool systems, whereas the rand is better drained. Thewet condition are created (in mo t cases) by anaccumulation <strong>of</strong> rainfall [1.7] and the chemicalcharacteristics <strong>of</strong> the bog water reflect the composition<strong>of</strong> the rainfall, modified by processes within the peatand by the growth <strong>of</strong> plants. The water <strong>of</strong> raised bogscan be <strong>de</strong>scribed simply as being 'acidic and nutrientpoor' [1.9.4].


8RESTORATION 01' DAMAGED PEATLANDS1.5 Occurrence <strong>of</strong> raised bogsRaised bogs occur wi<strong>de</strong>ly in temperate and borealregions <strong>of</strong> Eurasia and North America. They are (orwere) important features throughout much <strong>of</strong> northernEurope, being particularly wi<strong>de</strong>spread and extensive inBritain and Ireland, the Netherlands and north westGermany, southem Swe<strong>de</strong>n and Finland and in theBaltic States. Examples also occur, somewhat separatedfrom the main range, in the foothills and valleys <strong>of</strong>the Alps. There is a ten<strong>de</strong>ncy for raised bogs in differentregions to show sorne differences in gross morphology,particularly with respect to the concentricity <strong>of</strong>their domes and areal extent (Moore & Bellamy, 1974).In Britain, although many examples have beendamaged or <strong>de</strong>stroyed, lowland raised bogs still have awi<strong>de</strong> distribution. They are especially wi<strong>de</strong>spread inthe cooler, wetter regions <strong>of</strong> the north and west (northwestEngland and southern and central Scotland), butexamples also occur (or once occurred) in a number <strong>of</strong>southern and eastern localities, including sites in S.Yorkshire, Lincolnshire, Cambridgeshire, Somersetand Sussex. It is possible that raised bogs were onceeven more wi<strong>de</strong>spread in these drier regions than iscurrently recognised, as in sorne situations agriculturalconversion and ancient peat-cutting may have removedmost traces <strong>of</strong> former ombrotrophic peat. Figure 1.5shows the distribution <strong>of</strong> peat soils that are regar<strong>de</strong>d bythe National Peatland Resource Inventory (Lindsay elal, in prep) as being associated with raised bogs inEngland, Scotland and Wales.Raised bogs are particularly characteristic <strong>of</strong> lowlandregions <strong>of</strong> Britain, where they occur in basins, alongflood-plains, at the heads <strong>of</strong> estuaries elc. However,examples have been <strong>de</strong>scribed also from more uplandsituations, such as Tarn Moss, Malham (W. Yorks.)and Dun Moss (Perths.) which are both at about 350 maltitu<strong>de</strong>.Raised bogs have <strong>de</strong>veloped both by terrestrialisationand paludification processes and sometimes by acombination <strong>of</strong> the two mechanisms. Although they aremainly initiated in <strong>de</strong>pressions or on flat surfaces,continued upward accumulation <strong>of</strong> bog peat haspermitted sorne examples to spread onto adjoining,once-dry, slopes and to coalesce across ridges <strong>of</strong>mineral ground [Box 1.3].Box 1.3 Origins and <strong>de</strong>velopment o( raised bogsRaised bogs may originate and <strong>de</strong>velop by a variety <strong>of</strong>pathways. The 'c1assic' <strong>de</strong>velopmental sequence (Weber,1908) [Figure 1.3] shows initiation <strong>of</strong> ombrotrophic peat fromwithin minerotrophic swamp or fen, which has <strong>de</strong>veloped overa pool or lake as part <strong>of</strong> a hydroseral or lerreslrialisalionprocess. However, it has long been recognised that raisedbogs have also <strong>de</strong>veloped by the swamping <strong>of</strong> ground thatwas once relatively dry, either more-or-Iess direcUy or, moreusual/y, through an intervening (sometimes short-Iived) phase<strong>of</strong> fen (Cajan<strong>de</strong>r, 1913). This process is known aspaludification. Thus starting points for raised bog <strong>de</strong>velopmentinclu<strong>de</strong> such diverse habitats as reedswamp, f10atingvegetation mats, herbaceous fen, fen carr, woodland andsaltmarsh [Figure 1.4). Common to al/ <strong>of</strong> these <strong>de</strong>velopmentsis the progressive upward growth <strong>of</strong> peat aboye the level <strong>of</strong>influence <strong>of</strong> groundwater, leading to a surface irrigated almostentirely by precipitation inputs. The character <strong>of</strong> this is, in largemeasure, in<strong>de</strong>pen<strong>de</strong>nt <strong>of</strong> its starting 'conditions. The timetaken for the <strong>de</strong>velopment <strong>of</strong> bog peats from a precedingphase is also variable - it has been suggested that thetransition between fen vegetation and bog vegetation may takefrom between just a few years to about five centuries.Some examples <strong>of</strong> raised bog have <strong>de</strong>veloped initial/y in abasin, <strong>of</strong>ten as a late phase <strong>of</strong> hydroseral succession, buthave subsequently expan<strong>de</strong>d over adjoining 'dry' land. Thisprocess can lead to the fusion <strong>of</strong> adjoining raised bogs toproduce a larger unil. The very extensive raised bogs <strong>of</strong> TheNetherlands and Germany are thought to have formed in thisway, as have some UK examples (e.g. Bowness Common IGlasson Moss - Figure 1.1). In some cases the gradual'spilling' <strong>of</strong> ombrotrophic peat out <strong>of</strong> the original basin ontoadjoining mineral ground produces, at least initial/y, a thinhumified peat-type that, both in character and situation, isreminiscent <strong>of</strong> some types <strong>of</strong> blanket bog peal. This has beenIitUe documented in Britain but is probably quite wi<strong>de</strong>spread.Examples are thought to occur at Wedholme Flow and WaltonMoss (Cumbria).In some mires the <strong>de</strong>velopment <strong>of</strong> bog peat has been socomplete as to cover most traces <strong>of</strong> former fen. However,more usual/y the apparent present-day dominance <strong>of</strong> somepeaUand sites by bog reflects the drainage and agriculturalconversion <strong>of</strong> once-adjoining fen. This may be the case, forexample, in situations where some, or al/, <strong>of</strong> the bog peat hasbeen left unclaimed on account <strong>of</strong> the greater difficulties <strong>of</strong>converting it into productive agricultural land. Deep peatexcavation sometimes exposes un<strong>de</strong>rlying fen peat andprovi<strong>de</strong>s the possibility for the re-establishment <strong>of</strong> fenvegetation.The initiation <strong>of</strong> ombrotrophic peat implies impe<strong>de</strong>d drainage<strong>of</strong> precipitation inputs. This may be produced in various ways.Where the bog peat has <strong>de</strong>veloped from fen and swamp, thenthe low-permeability bottom <strong>of</strong> the bog is frxed either by thefen water table itself, or by the surface <strong>of</strong> low-permeability fenand wood peats. Where bogs have <strong>de</strong>veloped bypaludifrcation, the basis for the establishment <strong>of</strong> permanenUywet conditions may be provi<strong>de</strong>d by a variety <strong>of</strong> lowpermeabilityhorizons. These including crystal/ine bedrocks,glacial and estuarine c1ays ele. Nonetheless, paludification canalso occur upon more permeable substrata (e.g. sands andgravels). In this situation waterlogging may be possible eitherbeca use <strong>of</strong> a high groundwater table within the porousmedium (as in zones <strong>of</strong> groundwater discharge) or because <strong>of</strong>the <strong>de</strong>velopment <strong>of</strong> low permeability pans <strong>of</strong> iron or organicmaterial, in some cases possibly related to 'fossil' indurated,cemented layers formed in periglacial conditions.


CHAPTER 1: LOWLA P ATLA DS 9'::


10 RESTORATION OF DAMAGED PEATLANDSDistribution <strong>of</strong> raised bogs by 1ükm square.Scale 1:4087592Putland irlormation taPa rrom lJM. N'bODaI Pudlnd R.e.lOUt,* Invem.ory. &ndrtprUentl Che but infonnlÜon no.laMa ... pcuent. boundMiu ..,. reproducdi---:Pr:-od-'--uc-ed---b-y---tb-e---Up---I.-nds-"'-d---P:- ..-tJ:-"'---ds---B=-ranc-b:-,-=-R-es-eorc-:-b-"'---d---A---dV---is-ory--C:S-erv---ic-es---l[)irectorate. Scottish Natural Heritage. lime 03. 1994=::;n~u::;,otC:n:'~W::yC~.:2';"~·mlp with 1he pemuU10ft <strong>of</strong>Her MIJUty'J Slitionary Offic:.. Ce) erOW" Copyn&ht.Figure 1.5 Distribution <strong>of</strong> soils i<strong>de</strong>ntified by the National Peatland Resource Inventory as associated with raise!bogs in England, Scotland and Wales, by 10 km square. [Diagram provi<strong>de</strong>d by Scottish Natural Heritage].


CHAPTER 1: LOWLAND PEATLANDS111.6 Current condition <strong>of</strong> 8ritishraised bogsScottish Natural Heritage are preparing an inventory <strong>of</strong>the extent and condition <strong>of</strong> raised bogs in Great Britain(Lindsay el al.; in prep.), on behalf <strong>of</strong>the three countrystatutory nature conservation agencies. Summarystatistics from the draft inventory are presented inTable 1.2, although the data are still subject toverification and review. Categories given are for themajar land-cover classes <strong>of</strong> raised bogs and the 'bes1'land cover classes i<strong>de</strong>ntified for each site.The category <strong>of</strong> 'closed-canopy woodland' inclu<strong>de</strong>sboth forestry plantations and sites that have becomespontaneously woo<strong>de</strong>d, although the majority iscommercial plantation. Thus, woo<strong>de</strong>d bogs, togetherwith the agriculture,and urban categories, account forsome 48% <strong>of</strong> the original raised-bog area. These areasmay retain sorne general wildlife 'interes1' and, insome instances, are probably amenable for restorationto bogo If, however, they are consi<strong>de</strong>red to be areaseffectively 'los1' from the raised-bog resource, then theresidue represents some 36,000 ha <strong>of</strong> raised-bog sitesin variable condition. Only a small proportion <strong>of</strong> this isregar<strong>de</strong>d as being more-or-Iess 'natural' (littledamaged).The biological condition <strong>of</strong> the remain<strong>de</strong>r isnot specified, but it cannot be assumed that it has noconservation value, even in terms <strong>of</strong> bog species. Thisis not least because the areas given are based on themajor land-use class for each site: partly-damaged bogsand .revegetating peat cuttings can still provi<strong>de</strong> a richrepository <strong>of</strong> bog species. For example, WedholmeFlow, which retains some <strong>of</strong> the finest examples <strong>of</strong>little-damaged Sphagnum-rich raised-bog vegetation inEngland, is categorised un<strong>de</strong>r its major land-use class<strong>of</strong> 'secondary - revegetating'. Likewise, it should benoted also that the area <strong>of</strong> bog <strong>de</strong>signated as'secondary - active commercial peat extraction'contains some large expanses <strong>of</strong> vegetated (sometimesrevegetated) bog peat, as well as active peat fields.There can be little doubt that the total area <strong>of</strong> 'goodqualityraised bog' remaining in Britain is small, norabout the i<strong>de</strong>ntity <strong>of</strong> some <strong>of</strong> the main causes <strong>of</strong>damage. However, the loss <strong>of</strong> 'quality' in bogs may notjust be a product <strong>of</strong>direct damage <strong>of</strong> the type i<strong>de</strong>ntifiedin Table 1.2. In various lowland mires, once-diverseSphagnum communities have been replaced by lawnsdominated by one species, Sphagnum recurvum (Tallis,1973). The explanation <strong>of</strong> this is not known: pastsulphur pollution, enrichment with atmospheric nitrogensources, especially perhaps ammonia, or someother form <strong>of</strong>enrichment from agricultural sources, areall candidate hypotheses. Such consi<strong>de</strong>rations make itdifficult to be confi<strong>de</strong>nt about the full measure <strong>of</strong>impact and significance <strong>of</strong> the more direct forms <strong>of</strong>damage i<strong>de</strong>ntified in Table 1.2. It cannot be assumedthat former raised bogs would necessarily still support'good-quality' vegetation had they not been subject todirect drainage or <strong>de</strong>struction.Table 1.2 The major land cover classes* on raised bogs in Britain, as i<strong>de</strong>ntified by the National Peatland ResourceInventory (Lindsay et al, in prep). Source: Department <strong>of</strong> the Environment (1994).England Scotland WalesCondilion class Number Area Number Area Number Area<strong>of</strong> bogs (ha) <strong>of</strong> bogs (ha) <strong>of</strong> bogs (ha)Primary - near-nalural 1 8 49 2673 5 2694Primary - <strong>de</strong>gra<strong>de</strong>d (burnl I moribund) ,9 1699 83 3148 2 136Primary - drained 13 562 20 1192 5 35Primary - open canopy scrub or woodland 14 427 5 176 1 6Primary - closed canopy woodland 41 1734 193 9780 O OSecondary - revegelaling 15 1163 39 2881 3 790Secondary - active commercial peal 15 14498 12 2284 1 4exlraclion*Archaic - agricullure 92 16972 238 3048 3 247Archaic - buill (urban I wasle disposal etc.) 7 350 26 890 1 174Unknown O O 144 1818 O OTolal 207 37413 809 27890 21 4086* Note that lhese figures are based on assessmenl <strong>of</strong> lhe dominanI land cover c1ass on each site. Thus, for example, ~he figures foraclive commercial peal cutting inclu<strong>de</strong> more than just the area eilher permitted for, or aclually affecled by peal exlracllon (see lexl).


12RESTORATION 01' DAMAGEI) PEATLANDS//Increased waterretention I waterloggingEstablishment <strong>of</strong> /acidopllilous,oligotrophic /plant species.particularly Sphagna ~~'"l~-c-re-at-io-n-O-'f'-l\U-m-m-",,'~i9h tainfaJl1-;]~ 1 lowevapottanspiration_~ (coa/, wetclimate)~ ~ ~'---,---~LowerredOl( potential~,,-~ ..[-Isola~onOfPlantl ~~rootsfrom. [ r -------- Oecrease Inminerotrophlc ,--.-----II~~ _ o~creasein_PH --------~____ __ __ l_~lcr~bialaCtiW~_groundwaters _ __ _Peat accumulationDecrease <strong>of</strong><strong>de</strong>compositlonratesFigure 1.6Main mechanisms leading to accumulatíon <strong>of</strong> peat and bog succession.1.7 Hydrology and morphology<strong>of</strong> raised bogs1.7.1 IntroductionIn any wetland ecosystem, hydrological processes help<strong>de</strong>termine the character <strong>of</strong> various environmentalfeatures, such as water chemlstry, nutrlent avallabílltyand <strong>de</strong>gree <strong>of</strong> soil aeratión. These in turo influence thei<strong>de</strong>ntity <strong>of</strong> the flora and fauna <strong>of</strong> the mire. lnombrotrophic peatlands hydrological processes andvegetation are linked through a positive feed-backmechanism whereby the accumulation <strong>of</strong> the <strong>de</strong>adplant remains as peat also helps to <strong>de</strong>termine sorne <strong>of</strong>the hydrological processes [see Figure 1.6].1.7.2 The diplotelmic mireHydrologically, raised bogs can be consi<strong>de</strong>red as twolayered (diplotelmic) systems comprised <strong>of</strong> anuppermost 'active layer' (or acrotelm) and a lower socaBed•inert layer' 1 (or catote/m) [Figure 1.2). Thecatotelm is <strong>de</strong>fined as the zone <strong>of</strong> permanent saturationbut, in a litile-damaged bog, various additional featureshelp to distinguish the acrotelm from the catotelm. Theacrotelm forms the main functional horizon for plantl The catotelm is not, strictly speaking, 'inert'.growth. lt ís composed <strong>of</strong> the living vegetation covertogether with un<strong>de</strong>rlying, recentIy-<strong>de</strong>ad plant materialand fresh peal. The acrotelm is usually thin « 50 cm)because the peat that fonns within it gradualIy becomesincorporated into the catotelm below, as the upper level<strong>of</strong> the pennanent water table is elevated and the boggrows upwards. Water moves quite readily through theupper layers <strong>of</strong> the aerote/m, which both contains andhelps to regulate water·level fluetuations caused byvariation in water inputs and outputs. lt forros the maioconduit <strong>of</strong> water discharge from the bogo The aerotelmhas high perrneability to water near to the surface, butbecomes more impenneable with <strong>de</strong>pth as the peatbecomes more consolldated and <strong>de</strong>eomposed(humified). Water movement and fluctuations meanthat conditions in the acrotelm remain largely aerobicand it is here that microbial activity is strongest.The aerotelm <strong>of</strong> a little·damaged bog can be regar<strong>de</strong>das an integrated combination <strong>of</strong> plants (especiallySphagnum species), peat and water. Plant growthcontributes to the formation <strong>of</strong> a structure which hassorne capacity for hydrologícal self-regulation andwhich helps to maintain conditions suitable for thecontinued growth and survival <strong>of</strong> the plants. Suchfeedbacks help to rnaintain the growth and character <strong>of</strong>the bog surface [Figure 1.6], and the acrotelm is criticalto the nonnaJ <strong>de</strong>veJopment and functioning <strong>of</strong>a raisedbog [Box 1.4] (see also Joosten, 1993).


CHAPTER 1: LOWLAND PEATLANDS13Box 1.4 The acrote/m /ayer o,raised bogs in re/ation to restorationIn a little-damaged bog, the acrolelm layer funclionsessenlially (a) lo support lhe growth <strong>of</strong> bog planls; (b) toproduce lhe raw organic malerial whieh subsequentlyaccumulates in lhe ealolelm as peal; and (e) to feed thecalotelm wilh waler lo maintain and, as lhe bog grows, toinerease lhe zone <strong>of</strong> permanenl saluralion. Perhaps lhe moslremarkable fealure <strong>of</strong> lhe acrolelm <strong>of</strong> a growing raised bog isthal il provi<strong>de</strong>s a struclure which can aceommodaleconsi<strong>de</strong>rable fluctuation <strong>of</strong> water level whilst sustaining lheeonlinued growth (or al leasl survival) <strong>of</strong> the bog planls lhalullimately conlribule lo lhe aeeumulaling peat mass.The acrolelm layer <strong>of</strong> a Iittle-damaged bog may be readilymodified or <strong>de</strong>stroyed by various operalions. Peat exlraclion<strong>of</strong>ten leads to its complele and direcl removal. (A possibleexeeption oecurs in some hand-cutling operalions, where lheliving surface lurves are immedialely placed upon the floor <strong>of</strong>the cutling, thus providing direet re-inslatement <strong>of</strong> the surfaeelayer.) Other processes, such as drainage, <strong>de</strong>hydralion,repeated and <strong>de</strong>ep burning, can also much modify itsproperties. The primary objective <strong>of</strong> resloration <strong>of</strong> damagedbog surfaces must be to reereate an acrolelm with propertiessimilar to those <strong>of</strong> the original. The primary problem <strong>of</strong> suchiniliatives is that some <strong>of</strong> the properties thal are provi<strong>de</strong>d bythe original bog aerotelm (most nolably its capacily forhydrological self-regulalion) are lhemselves required loregenerale a new surface wilh a comparable functional róle.The 'trick' <strong>of</strong> much bog restoralion is lherefore to contrive tomimic on the exposed peat surface some <strong>of</strong> lhe. functionalproperties <strong>of</strong> the original acrotelm unlil a 'new' acrotelm has<strong>de</strong>veloped.It is possible lo envisage silualions (e.g. when a bog firstbegins to form) where an acrolelm layer can occur without anassocialed calolelm. 11 is somelimes also suggesled lhal whenlhe acrolelm has been removed from a bog, as by pealexlraclion, lhe resulling slruclure lhen becomes one-Iayered(haplotelmic), i.e. comprised only <strong>of</strong> a calotelm. However,such a residual peat body is unlikely ever lo be lrulyhaplolelmic (sensu stricto). This is because, after lhe acrolelmhas been removed, lhe newly exposed calotelm surface islikely lo dry oul occasionally, because <strong>of</strong> periodic lack <strong>of</strong>precipilalion inpul coupled with on-going evapotranspiralion.Hence lhe surface <strong>of</strong> lhe zone <strong>of</strong> perrnanent saturation willsink, leading once more lo a diplolelmie slruclure. This newsurfaee layer will serve lo feed lhe calolelm wilh rechargewater, thus providing one <strong>of</strong> lhe funclions <strong>of</strong> the originalacrotelm, bul il lacks some <strong>of</strong> lhe olher characlerislies <strong>of</strong> lheacrolelm as found on Iittle-damaged bogs. This circumslanceis frequenl in many bog siles lhal have been damaged by pealexlraclion (and olher operalions) and where, for variousreasons, lhe zone <strong>of</strong> permanent saturalion (i.e. lhe uppersurface <strong>of</strong> the calolelm) [see Box 1.5] has fallen to a lowerlevel in the peat mass. In lhis situation the peal below the newlevel <strong>of</strong> permanent saturation can still be regar<strong>de</strong>d as alegilimale 'calotelm', but the original catolelm peat aboye ildoes nol possess all lhe funclional characlerislics <strong>of</strong> lheoriginal acrolelm. Such consi<strong>de</strong>ralions suggesl lhat il isimportanl lo dislinguish belween an aerolelm <strong>de</strong>fined jusI asthe upper layer lacking permanenl saluration and an acrolelmas a slruclure possessing lhe properties characlerislic <strong>of</strong> alitlle-damaged bog surface. However, such a lerminologicaldislinetion has not yet been ma<strong>de</strong>, leading to correspondingconfusion in usage. In lhis report, unless qualified, lhe lerm'aerolelm' is restricted lo refer lo lhe 'fully-funelional' surfaeelayers sueh as eharaelerise litlle-damaged bogs.The lower layer <strong>of</strong> the bog (the catote/m) usuallycomprises the bulk <strong>of</strong>the peat in a raised bogo It is builtup from former acrotelm peat which has becomeincorporated into the catotelm. By contrast with theacrotelm, catotelm peat is typically well-consolidatedand <strong>of</strong>ien strongly-humified. It has a much lower permeabilitythan the acrotelm and correspondingly muchslower rates <strong>of</strong> water movement within it. By<strong>de</strong>finition, the catotelm is permanently saturated withwater. It provi<strong>de</strong>s a water-saturated, anaerobic base tothe acrotelm and the impe<strong>de</strong>d drainage therebyproduced gives the hydrological basis to <strong>de</strong>velopmentand growth <strong>of</strong> the raised bogo [This is additional to theimpe<strong>de</strong>d drainage in the un<strong>de</strong>rlying substratum orminerotrophic peat which permitted the initiation <strong>of</strong> anombrotrophic nucleus.] Although most microbialactivity occurs within the acrotelm, there is also sorneactivity <strong>of</strong>anaerobic microbes within the catotelm.1.7.3 The water balance <strong>of</strong>a I'aisedbogIn an ombrotrophic peatland, the only source <strong>of</strong> waterto the surface is from precipitation (rainfall, snow, fogetc.). Sorne <strong>of</strong> this is retumed to the atmospherethrough surface evaporation and plant transpiration(together termed evapotranspiration), while theremain<strong>de</strong>r gradually seeps laterally towards the edges<strong>of</strong> the bog, mainly through the surface layers(acrote/m) or vertically to become stored within thelower layers (catote/m) [see Figure 1.7]. Vertical loss<strong>of</strong>water downwards through the base <strong>of</strong>the bog via thecatotelm is generally assumed to be negligible, althoughthis may not always be the case [see Chapter 2].Although a raised bog <strong>de</strong>velops because <strong>of</strong> an overallprecipitation surplus, during sorne parts <strong>of</strong> the year,especially summer, evapotranspirative losses maytemporarily exceed precipitation inputs. On suchoccasions, the perched water level will faH, as water isremoved from storage. Subsequent precipitation willreplenish the storage water, before seepage towards themargins is increased as the water table rises again.


14 RESTORATION OF DAMAGED PEATLANDS~ 2L t:J~ ~ ~GThe water budget <strong>of</strong> a mire can be represented as: P - E - U - G - t,W =Owhere P =precipitation; E =evapotranspiration; U =flux <strong>de</strong>nsity with which water enters the catotelm;G =leakage through the base <strong>of</strong> the mire (generally very small); t,W =increase in storage.For a raised mire <strong>of</strong> approximately circular plan, the maximum height <strong>of</strong> the 'groundwater mound' (Zm)can be estimated from the equation:UIK=2Z m 2 IL 2where K =hydraulic conductivity <strong>of</strong> the peat; L =radius <strong>of</strong> the mire.Figure 1.7 Water budget <strong>of</strong> a raised bog and terms used in hydrological mo<strong>de</strong>lling <strong>of</strong> the 'groundwater mound'(after Ingram, 1987) 11.7.4 The shape and size <strong>of</strong>raisedbogsThe formation <strong>of</strong> a dome <strong>of</strong> ombrotrophic peat and, tosorne extent, its ultimate shape and height, is <strong>de</strong>pen<strong>de</strong>ntupon the climatic regime in which the peatland occursand most notably on the ratio <strong>of</strong> precipitation toevaporation [see Box 1.5]. A clear un<strong>de</strong>rstanding <strong>of</strong>thehydrodynamics <strong>of</strong> raised-bog systems has emergedonly in the last twenty years, with the recognition thatthe waterlogged conditions which permit ombrotrophicpeat to accumulate aboye the level <strong>of</strong> the regionalwater table (or impermeable substratum) are producedby impe<strong>de</strong>d drainage <strong>of</strong> rainwater through the peatmass (Ingram, 1982). This has lead to the formulation<strong>of</strong> mo<strong>de</strong>ls to predict the size and shape <strong>of</strong> raised bogs,based on standard groundwater hydrology and soilphysics [Box 1.5].A major limitation <strong>of</strong> aH mo<strong>de</strong>ls which attempt toexplain the shape and size <strong>of</strong> raised bogs just in terms<strong>of</strong> hydrodynamics is the likelihood that the dimensionsand pr<strong>of</strong>ile are actually <strong>de</strong>termined by several interactinginf1uences. These inclu<strong>de</strong> the constraints <strong>of</strong> thetopography <strong>of</strong> the landscape in which the bog occurs,the <strong>de</strong>gree <strong>of</strong> slope upon which it is <strong>de</strong>veloped, the ageand mo<strong>de</strong> <strong>of</strong> <strong>de</strong>velopment <strong>of</strong> the bog (i.e. by spreadingfrom a single nucleus or by multiple nucleation) andthe rate <strong>of</strong> peat <strong>de</strong>cay. Clymo (1991) has pointed outthat the calculated 'hydrologicallimit' <strong>of</strong> a bog may bevery much greater than its measured height on account<strong>of</strong> ongoing peat <strong>de</strong>composition. Disparities will begreatest in bogs <strong>of</strong> large basal area and thehydrological limit may only be reached in rather smallsites. A consequence <strong>of</strong> this is that, within a givenregion, strongly-domed bogs may be primarily afeature <strong>of</strong>small sites whereas bigger bogs may be moref1at-topped. Thus, in Britain, the two main 'types' <strong>of</strong>raised bog which sorne workers have i<strong>de</strong>ntified,plateau raised bog and concentric domed bog, maymore ref1ect the basal area <strong>of</strong> the peat <strong>de</strong>posit thanfundamental differences.1.8 Peat pr<strong>of</strong>iles and types <strong>of</strong>peatIn very broad terms, the stratigraphy <strong>of</strong> a Iittledamagedraised bog can be summarised as:living plants + loose acrotelm peatombrotrophic catotelm peatminerotrophic peat 2The acrotelm is usually sorne 10 - 40 cm <strong>de</strong>ep, but theother layers can show much variation in thickness,<strong>de</strong>pending on the age, situation and <strong>de</strong>velopment <strong>of</strong>thebogoThe ombrotrophic catotelm peat (which, in most cases,1 Reproduced from Ingram (1987) by permission <strong>of</strong> the RoyalSociety <strong>of</strong>Edinburgh and H.A.P. Ingram.2 This may be extremely thin in sorne examples that have<strong>de</strong>veloped by paludification.


CJlAPTER 1: LOWLA D PEATLA DS15is the focus <strong>of</strong> interest <strong>of</strong> the peat industry) <strong>of</strong>ien showssubstantial variation in character, between sites andwithin sites and both laterally and vertically [see Figure1.8]. The character, and stratigraphy, <strong>of</strong> bog peat is<strong>de</strong>termined by the vegetation that produced it, theconditions in which it formed (which affect lhe rate <strong>of</strong>accumulation) and post-<strong>de</strong>positional changes. Thelower peat layers <strong>of</strong> bogs are <strong>of</strong>ten darker, morehumified and more solid (greater bulk <strong>de</strong>nsity) than theupper layers. This is due in part to lhe effecls <strong>of</strong>compression and <strong>de</strong>composition coupled, but may alsoreflect differences in the composition <strong>of</strong> lhe peatformingvegetation and the circumstances <strong>of</strong> accumulation.In sorne peatlands, the catotelm peat is quitesharply divi<strong>de</strong>d into two distinct layers [see Plate 1.3].This can be observed clearly, for example, in sornebogs in north-west Germany (Weber, 1908) wherethere is <strong>of</strong>ten a sharp boundary between the lower'black peal' (<strong>de</strong>composition <strong>de</strong>gree usually H6 to H8or H9) and the overlying 'white peal' (usually H2 toH5). [' H' values refer to the von-Post scale <strong>of</strong><strong>de</strong>composition (humification), see Table 1.3]. Similarlayers can be found in sorne British bogs and the termsblack peal and while peal have also been applied tothese. However, such terms are <strong>of</strong>ten used as loose, ill<strong>de</strong>finedcategories <strong>of</strong> variable compass and it cannot beassumed lhat the black peat found at the base <strong>of</strong> sorneUK bogs is necessarily equivalent with the 'true' blackpeat <strong>of</strong> continental bogs. For example, sorne Britishbogs (mainly rather young examples) consist almostentirely <strong>of</strong> 'white peat' (senslI Weber, 1908), butnonetheless the lower peats are usually more humifiedand compacted lhan are the upper ones and they are<strong>of</strong>ten referred to as 'black peal'. In addilion, in lheSomerset Levels, the 'true' sedge peat is alsosometimes referred to as 'best black peal'. Thus, termssuch as black peal and while peal should be treatedwith sorne consi<strong>de</strong>rable circumspection. They are goo<strong>de</strong>xamples <strong>of</strong> terms that receive quite wi<strong>de</strong>spread usewithout agreement upon their exact meaning andcompass.Box 1.5 The 'Groundwater' Mound hypothesisIn an important contribution to un<strong>de</strong>rstanding the hydrology,<strong>de</strong>velopment and shape <strong>of</strong> raised bogs, Ingram (1982) pointedout: (a) that water and peat accumulates to form a raised bogon account <strong>of</strong> impe<strong>de</strong>d drainage <strong>of</strong> rainwater; (b) that thisgives rise to a characteristic near-hemi-elliptical mound <strong>of</strong>water perched aboye its surroundings and supported by thegrowing mass <strong>of</strong> vegetation and peat that has <strong>de</strong>velopedbecause <strong>of</strong> ils presence; and (c) that the surface <strong>of</strong> this mound<strong>de</strong>termines the surface <strong>of</strong> the catotelm (the zone <strong>of</strong> permanentsaturation) and hence the shape and dimensions <strong>of</strong> the bog(because the unsaturated zone is thin and is moul<strong>de</strong>d aroundthe catotelm). This suggestion, and ils implications, havecome to be known as the 'Groundwater Mound hypothesis'.The concepts and title <strong>of</strong> the 'Groundwater mound hypothesis'are based on standard groundwater hydrology and soilphysics. They recognise that the surface <strong>of</strong> the zone <strong>of</strong>permanent saturalion <strong>of</strong> a raised bog is analogous to thegroundwater table between ditches in a drained field (that ¡s,highest midway between the ditches and <strong>de</strong>clining towardsthem). Thus this hypothesis is not specific to peat soils or toombrogenous bogs - ¡n<strong>de</strong>ed, its importance is particularly inits recognition that the behaviour <strong>of</strong> the water table in bogscan be un<strong>de</strong>rstood and <strong>de</strong>scribed in terms <strong>of</strong> 'normal' soilhydrology and physics, with regard to the impe<strong>de</strong>d drainage <strong>of</strong>rainfall - and not, as some previous workers had supposed, interms <strong>of</strong> capillary rise <strong>of</strong> water up through the peat mass.Nonetheless, the title 'Groundwater Mound hypothesis', whilstaccurately reflecting its lineage, is perhaps rather unfortunatewith respect to ombrotrophic bogs, as it suggests precisely theopposite to what it means: the water that accumulates to formthe 'groundwater' mound is <strong>de</strong>rived from meteoric sources andis thus not what hydrologists most usually un<strong>de</strong>rstand bygroundwater, ;.e. water <strong>de</strong>rived from telluric sources. To helpavoid confusion, in this report reference is ma<strong>de</strong> to a'groundwater' mound or a 'perched water mound'.'Groundwater' Mound theory indicates thal the pr<strong>of</strong>ile anddimensions <strong>of</strong> the catotelm are a function <strong>of</strong> (i) the shape andsize <strong>of</strong> the basal plan <strong>of</strong> the bog; (ii) lhe net recharge to thecatotelm; and (iii) the overall permeability <strong>of</strong> the accumulatingcatotelm peat [see Figure 1.7]. The relationship thus infers thattaller groundwater mounds are associated with higher rates <strong>of</strong>water input or slower seepage and with greater basal area(Bragg, 1989). Support for the mo<strong>de</strong>l has been <strong>de</strong>rived from aquile close correspon<strong>de</strong>nce between observed and predictedpr<strong>of</strong>iles <strong>of</strong> some Scotlish bog sites (Dun Moss and EllergowerMoss).The 'Groundwater' Mound hypothesis undoubtedly provi<strong>de</strong>s avery useful conceptual basis for un<strong>de</strong>rstanding the<strong>de</strong>velopment and shape <strong>of</strong> raised bogs. It also helps to<strong>de</strong>monstrate some <strong>of</strong> the hydrological repercussions <strong>of</strong>damage to bogs. For example, an important consequence <strong>of</strong>the mo<strong>de</strong>l is that operations which serve to reduce the basalarea <strong>of</strong> a bog (such as extensive drainage and conversion foragriculture or peat extraction around its margins) may lead to aconcomitant reduction in the height <strong>of</strong> the water mound in theremnant <strong>of</strong> bog and hence a drying-out <strong>of</strong> some, or all, <strong>of</strong> itssurface.The 'simple' 'Groundwater' Mound mo<strong>de</strong>l does, however, havesome limitations. It is a static rather than a dynamic mo<strong>de</strong>l(Schouwenaars, 1995); it assumes a single value <strong>of</strong> hydraulicconductivity for the catotelm, whereas actual conductivitiesmay show very consi<strong>de</strong>rable spalial variation (Kneale, 1987); itassumes a flal base and is most readily solved for peatlands<strong>of</strong> relatively simple plan. Some <strong>of</strong> these limitations (e.g.difficulties <strong>of</strong> obtaining a meaningful estimate <strong>of</strong> catotelmpermeability) are common to all mo<strong>de</strong>ls; others may beresolved by more sophisticated <strong>de</strong>velopmenls (e.g. <strong>of</strong> finiteelement mo<strong>de</strong>ls).Some further practical limitalions <strong>of</strong> 'groundwater' moundmo<strong>de</strong>ls rest upon the possibility that, in some sites, 'true'groundwater may help to maintain, or even contribute to, thewater mound. 'Fen windows' ar'" known in various bogs andsome raised bogs have <strong>de</strong>veloped over zones <strong>of</strong> groundwaterdischarge. A mo<strong>de</strong>l, accurately but confusingly, known as the'groundwater' mo<strong>de</strong>l (Glaser, 1987; Glaser, Janssens &Siegel, 1990) has recently been <strong>de</strong>veloped to <strong>de</strong>scribe thistype <strong>of</strong> situalion. It is not known to what extent this may beapplicable to British bogs.


16RESTORATlO'" O!' DA~fAGED PEATLANDSYARDS360WESTEAST~350~«el 340~U Z 330«Zel 320c::::O310305~O 100 200 300 400 500600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 YARDSFigure 1.8 Stratigraphical section across Raheenmore Bog (Ireland) [Reproduced by permission <strong>of</strong> Bord na Mona.]H values indicate the humification <strong>de</strong>gree <strong>of</strong> the peat (von Post scale) [see Table 1.3]Plate 1.3 Section through raised bog peal (Solway Moss, Cumbria) showing the division belween lhe upper weaklyhumifiedpeal ('white peal') and lower slrongly-humified peat ('black peal'). [Photo: 1. Richardson]Differences occur between different types <strong>of</strong> peat insuch attributes as bulk <strong>de</strong>nsity, porosity and waterstorage capacity. This can affect the use <strong>of</strong> peat as ahorticultural medium and ils suitability as a substratumfor restoration [2.3l. Peat-based composts are <strong>of</strong>ienma<strong>de</strong> by blending different peat types from differinglocations in a bogoWeakly-humified light peats are particularly valuablefor horticulture because <strong>of</strong> their loose structure andhigh porosity. They are generally less <strong>de</strong>sirable thandarker peats as a fue!.Strongly-humified dark peats have been much-prizedas fuel peats but have been generally <strong>of</strong> less value tothe horticultural industry. Nonetheless, they are wi<strong>de</strong>lyused blen<strong>de</strong>d with light peats in sorne peat-basedcomposts and can a1so be used by themselves. Theirimportance to horticulture may be expected to increaseas reserves <strong>of</strong> the upper, lighter peats become <strong>de</strong>pleted.


CIIAPTER 1: LOWLA D PEATLA D 17Table 1.3 Modified version <strong>of</strong> the von Post Scale for assessing the <strong>de</strong>gree <strong>of</strong> <strong>de</strong>composition <strong>of</strong> peat (from Surton& Hodgson, 1987). [Reproduced by permission <strong>of</strong> the Soil Survey and Land Research Centre]Degree <strong>of</strong> Nature <strong>of</strong> liquid Proportion <strong>of</strong> peat Nature <strong>of</strong> plant residues Description<strong>de</strong>composition expressed on extru<strong>de</strong>d betweensqueezingfingersH1 Clear, colourless None Plant structure unaltered; fibrous, Un<strong>de</strong>compose<strong>de</strong>lasticH2 Almost clear, yellow- None Plant structure distinct; almost Almostbrown unaltered un<strong>de</strong>composedH3 Slightly turbid, brown None Plant structure distinct; most Very weaklyremains easily i<strong>de</strong>ntifiable <strong>de</strong>composedH4 Strongly turbid, brown None Plant structure distinct; most Weakly <strong>de</strong>composedremains i<strong>de</strong>ntifiableH5 Strongly turbid, Very little Plant structure clear but Mo<strong>de</strong>ratelycontains a little peat in becoming indistinct; most <strong>de</strong>composedsuspensionremains difficult to i<strong>de</strong>ntifyH6 Muddy, much peat in One-third Plant structure indistinct but Well <strong>de</strong>composedsuspensionclearer in the squeezed residuethan in the undisturbed peat;most remains uni<strong>de</strong>ntifiableH7 Strongly muddy One-half Plant structure indistinct but Stronglyrecognisable; few remains <strong>de</strong>composedi<strong>de</strong>ntifiableHa Thick mud, Iittle free Two thirds Plant structure very indistinct; Very stronglywater only resistant remains such as <strong>de</strong>composedroot fibres and wood i<strong>de</strong>ntifiableH9 No free water Nearlyall Plant structure almost Almost completelyunrecognisable; practically no <strong>de</strong>composedi<strong>de</strong>ntifiable remainsH10 No free water AII Plant structure unrecognisable; Completelycompletely amorphous<strong>de</strong>composed1.9 The vegetation <strong>of</strong> Britishraised bogs1.9.1 Plant species and vegetationtypesThe vegetation <strong>of</strong> ombrotrophic mires is <strong>of</strong> greatimportance, not just in its own right but because itprovi<strong>de</strong>s the physical basis <strong>of</strong> the mire itself and helpsto <strong>de</strong>fine some <strong>of</strong> its characteristics and conditions.This is because:• plant growth provi<strong>de</strong>s the basis for peat formation,water storage and impe<strong>de</strong>d drainage;• plant growth provi<strong>de</strong>s the basis for much <strong>of</strong> themicrotopography <strong>of</strong> the site and creates smallscalewater gradients;• the growth <strong>of</strong> Sphagnum species helps to createand regulate some characteristics <strong>of</strong> the bogsurface environment.Although a range <strong>of</strong> vascular plants are found in bogs,some <strong>of</strong> the most characteristic and important plantspecies <strong>of</strong> bog vegetation are the bog mosses <strong>of</strong> thegenus Sphagnum [Plates 1.4 and I.S]. Some ten speciesare common components <strong>of</strong> lowland bogs in Britain.They grow in pools, lawns and hummocks andcontribute to the formation <strong>of</strong> these structures. Sphagnapossess neither roots nor specialised conductive tissuesfor internal water transporto They do, however havesome capacity for external transport <strong>of</strong> water, bymovement between the stems, branches and leaves.The leaves <strong>of</strong> Sphagnum contain two types <strong>of</strong> ceIls:narrow, sinuous photosynthetic cells and large waterfilledhya/ine ceIls. These latter cells allow even <strong>de</strong>adremains <strong>of</strong> Sphagnum to store a great <strong>de</strong>al <strong>of</strong> water andSphagnul11 plants are reported to contain up to 40 timestheir dry weight as water (Romanov, 1968). Sphagnaare <strong>of</strong> great importance to the <strong>de</strong>velopment <strong>of</strong> manybogs. They are <strong>of</strong>ien the major peat-producing species,they help create the characteristically-low pHenvironment <strong>of</strong> bogs and they can store large volumes<strong>of</strong> water. They contribute to regulation <strong>of</strong> the waterbalance <strong>of</strong> a bog's surface, through the storage <strong>of</strong>water, a 'mulching' effect during dry periods and acapacity for 'bleaching' when drought-stressed (whichhelps to reflect solar radiation).The vegetation <strong>of</strong> ombrotrophic bogs is typically ratherspecies-poor and comparatively uniform, probablyreflecting the specialised nature <strong>of</strong> the habitat. Manybog species have a wi<strong>de</strong> global distribution and some(for example Sphagnum mage/lanicum) occur in bothsouthem and northem hem ispheres. Over 130 plantspecies have been recor<strong>de</strong>d from UK bogs (Wheeler,1993), but only sorne SO <strong>of</strong> these are particularly characteristic<strong>of</strong> little-damaged raised-bog sites [Appendix4]. Most <strong>of</strong> these species also occur, sorne wi<strong>de</strong>ly, in a


18RESTORATION OF DAMAGED PEATLANDSphagnum capillifolium tSphagnum magellanicum tSphagnum cuspidatum tSphagnum papillosum tSphagnum fuscumSphagnum recurvum tPlate 1.4 Sorne characteristic species <strong>of</strong> Sphagnum found on ornbrotrophic bogs.[Photos: tM.C.F. Proctor; 1: P.C. Roworth (ARPS)]


CHAPTER 1: LOWLA n PEATLAND19Drosera anglicaEriophorum angustifolium*Drosera rotundifolia on Sphagnum fimbriatum*Eriophorum vaginatum*Andromeda polifolia*Vaccinium oxycoccos*Plate 1.5 Sorne characteristic vascular plant species found on ornbrotrophic bogs. [*Photos: P.C. Roworth (ARPS)]


20RE TORATJO01' OAi\1AGED PEATLANDSyariety <strong>of</strong> other waterlogged habitats and some areabundant also in drier enyironlllents. A few areuneolllmon or rare, sueh as Androllleda polifolia,Drosera anglica, D. intermedia, Rhyncho!>pora fusca,Dicranum undulalum, Sphagnulll fuscum, S.imbricalum and S. pulchrum. Of these, A. polifolia andD. undula/um are largely speeifie to raised bogs inBritain; most <strong>of</strong> the others oeeur in poor fen as well asin bogs. When growing in the ombrotrophie habitatsome <strong>of</strong> these speeies, sueh as D. anglica, arepartieularly assoeiated with north-western bogs inBritain. It is not known to what extent this represents anatural oeeanie distribution or refleets their loss frolllmore south-eastern bogs, perhaps beeause <strong>of</strong> dalllageor atmospherie pollution.Although bog yegetation eontains a limited range <strong>of</strong>plant speeies, eertain speeies eombinations appear to beunique to bogs [Table lA]. [n a little-damaged raisedbog, small pools are typieally oeeupied by yegetation<strong>of</strong> the SphagnulII cuspidalulll-S. recurvulll bog poolTable 1.4 The main plant eommunity-types <strong>of</strong> ombrogenous mires in Britain, as i<strong>de</strong>ntified by the National VegetationClassification (Rodwell, 1991). The principal community-types <strong>of</strong> little-damaged raised bog are shown in bold type.For further <strong>de</strong>tails <strong>of</strong> community types <strong>of</strong> cut-oyer bogs, see Box 2.1.COMMUNITY-TYPES lARGElY CONFINED TO OMBROTROPHIC MIRESM17 Seirpus eespilosus- Eriophorum vaginatum blanket mire(a) Drosera rotundifotia-Sphagnum sub-eommunity(b) Ctadonia sub-eommunity(e) Juneus squarrosus-Rhytidia<strong>de</strong>tphus toreus sub-eommunityM18 Eriea tetralix-Sphagnum papillosum raised and blanket mire(a) Sphagnum magellanieum-Andromeda sub-eommunity(b) Empetrum nigrum-Cladonia sub-eommunityM19 Cal/una vulgaris-Eriophorum vaginatum blanket mire(a) Eriea tetralix sub-eommunity(b) Empetrum nigrum sub-eommunity(e) Vaeeinium vitis-idaea-Hyloeomium splen<strong>de</strong>ns sub-eommunityM20 Eriophorum vaginatum blanket and raised mire(a) speeies-poor sub-eommunity(b) Cal/una vulgaris-Cladonia sub-eommunityCOMMUNITY-TYPES ALSO FOUNO CHARACTERISTICAlLY IN OTHER HABITATS (MAINLY POOR FEN ANO WET HEATH)M1 Sphagnum aurieulatum bog pool eommunityM2 Sphagnum euspidatum / S. reeurvum bog pool eommunity(a) Rhynehospora alba sub-eommunity(b) Sphagnum reeurvum sub-eommunityM3 Eriophorum angustifolium bog pool eommunityM15 Seirpus eespitosus- Eriea tetralix wet heath{(a) Carex panieea sub-community - not strietly ombrotrophie}(b) typieal sub-eommunity(e) Cladonia sub-eommunity(d) Vaeeinium myrtil/us sub-eommunityCOMMUNITY-TYPES CHARACTERlsnc OF NON-OMBROTROPHIC HABITATS BUT PRESENT ON (USUALLY DAMAGED) OMBROTROPHIC BOGS.These inelu<strong>de</strong>:M25 Molinia eaerulea-Potenti/la erecta mire(a) Eriea tetralix sub-eommunily(b) Anthoxanthum odoratum sub-eommunilyW4 Be/ula pubeseens-Molinia eaerulea woodland(a) Dryopteris dilatata sub-eommunity(e) Sphagnum sub-eommunityH9 Cal/una vulgaris-Desehampsia flexuosa heathPteridium aquilinum standsVarious fen eommunity-types may oeeur in laggs


CHAPTER 1: LOWLAND PEATLANDS21community (M2) whilst much <strong>of</strong> the rest <strong>of</strong> the surfaceis referable to just one community-type, the Ericatetralix-Sphagnum papillosum community (M 18~,which is largely specific to raised-bog systems. Thlscommunity is split into two sub-units. One <strong>of</strong>these (theSphagnum magellanicum-Andromeda polifolia subcommunity,M18a) essentially refers to wet Sphagnumlawns and hummock-hollow complexes, that may beintermingled with, or occur peripheral, to the poolsystems, most typically in the central, wettest part <strong>of</strong>the bogo The other (the Empetrum nigrum-Cladoniasub-community, M18b) represents vegetation with agreater prominence <strong>of</strong> ericoid plants and usuallyoccupies rather drier conditions, such as may occurfurther from the centre <strong>of</strong>the bogo Near the edge <strong>of</strong>thebog, the drier rand may sometimes also support anErica tetralix-S. papillosum (M 18) community, but<strong>of</strong>ien has examples <strong>of</strong> a more heathy vegetation (e.g.Scirpus cespitosus-Erica tetralix wet heath, M 15) oreven Molinia grassland or birch scrub.A broad zonation can be recognised across the surface<strong>of</strong> at least sorne little-damaged raised bogs, from thecentral complex <strong>of</strong> shallow pools and hummocks to thedrier rand and thence to a minerotrophic lagg [Figure1.9]. In many sites, the natural character <strong>of</strong> a presumedlagg is not known, as marginal areas have <strong>of</strong>ien beendamaged or removed by drainage, agricultural conversionor peat cutting. Very <strong>of</strong>ien, even in little damagedbogs, the rand may also have been subject t~ s~m.emodification (improved drainage etc.) and agam It ISdifficult to be certain <strong>of</strong> its natural character. lt is <strong>of</strong>ienassumed that the rand is naturally drier than much <strong>of</strong>the bog and that it is naturally treeless but, given thecurrent propensity for tree invasion <strong>of</strong> slightly-driedsurfaces in little-damaged bogs, it would be <strong>of</strong> interestto know why trees were naturally absent from a drierrand, if in<strong>de</strong>ed they were.It can also be difficult to specify the presumed 'natural'condition <strong>of</strong> the main expanse <strong>of</strong> little-damaged bogs.This is partly because even little-damaged sites have<strong>of</strong>ien been subject to sorne disturbance (including, insorne cases, <strong>de</strong>position <strong>of</strong> atmospheric contaminants)but it is also because the vegetation <strong>of</strong> even anundisturbed bog is not completely stable. Peat stratigraphicalevi<strong>de</strong>nce points to both abrupt and gradualchanges in the past vegetation composition, with ashifiing ten<strong>de</strong>ncy for dominance <strong>of</strong> bog surfaces by'hummock species' versus 'hollow species', probablymainly in relation to changing conditions <strong>of</strong> surfacewetness, such as may sometimes reflect climatic shifis(Aaby, 1976; Barber, 1981). Dry phases may show anabundance <strong>of</strong> ericoid species with Sphagna suppressedand, sometimes, even localised tree invasion (Casparie,1972).The causes for sorne major changes in the composition<strong>of</strong> bog vegetation are not really known. For example,in many bogs in Britain (and elsewhere), Sphagnumimbricatum was replaced by S. magellanicum as a mainpeat-forming species, at about the Middle Ages(Barber, Dumayne & Stoneman, 1993). The reasons forthis have yet to be established, but the consequence isthat a once-dominant bog-building species in now rarein raised bogs. Such changes make it difficult tospecify the 'natural' character <strong>of</strong> bog vegetation - andthe <strong>de</strong>sired objective <strong>of</strong> bog restoration initiatives.However, the E. tetralix-S. papillosum community is<strong>of</strong>ien consi<strong>de</strong>red to be the 'natural' core community-Figure 1.9 Typical zonation <strong>of</strong> plant commu.nit~es across a .raised ?og ~after Rodwell, 1991). [see Table 1.4 fori<strong>de</strong>ntity <strong>of</strong> communities] [Reproduced by permlsslon <strong>of</strong> Cambridge Unlverslty Press.]


22RESTORATION OF DAMAGED PEATLANDStype <strong>of</strong> many lowland raised bogs, and its recreationforms a focus <strong>of</strong>the restoration <strong>of</strong> damaged raised bogs[see Chapter 3].The vegetation <strong>of</strong> bogs can also be broadly categorisedby its physiognomic characteristics and the habitatconditions in which it occurs. A broad, informalclassification is suggested in Table 1.5.1.9.2 Reproduction and spread <strong>of</strong>bogplant speciesSorne plant species <strong>of</strong> bogs are long-lived perennials(e.g. plants <strong>of</strong> Eriophorum vaginatum may live formore than 100 years) and, for these, recruitment <strong>of</strong>newindividuals may be <strong>of</strong> limited importance to speciessurvival in undisturbed bogs. However, other species(e.g. Drosera spp.) are short-Iived and have a greater<strong>de</strong>pen<strong>de</strong>nce upon seed production to maintain theirpopulations.Diaspore production and dissemination is important forall bog species in the context <strong>of</strong> restoration <strong>of</strong>damagedbogs because the ability <strong>of</strong> plant species to recolonisefresh peat surfaces, or to re-establish on 'old' ones,<strong>de</strong>pends largely upon their reproductive capacity andthe dispersal and survival <strong>of</strong> their propagules. Thedispersal agents <strong>of</strong> the seeds <strong>of</strong> sorne bog species arenot well known. The seeds <strong>of</strong> many species are small« 4 mm length) and Iight, leading to a presumptionthat wind dispersal may be <strong>of</strong> particular importanceand that the seeds may be able to travel over wi<strong>de</strong> areasfrom one isolated raised bog to another (Moore, 1990).However, sorne studies suggest rather limiteddispersability <strong>of</strong> certain species (Poschlod, 1995).Seeds <strong>of</strong> sorne bog species can be dispersed by wateror trampling, but the general significance <strong>of</strong> this inbogs in not well established.Sorne bog species form diaspore banks - i.e. theirseeds or spores can retain viability for long periods(years or <strong>de</strong>ca<strong>de</strong>s, but not in perpetuity), but there isconsi<strong>de</strong>rable variation in this capacity (Poschlod, 1988,1989, 1995) (Appendix 3). Consi<strong>de</strong>rations <strong>of</strong> diasporebanks are substantially irrelevant to many cut-overpeatlands, as the lower peats exposed by extraction donot contain viable seeds (Curran & MacNaeidhe, 1986;Salonen, 1987a). They may, however, be <strong>of</strong> greaterimportance to the rewetting <strong>of</strong> uncut bog surfaces.Most wetland plants have sorne mechanism forvegetative expansion, which can sometimes lead to the<strong>de</strong>velopment <strong>of</strong> large clonal patches <strong>of</strong> particularindividuals. This may be important for the maintenance<strong>of</strong> populations in situ but is Iikely to provi<strong>de</strong> ratherslow rates <strong>of</strong> recolonisation on abandoned, bare peatsurfaces.Wetland plants generally have a good capacity toregenerate from fragments but the actual significance<strong>of</strong> this for spontaneous recolonisation <strong>of</strong> cut-over peatsurfaces by bog species is not known. It does, however,facilitate the propagation and planting <strong>of</strong> bog species,should this be seen as <strong>de</strong>sirable. In particular,Sphagnum species can be readily propagated fromTable 1.5 Informal physiognomic-habitat categories <strong>of</strong> raised-bog vegetation in Britain. [NVC - see Table 1.4]'Bog-Sphagnum' vegetatíonAccommodates vegetation in which Sphagnum species typical <strong>of</strong> bogs are prominent, <strong>of</strong>ten dominant, components. It inclu<strong>de</strong>s theNVC mire-expanse community M18 and the bog-pool communities M2 and M3. These lalter may occur as a mosaic with M18vegetation, forming the so-called 'regeneration complex'. This vegetation is particularly characteristic <strong>of</strong> the surface <strong>of</strong> littledamagedraised bogs.'Para-bog-Sphagnum' vegetatíonRefers to vegetation with broad similarities to 'bog-Sphagnum' vegetation, but which differs either in not containing all <strong>of</strong> thespecies typical <strong>of</strong> the latter, or in having them but not with the same proportions or structure. Ericaceous species or Eríophorumvaginatum typically dominate (rarely Molinía caeru/ea). Sphagnum species are <strong>of</strong>ten sparse or represented mainly by taxacharacteristic <strong>of</strong> the drier microsites within bogs (e.g. S. capillito/ium), but in some (richer) examples it is possible to find most <strong>of</strong>the characteristic species <strong>of</strong> 'bog-Sphagnum' vegetation scattered sparsely. Various additional species, particularly taxa associatedwith drier conditions may also occur. This category inclu<strong>de</strong>s some examples <strong>of</strong> NVC communities M15, M20, M25a. Suchvegetation may be indicative <strong>of</strong> partial damage to a bog surface (e.g. burning or drainage) but it may possibly also be a naturalconstituent <strong>of</strong> some little-damaged bogs, as on the drier slopes <strong>of</strong> a rand or as part <strong>of</strong> a 'still-stand' condition.'Dry bog' vegetatíonInclu<strong>de</strong>s a range <strong>of</strong> vegetation-types which usually contain few typieal bog species. Those that do oceur are usually the moredrought-tolerant taxa sueh as Eriophorum vaginatum. Some examples are not readily referred to NVC vegetation-types. Wherei<strong>de</strong>ntifiable, the vegetation-types <strong>of</strong> this eategory inelu<strong>de</strong>:wet heath (some examples referable to M15)dry heath (e.g. H9)Molinia grassland (richer examples =M25; others are near-monocultures <strong>of</strong> Molinia)bracken-dominated vegetationbirch scrub ((some examples referable to W4)'Dry bog' vegetation-types are almost always assoeiated with some form <strong>of</strong> damage to raised-bog sites, most typically drainage.


CIIArTER 1: LOWLAND PEATLANDS23small fragments. The significance <strong>of</strong> these factors forthe revegetation <strong>of</strong> cut-over bogs is discussed further inChapter 4.1.9.3 Characteristics <strong>of</strong>bog plantspeciesExamination <strong>of</strong> sorne <strong>of</strong> the main characteristics <strong>of</strong>typical bog plant species enable the followinggeneralisations to be ma<strong>de</strong>:• mostly <strong>of</strong>geographic wi<strong>de</strong> distribution;• not specific to ombrolrophic bogs;• most are long-lived perennials;• seeds and spores may have IiUle importance inmaintaining populations <strong>of</strong> sorne species in undisturbedbogs;• seeds <strong>of</strong> most species are light and may be rcadilydispersed;• typically have slow relative growth rales;• apparenlly efficient at scavenging nutrients from dilulesolutions;• <strong>of</strong>ten efficient internal conservation <strong>of</strong> nulrienls;• ombrotrophic conditions scem generally sub-optimal forgrowth.The main characteristics <strong>of</strong> sorne <strong>of</strong> the typical speciesfound on raised bogs in Britain are given in Appendix3.1.9.4 Habitat conditions andvegetation <strong>of</strong>raised bogsThe environment <strong>of</strong> raised bogs is not well-suited tothe growth <strong>of</strong> many plant species. The low pH valuesand limited availability <strong>of</strong> nutrients makes theombrotrophic habitat 'difficult' even for the growth <strong>of</strong>species tolerant <strong>of</strong> high water levels. Those that dooccur may grow more slowly than in sorne otherhabitats.Microtopography and water levelsWithin raised bogs, plant species show various microhabitat'preferences'. Certain plant species <strong>of</strong>ienoccupy rather distinct positions with respect to waterlevel, either as part <strong>of</strong> the small-scale microtopographicalmosaic <strong>of</strong> a patterned bog surface (e.g.Ratcliffe & Walker, 1958; see Figure 1.10) or as part <strong>of</strong>a wi<strong>de</strong>r change in water level from the wet centre to thedrier margins <strong>of</strong> a bogo Species <strong>of</strong> the genus Sphagnum<strong>of</strong>ien show c1ear and well-documented distributionpattems with respect to water levels (Ratcliffe &Walker, 1958; Vitt, Crum & Sni<strong>de</strong>r, 1975, Andrus,Wagner & Titus, 1983; Wallén, Falkengren-Grerup &Malmer, 1988). Experimental studies suggest that withlow water tables the hummock species appear betterable to transport water up the stem and maintain watercontent at the top <strong>of</strong> the stem (capitulum) than canhollow or lawn species and they are thus better able togrow in relatively dry conditions. Their exc1usion frompools and lawns may not be because such conditionsare intrinsically unsuitable for them but because poolspecies grow more rapidly (Clymo & Reddaway, J971;Pe<strong>de</strong>rsen, 1975; Clymo & Hayward, 1982; Hayward &Clymo, 1983; Luken, 1985)pH and base-richnessThe ombrotrophic waters <strong>of</strong> raised bogs arecharacterised by having hydrogen (H+) as the dominantcation and su1phate (SO/,) as the main cation (Sjors,1950; Bellamy, 1967; Proctor, 1992). The highconcentration <strong>of</strong> hydrogen ions (pH values are <strong>of</strong>ienbelow 4) is partly a product <strong>of</strong> acidification induced bythe growth <strong>of</strong> species <strong>of</strong> Sphagnllm (Clymo, 1963;Clymo & Hayward, 1982; Andrus, 1986), whilst thesmall concentrations <strong>of</strong> other solutes reflect themeteoric water source. Characteristics such as a highcation exchange capacity confer upon Sphagnum sorneability to acidify its environment and, where Sphagnumspecies have colonised minerotrophic systems anincrease in hydrogen-ion activity by sorne three ormore or<strong>de</strong>rs <strong>of</strong> magnitu<strong>de</strong> has been reported (Bellamy& Rieley, 1967; Karlin & Bliss, 1984; Giller &Wheeler, 1988).The ionic composition <strong>of</strong> bog water shows quite stronggeographical variation, reflecting variation in soluteconcentrations in rainfall. There is a gradient <strong>of</strong>chemical conditions in bogs across both Britain and theEuropean mainland (Bellamy, 1967; Proctor, 1992). InBritish bogs, concentrations <strong>of</strong> several ions, especiallysodium, are greater than in more continental examples,reflecting maritime influence. [Sorne ranges <strong>of</strong>chemical concentrations are given in Table 2.1].Plants typical <strong>of</strong> ombrotrophic peatlands are notnecessarily confined to low pH environments. Mostalso grow in poor fens (pH < c. 5.5) and sorne grow inrich fens (pH > c. 5.5). In Britain, the Sphagnumspecies that are typical <strong>of</strong> bogs also grow in many poorfen sites, but are usually absent from rich fens, exceptwhere there are acidified microsites. Nonetheless, sorne(e.g. Sphagnum papil/osum, S. mage//anicum) havebeen recor<strong>de</strong>d from sites with water pH values <strong>of</strong> c. 6.5(Andrus, 1986; Lindholm & Vasan<strong>de</strong>r, 1990; Shaw &Wheeler, 1991). Several plant species that arecharacteristic constituents <strong>of</strong> bog vegetation in Britainare confined to fens in more continental parts <strong>of</strong> theirrange (e.g. Eriophorum angustifolium, Nartheciumossifragum, Sphagnum papil/osum). This phenomenonhas long been recognised (Aletsee, 1967; Müller, 1976;Ma1mer, 1986), but its explanation is not really known.


24RESTORATIO OF DAMAGED PEATLANDSOadonia silvaticaCal/una vulgarisScirpus caespitosusEriopllorum vnginntumEricn tctrnlixEriop/lorum nngustifoliumNnrt/lccium ossifragul1lRllyncllOspora albaSphagnum rubellllmS.plumulosllmSphagnum papillosumS.tencllllm etcS.rubellumSphagnum cllspidatumS.rubellumS.papilloslImPEATS.rubellllmPEATS.papillosumS. cuspidatllmPEATS. papillosllmS. cuspidatumS. cllspidahunFigure 1.10a Diagram <strong>of</strong> the succession <strong>of</strong> species forming the peat in a typical "hollow-hummock cycle(regeneration complex) (Tansley, 1939) [Reproduced by permission <strong>of</strong> Cambridge University Press].Round-Ieavedsun<strong>de</strong>w(Droserarotundifo/ia)1".' ."SOcm . ".:'. .' ¡';·,gl", :(20in}···.··· ···:.··· 2I ."'"::RIOGE


CHAPTER 1: LOWLAND PEATLANDS25It may partly relate to the higher pH values and greatersolute concentrations measured in more oceanicsituations (BeIlamy & BeIlamy, 1966; Sparling, 1967;Boatman, Hulme & Tomlinson, 1975; Proctor, 1992),which makes the chemical environment <strong>of</strong> such sitesapproach that <strong>of</strong> weakly minerotrophic fens (Shaw &Wheeler, 199 1; Proctor, 1992). However, it is far fromcIear that this is a sufficient explanation (Malmer,1986).The response <strong>of</strong> typical bog species to very low pHenvironments « 3.0) has been rather little studied, butthere is evi<strong>de</strong>nce that growth <strong>of</strong> sorne species isimpaired at such levels (Austin & Wie<strong>de</strong>r, 1987;Richards, Wheeler & WiIIis, 1995; Money, 1994).Sphagnum colonisation <strong>of</strong>rich fens in Britain is usuaIlypioneered by a smaIl range <strong>of</strong> species (e.g. S.squarrosum, S. fimbriatum, S. palustre and S. recurvum;Shaw & Wheeler, 1991) which are particularlytolerant <strong>of</strong> high pH or high calcium concentrations(Clymo, 1973). They form an acidic layer separatefrom the base-rich water (GilIer & Wheeler, 1988)upon which less base-tolerant species such as S. magellanicumand S. papillosum can become established.Productivity and nutrient availabilityRaised bogs are generaIly regar<strong>de</strong>d as being'unproductive' and infertile ecosystems. Estimates <strong>of</strong>vegetation production rates are hampered by thedifficuIties <strong>of</strong> obtaining meaningful measures <strong>of</strong>Sphagnum productivity (Clymo, 1970), but estimates<strong>of</strong> above-ground net production <strong>of</strong> ombrotrophicvegetation are typicaIly in the range <strong>of</strong> 300-700 g m'2(Doyle, 1973, Clymo & Reddaway, 1974; Forrest &Smith, 1975). It is notable that, whilst quite smaIl, suchrates are comparable with, or even greater than, thosereported from various types <strong>of</strong> fen (Wheeler & Shaw,1991).Low availability <strong>of</strong> nitrogen or phosphorus is likely tobe a major constraint upon primary production in bogs.Fertilisatiori <strong>of</strong> bog peats usuaIly increases theproduction rates <strong>of</strong> vascular plants and may evenenhance the growth <strong>of</strong> Sphagnum, at least in the shortterm(Tamm, 1954; Reinikainen, Vasan<strong>de</strong>r & Lindholm,1984; Baker & Boatman, 1989; Aerts, WaIlén &Malmer, 1992). It is less cIear which nutrient isnaturaIly growth-limiting in bogs, not least becausepresent-day N concentrations may be artificiaIlyelevatedby <strong>de</strong>position from atmospheric sources(Aerts et al., 1992). The low availability <strong>of</strong> nutrientshas led sorne, probably most, bog species to be weIladapted to scavenge solutes from dilute solutions, atrait seen cIearIy in Sphagnum species (Malmer, 1988).GeneraIly, bog plants may show a 'tight' redistribution<strong>of</strong> nutrients, so that scarce resources are not lost fromsenescing leaves etc. Rhynchospora alba seems to bean exception to this general rule (Ohlson & Malmer,1990) and there is sorne variation in nutrient retentionefficiencies amongst sorne other species. For example,whilst Eriophorum vaginatum is particularly weIl ableto retranslocate and accumulate nutrients (Goodman &Perkins, 1959; Jonasson & Chapin, 1985), Moliniacaerulea appears to have a smaIler capacity for this(Markert et al., 1990).Growth <strong>of</strong> Sphagnum species in water may also beconstrained by availability <strong>of</strong> carbon (as CO2) (Baker& Boatman, 1985; Baker & Macklon, 1987). This mayhelp to explain the poor growth <strong>of</strong> aquatic species (e.g.Sphagnum cuspidatum) that is sometimes observed in<strong>de</strong>ep water (Boatman, 1983; Paffen & Roel<strong>of</strong>s, 1991).Atmospheric pollutionAs raised bogs are irrigated directIy and more-or-IessexcIusively by precipitation inputs, and as theircomponent plant species may be weIl adapted to'scavenge' solutes from dilute solutions, they may beparticularIy susceptible to atmospheric contaminants.Tho~e most likely to affect plants growing on raisedbogs are the main constituents <strong>of</strong> 'acid rain' [i.e.sulphur dioxi<strong>de</strong> and <strong>de</strong>rivatives, especiaIly bisulphite;nitrogen oxi<strong>de</strong>s (N0x) and <strong>de</strong>rivatives,. especiaIlynitrate; and ammonia]. There is very little direct informationon <strong>de</strong>position <strong>of</strong>contaminants into British bogs,but interpolated maps provi<strong>de</strong> estimates <strong>of</strong> emissionsand possible rates <strong>of</strong><strong>de</strong>position (UKRGAR, 1990).Various experiments have <strong>de</strong>monstrated thatSphagnum species are differentiaIly sensitive to S02and <strong>de</strong>rivatives (HSO)-), but at concentrationsconsi<strong>de</strong>rably greater than current ambient values(Ferguson, Lee & BeIl, 1978; Ferguson & Lee, 1980).Total S02 emissions in the UK have <strong>de</strong>creased by sorne40% from national peak values at around 1970(Gilham, Leech & Eggleston, 1992) and, whilst highconcentrations <strong>of</strong> S02 may have led to thedisappearance <strong>of</strong> sorne Sphagnum species in the past,present concentrations are unlikely to be so acutelyinjurious to Sphagnum growth that the plants wiII beunable to survive (Ferguson & Lee, 1982; Press,Woodin & Lee, 1986).The importance <strong>of</strong> atmospheric sources <strong>of</strong> nitrogen(NOx and ammonia) to the growth <strong>of</strong> bog species is notwt:I1 un<strong>de</strong>rstood. There is a quite wi<strong>de</strong>spread suspicionthat <strong>de</strong>position <strong>of</strong> nitrogen may be responsible for theloss <strong>of</strong> sorne Sphagnum species from bogs and anexpansion <strong>of</strong> Molinia caerulea and perhaps even <strong>of</strong>birch, but critical evi<strong>de</strong>nce for this is lacking. N<strong>de</strong>position can act as a fertiliser for vascular plants andun<strong>de</strong>r certain circumstances is thought to encourage thegrowth <strong>of</strong> Molinia in wet heath ecosystems (Heil &Bruggink, 1987; Aerts & Berendse, 1988). Nonethelessits effects in bogs are obscure. Various experimental


26RESTORATION OF DAMAGED PEATL.ANDSinvestigations have examined the relationship betweenSphagnum growth and N supply, in the field andlaboratory, but have not reached consistent conclusions- both growth inhibition and stimulation has beenreported, probably due partly to variation inexperimental and other conditions (Clymo, 1987; Pressel al. 1986. Rudolph & Voight, 1986; Bayley el al.,1987' Baker & Boatman, 1990; Woodin, Parsons &McK~nzie, 1991; Aerts el al., 1992). Especially littIe isknown about the effects <strong>of</strong> dry <strong>de</strong>position <strong>of</strong> ammoniaupon bog plants, though UKRGAR (1990) suggest that"over much <strong>of</strong> the country ammonia dry <strong>de</strong>position isbelieved to dominate total nitrogen <strong>de</strong>position."1.10 The invertebrates <strong>of</strong> raisedbogslnvertebrates form an important part <strong>of</strong> the animal life<strong>of</strong> peatlands, living in and on the water and plants, butuntil recently they have received relatively littlesystematic attention. This is perhaps not surprisingsince there are so many species (even within differentinvertebrate groups) that even on peat bogs in the UKto attempt species-Ievel i<strong>de</strong>ntification <strong>of</strong> them allwould require the time and expertise <strong>of</strong> manyindividual specialists. The information reviewed for thepresent reports was thus mainly <strong>de</strong>rived from a largebody <strong>of</strong> mostly fragmentary evi<strong>de</strong>nce and ad hocrecords as most studies have concentrated onparticular invertebrate groups and have collectivelybeen conducted with a wi<strong>de</strong> range <strong>of</strong> aims. In general,invertebrate studies <strong>of</strong> raised bogs appear to have beenstrongly biased towards insects and arachnids (spi<strong>de</strong>rsand harvestmen).Invertebrate species found on bogs may be herbivores,camivores or <strong>de</strong>tritivores, but in general there are fewbog 'specialists', perhaps reflecting the waterlogged,oxygen-<strong>de</strong>ficient, acidic environment with 'poorquality'food sources. However, several invertebratesurveys to date have suggested that raised-bog sitessupport populations <strong>of</strong> a high proportion <strong>of</strong> notable andrare insect and spi<strong>de</strong>r species both within the UK andon mainland Europe. Lowland raised bogs in the UKappear to have particular conservation importance for anumber <strong>of</strong> species [Table 1.6], including the beetlesBembidion humerale and Curimopsis nigrila, bothknown thus far only from the Humberhead Levels inthe UK. However, there are very few true indicatorspecies for lowland raised bogs. Most species. thatshowa 'preference' for this habitat are also sometlmesfound in other situations (although interpretation <strong>of</strong>data is <strong>of</strong>ien hampered by lack <strong>of</strong> <strong>de</strong>tailed habitatinformation). Many species also show markeddifferences in their <strong>de</strong>gree <strong>of</strong> specificity to raised bogsin different parts <strong>of</strong> their geographical range. TheBritish Isles are on the edge <strong>of</strong> the natural range formany species.Several major insect groups appear to have no, or veryfew, species that are specifically associated with raised(or other) bogs within the UK, and certainly no notableor rare ones. The Hymenoptera (sawflies, parasiticwasps, gall wasps, bees wasps and ants) is the largestOr<strong>de</strong>r <strong>of</strong> insects within the UK with more than 6,000known species. However, most <strong>of</strong> the more familiarstinging species (the aculeate wasps, bees and ants) arelargely associated with dry habitats, and those that maybe caught within raised-bog sites inclu<strong>de</strong> many that areeither transient or nest or forage outsi<strong>de</strong> <strong>of</strong> the boghabitat (von <strong>de</strong>r Hei<strong>de</strong>, 1991). Only one species, theant Formica Iranskaucasica, is typically associatedwith Sphagnum bogs, though its nest sites are in driergrassy tussocks. In other groups, it is <strong>of</strong>ten the case thatonly a very few species are associated with bogs andthese are seldom restricted to lowland raised bogs.Nevertheless, there is a general consensus that <strong>of</strong> theHymenoptera species associated with peat bogs, a highproportion are <strong>of</strong> conservation interest. For example,Kirby (1992) suggests that "[t]here are relatively fewHeteroptera associated specifically with bogs, but alarge proportion <strong>of</strong> them are local or rare". Thisprobably largely reflects the scarcity <strong>of</strong>the bog habitat.Herbivorous insects are <strong>of</strong>ien oligophagous (occasionallymonophagous) 1 and may be limited in theirdistribution by the availability <strong>of</strong> suitable foodplants.Thus, the great majority <strong>of</strong> species with conservationinterest are likely to occur in habitats which inclu<strong>de</strong> thegreatest diversities <strong>of</strong> potential foodplant species. withlimited distributions. The limited herbivorous msectfauna <strong>of</strong> raised bogs may therefore reflect the floristicpoverty <strong>of</strong> raised bogs.Bogs that have been subjected to hand-cutting orsimilar peat-removal regimes and which have sincerevegetated may <strong>of</strong>fer a wi<strong>de</strong>r range <strong>of</strong> invertebratehabitats than little-damaged raised bogs andconsequently, may support a wi<strong>de</strong>r range <strong>of</strong> species.Many taxa seem to have either a preference orrequirement for the range <strong>of</strong> micro-habitat conditionsthat are created by certain peat-cutting regimes (i.e.Iimited hand cutting) and such species may be scarce orabsent in little-damaged bogs. For many speciesregar<strong>de</strong>d as having great conservation interest inlowland raised bogs, it is the mix <strong>of</strong> microhabitatspresent in areas that have been subjected to traditionalhand-cutting over a period <strong>of</strong> time that seems to beimportant in their continued survivaI. In sorne sites,hand cuttings may also <strong>of</strong>fer wet refugia for sornespecies when much <strong>of</strong> the remain<strong>de</strong>r <strong>of</strong> the site surface1 Oligophagous: restricted to a small number <strong>of</strong> food plants;monophagous: restricted to one species or variety <strong>of</strong>food plan!.


CHAPTER 1: LOWLAND PEATLANDS27has become damaged and dry. However, an increase inhabitat and species diversity due to disturbance is notconsi<strong>de</strong>red by the conservation agencies to provi<strong>de</strong> anincrease in conservational 'value' over the naturalness<strong>of</strong> an undamaged bogo The extensive, bare surfacescreated by mo<strong>de</strong>m extraction methods may be far lessamenable to recolonisation than the small-scale handpeat cuttings.There have been few studies <strong>of</strong> the behavioural orphysiological selection processes that lead to peatlandspecies being found in a particular habitat, but thehabitat requirements <strong>of</strong> many invertebrate species willbe govemed by both the requirements <strong>of</strong> the adult andthe juvenile stages (larva, pupa, etc.). These may berather different, necessitating the presence <strong>of</strong> two ormore different and perhaps even spatially separatedfeatures. Natural Sphagnum hummocks and hollowsserve in part to provi<strong>de</strong> this sort <strong>of</strong> microtopographicalheterogeneity. However, in general, high water tables,ensuring that Sphagnum remains saturated, appear tobe essential for the continued existence <strong>of</strong> many'<strong>de</strong>sirable' species in raised-bog sites, even thoughmany <strong>of</strong> them [see Table 1.6] seem to require an'interface' situation between Sphagnum and/or barepeat and drier zones.Dragonflies are <strong>of</strong>ien top predators in bog pools,which, due to their acidity, lack fish. Many dragonfliesare able to tolerate highly acidic conditions as larvae,favouring pools with Sphagnum (e.g. Soeffing &Kazda, 1993). Different species may favour pools <strong>of</strong>different sizes. In general, dragonflies benefit fromsome protection from the wind and are favoured bysites with peat walls, adjacent scrub or at the edges <strong>of</strong>raised bogs where woodland may act as a windbreak(R.G. Kemp,pers. comm).Most species <strong>of</strong> carabid beetle display a consi<strong>de</strong>rable<strong>de</strong>gree <strong>of</strong> latitu<strong>de</strong> in their habitat preferences and arenot restricted to a single vegetation or soil type. Rather,it is thought that physical factors " ...such as soil watercontent, ...vegetation height and temperature..." may beimportant (Butterfield & Coulson, 1983). Thus fewcarabids are likely to be entirely restricted to a singleTable 1.6 Invertebrate species for which raised bogs are consi<strong>de</strong>red to have particular conservation importance inthe UK.Species Or<strong>de</strong>r RDB 1 NotesstatusHeliophanus dampfi Aranae RDB Associated with peat in Europe, and in the UK known only fromCors Fochno (Dyfed) and Flan<strong>de</strong>rs Moss (Stirling).Coenagrion mercuriale Odonata RDB3 Paradoxically associated with basic seepages in UK oligotrophicmires, though also found in heathlandsSomatochlora· arctica Odonata RDB3Hagenella (=Oligotricha) Trichoptera RDB 1 Specifically associated with raised peat bogs;clathrataprobably favoured by old hand peat cullingsAcilius canaliculatus Coleoptera RDB3 Associated with old, exposed peat cultingsBembidion humerale Coleoptera RDB 1 Favoured by bare wet peat as found in old peat cullings (Key,1991)Curimopsis nigrita Coleoptera RDB 1 Associated with the interface between wet peat and damp lillerwhere there is heather growing, therefore probably favoured by oldhand peat cultings.Hydrochara caraboi<strong>de</strong>s Coleoptera RDB2 Occurs in a range <strong>of</strong> aquatic habitats in Europe, though in the UKits distribution is very Iimited.Eilema sericea Lepidoptera RDB 3 Although found on 'mosses' its larvae feed on algae growing onheathers etc., and therefore it will be absent from SphagnumcarpetsEugraphe subrosea Lepidoptera RDB 1 In UK for some years only found known from Cors Fochno (Dyfed)though previously found in other bogs and fens; it has now beenrecor<strong>de</strong>d from a number <strong>of</strong> other raised bogs in mid Wales.Hercostomus angustifrons Díptera RDB2Limnophila heterogyna Díptera RDB 1 Likely to be associated with disturbed bog sites; (so far known onlyfrom canallagg at Whixall Moss)Phaonia jaroschewskii Diptera RDB2 Not restricted to lowland raised bogs; sensitive to falls in water(=crinipes)tablePrionocera pubescens Diptera RDB2Tipula grisescens Diptera RDB3 More typically an upland bog speciesPachybrachius luridus Hemiptera RDB3 Requires grassy tussocksFormica transkaucasica Hymenoptera ,RDB1 Associated with lowland bogs with Molinia1 Red Data Book (Shirt, 1987); see also Brallon (1990) and Falk (1991 a, b) for <strong>de</strong>finitions.


28RESTORATlON OF DAMAGED PEATLANDShabitat type, such as lowland raised bogs, at leastthroughout aH <strong>of</strong>their range.Many invertebrate species, including dragonflies,benefit from areas <strong>of</strong> open water and would bedisadvantaged by loss <strong>of</strong> pools induced throughdrainage or successional overgrowth, though sorneopen pools in bogs, particularly the large examples,may be permanent. Management which restores theopen-water habitat may benefit these species. Forvirtually aH threatened invertebrates, two factorsappear to be <strong>of</strong> critical importance: (i) the maintenance<strong>of</strong> high water tables and (ii) the presence <strong>of</strong>a mo<strong>de</strong>ratediversity <strong>of</strong> habitat types with elements <strong>of</strong> bare peat,open water <strong>of</strong> various sizes, Sphagnum hummocks,sorne grass, sedge ami/or heather c1umps and sornerather drier banks.1.11 The birds <strong>of</strong> raised bogsRaised bogs in Britain have been modified andfragmented to such an extent that an assessment <strong>of</strong> the'typical' omithological resource <strong>of</strong> 'intact' raised bogsin Britain is difficult, and must rely heavily uponhistorical records and on data from the few remainingextensive bogs in Britain. Available informationsuggests that no bird species is exclusive to raised bogsin Britain, although certain birds are consi<strong>de</strong>red to becharacteristic <strong>of</strong>the habitat.There is a paucity <strong>of</strong> <strong>de</strong>tailed site-specific omithologicaldata from raised bogs in Britain. Available dataindicate low bird <strong>de</strong>nsity and low species richness onopen areas <strong>of</strong> Iittle-damaged bogs. The lack <strong>of</strong> treesand shrubs make them largely unsuitable for passerinesthat require perching posts and nesting sites aboyeground leve!. The vascular plants <strong>of</strong> bogs <strong>of</strong>fer aIimited food supply to birds and sorne <strong>of</strong> the specieswhich do breed are common and wi<strong>de</strong>spread breedingspecies elsewhere in Britain.The naturaHy low <strong>de</strong>nsity and species richness <strong>of</strong> birdpopulations on raised bogs does not imply lack <strong>of</strong>conservation interest. Birds <strong>of</strong> particular conservationvalue (see Batten el al, 1990) which occur on lowlandraised bogs in Britain inclu<strong>de</strong> significant populations <strong>of</strong>breeding teal 1 , red grouse, black grouse, dunlin,curlew, redshank, nightjar and twite, and winteringpopulations <strong>of</strong> pink-footed geese, Greenland whitefrontedgeese, greylag geese, hen harrier and merlin.The number <strong>of</strong> bird species breeding on the opensurface <strong>of</strong> an unmodified raised bog is small andbreeding <strong>de</strong>nsities are generally low. Meadow pipit andskylark are the two most characteristic species <strong>of</strong> raised1 Latin names <strong>of</strong> bird species mentioned in the text are given inAppendix 5.bogs (Stroud, 1989), with mallard, curlew, snipe andcuckoo also typically present, with the local addition <strong>of</strong>other species. Red grouse occur on sorne northem andIrish raised bogs. Of the rarer species, merlin and henharrier may occasionally breed on extensive raisedbogs in Scotland, northem England and Ireland.Several species, including gol<strong>de</strong>n plover and dunlin,seem to have <strong>de</strong>clined in numbers or have ceased tobreed on lowland bogs during the last century,although they have continued to breed in the uplandsand on blanket bogs. Others, such as black-tailedgodwit, ruff, and Montagu's harrier have not bred onraised bogs for at least 50 years. Twite were oncewi<strong>de</strong>ly distributed on the Lancashire and Cheshiremosses and have since disappeared (Orford, 1973).Gull colonies are also thought to have become morelocalised than in the past (Ratcliffe, 1977). The <strong>de</strong>cline<strong>of</strong> these breeding species <strong>of</strong> little-damaged lowlandbogs has received Iittle attention. It is c1early arelatively recent phenomenon which may possibly beattributed to habitat fragmentation and lowering <strong>of</strong>water levels.Sorne <strong>of</strong> the more extensive raised bogs are importantas wintering sites for grazing wildfowl species. Ofthese, the Greenland race <strong>of</strong> white-fronted geese hasreceived much attention. A significant proportion <strong>of</strong>the world population <strong>of</strong> this distinctive race winter inthe British Isles (Batten el al., 1990), historicallyretuming each year to certain lowland bogs. AlthoughtraditionaHy associated with these bogs many <strong>of</strong> the'Greenland white-fronts' have abandoned raised-bogwintering sites in Britain and Ireland in favour <strong>of</strong>altemative habitats (Pollard & Walters-Davies, 1968;Ruttledge & Ogilvie, 1979; Fox & Stroud, 1986;Mad<strong>de</strong>n, 1987; Foss, 1991; Warren el al., 1992). Thereasons for this behavioural change may inclu<strong>de</strong>increased disturbance and habitat loss, together withestablishment <strong>of</strong>wildfowl refuges in, other areas.Modification <strong>of</strong> raised bogs has introduced a newmosaic <strong>of</strong> habitats which has increased the diversity <strong>of</strong>the bird species occurring on the former open areas,although many <strong>of</strong> the additional species are thosewhich naturally occupy the bog margins. The response<strong>of</strong> bird communities to peat cutting and associatedchanges is complex because <strong>of</strong>the diverse nature <strong>of</strong>thechanges that can be induced by these activities.Depending on the <strong>de</strong>gree <strong>of</strong> damage, such changes mayhave a more marked effect on spatial distributions andrelative abundances <strong>of</strong> species rather than increasingspecies diversity in a particular site. Many specieswhich occur on 'intact' bogs also occur on modifiedsites, provi<strong>de</strong>d that sufficiently large areas <strong>of</strong> their'preferred' habitat remain. However, if treesextensively inva<strong>de</strong> damaged bog surfaces, such speciesare eventually replaced by woodland birds.


CHAPTER 1: LOWLANO PEATLANOS29Species richne s and bird <strong>de</strong>nsity generally increaseswith the <strong>de</strong>velopment <strong>of</strong> scrub or occurrence <strong>of</strong> fen.Although the early stages <strong>of</strong> succession benefit certainimportant species, such as nightjar (Fuller, 1982), anincipient clímax community dominated by generalistpasserine species seems Iikely on such sites. However,species composition can be dramatically affected bythe relative <strong>de</strong>gree <strong>of</strong> flooding, <strong>de</strong>siccation and scrubc1earance on damaged sites. Bog restoration initiativeswhich involve impoundment <strong>of</strong> surface water maysuffer from the effects <strong>of</strong> pioneer bird colonists, suchas wintering gulls, for example through guanotrophicationand physical damage.1.12 Non-avian vertebrates <strong>of</strong>raised bogsNon-avian vertebrates (mammals, amphibians reptiles)usually form a relatively minor part <strong>of</strong> the conservationinterest <strong>of</strong> raised-bog sites but records from raised-bogsites have inclu<strong>de</strong>d such species as otter, mountainhare, <strong>de</strong>er and ad<strong>de</strong>r. Bogs may also constituteimportant feeding areas for bats, especially aroundmarginal habitats.1.13 Archaeology, palaeoecologyand restoration<strong>Peatlands</strong> are important for archaeology andpalaeoecology. They preserve remains <strong>of</strong> many <strong>of</strong> theplants that onCe formed their living surface and <strong>of</strong>sorne <strong>of</strong> the animals (especially Coleoptera) thatinhabited this. The pollen rain, produced from thebog's surface and from the surrounding landscape, is<strong>of</strong>ien preserved exceptionally well. The e, and otherfeatures, provi<strong>de</strong> a valuable palaeoecological archive.This can be used, for example, to reconstruct, thecharacter <strong>of</strong> past post-glacial environments, climaticchange and flooding episo<strong>de</strong>s, vegetational history,human occupation and management history.Some peatlands (especially fens) have been a focus <strong>of</strong>past human activity and a rich range <strong>of</strong> artefacts maybe preserved in the peal. Peat excavation has <strong>of</strong>ienhelped to reveal sorne artefacts, for example the head<strong>of</strong> a cow found at Solway Moss, Cumbria (Middleton,1992) [PIate 1.6], and •Lindow Man' at Lindow Moss,Cheshire (Stead, Bourke & Brothwell, 1986), but it hasdoubtless <strong>de</strong>stroyed others. The peatlands <strong>of</strong> theSomerset Levels have provi<strong>de</strong>d particularly greatarchaeological interest (e.g. Coles & Coles, 1986;Plata ~.6 Remains <strong>of</strong> a cow le. 800-900 AD] found during peat extraction operations at Solway Moss (Cumbria).[Photo. North West Wetland Survey, © Lancaster University Archaeology Unit]


30RESTORATION OF DAMAGED PEATLANDSPlate 1.7 The Sweet Track - built in 3806 BC across aPhragmites reed swamp in he Somerset Levels.Excavated by the Somerset Levels Project (fun<strong>de</strong>d byEnglish Heritage and the Universities <strong>of</strong> Cambridge andExeter). [Photo: Somerset Levels Project].Somerset Levels Papers, 1-15, (1975-1989), asexemplified by the Sweet Track [Plate 1.7]. Bycontrast, sorne <strong>of</strong> the raised-bog sites investigated bythe North-West Wetland Survey have, as yet, yiel<strong>de</strong>dfew artefacts (Middleton, 1990-1992).Peatland restoration schemes may need to consi<strong>de</strong>r therequirements for preservation <strong>of</strong> archaeological andpalaeoecological interests and in sorne cases they mayrequire c10se co-operation between conservationistsand archaeologists, to arrive at the optimum solutionsfor site restoration. Nonetheless, it must be recognisedthat if the object <strong>of</strong> raised-bog restoration is toregenerate a new raised bog, at the very least this willrequire effective rewetting <strong>of</strong> the peatland. The followingfactors merit consi<strong>de</strong>ration [see also Chapter 7]:• the removal or disturbance <strong>of</strong> peat will also remove thehistorie and industrial landscape, the immediate palaeoenvironmentalrecord and any artefacts.• survey <strong>of</strong> the landscape and <strong>of</strong> archaeological featurescould form part <strong>of</strong> fteld investigations prior to initiation<strong>of</strong>a restoration schcme [Chapter 7].• raised water levels can lead to erosion where they adjoinupstanding blocks <strong>of</strong> peat, thus <strong>de</strong>stroying both thepalaeo-environmental record and surviving structures. Itmay be necessary, both to minimise erosion and toencourage revegetation, to construct breakwaters in largeareas <strong>of</strong> open water.• the potential for damage to in situ artefacts, sites and thepalaeo-environmenta1 record by the roots or rhizornes <strong>of</strong>such species as Phragmites should be consi<strong>de</strong>red in boththe <strong>de</strong>liberate encouragement and potential forcolonisation b such species (although such species areunlikely to prov'<strong>de</strong> much <strong>of</strong> a problem in ombrotrophicsystems).• in sorne cases, it will be <strong>de</strong>sirable to preserve peat<strong>de</strong>posits and archaeological structures in situ. Schernes<strong>de</strong>signed speciftcally for nature conservation should alsoconsi<strong>de</strong>r the in situ conservation <strong>of</strong> archaeological<strong>de</strong>posits.Peat extraction is also part <strong>of</strong> the 'industrial heritage'<strong>of</strong> Britain and abandoned, cut-over bogs forro a'<strong>de</strong>relict industrial landscape'. Even drainage schemesand methods used can have historical interest. If suchtopics and artefacts are perceived as legitimate areas <strong>of</strong>interest, their preservation may impose its ownconstraints upon restoration procedure and objectivesfor damaged bogs. Conservation and restorationschemes can also be seen as yet another stage in thehi tory <strong>of</strong> human intervention in peatland ecosystems,and, perhaps in the future, constructs associated withrestoration may be valued as much as artefacts <strong>of</strong>'conservation archaeology' as for their ecologicaleffects.


Chapter 2Characteristics <strong>of</strong> cut-over raised bogs2.1 IntroductionPeat extraction directly removes both the peat and theliving surface from those areas <strong>of</strong> bog where it occurs.lt may also affect adjoining areas <strong>of</strong> uncut peat,particularly through indirect drainage. Thus it is importantto consi<strong>de</strong>r not only the direct effects <strong>of</strong> peatextraction, and their implications for restoration, butalso its inf1uence (or that <strong>of</strong> other reclamationmeasures) on bog remnants. The various techniques <strong>of</strong>peat ex raction used may inf1uence restoration options,as the conditions remaining when the sites areabandoned differ. Approaches to the rewetting <strong>of</strong> sitescut-over by different methods and the preservation <strong>of</strong>bog remnants are consi<strong>de</strong>red in Chapter 5.Where any substantial peat extraction has taken place itis likely to have much modified the topography <strong>of</strong> theoriginal bog and the resulting conformation will be animportant <strong>de</strong>terminant <strong>of</strong> rewetting approaches. Twobroad, but not exact, topographical situations can berecognised, <strong>de</strong>pending on whether the area in questiontends to shed or hold water. These situations will bereferred to respectively as massifs and <strong>de</strong>pressions[Figure 2.1].A massifcan inclu<strong>de</strong>:• tbe entire mire, in relation to the topography <strong>of</strong> thesurrounding landscape;• a remnant <strong>of</strong>the original ombrotrophic dome;• a surface that has been cut-over but which is proud<strong>of</strong>surrounding cut-over areas;At each particular scale the structure tends to have anoverall convex or water shedding pr<strong>of</strong>ile.Depressions effectively refer to areas that have' beencut for peat and which form hollows or flat surfaces inrelation to adjoining blocks. They tend to have anoverall concave or water holding pr<strong>of</strong>ile.Note tbat this terminology is relative - for example, anindividual baulk may form a 'massif in relation to theadjacent peat cutting, but lie within a mire which is in a<strong>de</strong>pression relative to the surrounding land. Similarly, apeat cutting or field may form a <strong>de</strong>pression within amire remnant which is itself a 'massif as the generalsurface lies aboye the level <strong>of</strong>the surrounding land.M ------.PeatDMOMineral substratumMassif(water-shedding area)Depression(water-col/ecting area)Figure 2.1The concept <strong>of</strong> massifs & <strong>de</strong>pressions [see text].


32REsrORATION OF DAMAGED PEATLANDS2.2 Effects <strong>of</strong> peat extraction onbog remnants and refugia2.2.1 IntroductionSorne sites affected by peat extraction retainundisturbed areas <strong>of</strong> vegetation that support typical bogspecies. In others, recolonised, formerly-disturbedareas may provi<strong>de</strong> refugia. In botb cases, they maysustain an important biological resource and tbeirprotection may be important both in terms <strong>of</strong>an overallprogramme <strong>of</strong> mire conservation and as a means <strong>of</strong>conserving plants and animals adjacenrto areas <strong>of</strong> ongoingpeat extraction as sources <strong>of</strong> recolonist species[see Chapter 4]. The preservation <strong>of</strong> undisturbed areasshould be an important part <strong>of</strong> a restoration strategyoManagement and maintenance <strong>of</strong> such refugia need tobe carried out alongsi<strong>de</strong> ongoing peat extraction andnot left until extraction has ceased [Chapter 6].In gross terms, marginal damage, including peatextraction, can be consi<strong>de</strong>red to have two major effectson bog remnants:a) hydrologicaI - disruption <strong>of</strong> the hydrological integrity <strong>of</strong>the 'groundwater' mound; increase in the hydraulicgradient between the remnant and its surroundings;b) fragmentation <strong>of</strong> habitat.These effects are consi<strong>de</strong>red belowoon such factors as the nature <strong>of</strong> the un<strong>de</strong>rlying mineralsubstratum].• increase in evapotranspirative losses through the growth<strong>of</strong> 'un<strong>de</strong>sirable' vegetation (e.go Molinia, birch)o [ThiswiIl be particularly important in relation to waterconditions in ummer.]Most damaged sites are likely to be affected by one ormore <strong>of</strong> these factors, altbough the first two areperhaps the most common causes <strong>of</strong> <strong>de</strong>hydration. Thefactors leading to <strong>de</strong>hydration are perhaps tbe greatestthreat to the ecohydrology <strong>of</strong> mires because bylowering tbe water table and accelerating the rate <strong>of</strong>Direct dramageReduction in basal area2.2.2 Hydrological effectsIntroductionThe surface <strong>of</strong> bog massifs can be dry for variousreasons, <strong>of</strong>which drainage is one <strong>of</strong>tbe most direct andobvious. However, even without direct drainage <strong>of</strong> themassif, water conditions may be consi<strong>de</strong>rablyinfluenced by otber factors, for example, extraction <strong>of</strong>surrounding peat, since one <strong>of</strong> tbe features <strong>of</strong> tbe'groundwater mound' concept is that the height <strong>of</strong> thewater mound may be consi<strong>de</strong>rably in.f1uenced by itseffective basal area [Chapter 1].Surface drying may thus be promoted by variousagents, <strong>de</strong>pending on the situation [see Figure 2.2].These inclu<strong>de</strong>:• direct drainage <strong>of</strong>the peat body;• indirect drainage through loss <strong>of</strong> basal area <strong>of</strong> the peatbody, by agricultural conversion or peat extraction;• indirect drainage through lowering <strong>of</strong> adjacent watercourses, or regional groundwater tables (this wil1 <strong>de</strong>pendon the permeability <strong>of</strong>the un<strong>de</strong>rlying mineral ground);• reduced water storage capacity <strong>of</strong>the <strong>de</strong>hydrating peat orpeat layers remaining after extraction;• reduction in <strong>de</strong>pth <strong>of</strong> peat may be associated with<strong>de</strong>creased resistance to vertical seepage through thebottom <strong>of</strong> the bogo [The importance <strong>of</strong> this wil1 <strong>de</strong>pendLowering o(adjacent water courses orregional groundwater tablas (?)Growth o( 'un<strong>de</strong>sirable' speciesDecreased reslstanca to vertIcal seepagePeat :~.:~. Mineral substratumFigure 2.2 Potential causes <strong>of</strong> <strong>de</strong>hydration <strong>of</strong> a raisedbog massif (see text).


CH PTER 2: CHARACTERISTICOF CUT-OVER BOGS33<strong>de</strong>composition <strong>of</strong> the peat, changes in the physicalproperties <strong>of</strong> the peat, and the hydrology, morphologyand ecology <strong>of</strong> a mire are likely to take place, some <strong>of</strong>which may be irreversible. Although any assessment <strong>of</strong>the effects <strong>of</strong> drainage on the physical properties <strong>of</strong>peat have to qualified by reference to peat types, thefollowing responses are sorne <strong>of</strong> those which have beensuggested as typicaJ following drainage <strong>of</strong> peatland(see e.g. Clausen & Brooks, 1980):¡!lcrease ;!l:<strong>de</strong>crease ;n:subsi<strong>de</strong>nce;bulk <strong>de</strong>nsity;amplitu<strong>de</strong> <strong>of</strong>water fluctuation;active porosity;water content;water storage coefficient;permeability.Thus, for example, drainage results in primaryconsolidation followed by shrinkage, secondarycompression and flllally wastage <strong>of</strong> the upper layers <strong>of</strong>the bog (Hobbs 1986), and can lead to consi<strong>de</strong>rablereduction in the height <strong>of</strong> the peat surface. Observationsat the Holme Post (Hutchinson, 1980) provi<strong>de</strong>graphic evi<strong>de</strong>nce <strong>of</strong> the effects <strong>of</strong> drainage andagriculture in the progressive lowering <strong>of</strong> a peatPlate 2.1 Vertical peat face between cut-over area and'remnant' uncut peat block (Breitenmoos, S. Germany).surface, even without peat extraction. Over a period <strong>of</strong>130 years, tbe surface has fallen by nearly 4 m. In theearly stages <strong>of</strong> drainage <strong>of</strong> a virgin bog, the peatshrinkage could be as much as 0.2 m per year.,although the rate <strong>of</strong> peat loss may <strong>de</strong>crease with time.Ivanov (1981) suggests that an average rate <strong>of</strong> collapseafier drying over a period <strong>of</strong> 40-50 years varies wi<strong>de</strong>lyfrom 1-2 to 8 cm per year, and cites the formula givenby Maslov (1970) for calculating rates <strong>of</strong> peatshrinkage. .Many, perhaps most, British bogs have been affectedby drainage to some <strong>de</strong>gree. This can range fromextensive drainage in preparation for peat extraction,which was subsequently abandoned (e.g. RoudseaMoss, Cumbria) to the digging <strong>of</strong> one or moreboundary drains across the bog, marking ownership(e.g. Wedholme Flow, Cumbria), and to the grosseffects <strong>of</strong> adjacent peat extraction and conversion foragricult}lTe. In most cases it is difficult to separate theeffec~ <strong>of</strong> peat extraction upon adjacent bog remnantsfrom other causes <strong>of</strong> damage such as drainage, as bogshave <strong>of</strong>ien been subject to various forms <strong>of</strong> damage.However, it seems likely that effects are <strong>of</strong>iensynergistic. For example, lowering <strong>of</strong> the surroundingground surface <strong>of</strong>ien produces a sharp boundary [Plate2.1], and will increase the hydraulic gradient betweenthis and the uncut surface, thereby increasing theefficiency <strong>of</strong> any drains. As the basal area is reduced asa result <strong>of</strong> peat extraction, a new perched water moundis formed within the peat remnant. The shape andposition <strong>of</strong>the new water mound will be <strong>de</strong>termined bysite-specific conditions. In sorne examples it may nolonger reach the surface <strong>of</strong> the bog, which iscorrespondingly dry [Figure 2.3]; in others, where thedrop <strong>of</strong> water level has not been great, or where theamount <strong>of</strong> marginal damage is small in proportion tothe residual area <strong>of</strong> bog (or possibly where a change inthe permeability <strong>of</strong> the peat has lead to a reduction inwater run<strong>of</strong>t) the water level may still reach the surface<strong>of</strong> the bog peat, at least in the more central areas.lnterpreting the impact <strong>of</strong> drainage on bog systems iscomplicated by their 'diploteLmic' or two-Iayeredstructure and its role in maintaining the hydrologicalstability <strong>of</strong> the bog; in undisturbed bogs the acroteLmbuffers the catoteLm from sorne extemal influences[1.7]. Where drains are cut into a well-<strong>de</strong>velopedSphagnum-rich acroteLm, the hydrological an<strong>de</strong>cological impact <strong>of</strong> drainage may be expected to bewi<strong>de</strong>spread on the bog surface because <strong>of</strong> the hightransmissivity <strong>of</strong> the acrotelm (lngram & Bragg, 1984;van <strong>de</strong>r Schaaf el al, 1992). The plant species(particu1arly Sphagnum mosses) that are particularIycharacteristic <strong>of</strong> little-damaged acrotelms may beespecially susceptible to any induced periods <strong>of</strong><strong>de</strong>hydration and there may be an interaction betweenchanges in the character <strong>of</strong> the bog vegetation and


34RE TORATION Of DAMAGED PEATLADOriginal mire/ / / / / / / / / / / // / / / /[Saturated peaU/ / / / // / / / / / / / / / / / / / / / / /Unsaturated pealOamaged mire­ ~~/7,T~/ /"///////// "1_--.JI..- I ////////// ~__ \Figure 2.3 Conceptual iliuslralion <strong>of</strong> the potential waterdrawdown <strong>of</strong> the perched water mound in a raised bogas a result <strong>of</strong> marginal damage.hydrological [unctioning <strong>of</strong> the bog as a result <strong>of</strong>drainage. For example, drainage may lead to a bogsurface from which former hollows and pools havebeen lost, thus affecting factors such as water storageand run-<strong>of</strong>f (Ivanov, 1981) (see below) and reduce thecapacity <strong>of</strong> the acrotelm to consistently 'feed' thecatotelm with water and maintain a relatively stablewater regime. The small hydraulic conductivity <strong>of</strong> thecatotelm means that the effect <strong>of</strong> an individual drainageditch upon the water table in the catotelm may beconfined to a few metres either si<strong>de</strong> <strong>of</strong> the drainageditch. This is recognised in the preparation andmaintenance <strong>of</strong> bogs for peat extraction, where ditchspacings <strong>of</strong> c. 10-20 m are nee<strong>de</strong>d to provi<strong>de</strong> effectivedrainage <strong>of</strong> the upper layers <strong>of</strong> peal. Shrinkage as aresult <strong>of</strong> loss <strong>of</strong> water from these layers usually meansthat drains have to be <strong>de</strong>epened each year, and it maytake up lo ten years for a newly drained bog to be in asuitable condition for extraction to commence.Effects <strong>of</strong> drainage upon chemicalcharacteristicsBesi<strong>de</strong>s causing physical loss, drying <strong>of</strong> peat is likelyto induce biochemical oxidation, mineralisation andrelease <strong>of</strong> hydrogen ions and nutrients. Even on littledamagedbogs, seasonally low water levels maysubstantially increase acidity, and subsequent rewettingcan lead to the release <strong>of</strong> various ions on the risingwater table (e.g. Braekke, 198 J). rn damaged sites,with frequent or protracted dry episo<strong>de</strong>s, theseprocesses may be accentuated. It is likely that theoxidation <strong>of</strong> reduced sulphur compounds during dryperiod may be an important mechanism <strong>of</strong>(temporary) acidification. In sorne circumstances,concentrations <strong>of</strong> S04 2 - may reach potentially toxic(but not lethal) levels for Sphagnum (Ferguson andLee, 1982-3). pH values may fall below 3.0, to valuesthat may be suboptimal for growth <strong>of</strong> Sphagnum andsorne other typical bog species. Mineralisation <strong>of</strong> thedrying peat mayal o contribute to nutrient release andsuch effects may be exacerbated by water table instabilityand recurrent dry periods. Certainly, increasedconcentrations <strong>of</strong> various solutes have been measuredin water draining cut-over bogs compared with littledamagedbogs (e.g. Clausen & Brooks, J983a, b).However, the permanence <strong>of</strong> these effects, or theirsignificance to revegetation prospects is not known.E ects <strong>of</strong> drainage on bog vegetationAs a result <strong>of</strong> the c10se relationship between waterlevels and the distribution <strong>of</strong> plant species on bogs, it isc1ear that drainage will affect the vegetation, as well asthe peat <strong>of</strong> raised bogs. The <strong>de</strong>finition o[ bog communitiesis likely to become 'blurred' un<strong>de</strong>r the impact <strong>of</strong>drainage, leading to impoverished types. The magnitu<strong>de</strong><strong>of</strong> the effect will <strong>de</strong>pend on the <strong>de</strong>gree <strong>of</strong> watertable change. A small, but sustained reduction in waterlevel in a bog is likely to cause a shift in speciescomposition towards 'para-bog-Sphagnllln vegetation',i.e. away from the natural hummock-hollow complex,towards those species normally associated withhummocks, with overgrowth <strong>of</strong> the hollows, anincrease in species such as Calluna and Molinia and,possibly, invasion <strong>of</strong> woody species, particularlybirches (e.g. Eigner & Schmatzler, 1980; Bolte,Flügger & Cor<strong>de</strong>s, 1985; Montag, 1989) [Plates 2.2,2.3,2.4]. A large sustained reduction <strong>of</strong> water levels isIikely to lead to an eventual los <strong>of</strong> bog speciestogether with loss <strong>of</strong> the original acrotetm and aeration<strong>of</strong> lhe upper catotelm peat, leading to cessation <strong>of</strong> peat<strong>de</strong>position and bog growth.In many sites damage (from whatever source) hascaused significant drying-out <strong>of</strong> the uncut surfaces suchthat the only remaining bog flora survives in the wetterconditions <strong>of</strong> abandoned workings. In other cases, bogremnants have survived alongsi<strong>de</strong> peat extraction,Plate 2.2 Molinia-dominated surface <strong>of</strong> raised-bog'remnant'; Holcr<strong>of</strong>t Moss (Cheshire).


CHAPTER 2: CI-IARACTERI TIC OF C T-O ER BO35Plate 2.3 Cal/una-dominated vegetation on drainedraised-bog surface at Moine-Mhor (Argyll).apparently still retaining reasonably wet conditions atthe surface <strong>de</strong> pite removal <strong>of</strong> adjacent peat. Examplesinelu<strong>de</strong> Wedholme Flow (Cumbria), where l11uch <strong>of</strong> theuncut dome appears to retain high water levels withtypical bog vegetation, <strong>de</strong>spite continued adjacent peatextraction. However, the long-term effects <strong>of</strong> this arenot known.The effects <strong>of</strong> drainage on the bog vegetation can beseen in microco m in many damaged sites and peatextractioncomplexes, where the cuttings ma supportSphagna and other bog species while the baulks orupstanding remnants have lost such taxa and havebecome dominated by species such as Ca/luna, Mo/iniaand birch (e.g. Thorne Waste, S. Yorkshire; CrowleMoors, Lincolnshire; Risley Moss, Cheshire; BankheadMoss, Fife [Plate 2.5]). [n general plant species changesconcomitant on drainage <strong>of</strong> bog surfaces are usualIyregar<strong>de</strong>d as un<strong>de</strong>sirable: the taxa that replace typica[bog species have less intrinsic con ervation 'value'.Plate 2.4 Birch and Rhodo<strong>de</strong>ndron invasion on raisedbog'remnant'; Wreaks Moss (Cumbria). [see also Plate10.1]Plate 2.5 Sphagnum-dominated bog vegetationconfined to cut-out pools, surroun<strong>de</strong>d by Cal/unadominateddry bog surface; Bankhead Moss (Fife).Effects <strong>of</strong> drainage on bog ¡nvertebrates andbirdsThe changes in the hydrology and vegetation <strong>of</strong> a bogoutlined above will affect the bog fauna through changesin habitat and concomitant changes in vegetationstructure and food sources ele. (for example, loss <strong>of</strong>open water or wet, Sphagnllm-dominated areas,increase in heathy-bog or scrub). The e may [ead tochanges in population size and species composition.[n general, high water tables which ensure that areas <strong>of</strong>Sphagnum remain saturated appear to be essential forthe continued existence <strong>of</strong> sorne '<strong>de</strong>sirable' invertebratespecies in raised-bog sites, though sorne <strong>of</strong> themmay also require an 'interface' between Sphagnum andbare peat or drier zones. For example, drying appearsto have had <strong>de</strong>leterious effects on populations <strong>of</strong> theRDB 2 category muscid fly, Phaonia jaroschewskii (=crinipes), at Thorne Waste (Skidmore, 199 [). The rarebeetle Bembidion humeraLe may also be favoured bythe maintenance <strong>of</strong> high water tables so that the peatsurface is kept moist (Hyman, 1992 rey; Shirt, 1987).High water levels are also cited as an importantcriterion for a number <strong>of</strong> mire-associated bugs, forexample, Micran/ha marginaLis and PachybrachiusLuridlls (Kirby, 1992a). Many dragonfly species benefitfrom the maintenance <strong>of</strong> areas <strong>of</strong> open water (e.g.Sphagnum pools <strong>of</strong> various sizes) and may be expectedto suffer if these disappear, either through drainage orby them becoming choked with vegetation. tudies <strong>of</strong>the effects <strong>of</strong> raising water tables in bogs that hadpreviously been partially drained have generally shownwhat have been interpreted as favourable responses <strong>of</strong>invertebrate populations (e.g. Fox, 1986b), particularlywhere this has led to an increase in open water habitats.


36RESTORATlON OF DAMAGED PEATLANDSAn increase in heathland vegetation and progressiveencroachment <strong>of</strong> birch scrub as a result <strong>of</strong> dryingprovi<strong>de</strong>s a mosaic <strong>of</strong> different habitats which mayfavour various non-mire invertebrate species, some <strong>of</strong>which may be uncommon, for example, the bog bushcricket, Metrioptera braehyptera (Shirt, 1987), theclou<strong>de</strong>d buff moth, Diaerisia sannio and the cranefly,Pi/aria meridiana. It usually leads also to an increasein the number <strong>of</strong> breeding bird species compared withthose typical <strong>of</strong> open bogo For example, the drierconditions in combination with the provision <strong>of</strong> songposts, in the form <strong>of</strong> birch scrub, undoubtedly favourthe spread <strong>of</strong> such species as tree pipit, whinchat andstonechat on certain sites. Light scrub, characterised byscattered pioneer birch and Scots pine, can favour thecolonisation <strong>of</strong> bogs by nightjar. Nightjars usually nestat the base <strong>of</strong> saplings and also require trees fromwhich to proclairn their territories and as roosting sites;for these re~sons nightjars do not usually nest beyondthe edges <strong>of</strong> 'intact' treeless bogs, although the bogsare important feeding areas. Nonetheless, as treeinvasion continues, the habitat structure will eventuallybecome less suitable for nightjars - light scrub isessentially a transitional habitat on damaged bogs, andthe <strong>de</strong>velopment <strong>of</strong> <strong>de</strong>nser scrub encourages anessentially woodland bird community to <strong>de</strong>velop(RSPB, 1983; Fuller, 1982).2.2.3 Habitat fragmentationIntroductionUtilisation <strong>of</strong> bogs for agriculture and forestry has leadto a large loss <strong>of</strong> former raised-bog sites and to habitatfragmentation (Lindsay, 1993); buming, drainage andpeat extraction (domestic and commercial) hascontributed further damage to remaining sites.Fragmentation has increased the distances betweensites supporting typical bog flora and fauna, which mayhave implications for the recolonisation <strong>of</strong> peatworkings. Changes in the size and shape <strong>of</strong> the remnantbogs may have various repercussions. As well aspossible effects upon the hydrologic stability <strong>of</strong> theremnants, it may also affect their capacity to sustaincommunities or in<strong>de</strong>pen<strong>de</strong>nt populations <strong>of</strong> particularspecies (in which case it may be impossible to maintainthem).Size <strong>of</strong> remnantsThere is consi<strong>de</strong>rable interest amongst conservationistsin the relative merits <strong>of</strong> several small, versus singlelarge reserves in the conservation <strong>of</strong> biodiversity <strong>of</strong>threatened habitats. May (1975) pointed out that, as arough rule, a ten fold <strong>de</strong>crease in area would lead to ahalving <strong>of</strong> the equilibrium number <strong>of</strong> species presentand conclu<strong>de</strong>d that several small areas would supportless species than a large area <strong>of</strong> equivalent size.However the general conclusion <strong>of</strong> most <strong>of</strong> the studiesconceming the single large or several small(S.L.O.S.S.) <strong>de</strong>bate was that several smaller reservescontain more species than a single large reserve <strong>of</strong>equivalent total area. However, the advantage <strong>of</strong>conserving a number <strong>of</strong> small sites rather than a singlelarge reserve will also <strong>de</strong>pend on such factors as theoverlap <strong>of</strong> species present in the small sites (Higgs,1981), the stability <strong>of</strong> the sites, and geographicaldistribution and requirements <strong>of</strong> the species.The importance <strong>of</strong> critical minimal areas forconservation <strong>of</strong> plant communities has not been wi<strong>de</strong>lystudied, mainly because area usually accounts for onlya small amount <strong>of</strong> the variation in species richness indifferent sites and ultimately sites and species mayneed to be consi<strong>de</strong>red individually for conservationpurposes. However, typical bog vegetation occurs insome tiny sites « 2 ha), when habitat conditions areappropriate.For animal populations the importance <strong>of</strong> the size <strong>of</strong>the site relates to such factors as habitat specificity andterritoriality, together with reliability and availability <strong>of</strong>food source. Fragmentation <strong>of</strong> habitat is particularlyimportant in those species with low dispersal abilitiesand high habitat specificity. Thus it has been suggestedthat species composition within a site may change witha reduction in available habitat, and that speciesspecific to a particular habitat would suffer greaterlosses than more generalist species and need largerareas for their preservation (e.g. Humphreys &Kitchener, 1982). The sarne principie is likely to applyto plant populations and species, and there are c1earlyproblems in trying to <strong>de</strong>fine critical minimum areas forprotection <strong>of</strong> both plant and animal populations in bogs(e.g. Kuntze & Eggelsmann, 1981).InvertebratesFor invertebrates, assuming a species in which allindividuaIs contribute to the future generation, a roughrule-<strong>of</strong>-thumb for a genetically viable populationwould be about 500 individuals. Kirby (1992a)suggests that small insects such as the bug Mieranthiamargina/is require only a few square feet <strong>of</strong> bare orsparsely vegetated ground for a viable population. Forsome species (for example, the dragonfliesSomatoehlora alpestris and S. aretiea) only extremelysmall pools are nee<strong>de</strong>d for larval survival (Stemberg,1982), though for the maintenance <strong>of</strong> viablepopulations a number <strong>of</strong> such pools may be required.In addition, suitable areas need to be present for theadults to catch their prey, hold territories and conductcourtship. The area required by a species <strong>de</strong>pendspartly on the distribution and <strong>de</strong>nsity <strong>of</strong> its food supply.Thus, predators might be expected to be more abundantin areas where there is an abundance <strong>of</strong>their prey.


CIIAPTER 2: CIIARAeTERISTICS 01' CUT-OVER DOGS37In the case <strong>of</strong> dragonflies, which are amongst thelargest insects inhabiting raised bogs, sorne measures<strong>of</strong> male territory size suggest that the minimum size <strong>of</strong>refugium would seem to be 50 ha. However, largedragonflies may not be a good example on which tobase this calculation because they probably haveeffective dispersal and the gene pool <strong>of</strong> the populationin the refugium may be supplemented by immigrantsfrom time to time. It is likely therefore that geneticallysensible raised-bog refugia, even for large dragonflies,could be significantly smaller than 50 ha. In general,however, it should be expected that larger species willrequire larger areas <strong>of</strong> habitat for maintenance <strong>of</strong> aviable population than smaller ones. Hence, for the vastmajority <strong>of</strong> insects and arachnids inhabiting lowlandraised bogs, nearly all <strong>of</strong> which are significantlysmaller than dragonflies, the minimum effective areafor a refugium is likely to be far smaller.It should be noted that maintenance <strong>of</strong> minimum areasfor conservation <strong>of</strong> any particular species presupposesthat conditions within such refugia can be maintainedin the same condition as they would have had when thearea was surroun<strong>de</strong>d by larger areas <strong>of</strong> bogo Further, itremains an unresolved problem to know whetherefforts aimed at maintaining populations <strong>of</strong> any givensingle species would also ensure survival <strong>of</strong> thecommunity <strong>of</strong> invertebrates as a whole.BirdsThere have been very few studies relating to the spatialrequirements <strong>of</strong> birds occurring on raised bogs. InSwe<strong>de</strong>n, Bostrom and Nilsson (1983) observed thatbreeding-bird species richness increased strongly withbog area and that the <strong>de</strong>nsity bf most wa<strong>de</strong>rs washigher on larger (>50 ha) than smaller bogs. Theseauthors consi<strong>de</strong>red that, from a conservation point <strong>of</strong>view, one large bog is on average more valuable thanseveral small bogs with the same area. Certain speciesalso have specific requirements within the bog habitat(Bolscher, 1995) which are likely to <strong>de</strong>termine theminimum areas <strong>of</strong> refugium for those species. It mustalso be recognised that the requirements <strong>of</strong> certainspecies may also inelu<strong>de</strong> adjacent (o~ nearby) habitats,thus further complicating the application <strong>of</strong> the refugiaconcept to birds on bog habitats.Examination <strong>of</strong> notification documentation for Sites <strong>of</strong>Special Scientific Interest containing raised bog 1 , hasfound records <strong>of</strong> six taxa which have only beenrecor<strong>de</strong>d from sites greater than 100 ha. These inelu<strong>de</strong>five very rare breeding species on raised bogs (merlin,hen harrier, Montagu's harrier, dunlin, gol<strong>de</strong>n plover)and one wintering subspecies (Greenland white-frontedI Many <strong>of</strong> these inelu<strong>de</strong> habitat other than raised bogo or <strong>de</strong>rivedhabitats, which represents a significant limitation <strong>of</strong>the data source.goose). These species have only occasionally nested onraised bogs in the British Isles over the last hundredyears, and several may now be extinct on this habitat.Breeding teal, black-hea<strong>de</strong>d gull, short-eared owl,grasshopper warbler and reed bunting, and winteringmerlin and hen harrier seem to be associated with sites<strong>of</strong> between 50-) 00 ha in Britain. Black grouse andtwite have only rarely bred on raised bogs <strong>of</strong> this size.Birds also found on smal\er raised-bog sites in Britain«50 ha) inclu<strong>de</strong> breeding mallard, red grouse, curlew,snipe, redshank, nightjar, cuckoo, meadow pipit,whinchat and skylark, plus wintering short-eared owl.Shape <strong>of</strong> remnantsThe shape <strong>of</strong> a habitat remnant has been consi<strong>de</strong>red tobe important in the minimisation <strong>of</strong> edge effects [seeGlossary] and it has been suggested that circular sites,with the smallest edge : area ratio, are most suitable asreserves for species conservation, minimising the risk<strong>of</strong> invasion by uncharacteristic species and input <strong>of</strong>agro-chemicals etc. which may lead to eutrophication,mineral-enrichment etc. The effect <strong>of</strong> shape may beobscured by other uni<strong>de</strong>ntified sources <strong>of</strong> variation.Although shape itself is probably not <strong>of</strong> major concemin the general preservation <strong>of</strong> nature reserves, forraised-bog remnants the importance <strong>of</strong> shape is morelikely to relate to the preservation <strong>of</strong> a favourable waterbalance, than preservation <strong>of</strong> species per se - a bogremnant <strong>of</strong> 'simple' plan shape is likely to be easier torestore hydrologically than one with a complex marginoThe provision <strong>of</strong> buffer zones to reduce edge effects isperceived to be one practical solution to the protection<strong>of</strong> particularly susceptible sites [8.3].2.3 Peat extraction methods andhabitat conditions2.3.1 Peat extraction and residualtopographyThe surface configuration <strong>of</strong> the cut-over areasremaining after peat extraction has stopped <strong>de</strong>pendslargely on the method and duration <strong>of</strong> the peatextraction and the extent <strong>of</strong> drainage, both throughdirect alterations in topography and indirect effectssuch as slumping <strong>of</strong> the peat.There are three main methods <strong>of</strong> peat extraction in theUK: block cutting (by hand or commercial\y), surfacemilling and extrusion. Local\y other methods are used,for example open-cast harvesting and wet mining.Certain procedures are common to most <strong>of</strong> theseoperations: drainage; removal <strong>of</strong> surface vegetation;drying <strong>of</strong>the excavated peat on the surface to achieve asuitable moisture content (typically c. 50%); provision


38RESTORAnON OF DAMAGED PEATLANDS<strong>of</strong> trackways for acce s, passage <strong>of</strong> vehicles, trains etc.Main baulks are <strong>of</strong>ten left at intervals for passage <strong>of</strong>machinery, or, in the larger operations, upon which alight railway can be laid, to remove the peat either tocollection points or directly to the peat works [see Plate2.9]. This infrastructure can be useful in restorationafter peat extraction both in providing a means <strong>of</strong>transporting equipment and materials acros a site, andalso acting as bunds l to retain water in the peatworkings 2 .The main extraction techniques are <strong>de</strong>scribed below, inrelation to the conditions remaining on the site whenthe extraction ceases.Block cuttingBlocks <strong>of</strong> peat are cut out from a vertical face andstacked on baulks alongsi<strong>de</strong> to dry. Drying <strong>of</strong> the peatis thus more <strong>de</strong>pen<strong>de</strong>nt on winter c1imatic conditionsthan is the case for milled peat production.Block cutting can create a range <strong>of</strong> surfacetopographies, <strong>de</strong>pen<strong>de</strong>nt upon the exact proceduresused. The method <strong>of</strong>ten produces a regular system <strong>of</strong>baulks, flats and trenches which are usually dry, dampand wet (respectively) when cutting ceases. However,when carried to its conclusion it can also produce avery extensive, largely flat surface. In sornecircumstances, following block cutting, other methodsmay be used to extract the lower peats. Trenchessometimes retain water and may even support a usuallylimited flora, <strong>of</strong>, for example, a few Sphagnum species.The character <strong>of</strong> the surface is important in consi<strong>de</strong>ringrestoration options. It may <strong>of</strong>ten be possible to useexisting baulks and tramways to increase waterretention; in other cases, as where there are numerousnarrow ridges, it may be <strong>de</strong>sirable to level the surfacesand fill in sorne <strong>of</strong> the trenches by bulldozing thebaulks into them.Traditional hand cuttingWhen carried out on a small scale, the results <strong>of</strong> peatcutting by hand can be a fairly haphazard disposition <strong>of</strong>the surface topography [Plate 2.6]. However,'organised' (± commercial) hand cutting could be asextensive as machine block-cutting, sometimes leavinglarge areas <strong>de</strong>nu<strong>de</strong>d <strong>of</strong> peat and vegetation and with asimilar regular topography <strong>of</strong>baulks and cuttings [as inPlate 2.7]. In sorne cases however, hand cutting mayproduce a relatively level area, as, for example at CorsI The term 'bund' is used here to mean an embankment used topond back water over a large area. By contrast, use <strong>of</strong> the term damhas been restricted to refer to structures built to block linear watercourses [see Chapter 8].2 The efficacy <strong>of</strong> the baulks as bunds will <strong>de</strong>pend on their size,intactness and <strong>de</strong>gree <strong>of</strong><strong>de</strong>hydration <strong>of</strong>the peal.Plate 2.6 Small-scale hand peat cutting at GlassonMoss (Cumbria) (top; centre) and Montiaghs Moss(Antrim) (bottom).


CHAPTER 2: HARACfERlSTIC OF CUT-OVER BOGS 39Plate 2.7 Left: Block cutting at Solway Moss, Cumbria [Photo: A. Lynn] Right: Block-cut peat fields in theSomerset Levels. [See also Plates 4.1, 5.3, 5.4, 5.5]Caron (Dyfed) where the peat was stripped to thelowest water level attainable by drainage.One <strong>of</strong> the rnain 'advantages' <strong>of</strong> hand cutting (forsubsequent restoration) is that the surface vegetationwas sometimes thrown back into the trenches, and mayprovi<strong>de</strong> inoculurn for revegetation. The slow speed <strong>of</strong>extraction also allows the bog species (plants andinvertebrates) in the trenches to become establishedbetween successive cuts. This 'shoeing' is probably <strong>of</strong>great importance in <strong>de</strong>termining the course and time <strong>of</strong>recolonisation [Chapter 4]. Revegetation <strong>of</strong> such areas<strong>de</strong>pends critically on the hydrological regime that hasbeen maintained after the cessation <strong>of</strong> operations.Where the cuttings have been kept sufficiently wet,they have <strong>of</strong>ten <strong>de</strong>veloped sorne 'good' examples oL.bog vegetation.Machine block-cuttingMachine block cutting is essentially a rnechanisedversion <strong>of</strong> the traditional hand cutting method, but canbe carried out on a larger scale with greater speed an<strong>de</strong>ach cut is usually <strong>de</strong>eper [Plate 2.7]. The ground isusually prepared by drainage (both open drains and slitor mole drains), rernoval <strong>of</strong> trees and scrub andlevelling <strong>of</strong> the surface. The 'topsoil' is removed fromthe area to be cut, and either spread alongsi<strong>de</strong> orpushed into the trenches. Cuts are typically e. 50' apart,3' <strong>de</strong>epi x 2'4" wi<strong>de</strong> (c. 15 x 1 x 0.7 rn). The peat is cutinto blocks, and stacked alongsi<strong>de</strong> the trenches. Thepeat rnay take up to 9-12 rnonths to dry sufficiently forcollection and use. A complete cut can take 5-7 years,which can sornetimes allow sorne recolonisation bybog species in the trenches if the water table is not toolow. Sorne species may also survive on (or recolonise)the baulks, but in many cases they may be too dry, orcovered by drying peat blocks, to support more than afew ru<strong>de</strong>ral, non-wetland species.The presence <strong>of</strong> the slit drains has proved a particularproblern for rewetting block-cut areas at Glasson andWedholme Mosses (Curnbria) because they can bedifficult to locate and block. Practical problems forrewetting may also be created where cuttings exist atsubstantially different levels, or wheré there is a bigheight difference between the top <strong>of</strong> baulks and thefloor <strong>of</strong> cuttings.Milling (or rotavation)Milled peat production involves scraping or vacuuming<strong>of</strong>f a thin layer <strong>of</strong>peat (15-50 mm) from the surface <strong>of</strong>bare peat fields. The surface <strong>of</strong> the moss is firstprepared for peat extraction by drainage at e. 15-20 mintervals and stripping <strong>of</strong>f the surface vegetation with ascrew leveller sorne 5-10 years before extraction canbegin 2 . This reduces the water content <strong>of</strong> the peat andincreases the load-bearing capacity to facilitate harvestby machinery. The vegetation may be removed, or ispushed into the middle <strong>of</strong> the extraction fields andcornpressed by peat-extraction machinery. It graduallyrots and can be further worked to provi<strong>de</strong> a camber tothe bed to irnprove the surface drainage. In bogscontaining a high proportion <strong>of</strong> highly humified peats,surface run<strong>of</strong>f to drainage ditches may account for arelatively high proportion <strong>of</strong> the rainfall input; inweakly-humified peat, rainfall is largely absorbed bythe peat and little free drainage occurs.After the initial reduction in water content by <strong>de</strong>epdrains, a system <strong>of</strong> un<strong>de</strong>r-drainage by mole drains maybe installed [Plate 2.8]. Drainage reduces the waterI The effective <strong>de</strong>pth <strong>of</strong> each cut is usually less than 3' as there issorne wastage.2 The time taken will <strong>de</strong>pend on the permeability <strong>of</strong> the peal, thehydraulic gradient and the recharge.


40RESTORAnON OF DAMAGED PEATLANDScontent to c. 85-90%, and this is further reduced to c.55-65% by the milling and harrowing operations priorto collection <strong>of</strong> the peat. In general, the harvestingcycle takes about three days, but this <strong>de</strong>pends on dryweather to air-dry the peat. Sorne 8-12 harvests may betaken each season.The milled surfaces remaining after peat extractionceases are bare and dry, and usually cover large areas[PIate 2.9]. The remaining peat is likely to becompressed, partly as a result <strong>of</strong> drainage, but als<strong>of</strong>rom the repeated passage <strong>of</strong> the harvesting machinery.These bare surfaces are prone to invasion by 'weed'species unless rewetting procedures are adopted.Milled fields are generally much less well suited to thespontaneous re-establishment <strong>of</strong> bog species than aresorne block-cut areas as they usually do not have closedhollows which naturally accumulate water as is thecase with sorne traditiona block-cutting complexes.They may also have various other features which mayinfluence the <strong>de</strong>velopment <strong>of</strong> restoration strategies. Forexample, large areas must be worked simultaneously tobe economic (e.g. for efficient use <strong>of</strong> personnel an<strong>de</strong>quipment when climatic conditions are suitable forharvesting) such that an integrated, phased program <strong>of</strong>extraction followed by restoration may be difficult toachieve [6.5].Extrusion ('Sausage') peat productionThis technique is mostly used for production <strong>of</strong> fuelpeat, and is used on both raised and blanket bogs. It isused both on a small scale, for example by cr<strong>of</strong>ters inScotland and lreland, and commercially. The rotatingbla<strong>de</strong> <strong>of</strong> the cutter extracts peat from up to about 1 mbelow the surface, before extruding it as 'sausages'through nozzles onto the ground to dry [Plate 2.10].Thus there is a minimum <strong>de</strong>pth <strong>of</strong> peat that can beworked, although when this is reached, it would bepossible to continue extraction by surface milling.As for all methods, the peat <strong>de</strong>posit must be drainedprior to extraction. The fields are also cambered toincrease surface run-<strong>of</strong>f and avoid puddles etc.Intensive drainage is not always consi<strong>de</strong>red necessaryas increased energy would be nee<strong>de</strong>d to extru<strong>de</strong> thepeat if it was too dry.Plate 2.8 Mole drains in milled peat field.Plate 2.9 Milled-peat fields, with temporary rail-trackfor removal <strong>of</strong> peat stockpiles; 80lton Fell (Cumbria).[See also cover photograph <strong>of</strong> milling at Thorne Waste]Plate 2.10 Peat extracted by the extrusion method;Montiaghs Moss (Antrim).


CHAPTER 2: CHARACfERISTICS OF CUT-OVER Boes41The surface vegetation is sometimes removed t<strong>of</strong>acilitate collection <strong>of</strong> the peat 'sausages' by machinerather than by hand. In this case, the residual surface issimilar to that left by milling. However, the method <strong>of</strong>extraction means that there are usually more subsurfacedrainage channels, (although the sJots areusually cut at an angle to encourage cJosure). Evenwhere the vegetation is not removed, consi<strong>de</strong>rabledamage to the plants and microtopography still occurs,mainly through cutting <strong>of</strong> the roots and fibrous 1ayer,compaction due to the passage <strong>of</strong> machinery andpersonnel and <strong>de</strong>position <strong>of</strong> peat on the surface(Bayfield el al., 1991; Meharg, Montgomery &McFerran, 1992; I Miller, pers. comm.). Bayfield el al.(1991) consi<strong>de</strong>r in <strong>de</strong>tail the impacts <strong>of</strong> extrusioncutting on the vegetation <strong>of</strong> and run<strong>of</strong>f from blanketpeats.Other production methodsPeat may be won by methods other than those<strong>de</strong>scribed aboye. For example, fuel peat is sometimesextracted from <strong>de</strong>ep trenches, whereby the s<strong>of</strong>t peat isextru<strong>de</strong>d onto a conveyor belt and then cut into blocksbefore being laid on the ground to dry. This leaves<strong>de</strong>ep, wet trenches and may sometimes create 'islands'<strong>of</strong> peat [Plate 2. 11], both <strong>of</strong> which may provi<strong>de</strong> asuitable habitat for recolonisation, particularly ifsurface vegetation were to be returned directly,although further examination <strong>of</strong> such sites is required.In Somerset, smaJl-scale peat extraction is <strong>of</strong>ten carriedout by rotavating the peat and forming into ridges todry [Plate 2.12] before removal to stockpiles.Plate 2.11 Large-scale extraction <strong>of</strong> 'fuel-peat' (top),leaves trenches and 'islands'; Solway Moss (Cumbria).Plate 2.12 Peat extraction by the rotavating andridging method (Somerset Levels).2.3.2 The hydralagical enviranment afcut-aYer bags<strong>Peatlands</strong> have to be drained for efficient peatextraction. The <strong>de</strong>gree to which sites are drained<strong>de</strong>pends upon individual site characteristics and thepeat extraction technique used. Drainage is primarilynee<strong>de</strong>d for permitting access by machinery but it is alsoa prerequisite for some drying <strong>of</strong> the peat, espeeiaJly insurfaee milled sites. However, it is not the aim <strong>of</strong>drainage to remove as much water as possible, as toomuch drainage would allow the lower layers <strong>of</strong> peat tooxidise and waste. The drains are therefore <strong>de</strong>epened asneeessary, usually annu By.Few data are available on the hydrology <strong>of</strong> raised bogsduring peat extraetion, but it is evi<strong>de</strong>nt, for example,that whilst removal <strong>of</strong> vegetation may reduce waterlosses by evapotranspiration, the <strong>de</strong>nse network <strong>of</strong>drains (whieh may be linked to a pumping system)ensures that the rate <strong>of</strong> water loss through run<strong>of</strong>f willbe higher than that <strong>of</strong> undrained bogs. In cut-over bogsit must be aeeepted that drainage wiU cause alterationsto some <strong>of</strong> the eharaeteristies <strong>of</strong> the original bog, forexample, changes to sorne <strong>of</strong> the hydrophysiealattributes, such as water storage eapacity and peatpermeability, sorne <strong>of</strong>whieh may be irreversible [2.2].The water level that <strong>de</strong>velops, spontaneously or byengineering, within an abandoned extraetion complex


42RESTORATlON OF DAMAGEO PEATLANOSis <strong>of</strong> crucial importance to the subsequent revegetation.In large measure, it will be a product <strong>of</strong> the topography<strong>of</strong> the abandoned peat workings (see aboye), c1imateand functioning <strong>of</strong>the drainage system. The water table<strong>of</strong> cut-over bogs is <strong>of</strong>ien characterised by a greater<strong>de</strong>gree <strong>of</strong> fluctuation than that found in intact systems(Mea<strong>de</strong>, 1992; Money, 1994, 1995). This may partly bea reflection <strong>of</strong> the existence <strong>of</strong> drains, but also becausethe exposed peat surface lacks the hydro-regulatoryproperties <strong>of</strong> an intact bog surface [1.7]. Hence, cutoversurfaces may be very wet, or floo<strong>de</strong>d during thewinter, but dry and dusty during the summer.Water storage characteristics <strong>of</strong> residual peatsThe lower peats that are lefi following peat extractionmay differ in various properties from the peats aboyethem, either in consequence <strong>of</strong> changes induced bydrainage (Hobbs, 1986) or because <strong>of</strong> their intrinsiccharacter [1.8]. This may influence their suitability forrestoration. It is wi<strong>de</strong>ly consi<strong>de</strong>red that variation incapacity for water storage may be important in thisrespecl. Even <strong>de</strong>ep catotelm peat may have high totalporosity (Reynolds el al., 1992), but the ratio <strong>of</strong>macropores (> 50 ¡.tm) to micropores is thought to be<strong>of</strong> more importance to water storage capacity(Schouwenaars, 1982; Blankenburg & Kuntze, 1986);the structure <strong>of</strong> strongly-humified peat gives it a higherratio <strong>of</strong>small to large pores than weakly-humified peat,and thus although the former may in fact lose lesswater than the latter on drainage, it contains a Iowerpercentage <strong>of</strong> 'free' water (the loose Sphagnum peat <strong>of</strong>a typical bog acrotelm can contain sorne 85% <strong>of</strong> 'free'water compared with only sorne 8% in stronglyhumifiedpeat (Streefkerk & Casparie, 1989)). Thisleads to higher water table fluctuations, as for the sameamount <strong>of</strong> water lost lhrough evapotranspiration, thewater table will fall further in a strongly-humified peatthan a weakly-humified peat (Schouwenaars & Vink,1992).Although there is a c1ear difference between the waterstorage coefficients <strong>of</strong> the acrotelm and the catotelmpeats, trends are less readily apparent within thecatotelm peal. Porosity and bulk <strong>de</strong>nsity t:!1ay vary bothwithin and between peat types and the broad categories<strong>of</strong> 'Iight' and 'dark' peat do not necessarily havedifferent water storage coefficients (Streefkerk &Casparie, 1989; Schouwenaars & Vink, 1992).Peat thickness and vertical water lossThe perched water table in a raised bog ís <strong>of</strong>ienregar<strong>de</strong>d as being in<strong>de</strong>pen<strong>de</strong>nt <strong>of</strong> the behaviour <strong>of</strong>groundwater in the fen peat or subsoil aquifers belowit. In<strong>de</strong>ed, the 'groundwater mound' hypothesis [1.7]effectively assumes an impermeable base to the watermound. These conditions may well be satisfied in manyUK raised bogs. Nonetheless, it is clear that theperched water mound may, in sorne situations, showconnectivity to un<strong>de</strong>rlying ground-water tables, whichmay even make a positive contribution to its waterbalance. This situatíon occurs in The Netherlands andNW Germany where the bogs overlie fluvio-glacialsands and where, due to falling regional water tables,there is now thought to be an unsaturated layer in themineral ground beneath the base <strong>of</strong>the peat (Joosten &Bakker, 1987; Blankenburg & Kuntze, 1987;Schouwenaars, 1992, 1993). It is not known to whatextent this situation exists in the UK, although it hasbeen suggested that this could be the case at Thomeand Hatfield Moors - work is in progress to investigatethis. Even where sites seem to overlie an impermeablesubstratum (e.g. clay) the possibility that there may bepermeable windows within these cannot be discounted.The importance <strong>of</strong> residual peat thickness to rewettingand revegetation prospects is discussed in section 4.3.5.2.3.3 The chemical enviranment afcut-aver bagsThe ombrotrophic waters <strong>of</strong> raised bogs arecharacterised by hydrogen (H+) as the principie cationwith sulphate (SO/") as the main anion (Sjors, 1950).Nutrients such as N, P and K are usually in shortsupply (Waughman, 1980). A bog surface is typically<strong>of</strong> low fertility and supports low rates <strong>of</strong> primaryproduction. The chemical characteristics <strong>of</strong> raised-bogwaters vary temporally and spatially. Typical valuesare summarised in Table 2.1. A major control on thepattern <strong>of</strong> variation is rainfall quantity and quality,itself controlled by factors such as proximity to the seaand <strong>de</strong>gree <strong>of</strong> atmospheric pollution. Coastal raisedbogs are generally richer in solutes (see for example,Boatman el al., 1975; Sparling, 1967) and the chemicalenvironment may approach that <strong>of</strong> weaklyminerotrophic fens (Wheeler, 1988; Shaw & Wheeler,1991 ).There has been ¡ittle <strong>de</strong>tailed work on the effect <strong>of</strong> peatextraction on the chemical environment <strong>of</strong> raised bogs,but there is sorne empirical evi<strong>de</strong>nce to point to sorne<strong>de</strong>gree <strong>of</strong> chemical enrichment (e.g. Clausen & Brooks,1980). This may be as a result <strong>of</strong>:J. chemical changes caused by drainage (e.g. acidificationand mineralisation + nutrient release from the aeratedpeat layers);ii. exposure <strong>of</strong> the un<strong>de</strong>rlying fen peat or mineral sub-soil;iii. nutrient run<strong>of</strong>ffrom the surrounding catchment. .Few chemical data exist for peat extraction complexesin the UK, but a number <strong>of</strong> samples have been takenfrom parts <strong>of</strong> Thome Waste (Smart, Wheeler & Willis,1989; Money, 1994) and from Danes Moss, Cheshire(Mea<strong>de</strong>, 1992). In general the concentration <strong>of</strong> mostions is higher in the samples from peat extraction sites


CJlAPTER 2: CJlARACTEIUSTICS OF CUT-OVER BOGS43than in little-disturbed sites, and in some casesresembles the chemical characteristics <strong>of</strong> poor fenrather than ombrotrophic bog (Tallis, 1973) (Table2.1). It is not always evi<strong>de</strong>nt why such chem icaldifferences occur: for example, the high concentrations<strong>of</strong> NH 4 recor<strong>de</strong>d from the milling fields at ThorneWaste, in comparison with vegetated cuttings, may bebecause it is released in consequence <strong>of</strong> peat operationsor because it is <strong>de</strong>rived from other sources (e.g.atmospheric inputs) but lack <strong>of</strong> vegetation cover meansthat it is not assimilated by plants. At theseconcentrations <strong>of</strong> NH 4 some <strong>de</strong>gree <strong>of</strong> toxicity toSphagnum magellanicum (Rudolph & Voight, 1986)and S. cuspidalum (Press el al, 1986) may occur,though evi<strong>de</strong>nce <strong>of</strong> the response <strong>of</strong> Sphagnllln speciesto N enrichment is inconsistent.MineralisationMineralisation <strong>of</strong> drying peat [2.2] may contribute torelease <strong>of</strong> solutes and increase availability <strong>of</strong> pIantnutrients (Gorham, 1956; Braekke, 1981). It has beensuggested that in block-cut sites mineralisation maylead to some movement <strong>of</strong> nutrients from the drier peatin the baulks into the wet cuttings (Smart el al, 1986;Beckelman & Burghardt, 1990; Nilsson, Famous &Spencer, 1990), but this needs further evi<strong>de</strong>nce to besubstantiated. The amount <strong>of</strong> recolonist vegetationpresent able to take up the released nutrients is al solikely to affect the measured concentrations.Peat mineralisation and oxidation may producechanges in the chemical environment which couldconceivably affect the growth <strong>of</strong> Sphagnum and othervascular plants. For example, extremely low pH values« 3.0) may be <strong>de</strong>trimental to the growth <strong>of</strong> some bogspecies, including some species <strong>of</strong> Sphagnlll11 (Austin& Wie<strong>de</strong>r, 1987; Richards el al. 1995; Money, 1,994).Very high concentrations <strong>of</strong> nitrogen may be damagingto some SphagnulII species (Press el al., 1986;Twenhoven, 1992), though evi<strong>de</strong>nce for this is notc1ear-cut (Rudolf & Voight, 1986; Baker & Boatman,1990; Aerts el al., 1992), nor is the likely effects <strong>of</strong>very high concentrations <strong>of</strong> sot (Ferguson el al.,1978; Ferguson & Lee, 1982-3; Austin & Wie<strong>de</strong>r,1987; Rochefort, Vitt & Bayley, 1990). The significance<strong>of</strong> this to restoration is not known, though asrecolonisation by bog species has occurred innumerous cut-over situations it seems unlikely topresent an insuperable, or universal, problem,especially when cuttings have been effectivelyrewetted. Moreover, mo<strong>de</strong>st enrichment <strong>of</strong> someelements (e.g. phosphorus) may enhance the growth <strong>of</strong>some bog species including some Sphagna (Baker &Boatman, 1992; Money, 1994, 1995).Exposure <strong>of</strong> fen peat or un<strong>de</strong>rlying mineralgroundThe domes <strong>of</strong> ombrotrophic peat which form raisedbog have <strong>of</strong>ten <strong>de</strong>veloped over fen peat, which usuallyhas greater base-richness than the former. This isreadily shown in chemical pr<strong>of</strong>iles. For example,samples from Striber's Moss (Roudsea Mosses,Cumbria; Gorham, 1949) showed the trend <strong>of</strong>increasing pH (and conductivity) with <strong>de</strong>pth, from thesurface Sphagnllm peat (pH 3.8) through to fen peat(pH 4.8) and basal c1ay (pH 6.1). Thus where peatextraction has exposed fen peat, the chemicalenvironment is likely to be more conducive to theestablishment <strong>of</strong> fen rather than bog vegetation (White,1930; Poschlod, 1989, 1992). Even where fen peat isnot directly exposed, a shallow layer <strong>of</strong> residual peatmay be penetrated by some fen plants rooting in theun<strong>de</strong>rlying mineral ground. As well as modifying thetloristic composition <strong>of</strong> the revegetating cut-over, suchplants may conceivably serve as chemical pumps,Table 2.1 Some chemical conditions in waters sampled from little-disturbed bogs compared with peat extractionsites. [Concentrations are mg ¡-1; blank cells indicate no data; nd = not <strong>de</strong>tected].Natural bog waters(UK & Ireland)*Danes Moss,(Cheshire)vegetated block-cuttings(Mea<strong>de</strong>, 1992)Thorne Waste,(S. Yorks.)vegetated block-cuttings(Smart et al., 1989)Thorne Waste,(S. Yorks.)milled-peat field(Money, 1994)pHCaMgKNaFeS04N03NH4SRP**3.2 -4.50.2 -3.00.1 - 2.50.04 -2.02.3 - 23.0< 1.02.4 -18.00.1 - 0.3nd I 0.053.0 - 3.73.2 - 11.41.7-2.90.5 -0.818.6 - 32.91.3 - 2.20.4 - 0.70.0 - 0.33.8 - > 5.03.8 -6.21.8 - 4.50.6 - 2.14.6-6.36.2 -13.80.04 - 0.200.0 - 0.30.0 - 0.083.2 - 3.65.1 -18.22.1 - 6.60.6-2.230.0 -42.01.8 - 6.29.2 - 29.00.0 - 0.06* Sources: Clausen & Brooks (1980); Proctor (1992); Bellamy & Bellamy (1966). ** Soluble reactive phosphorus


44RE TORATION OF DAMAGED PEATLADSenriching the ombrotrophic surface with nutrients from<strong>de</strong>eper layers.Exposure <strong>of</strong> un<strong>de</strong>rlying mineral material may also leadto base-enrichment, but this effect will much <strong>de</strong>pend onthe chemical characteristics <strong>of</strong> the sub-soil. In sornesites (e.g. parts <strong>of</strong> Thome and Hatfield Moors),un<strong>de</strong>rIying sands and gravels are themselves <strong>of</strong> low pHand base status (pH 3 - 4) (B.D. Wheeler, unpublisheddata). There have also been reports <strong>of</strong> low pH valuesassociated with sorne basal clays.Where the exposed substrata are very base rich (forexample, exposure <strong>of</strong> marl at Turraun Bog, Ireland)[Plate 2.13], rich-fen vegetation is likely to re<strong>de</strong>velop.Most typical raised-bog species do not occur in suchsituations and re<strong>de</strong>velopment <strong>of</strong> raised bog will <strong>de</strong>pendon a slow build-up <strong>of</strong> peat and acidification (e.g. GiUer& Wheeler, 1988). By contrast, most bog species cangrow in base-poor fen conditions, though they willnonnally be accompanied by a range <strong>of</strong> poor-fen plantspecies.Run<strong>of</strong>f from the surrounding catchmentIn areas where peat has been extracted to below thelevel <strong>of</strong> the regional ground water table or to a positionwhere the surface may receive run-<strong>of</strong>f from thesurrounding catchment, there is a possibility thatgroundwater may be able to run onto sorne or all <strong>of</strong>thesite, and cause nutrient or base enrichment (Pigott &Pigott, 1959; Mea<strong>de</strong>, 1992). The potential for a generalingress <strong>of</strong> groundwater will <strong>de</strong>pend on the topography<strong>of</strong> the site. It may be particularly likely to occur in sitesin basins; where areas <strong>of</strong> fen, which buffered the raisedbog against ingress <strong>of</strong> groundwater have been<strong>de</strong>stroyed; or where ditches draining adjoining landhave been <strong>de</strong>liberately introduced into the bogoExamples <strong>of</strong> the latter inelu<strong>de</strong> Dane Moss (Cheshire),Plate 2.13 White marl <strong>de</strong>posit un<strong>de</strong>rlying peat.exposed in a drainage channel through cut-over bog;Turraun 80g (Offaly, Ireland).Brackagh Bog (Co. Down), Fenns &(Shropshire / Clywd).Whixall MossWhere enrichment from the surrounding eatchment isseen as a particular problem, it will be necessary totake this into account in <strong>de</strong>velopment <strong>of</strong> an appropriaterestoration strategy, as it may severely limit thepotential options for after-use, if remedial action is notfeasible.2.3.4 The physical environment <strong>of</strong>cutoverbogsPeat extraction leaves abare peat surface, which isusually dry, at least in summer. Bare peat is also proneto erosion by wind or water, particularIy where sloping,and if dark, is Jikely to absorb heat; increased temperaturewill exacerbate moisture loss. The surfaee maybe physically unstable and show consi<strong>de</strong>rable temperaturetluctuations (Tallis & Yal<strong>de</strong>n, 1983; Heikurainen& Sepplilli, 1963; Salonen, 1992) and thus provi<strong>de</strong> aninhospitable environment for establishment <strong>of</strong> plantpropagules and animal colonists. [see also 4.4.2]2.3.5 The vegetation <strong>of</strong>cut-over bogsThe vegetation <strong>of</strong> remnant peat surfaees and <strong>of</strong>abandoned peat workings can be extremely variable,<strong>de</strong>pending upon sueh constraints as <strong>de</strong>gree <strong>of</strong> damage,<strong>de</strong>pth <strong>of</strong> extraction, topography, base status, nutrientstatus, water level (and souree) and length <strong>of</strong>time sincelast worked. Money (1994) has surveyed the vegetation<strong>of</strong> peat cuttings in a range <strong>of</strong> British bogs - all <strong>of</strong> thevegetation-types recor<strong>de</strong>d from uncut bog surfaeeshave also been reeor<strong>de</strong>d from cut-over areas (althoughusually in fragmentary fonn); euttings may alsosupport various additional community-types, mostnotably where they have exposed fen peat [Box 2.1].Similarly, most <strong>of</strong> the speeies characteristie <strong>of</strong> raisedbogvegetation on uncut surfaces have also beenrecor<strong>de</strong>d from cut-over areas [Appendix 4].A few bog specie are sometimes mo e abundant inrevegetated peat cuttings than they are on uneutsurfaces (e.g. Rhynchospora alba). Moreover, innumerous raised-bog sites, revegetated cuttings provi<strong>de</strong>the main reservoir for sorne bog speeies, as the uneutsurfaces are too dry to support any but the moretolerant bog taxa [PIate 2.14 and 2.15]. There is abroad relationship between the eommonness <strong>of</strong> specieson uncut surfaces <strong>of</strong> British raised bogs and theiroccurrenee within peat cuttings. TIle rarer bog speciesare rare also in peat cuttings or have not been recor<strong>de</strong>dat all from them. Some species (e.g. Sphagnumimbricatum and S. fuscum) whieh have not beenrecor<strong>de</strong>d from peat cuttings in Britain have been foundin peat cuttings elsewhere (van Wirdum, pers. comm.).


CHAPTER 2: HARACrERJ TI OF T-OVER BOGS45Jt can be conclu<strong>de</strong>d that peat cuttings are notintrinsically unsuitable for the growth <strong>of</strong> most, or all, <strong>of</strong>typical bog species (including rare specie ). However,many <strong>of</strong> the cuttings that support a rich variety <strong>of</strong>typical bog species are relatively small scale, domesticexcavations (sorne are old commercial excavations, asat Thome Waste). This is not least because suchworkings are lhe only ones that have been abandoned(and kept wet) for sufficiently long for 'good'revegetation to have occurred, but at sorne sites thismay also relate to a former greater availability <strong>of</strong>propagules.The main factors influencing the natural, spontaneousrevegetation <strong>of</strong> cut-over bogs are discussed further inChapter 4.Plate 2.14 Eriophorum angustifo/ium growing inexcavated peat pit, surroun<strong>de</strong>d by Molinia-dominatedvegetation on drained bog surface; Astley Moss(Lancashire). [see also Plate 2.5]2.3.6 The fauna <strong>of</strong>cut-over bogsPeat extraction creates disturbance and <strong>de</strong>stroys theimmediate habitat for animals, removing importantstructural features as well as food sources so that thecapacity <strong>of</strong> much <strong>of</strong> the bog fauna to survive peatoperations will <strong>de</strong>pend upon the availability <strong>of</strong>proximate little-disturbed habitats, or <strong>of</strong> abandonedworkings that are suitable for recolonisation. Largescalecommercial peat extraction inevitably reduces theopportunities for such survival compared to smallerhand-digging operations.Once revegetated, bogs that have been subjected tohand-cutting or similar peat-removal regimes, <strong>of</strong>ien<strong>of</strong>fer a wi<strong>de</strong>r range <strong>of</strong> habitats for birds andinvertebrates than do undamaged raised bogs and maysupport a wi<strong>de</strong>r range <strong>of</strong> species, or at least, a changein relative abundances (e.g. Ball, 1992; Andreessen,1993). Such an increase in habitat and species diversitydue to disturbance does nol necessarily increase theperceived conservational 'value' <strong>of</strong> such sites over thenaturalness <strong>of</strong> an undamaged bog, particularly wheregeneralist species replace specialists. However, sorne<strong>of</strong> the species that are prevalenl on damaged bogs arethemselves uncommon.Plate 2.15 Wet hand-peat cutting colonised by suchspecies as Sphagnum cuspidatum, S. papilllosum,Eriophorum angustifolium and Narlhecium ossifragum,surroun<strong>de</strong>d by Calluna-dominated vegetation on drycut-over bog surface; Killaun 80g (Ireland).Invertebratesome abandoned peat workings are rich in invertebratespecies. A number <strong>of</strong> 'conservationally-<strong>de</strong>sirable' taxaseem to have either a preference or requirement for therange <strong>of</strong> micro-habitat conditions that are created bycertain peat-cutting regimes (Le. limited hand cutting)and such species may be scarce or absent inundamaged bogs, although such conditions may beprovi<strong>de</strong>d locally (Kirby, 1992a). An example <strong>of</strong> suchan insect is the caddisfly Hagenella c/a[hra[a (Wallace,199 1). For many species that are cited as being <strong>of</strong> greatconservation interest in 10wland raised bogs, it is themix <strong>of</strong> microhabitats present in areas that haverevegetated over a period <strong>of</strong> time following traditionalhand-cutting that seem to be important in theircontinued survival. Thus, for example both the RDB l


46RESTORATlON OF OAMAGEO PEATLA osBox 2.1 Main vegetation·types occurring in cut-over bogs in the Uníted Kíngdom [nomenelature fol/ows theNational Vegetation Classifieatíon (Rodwell, 1991; in prep.) - see also Table 1.4].The vegetation <strong>of</strong> cut-over bogs is extremely variable, <strong>de</strong>pending upon such constraints as <strong>de</strong>pth <strong>of</strong> extraction,topography, nutrient status, water level and age (i.e. length <strong>of</strong> time since last worked). In sorne examples, cuttingshave recolonised to produce clearly i<strong>de</strong>ntifiable examples <strong>of</strong> specific NVC community-types [see Table 1.4] (whichin sorne cases may be absent from the rest <strong>of</strong> the site), although these may not have <strong>de</strong>veloped the full associatedtypical microtopographical structure <strong>of</strong> hummocks and hollows. In other cases, the vegetation may be an atypicalspecies mix, either because <strong>of</strong> sorne extraneous influence (e.g. nutrient input), extreme environmentalheterogeneity within the cuttings or the vagaries <strong>of</strong> the recolonisation process. In the lalter case it is possible thatthe vegetation may <strong>de</strong>velop towards a recognisable NVC community-type in time.(1) 'Bag-Sphagnum' vegetatían: Sphagnum-based vegetalion sueh as is eharaeteristie <strong>of</strong> liltle-damaged raisedbogs in lhe UK (M18) and bog pool communilies (M2, M3) occur wilhin peat workings, lhough they vary in the<strong>de</strong>gree to which they conform to NVC vegetation-types. Examples have been noted at Bankhead Moss (Fife), CorsCaron and Cors Fochno (Oyfed), Glasson Moss (Cumbria), Moss <strong>of</strong> Aehnaeree (Argyll), Thorne & Crowle Moors (S.Yorks. lUnes.). In sorne sites, such communities are better <strong>de</strong>veloped in peat cuttings than on the 'intact' peal.(ii) 'Para-bog-Sphagnum' vegetatíon: Many peat workings support examples <strong>of</strong> this vegetation category, whichinclu<strong>de</strong>s surfaces that may support a wi<strong>de</strong> varjety <strong>of</strong> typieal bog species, though no!' in the same proportions, orwith the same vegetation strueture, as is charaeteristie <strong>of</strong> bog-Sphagnum vegetation. Typieal dominants areCal/una vulgaris, Eriea tetralíx, Eriophorum vaginatum and, sometimes, Molinia eaerulea. Sorne examples are referableto NVC communities M15, M20 and M25a but others are not obviously referable to any NVC eommunities.Examples have been noted at Oanes Moss (Cheshire), <strong>Peatlands</strong> Park (Armagh) and Thorne & Crowle Moors.(iii) 'Dry bog' vegetation: Orier peat workings support a range <strong>of</strong> vegetation types with few, if any bog species.They inclu<strong>de</strong> the physiognomic eategories <strong>of</strong> wet heath, dry heath, Molinia grassland, birch scrub, bracken etc.Some examples are impoverished versions <strong>of</strong> M15, M19, M25 and W4 communíties, but many are not c1earlyreferable to any NVC vegelation-type. There are numerous examples <strong>of</strong> these vegetalion-lypes, including AstleyMoss (Lancashire), Cors Caron, Oanes Moss, Fenns & Whixall Moss (Shropshire I Clwyd), Glasson Moss, Holcr<strong>of</strong>tMoss (Cheshire) [Plate 2.2], Moss Moran (Ounfermline), <strong>Peatlands</strong> Park, Roudsea Moss (Cumbria), SomersetLevels and Thorne & Crowle Moors.(iv) Fen vegetatíon: A few fen species may occur in peat cuttings on ombrotrophic peat, when there is sorne<strong>de</strong>gree <strong>of</strong> enrichment (e.g. Thorne Waste: Smart et al., 1986). However, where un<strong>de</strong>rlying fen peat has beenexposed by extraction, or where there is substantial ingress <strong>of</strong> minerotrophic water, true fen vegetation may occur.A large range <strong>of</strong> fen vegetation-types have been recor<strong>de</strong>d from cut-over bogs, the variety reflecting differences inwater quality (base status and nutrient status), <strong>de</strong>pth and vegetation management. Examples inclu<strong>de</strong> a number <strong>of</strong>mires at whieh little, if any, raised bog now remains 1 ; sites whieh are more obviously raised-bog sites inclu<strong>de</strong>Brackagh Bog (Armagh), Cors Caron, Cors Fochno, Tarn Moss (Malham) and the Somerset Levels.Fen community-types recor<strong>de</strong>d from cut-over bogs inclu<strong>de</strong>:M4M5M6M9M22M23M24M2551535459510512513524525526527W1W2W3W4W5W24W25Carex rostrata-Sphagnum recurvum mireCarex rostrata-Sphagnum squarrosum mireCarex echinata-Sphagnum recurvum/Sphagnum auriculatum mireCarex rostrata-Calliergon cuspidatum mireJuncus subnodulosus-Cirsium palustre fen meadowJuncus effusus/aeutiflorus-Galium palustre rush pastureMolinia caerulea-Cirsium dissectum fen meadowMolinia caerulea-Potentilla erecta mireCarex elata swampCarex paniculata swampPhragmites australis swamp & reed bedsCarex rostrata swampEquisetum fluviati/e swampTypha latifolia swampTypha angustifolia swampPhragmites australis-Peucedanum palustre lall-herb fenPhragmites australis-Eupatorium cannabinum tall-herb fenPhragmites australis-Urlica dioica tall-herb fenCarex rostrata-Potentilla palustris fenSalix cinerea-Galium palustre woodlandSalix cinerea-Betula pubescens-Phragmites australis woodlandSalix pentandra-Carex rostrata woodlandBetula pubescens-Molinia caerulea woodlandAlnus glutinosa-Carex paniculata woodlandRubus fruticosus agg.-Holcus lanatus un<strong>de</strong>rserubPteridium aquilinum-Rubus fruticosus agg. un<strong>de</strong>rserubCommon physiognomic orhabitat <strong>de</strong>scriptorspoor fen I fenpoor fen I fenpoor fen I fenpoor fen I rich fen I fenfen meadowfen meadowfen meadowpoor fen I fen meadowsedge swampsedge swampreedbedsedge swampswampswamp I 'reedbed'swamp I 'reedbed'rieh fen I fen I reedbedrich fen I fen I reedbedrich fen I fen I reedbedpoor fen I rich fen I fenfen earr I woodlandfen earr I woodlandfen carr I woodlandfen carr I woodlandfen earr I woodlandun<strong>de</strong>rserubun<strong>de</strong>rserub, 50me (perhaps most) <strong>of</strong> the basin mires in northern England and southern 5eotland, whieh are eurrently valued (byeonservationists) primarily for their fen vegetation, are former bog sites from whieh most, or all, <strong>of</strong> the ombrotrophie peat has beenstripped away, presumably by domestie eutting (e.g. Cliburn Moss (Cumbria), Heart Moss (Kirkcudbrightshire). Examples fromelsewhere inelu<strong>de</strong> Woodwalton Fen (Cambridgeshire) and Wartle Moss (Aber<strong>de</strong>enshire).


CHAPTER 2: CHARACTERISTICS OF CUT-OVER BOGS47category (endangered) beetles present at Thome &Hatfield Moors (viz. Bembidion humerale andCurimopsis nigrita) appear to be associated with eitherexposed peat 01' relatively dry Calluna-dorninatedvegetation. Conversely, as discussed aboye forSphagnum species [2.3.5], in sorne sites, wet peatcuttings rnay provi<strong>de</strong> an irnportant refugiurn habitat forsorne invertebrates where the uncut surface has becornetoo dry (e.g. Konig, 1992).The extensive, bare surfaces lefi by rnilling rnay be lessarnenable to recolonisation by typical bog invertebratesthan are srnall-scale hand peat cuttings, though as rnostrnilling fields have yet to be abandoned and rewetted,evi<strong>de</strong>nce for this proposition is rnostly absent.Nonetheless, the large size <strong>of</strong> rnilled surfaces wouldsuggest that cornprehensive recolonisation is likely tobe slower than in srnall, hand-cut sites.The invert.ebrate fauna that rnay colonise peat cuttingsin fen peat is potentially extrernely rich, but it isbeyond the scope <strong>of</strong> this report, not least becausecornprehensive data do not exist. [This is partlybecause rnany fen and raised-bog sites have notreceived <strong>de</strong>tailed invertebrate surveys but particularlybecause it is not clear to what extent records refer topeat cuttings; this is a particular problern in rnany cutayerfen sites as their status as peat cuttings is <strong>of</strong>ien notvisually evi<strong>de</strong>nt.]BirdsThe response <strong>of</strong> bird cornrnunities to peat extractionand associated changes is cornplex because <strong>of</strong> thediverse nature <strong>of</strong> the changes that can be induced bysuch activities. Many species which occur on intactbogs also occur on rnodified sites, provi<strong>de</strong>d that sufficientlylarge areas <strong>of</strong> their preferred habitat rernain.Srnall-scale hand cutting rnay result in an increase inavailable habitat, and an increase in bird speciesrichness.Conversely, at Thome Waste for exarnple,large reductions in populations <strong>of</strong> wildfowl, wa<strong>de</strong>rsand birds <strong>of</strong> prey have been attributed to the effects <strong>of</strong>the expansion <strong>of</strong> intensive peat extraction (Lirnbert,Mitchell & Rho<strong>de</strong>s, 1986).Disturbance, lack <strong>of</strong> food sources and nest sites islikely to severely lirnit the use <strong>of</strong> cut-over areas bybirds. However, as bare areas revegetate, the birdspecies which recolonise will <strong>de</strong>pend on such factors asthe distribution and arnount <strong>of</strong> open water and the type<strong>of</strong>vegetation which <strong>de</strong>velops, and the site's geographicallocation. Thus, for exarnple, an increase in openwater habitat is likely to attract wa<strong>de</strong>rs, wildfowl andgu[[s. However, as open water becomes occlu<strong>de</strong>d byvegetation, such species rnay be eventually displaced.Sorne species <strong>of</strong> conservation irnportance rnay have'unnatural' spatial distributions on damaged bogs, forexarnple, species naturally occurring in scrub 01' fenaround the rnargins <strong>of</strong> little-darnaged bogs rnay extendinto the central areas <strong>of</strong> darnaged examples where thereis an increase in these habitats [see also 2.2.2].<strong>Restoration</strong> objectives need not be in contlict with theconservation <strong>of</strong> these species provi<strong>de</strong>d sufficient effortis put into ensuring the availability <strong>of</strong> sufficientsuitable habitat in the appropriate sector <strong>of</strong> the bogo Forexarnple, Thome Waste is estirnated to hold alrnost 2%<strong>of</strong> the British breeding nightjar population (Roworth,1992), but it has been suggested that those currentlynesting towards the centre <strong>of</strong> the bog rnay beaccornrnodated on the bog rnargins through properrnanagernent <strong>of</strong> over-<strong>de</strong>nse scrub there.Heathland bird species are likely to increase on a dry,cut-over site. Tree pipit, whinchat and stonechat areirnportant additions to sorne cut-over bogs; the drierconditions in combination with the provision <strong>of</strong> songposts, in the form <strong>of</strong> birch scrub, undoubtedly favourthe spread <strong>of</strong>these species on certain sites. An increasein open scrub habitat rnay benefit species such asnightjar [2.2.2].A wi<strong>de</strong> range <strong>of</strong> bird species are potential recolonists<strong>of</strong> peat cuttings in fen peat, and rnay inelu<strong>de</strong> suchspecies as sedge warbler, reed warbler, water rail,rnoorhen and coot. They are likely to be <strong>de</strong>terminedparticularly by the character and area <strong>of</strong> the vegetationand <strong>de</strong>pth <strong>of</strong> water. Extensive reedbeds occur in sornefen peat cuttings and rnay support such species asbittern, bear<strong>de</strong>d tit and rnarsh harrier as well as variouswildfowl. The avifauna associated with other types <strong>of</strong>fen vegetation and habitats has not been systernaticallystudied, but a range <strong>of</strong>wetland birds rnay be supported:Fuller (1982) provi<strong>de</strong>s sorne surnrnary inforrnation. Fencarr rnostly supports woodland birds, rather thanwetland specialists, but rnay nonetheless provi<strong>de</strong> a veryrich bird resource. The perceived <strong>de</strong>sirability <strong>of</strong>populations <strong>of</strong>, say, nightingales within a raised-bogsite is likely to <strong>de</strong>pend upon particular views <strong>of</strong> theairns and objectives (and practical possibilities) <strong>of</strong>conservation and restoration at particular sites [Chapter3]. Sorne former raised-bog sites on the SornersetLevels have already <strong>de</strong>veloped into nationallyirnportantwetlands for birds.


PART 11PrincipIes <strong>of</strong> <strong>Restoration</strong>


Chapter 3Aims and general principies tor peatlandrestoration3.1 Options for after-use <strong>of</strong>damaged peatlandsPeatland sites that have been damaged by peatextraction- or other operations have various possibleafter-uses. In the past, these have <strong>of</strong>ten inelu<strong>de</strong>dafforestation, conversion to agriculture, use as refusetips etc. and there has sometimes been a presumptionthat similar use might be ma<strong>de</strong> <strong>of</strong> some currentworkings, once they had been abandoned. However,changing attitu<strong>de</strong>s and circumstances, coupled with arecognition <strong>of</strong> the conservational value <strong>of</strong> somepeatlands and their potential for regeneration, have ledto the view amongst conservationists and others thatthe after-use presumption for many, if not aH, peatcuttingsites should be for nature conservation. It is thispossibility which is the subject <strong>of</strong> this reportoLowland peatlands are perceived to be important forvarious features additional to their potential forexploitation. These inelu<strong>de</strong> their value as a 'peatlandlandscape', for their archaeological and palaeoecologicalarchive and for wildlife. The requirements for thepreservation or, where appropriate, restoration <strong>of</strong> thesefeatures are not i<strong>de</strong>ntical. For example, it may bepossible to preserve sorne <strong>of</strong> the features <strong>of</strong> a 'boglandscape' or the archival value <strong>of</strong> a raised-bog peat<strong>de</strong>posit without necessarily retaining, or re<strong>de</strong>veloping,aH <strong>of</strong> the characteristic biota <strong>of</strong> such an ecosystem.Conversely, in an extensively cut-over raised bog itmay be possible to regenerate a typical bog surface,with characteristic biota, but the peat archive cannot bereplaced and the re<strong>de</strong>velopment c:if a 'bog landscape',whilst probably·possible, is likely to be long-term andoutwith the foreseeable future. This report focuses onthe requirements for reinstatement <strong>of</strong> wildlife interestin damaged peatland sites. No attempt is ma<strong>de</strong> tospecify conservation policy by recommendingparticular objectives - rather, some possible objectivesand options are i<strong>de</strong>ntified and discussed.3.2 Aims <strong>of</strong> restoration3.2.1 The concept <strong>of</strong>restoratiolJThe word 'restoration' has a broad compass (Wheeler,1995), but is nonetheless <strong>of</strong>ten misused, sometimesbecause <strong>of</strong> a failure to recognise that it mus! refer to aspecific object or objective. In a1l <strong>of</strong> its nuances <strong>of</strong>meaning, restoration implies an attempt to retum anobject to something like its 'former condition'.However, peatland ecosystems <strong>of</strong>ten un<strong>de</strong>rgoconsi<strong>de</strong>rable changes as they <strong>de</strong>velop and a damagedsite may have had several distinct 'forroer conditions'.Semantica1ly, it would be legitimate to try to restore asite to any <strong>of</strong> these, be it the last-known state or anearlier condition. However it is not possible,semantically, to restore a site to something it has neverbeen. Thus, strictly-speaking it is not possible to'restore' a damaged raised-bog site to grassland, but inmany cases it could be 'restored' to fen. Of course, it issemantically acceptable to restore 'wildlife interest' toa damaged raised-bog site by converting it intograssland.The specific connotations <strong>of</strong> 'restoration' have ledsome workers to search for other terros to refer a nonspecificrecreation <strong>of</strong> natural history interest.'Rehabilitation' is sometimes used for this, but with nomore legitimacy than 'restoration'. 'Renaturation' maybe a better, neutral term, though it has Iittle generalcurrency in English.3.2.2 <strong>Restoration</strong> objectivesFoci <strong>of</strong> conservation interest in lowland peatland sitescan be recognised at various levels:• plant and animal species;• vegetation-types ('communities');• habitat-types;• mire system.Conservation priorities and restoration preferences fordamaged peatlands will be influenced by the perceivedimportance <strong>of</strong> these foci. For example, it is possible tomaintain or recreate typical bog plant communities


52 RESTORATION OF DAMAGED PEATLANDSTable 3.1 Occurrence <strong>of</strong> physiognomic categories <strong>of</strong> vegetation within cut-over peatlands. (For i<strong>de</strong>ntity <strong>of</strong>physiognomic categories, see Table 1.5).RemnantsPeat workings'Bog-Sphagnum' vegelalion'Para-bog-Sphagnum' vegelalionWel healhDry healhMolinia grasslandBracken slandsBirch scrubReedbedsFen (including fen meadow and carr)Open walerWoodland* Pool syslems are wi<strong>de</strong>spread on some UK mire remnanls; bog lakes do nol appear lo occurwithout attempting to rebuild or re-establish an entire,regenerating mire (this is possible, for example, whererecolonised peat workings are situated within atruncated, remnant mire massif).Whereas conservation initiatives and priorities <strong>of</strong>ienrelate to the maintenance or enhancement <strong>of</strong> existing'interest' <strong>of</strong>peatlands, restoration initiatives can have abroa<strong>de</strong>r scope as, <strong>of</strong>ien, badly-damaged sites may havevery limited existing interest and various restorationpossibilities can be explored.<strong>Restoration</strong> objectives (for nature conservation) areusually a combined product <strong>of</strong> the perceived<strong>de</strong>sirability <strong>of</strong> a particular option, its cost andpossibility. The first two <strong>of</strong> these consi<strong>de</strong>rations areessentially <strong>de</strong>termined by choice and budget; only thelatter provi<strong>de</strong>s an absolute constraint.An assessment <strong>of</strong> the conservational '<strong>de</strong>sirability' <strong>of</strong>these objectives may need to take into account:• the intrinsic interest and importance for natureconservation <strong>of</strong> the habilat-type and associated biota,locally, regionally and nationally;• the scarcity <strong>of</strong> the habitat-type and biota, locally,regionally and nationally• local objectives for nature conservation;• national (and international) objectives for natureconservation.Freedom <strong>of</strong> choice <strong>of</strong> restoration options is sometimesconstrained by existing conservation interest. This maybe the case, for example, where raised-bog sites havebeen badly damaged but have <strong>de</strong>veloped a replacementhabitat with high conservation value centred on speciesand habitat conditions that are atypical <strong>of</strong> raised bogs.In this circumstance, restoration <strong>of</strong> ombrotrophicconditions may not be universally welcomed. In sorneformer raised-bog sites 'restoration' consists <strong>of</strong>preventing spontaneous re<strong>de</strong>velopment <strong>of</strong> bog, in or<strong>de</strong>rto retain prized fen habitats (Beltman, van <strong>de</strong>r Broek &Bloemen, 1995).<strong>Damaged</strong> raised bogs can support a variety <strong>of</strong>vegetation-types and habitats, <strong>de</strong>pending upon specificconditions [Table 3.1]. An informal assessment <strong>of</strong> theintrinsic 'interest' and scarcity <strong>of</strong> these is given in Box3.1. A number <strong>of</strong> these may be seen as an acceptable,or <strong>de</strong>sirable, focus for conservation, restoration orrenaturation.3.2.3 Choice <strong>of</strong>optionsIn practice, cut-over raised bogs in Britain are valuedfor various reasons. Their actual or potential perceivedimportance for nature conservation can be broadlyascribed to three main foci. Sorne sites are perceived tobe important for more than one <strong>of</strong>these.(i) Maintenance or recreation <strong>of</strong> wildlifeinterest not pertaining to bogsA number <strong>of</strong> former raised-bog sites in Britain arecurrently prized and conserved partly or completely forhabitats and species that are not typical <strong>of</strong> raised bogs.This category <strong>of</strong> 'interest' is rather broad.One category <strong>of</strong> replacement habitat that is conservedon a number <strong>of</strong> former raised-bog sites is fen (<strong>of</strong>ienwith open water habitat). This has usually <strong>de</strong>velope<strong>de</strong>ither because past peat extraction has exposedun<strong>de</strong>rlying fen peat or mineral soil, or because theombrotrophic surface has been lowered sufficiently toallow ingress <strong>of</strong> groundwater (or both) (e.g. BrackaghBog, Armagh [Plate 3.1]; Somerset Levels; LeightonMoss, Lancashire [Plate 3.2]; Woodwalton Fen,Cambridgeshire). In sorne examples baulks retain..areservoir <strong>of</strong> bog species. whilst cuttings contain fenspecies. Such sites may have very consi<strong>de</strong>rable interest,both for their vegetation and for other taxonomic


CHAPTER 3: AIMS AND GE ERAL PRl CIPLES53Box 3.1. Informal physiognomic vegetation categories in re/ation to restoration objectives{Far the i<strong>de</strong>ntity and characteristics afphysiagnamic categaries, see Table 1.5 and Bax 2.1J'Bog-Sphagnum' vegetation.Bog-Sphagnum vegetation is particularly characteristic <strong>of</strong>Iittle-damaged bogs; it is uncommon and is <strong>of</strong>ten cited asthe preferred, or ultimate, vegetation goal <strong>of</strong> restorationinitiatives in raised bogs, in terms <strong>of</strong> the species it supportsand beca use <strong>of</strong> its (inferred) association with regenerating,self-sustaining mires.'Para-bog-Sphagnum' vegetation.This broad category represents vegetation that may containa wi<strong>de</strong> range <strong>of</strong> bog species. In richer examples it may bepossible to find most <strong>of</strong> the characteristic species <strong>of</strong> bog­Sphagnum vegetation, though perhaps scattered over largeareas and <strong>of</strong>ten with various additional species, particularlytaxa associated with drier conditions. Such vegetation maybe a natural component <strong>of</strong> some bog sites, but it tends to beregar<strong>de</strong>d as not being 'true' bog vegetation and in manyinstances may represent a <strong>de</strong>rivative <strong>of</strong> 'bog-Sphagnum'vegetation associated with some form <strong>of</strong> damage.Nonetheless, it may provi<strong>de</strong> a substantial reservoir <strong>of</strong> bogspecies. It is <strong>of</strong>ten susceptible to invasion by birch thoughthis cannot be taken as axiomatic (birch establishment uponsome moribund surfaces can sometimes be very slow,especially where there is minimal disturbance).Wet / dry heathTypically rather species-poor vegetation, not confined tobogs. Wetter examples may support a smattering <strong>of</strong> bogspecies, including some Sphagna. Drier examples arereferable to various types <strong>of</strong> dry heath. May support someuncommon bird and invertebrate species and is regar<strong>de</strong>d asan important component <strong>of</strong> some damaged bog sites (e.g.Thorne and Hatfield Moors). Wi<strong>de</strong>spread in some parts <strong>of</strong>the UK but uncommon in many lowland agricultural districts.In some areas, dry raised bogs provi<strong>de</strong> important heathlandsites. Some examples are susceptible to invasion by birchand, in dry situations, bracken.Molinia grasslandExamples on bog peat range consi<strong>de</strong>rably in character fromricher examples that support a small range <strong>of</strong> typical bogspecies to those that are very species-poor and coarse.Robust Molinia is <strong>of</strong>ten effective in suppressing associates,even in quite wet conditions. Usually regar<strong>de</strong>d as'un<strong>de</strong>sirable' by conservationists. May be susceptible toinvasion by birch. Wi<strong>de</strong>spread outwith peat/ands. Exampleson fen peat may be much more species-rich.BrackenTypically species-poor vegetation, confined to dry sites inbogs. Wi<strong>de</strong>spread in other habitats. Potential associatesare suppressed by the strongly-dominant fern. May inva<strong>de</strong>and replace drier examples <strong>of</strong> heathland and Moliniagrassland. Generally regar<strong>de</strong>d as 'un<strong>de</strong>sirable' byconservationists.Birch scrubBirch can colonise over a wi<strong>de</strong> range <strong>of</strong> wetness conditionsand is a potential invasive species <strong>of</strong> some bog, heath andMolinia stands. Its ground vegetation is strongly <strong>de</strong>terminedby the character <strong>of</strong> the vegetation colonised by the birch.Early stages <strong>of</strong> birch encroachment may have little impactupon the characler <strong>of</strong> the biota, but the <strong>de</strong>velopment <strong>of</strong>closed-canopy scrub is usually associated with aconsi<strong>de</strong>rable change in the character <strong>of</strong> the groundvegetation and fauna. For this reason birch encroachment isusually regar<strong>de</strong>d as 'un<strong>de</strong>sirable', though sometimesvarious bog species can persist beneath even closedcanopyscrub. Note also that in some conditions someSphagnum species have been reported to survive betterbeneath young birch scrub than they can in more openvegetation, presumably on account <strong>of</strong> increased humidityand sha<strong>de</strong>. Birch scrub may support a quite rich avifauna,comprised mainly <strong>of</strong> woodland species.Open waterLarge expanses <strong>of</strong> <strong>de</strong>ep open water within bog peatgenerally have a sparse vegetation. Shallower examplescan <strong>de</strong>velop <strong>de</strong>nse mats <strong>of</strong> aquatic Sphagna which may bea precursor to the re<strong>de</strong>velopment <strong>of</strong> regenerating bogvegetation. Open water in peat workings within fen peat cansupport a rich assemblage <strong>of</strong> aquatic macrophytes andsome abandoned peat workings are prized by naturalists forthis. In some cases (e.g. Norfolk Broads) once-rich macrophytepopulations have largely disappeared, largely inconsequence, it is thought, <strong>of</strong> complex food-chain interactions.When present, some aquatic plants are thought t<strong>of</strong>orm the basis <strong>of</strong> fen-raft <strong>de</strong>velopment. Open water is alsosusceptible to hydroseral colonisation (by swamp species)from the margins.ReedbedsBeds <strong>of</strong> Phragmites australis and Typha spp. occur wi<strong>de</strong>lyas recolonist species <strong>of</strong> shallow-water peat pits, <strong>of</strong>ten, butnot exclusively, in sites irrigated with nutrient-rich water.They <strong>of</strong>ten have very low botanical diversity but maysupport notable bird species (especially in the moreextensive examples). [Note that the term reedbeds is alsosometimes applied to more diverse, mixed fen vegetationwhich is dominated by reed; these may have greaterbotanical value.] Wi<strong>de</strong>ly distributed, but extensive (>20 ha)examples are infrequent. Drier examples are <strong>of</strong>tensusceptible to scrub encroachment.Fen vegetationA wi<strong>de</strong> range <strong>of</strong> types <strong>of</strong> non-reed fen vegetation can<strong>de</strong>velop in peat pits, including some types that arenationally scarce. Some former raised-bog sites are nowprized for their extensive fen vegetation. Broadly, thebotanical diversity and scarcity <strong>of</strong> fen vegetation is inverselyproportional to the nutrient-richness <strong>of</strong> the irrigating water;examples <strong>de</strong>veloped un<strong>de</strong>r the influence <strong>of</strong> nutrient-poorbut base-rich water are <strong>of</strong>ten particularly scarce and valuedby conservationists. Base-richness and water level alsoinf1uences vegetation composition. Many types <strong>of</strong> open fenvegetation require management to maintain speciesdiversity and to retard scrub colonisation, which <strong>of</strong>ten leadsto 1055 <strong>of</strong> some uncommon species typical <strong>of</strong> open fen.Invasion by Sphagna can also occur, in some cases as part<strong>of</strong> the process by which fen <strong>de</strong>velops into bogoFen meadowsVarious types <strong>of</strong> fen meadow vegetation can occur on fenpeat surfaces, ranging from examples dominated by rushes(Juncus spp.) and sedges (Carex spp.) to fen grasslandcommunities. Some <strong>of</strong> these communities may be speciesrichand have consi<strong>de</strong>rable biological value.Fen woodlandMuch conservation management <strong>of</strong> fens attempts toprevent extensive <strong>de</strong>velopment <strong>of</strong> scrub and carroNonetheless, fen woodland is <strong>of</strong>ten rich in plant species,though many taxa <strong>of</strong> open situations are absent from <strong>de</strong>nsesha<strong>de</strong>. It may also support a rich avifauna, most typicallycomprised <strong>of</strong> woodland species. Various types <strong>of</strong> fenwoodland occur.


54 RESTORATION OF DAMAGED PEATLANDSPlate 3.1Recolonisation ot ten peat by herbaceous ten vegetation; Brackagh Bog (Armagh).Plate 3.2 Lake and reedbeds at Leighton Moss RSPB reserve (Lancashire).


HAPTER 3: AIM A D GE ERAL PRINCIPLES 55Plate 3.3 Lake with islands and reedbeds, ereated using elay bunds. Burtle, Somerset Levels.groups. Some are <strong>de</strong>liberately managed as fen (reedbeds)for their omíthologieaJ interest (e.g. LeightonMoss - Plate 3.2). ome examples are likely to <strong>de</strong>velopspontaneously into bog, but this will be at the expense<strong>of</strong> mueh or all <strong>of</strong> the fen habitat and speeies and suehan event may be regar<strong>de</strong>d as un<strong>de</strong>sirable by sorneeonservationists.Also inelu<strong>de</strong>d in this eategory are conservation siteswhieh support replaeement habitats <strong>of</strong> relatively lowconservation interest assessed nationally, but whichmay be important locally as wildlife habitats or aslandseape features. Examples <strong>of</strong> this inelu<strong>de</strong> wetlandsites within worked-out peat-extraction sites [Plate 3.3]and dry raised bogs that have <strong>de</strong>veloped into birchwoods' some are managed as nature reserves, othershave trees protected by Tree Preservation Or<strong>de</strong>rs.(ii) Maintenance or re-establishment <strong>of</strong> viablepopulations <strong>of</strong> typical bog speciesThe objeet <strong>of</strong> eonservation and restoration management<strong>of</strong> many raised-bog sites is to maintain or re-establishviable population <strong>of</strong> typical bog species. [n manyinstances, the objeetive is to re-establish Sphagnumrichvegetation (comparable to the MI8 communitytype<strong>of</strong> the National Vegetation Classification) oversorne or all <strong>of</strong> the site. In other cases it i consi<strong>de</strong>redthat it may only be feasible to retªin or recreatecommunities typical <strong>of</strong> damaged bog surfaces (whichmay nonetheless support a very wi<strong>de</strong> range <strong>of</strong> typicalbog species).In a number <strong>of</strong> peat extraetion sites, typical bog speciesare supplemented by sorne species <strong>of</strong> other (drier)habitats, usually in sorne forro <strong>of</strong> habitat mosaie. Sorne<strong>of</strong> these species are themselves uncommon and form animportant part <strong>of</strong> the perceived conservationimportance <strong>of</strong> the mire. lt is recognised that at sornesites (e.g. Danes Moss, Cheshire) management thatfavours the <strong>de</strong>velopment <strong>of</strong> bog may be <strong>de</strong>trimental tosome non-bog bird specie .In sorne peat extraction complexes, the reestablishment<strong>of</strong> typical bog vegetation (especiallyM18) may represent a 'value-ad<strong>de</strong>d' approach, in thatthe vegetation present prior to current peat extractionwas not 'good-quality' bog vegetation.(iii) Maintenance or re-establishment <strong>of</strong> aregenerating, self-sustaining bogecosystemThe object <strong>of</strong> conservatíon and restoratíon management<strong>of</strong> a number <strong>of</strong> raised-bog sites is to restore them to aregenerating, self-sustaining ecosystem with theappearance and composition <strong>of</strong> a 'natural' (Le. littledisturbed) bogo This is particularly the case for those


56RESTORATION 01' DAMAGED PEATLANDSremaining bogs which have retained 'good quality' bogvegetation over substantial parts <strong>of</strong> their surface alongwith an appropriate topographical conformation (e.g.Cors Caron, Wedholme Flow) but it may also be seenas a <strong>de</strong>sirable restoration objective for sites that havebeen much-darnaged by peat extraction. Such anobjective is obviously well suited to the maintenance,or increase, <strong>of</strong>populations <strong>of</strong> typical bog species, but itmay be <strong>de</strong>trimental to non-bog species that form part<strong>of</strong>the existing wildlife resource <strong>of</strong>sorne sites.Regeneration <strong>of</strong> a 'new' raised-bog system does not <strong>of</strong>necessity have to occupy the entire former area <strong>of</strong> thecut-over bog; moreover, in large cut-over sites it wouldbe possible to initiate more than one regenerating mire.In sorne peat-extraction complexes, the re-establishment<strong>of</strong> a 'regenerating bog' may represent a 'valuead<strong>de</strong>d'approach,' in that the mire had beenconsi<strong>de</strong>rab}y darnaged prior to current peat extraction.3.2.4 Species-centred versus mirecentredrestorationThere are at least two rather different approachesadopted for the conservation and restoration <strong>of</strong> naturalhistory interest on damaged raised bogs. They are not,<strong>of</strong> necessity, mutually exclusive. One is essentiallyspecies-centred and aims to maintain or re-establishviable populations <strong>of</strong> typical bog (or other) species.The other approach is mire-centred, and aims tomaintain or recreate a <strong>de</strong>veloping raised-bog ecosystem.The species-centred approach does not <strong>de</strong>mand aregenerating mire. It is possible to maintain or reestablishpopulations <strong>of</strong> many bog species on damagedbog surfaces or in peat pits. Is sorne, but not all, casesplant species may form a vegetation similar to that <strong>of</strong>little-damaged bogs. Such artificial situations maymaintain numbers <strong>of</strong> typical bog species as effectivelyas on a little-darnaged or regenerating bogo Biodiversitymay even be increased relative to a Iittledarnaged bog by the growth <strong>of</strong> supplementary specieson darnaged sites, sometimes ref1ecting the habitatmosaics which have been produced by peat extraction.This is seen clearly in former block-cut sites where wetcuttings support regenerating bog vegetation(equivalent to MI8) whilst the adjoining baulks havewet and dry heath. This juxtaposition <strong>of</strong> contrastinghabitats accounts for the high biological interest <strong>of</strong>sorne cut-over raised-bog sites, especially when theinterface between adjoining habitats supportsspecialised organisms.<strong>Restoration</strong> initiatives which attempt to restore thewhole site as a single, regenerating mire are less Iikelyto result in a close juxtaposition <strong>of</strong> contrasting habitatsand may produce sites with lower biodiversities than isthe case with a species-centred approach, but the biotawill be comprised mainly <strong>of</strong>typical bog species.The choice between species-centred and mire-centredconservation and restoration initiatives is likely to beinfluenced by a variety <strong>of</strong> consi<strong>de</strong>rations, not leastpracticability and costoAttempts to regenerate the entire mire as a growingentity are arguably more 'natural' than is themaintenance <strong>of</strong> artificial habitat mosaics. In<strong>de</strong>ed,sometimes the latter strategy is effectively a form <strong>of</strong>'bog gar<strong>de</strong>ning' with an ongoing requirement forperiodic 'weeding' (e.g. birch clearance etc.) andsometimes even 'watering' (e.g. supplementaryirrigation). A practical consequence <strong>of</strong> this is that themaintenance <strong>of</strong> artificial bog habitat mosaics willusually have a recurrent management cost whereas thiswill be less true <strong>of</strong> a naturaJly regenerating bogoHowever, the initial outlay <strong>of</strong> attempts to regenerate anentire mire may be consi<strong>de</strong>rably greater th3n thatrequired just for the protection <strong>of</strong> existing interest,though this will <strong>de</strong>pend strongly upon the startingpoint.In sorne cases, it may be possible to provi<strong>de</strong> suitablehabitats for atypical bog species <strong>of</strong> great conservationvalue around the periphery <strong>of</strong> a regenerating mire, thuscombining to sorne extent the species-centred andmire-centred approaches.Ultimately, the choice between the species-centred andmire-centred approaches is likely to ref1ect personalpreference, philosophy and practicality rather than tohave a clear objective resolution. Both approaches havevalidity and there seems no objective necessity toimpose a single, universal restoration solution upon allsites. Eggelsmann (1987) comments that the purposeand objective <strong>of</strong> all rewetting and regenerationmeasures taken in Germany is to produce suchecological conditions that in the long term naturalprocesses will achieve an actively growing raised bog,without further human intervention. But he alsorecognises that this may not always be achievable. Forindividual sites, the choice may ultimately be resolvedby practicability. For example, in sorne remnantmassifs it may be impractical, either throughconstraints <strong>of</strong> topography or cost, to rewet the areasufficiently well for bog regeneration without furtherremoval <strong>of</strong> peat. In this situation there may be littlechoice but to accept that it may be possible only tomaintain, or create, artificial habitat mixtures. Thesewill at least help ensure the survival <strong>of</strong> bog species onthe site (though recurrent management costs andpossible on-going hydrological instability may meanthat this is not always in perpetuity). By contrast,where extensive, f1at peat fields become available forrestoration, it may be more appropriate to look towardshabitat regeneration rather than just species survival.


CHAPTER 3: AIMS AND GENERAL PRINCIPLES573.2.5 <strong>Restoration</strong> opportunities incurrentpeatworkingsIn general, where parts <strong>of</strong> cut-over raised-bog siteshave consi<strong>de</strong>rable existing conservation interest, be itan 'original' bog surface on a remnant massif, or bogspecies that have recolonised abandoned peat pits, orareas <strong>of</strong> fen which have <strong>de</strong>veloped in minerotrophicworkings, there is <strong>of</strong>ien an un<strong>de</strong>rstandable <strong>de</strong>sireamongst conservationists to maintain the status quo, orto enhance it By contrast, there may be more scope foran open choice <strong>of</strong> restoration objectives in plans forcurrent workings where the existing biological interestis minimal.Even in current peat workings restoration opportunitiesmay be constrained by practicalities and what isconsi<strong>de</strong>red <strong>de</strong>sirable may have to be subsumed to whatis feasible. For example, in sites where operational peatextraction is now largely in fen peat (as in the SomersetLevels), or where a base-rich subsoil has been exposed,or where the workings are subject to ingress <strong>of</strong>groundwater, there is little option but to accept that wetrestoration will, in the first instance, be to a minerotrophichabitat. In such situations, if revegetationprocesses are open to sorne possibility <strong>of</strong> environmentalmanipulation, the only real choice is in the type<strong>of</strong> minerotrophic wetland that is to be recreated (or, orcourse, sorne form <strong>of</strong>altemative 'dryland' habitat).Where fen peat remains covered by bog peat, direct reestablishment<strong>of</strong> raised bog is more feasible, but evenhere it would, <strong>of</strong>course, also be possible to <strong>de</strong>liberatelyexpose the minerotrophic <strong>de</strong>posits to recreate fen overall or part <strong>of</strong> the site. For whilst there is sometimes aten<strong>de</strong>ncy to regard the exposure <strong>of</strong> fen peat in cut-overraised bogs as a restoration problem, it can also be seenas a restoration opportunity. It would not be difficuIt toargue that as the bog initially <strong>de</strong>veloped from fen itwould be a more 'natural', and possibly more stable,way <strong>of</strong>regenerating it by re-establishing the conditionsfrom which it originated (el Chambers, Lageard &ElIiott, 1992); or that as minerotrophic mires are lessextensive (in aggregate) than are ombrotrophic mires,in the UK, there may be merit in their recreation,especially in those situations where the expected fentypewould itself be specified as a 'priority' habitat inthe EC Habitats Directive.Peatland restoration <strong>of</strong>fers a wi<strong>de</strong> range <strong>of</strong> opportunitiesfor the creative restoration <strong>of</strong> mires. Whilst alaissez¡aire approach may be un<strong>de</strong>sirable, equally withsorne 36,000 ha <strong>of</strong> damaged raised bog potentiallyavailable for restoration [1.6], there is scope for avariety <strong>of</strong> objectives to be realised. However, there is areal need to <strong>de</strong>velop objective ground-rules to help<strong>de</strong>ci<strong>de</strong> restoration and renaturation options, prioritiesand areas in situations, such as <strong>de</strong>nu<strong>de</strong>d peatlandswhere there may be much scope for choice.As one <strong>of</strong> the main objectives <strong>of</strong> bog restoration is tocreate a Sphagnum-based bog vegetation and a regeneratingbog, and as this is likely to be consi<strong>de</strong>rablymore difficult than the re<strong>de</strong>velopment <strong>of</strong> sorne otherspontaneous vegetation-types (e.g. birch scrub), thiswill provi<strong>de</strong> the main focus <strong>of</strong> much <strong>of</strong> this reportoHowever, sorne attention is also given to the optionsfor the creation <strong>of</strong> certain types <strong>of</strong> fen vegetation. Thecircumstances likely to lead to the <strong>de</strong>velopment <strong>of</strong>sorne other types <strong>of</strong> habitat with natural history valueare summarised in Chapter 6.3.2.6 Constraints on restorationobjectivesThe realisation <strong>of</strong> particular restoration options is<strong>de</strong>termined by consi<strong>de</strong>rations <strong>of</strong> feasibility andpracticability. Sorne potential constraints inclu<strong>de</strong>:• unfavourable starting conditions (see below);• lack <strong>of</strong>resources;• legal constraints (for example, obligation to maintaindrains in or around site);• obligations to neíghbouring land-owners (for example,need to avoid waterlogging <strong>of</strong>adjoining land);• conflicting conservation aims:these may be induced, for example, by the presence <strong>of</strong>arare species, which is not typical <strong>of</strong> the bog habitat.Opinions vary on the merits <strong>of</strong> conserving atypical,rare species versus regeneration <strong>of</strong> the mire. Thispartly retlects the 'species-centred approach' and'mire-centred approach' to restoration. In sorne casesthe rare species may have legal protection. It issometimes possible to accommodate their needs, orthose <strong>of</strong> other special interests, without abandoningan objective <strong>of</strong> bog restoration.A summary <strong>of</strong> the main factors affecting restorationoptions is given in Table S2 [Summary].3.3 Sorne principies <strong>of</strong> peatlandrestoration3.3.1 Scope <strong>of</strong>restorationThe term 'restoration' can be used to apply to variousobjects. Sorne workers use it loosely to refer just toprocess <strong>of</strong> reinstatement <strong>of</strong> habitat conditions thoughtto be appropriate to the objectives. Thus rewetting <strong>of</strong> apeatland is sometimes referred to as 'restoration'. It is,<strong>of</strong> course, semantically legitimate to claim to have'restored' former water levels to a drying-out sitewithout taking into account the wi<strong>de</strong>r repercussions <strong>of</strong>this process. However, comprehensive site restorationimplies not only reinstatement <strong>of</strong> former environments,but also re<strong>de</strong>velopment <strong>of</strong> a biota similar to a formercondition and, where applicable, re-establishment <strong>of</strong>the 'natural ecosystem processes' which sustain the


58RESTORATION OF DAMAGED PEATLANDSsite. In this report, the unqualified tenn 'restoration' isused in this comprehensive sense.Effective restoration sensu lato has two main features:(i) the establishment <strong>of</strong> appropriate environmentalconditions and (ii) subsequent colonisation by targetspecies. Kuntze & Eggelsmann (198 1) subdivi<strong>de</strong>drestoration, conceptuaIly, into three distinct butoverlapping phases:• rewetting• renaturation• regeneration'Rewetting' may be too narrow a tenn for general usein peatIand restoration as in sorne cases environmentalmanipulation other than, or addition~1 to, rewettingmay berequired (e.g. nutrient stripping). Nonetheless,the establishment <strong>of</strong> appropriate water levels is usuaIlythe primary task in the restoration <strong>of</strong> peatIandsdamaged by commercial peat extraction.'Renaturation' refers to recolonisation <strong>of</strong> the peatIandby plant and animal species and the fonnation <strong>of</strong>characteristic communities. 'Regeneration' refers to bere-establishment <strong>of</strong> sorne ecosystem processes, such aspeat accumulation. This phase is fundamental torestoration strategies which aim at whole mireregeneration, but is <strong>of</strong> less consequence when theobjective is primarily to maintain species populations.3.3.2 Approaches to restorationAs different species and restoration objectives mayhave markedly different environmental requirements,the creation <strong>of</strong> appropriate habitat conditions can onlybe consi<strong>de</strong>red in tenns <strong>of</strong> the specified objectives. Thepurpose <strong>of</strong> rewetting damaged peatIands is not just tomake them wet, but to provi<strong>de</strong> conditions appropriatefor the <strong>de</strong>sired renaturation and regeneration objectives.The <strong>de</strong>velopment <strong>of</strong>restoration strategies needs toconsi<strong>de</strong>r the conditions required to realise the specifiedobjectives, whilst recognising, for example, that theconditions nee<strong>de</strong>d to re-establish <strong>de</strong>sired types <strong>of</strong>vegetation may differ from those required to rnaintainexisting examples.Two broad approaches to peatIand restoration can bedistinguished: repair and rebuilding. Repair usuaIlyentails relatively minor restorative operations (ditchblocking etc.) and aims at direct reinstaternent <strong>of</strong> the<strong>de</strong>sired objectives. It is particularIy appropriate forsites with Iimited damage. Rebuilding involves there<strong>de</strong>veloprnent <strong>of</strong> the peatIand and implies that the<strong>de</strong>sired endpoint cannot be produced directly butrequires phased reconstruction, with a starting point<strong>of</strong>ien rather different from the final product. In sornecases, further 'damage' may be required to produce asecure foundation for rebuilding. Depending on therestoration objective, the restoration <strong>of</strong> bogsextensively damaged by commercial peat extractionwiII usuaIly require rebuilding rather than repair.3.4 Principies for restoration <strong>of</strong>raised bogs3.4.1 IntroductionIn principie at least, the restoration <strong>of</strong> damaged raisedbogs may be easier than that <strong>of</strong> sorne other habitats.This is because, whilst peat e'xtraction consi<strong>de</strong>rablydamages raised bogs, it does not affect the most fundamentalcondition required for their fonnation andgrowth, namely a climaticaIly-controIled precipitationexcess. Moreover, raised bogs are thought to be climaxecosystems that have, in the past, <strong>de</strong>veloped spontaneouslyfrom a variety <strong>of</strong> starting-points, including fenand wet mineral soil. This suggests that renewed<strong>de</strong>velopment <strong>of</strong>raised-bog ecosystems may be possiblein a quite wi<strong>de</strong> range <strong>of</strong> circumstances. In<strong>de</strong>ed, givenappropriate conditions, it may be difficult to prevent'ombrotrophication' from taking place.There are two major requirements for raised-bogrestoration: (i) availability <strong>of</strong> an a<strong>de</strong>quate supply <strong>of</strong>precipitation <strong>of</strong> appropriate quality and its sufficientretention at the bog's surface to provi<strong>de</strong> effeotiverewetting; (ii) availability <strong>of</strong> suitable recolonist speciesfor renaturation. However, there are several reasonswhy these conditions cannot always be met, even insorne fonner raised-bog sites [see also Box 3.2]:(i) the peat surface may not readily retain rainwater (usuallybecause <strong>of</strong> drainage systems, because the surfaceconformation tends to shed water and because the capacity <strong>of</strong>the natural bog surface for hydrological self-regulation hasbeen lost (see below);(ii) <strong>de</strong>ep land drainage around the bog may substantiallyaffeet its water balance (this is not invariably the case);(jii) drainage beneath the bog may substantially affeet itswater balance (this may oecur when groundwater isabstracted from a permeable substratum beneath the bog; itsimportanee in Britain is not known);(iv) the peat surface may be minerotrophic in character(usually because <strong>of</strong> exposure <strong>of</strong> fen peats by excavation,ingress <strong>of</strong> groundwater or other contamination); bogvegetation may not be able to <strong>de</strong>velop directly in suchsituations, though it may be able to <strong>de</strong>velop indirectly bylonger-term successional processes;(v) atmospherie pollutants may be <strong>de</strong>trimental to the growth<strong>of</strong>sorne bog plants;(vi) recolonist species may not be available c10se to the bogbecause <strong>of</strong> <strong>de</strong>struction <strong>of</strong>their refugia.


CHAPTER 3: AIMS AND GENERAL PRINCIPLES59Box 3.2 Hydrochemical constraints on bog restorationIndividual cut-over raised-bog sites vary consi<strong>de</strong>rably in theirconditions and characteristics. Although certain features (suchas the presence <strong>of</strong> a layer <strong>of</strong> ombrotrophic peat) may facilitatesome restoration options, and hence <strong>de</strong>termine theirfeasibility, or priority, in a resource-limited context, this doesnot mean that sites lacking such attributes cannot be restored.As raised bogs are c1imax ecosystems, which have <strong>de</strong>velopedspontaneously, they are Iikely to be able to re<strong>de</strong>velop from arange <strong>of</strong> starting conditions on sites where they onceoccurred, though undoubtedly this process will takeconsi<strong>de</strong>rably longer from some ~tarting points than others.Ultimately, there are two main constraints on the potential <strong>of</strong>sites to re<strong>de</strong>velop into raised bogs: (i) availability and reterition<strong>of</strong> an a<strong>de</strong>quate supply <strong>of</strong> meteoric water <strong>of</strong> appropriate quality;and (ii) availabi/ity <strong>of</strong> recolonist species. The first <strong>of</strong> these maybe influenced by conditions external to the raised bog and,because <strong>of</strong> this, be particularly intractable.The input <strong>of</strong> sufficient meteoric recharge water to bog surfacesis a prerequisite for bog <strong>de</strong>velopment and climatic conditionsprovi<strong>de</strong> a primary regulation <strong>of</strong> bog restoration options[Chapter 1], though the exact nature <strong>of</strong> climatic constraintsupon ombrotrophic peat <strong>de</strong>velopment and the range <strong>of</strong> climaticconditions un<strong>de</strong>r which this may occur is not known withprecision: suggested threshold values <strong>of</strong> annual precipitationrecharge required for bog <strong>de</strong>velopment have been <strong>de</strong>rivedmainly by correlations based on the known distribution <strong>of</strong> bogsand the seasonal distribution <strong>of</strong> precipitation is almost certainlyimportant in <strong>de</strong>termining the growth <strong>of</strong> bogs [see Chapter 1],though its effect has not been well quantified. Workers in NWEurope (Kuntze & Eggelsmann, 1982; Streefkerk & Casparie,1989) consi<strong>de</strong>r that the current precipitation : evaporationbalance is suitable for raised-bog <strong>de</strong>velopment in much <strong>of</strong> thisregion, though it is difficult to predict effects <strong>of</strong> future climaticpatterns. In some sites, groundwater discharge may also havesome importance to the overall water balance <strong>of</strong> the bog eventhough the surfaces are fed exclusively by precipitation[Chapter 1]. The interaction <strong>of</strong> this with other components <strong>of</strong>the water balance in relation to threshold precipitation valuesis not well known.The suitability <strong>of</strong> me~eoric water for raised-bog re<strong>de</strong>velopment,in parts <strong>of</strong> NW Europe at least, is open to question. It ispossible that atmospheric contamination <strong>of</strong> rainwater ('acidrain') plus dry <strong>de</strong>position <strong>of</strong> atmospheric N may constrain thepossibilities for bog growth, especially with regard to thegrowth <strong>of</strong> certain Sphagnum species. As discussed elsewhere[4.5] the significance <strong>of</strong> this problem is not really known, butmay be serious.The retention <strong>of</strong> water within bog sites may be <strong>de</strong>terminedboth by conditions within the mire and by those outsi<strong>de</strong> it.Retention problems internal to the mire can <strong>of</strong>ten be remedied(though it may not always be cost-effective to do so): drainsthat remove water from the bog can be blocked; lateral waterloss across peat surfaces can be prevented by bunding;temporary water shortage can be alleviated by storing water inlagoons at times <strong>of</strong> surplus. ExternaI influences upon thewater balance may be less tractable, such as those created byregional changes in hydrology. A lowering <strong>of</strong> groundwaterlevels is seen as a consi<strong>de</strong>rable constraint upon bogrestoration in parts <strong>of</strong> NW Germany and The Netherlandswhere bogs have <strong>de</strong>veloped over permeable substrata inwhich a high groundwater level has effectively provi<strong>de</strong>d thebase <strong>of</strong> the perched water mound. The extent to which this isan important component in the water balance <strong>of</strong> British bogs isnot known, but it is almost certainly a feature <strong>of</strong> some sites. Itcannot be divorced from other conditions within the peatland.Thus, the 'problem' <strong>of</strong> ditches which cut through to the mineralsubstrata is only Iikely to affect substantially the hydrologicalintegrity <strong>of</strong> the mire where the mineral ground acts as a watersink; otherwise such ditches can be readily dammed, as anyother drain. Similarly, it may be <strong>of</strong> greater importance in peatcutting sites where only a thin layer <strong>of</strong> residual bog peat isavailable to constrain downwards seepage <strong>of</strong> water(Schouwenaars, 1993).The retention <strong>of</strong> water within specific parts <strong>of</strong> bog sites isconstrained by the same consi<strong>de</strong>rations mentioned aboye, butmay be <strong>de</strong>termined additionally by the surface topographycreated by peat extraction (Joosten, 1992). This may <strong>de</strong>mandadditional attention, if it is inten<strong>de</strong>d to rewet all, or most, <strong>of</strong> thesite.In many cut-over sites, water retention problems are stronglyexacerbated by the lack <strong>of</strong> a<strong>de</strong>quate water storage within thepeal. Peat extraction usually removes the upper fibrous layers<strong>of</strong> moss and peat and exposes the lower, more humified peatlayers. The latter, more highly <strong>de</strong>composed peat, typically hasa much lower water storage capacity than the former (theoriginal acrotelm [1.8, 2.3]). Moreover, the plant species that<strong>of</strong>ten readily colonise such surfaces (e.g. Molinia caerulea)may induce high rates <strong>of</strong> evapotranspirative water 1055 andmake summer surface conditions even less suitable forSphagnum regeneration (Poschlod, 1988, 1992; Schouwenaars,1992). In a Iittle-damaged bog the Sphagnum layeris reported to be able to reduce evapotranspiration losses byforming a 'mulch' in its upper layers, whilst in the early stages<strong>of</strong> renaturation, the Sphagnum layer, if present at all, is notthick enough to regulate evapotranspiration losses effectively.Strategies aimed at regenerating bog vegetation may need t<strong>of</strong>ind surrogate methods for increasing surface storage as aprecursor to re-establishing an acrotelm with an effectivecapacity for its own water regulation. In some climatic regionsthis may be achieved only by permanent inundation(Schouwenaars, 1992). This <strong>de</strong>mands some substantialhydrological control <strong>of</strong> a disturbed or regenerating mire beforeattention focuses on revegetation.The impact <strong>of</strong> minerotrophic surface conditions (created byexposure <strong>of</strong> un<strong>de</strong>rlying fen peat or mineral sail, or by ingress<strong>of</strong> telluric water) upon restoration prospects <strong>de</strong>pends largelyupon their character. Many bog plant species are able to growin weakly minerotrophic (poor-fen) conditions, and some growbetter in such conditions than in bog [1.9]. Weaklyminerotrophic workings thus <strong>of</strong>ten support a mixture <strong>of</strong> speciesfound both in bogs and fens. By contrast, ·few typical bogspecies normally grow in rich fens and where peat workingsreceive base-rich or nutrient-rich water, their vegetation isstrikingly different to that <strong>of</strong> bogo It is possible that bog willeventually <strong>de</strong>velop spontaneously from fen in such conditions,but it is likely to take longer than in poor fen. This is, however,partly <strong>de</strong>pen<strong>de</strong>nt upon the water regime: given appropriateconditions ombrotrophic communities can dElVelop from richfen within C. 100-200 years, especially where peat cuttingsare sufficiently inundated to permit the <strong>de</strong>velopment <strong>of</strong> semif10atingrafts <strong>of</strong> vegetation.


60REsrORATION OF DAM¡\GED PEATLANDSIt may be noted that sorne <strong>of</strong> these constraints areinternal to the peatland, others are external; sorne mayprevent restoration, other may just retard it; sorne canbe readily remedied, others not so; sorne apply to intactbogs, others are confined to, or intensified in, cut-oversites. Very <strong>of</strong>ten 'external' constraints are less easilyremedied than are 'interna!' ones.3.4.2 Conditions required for theestablishment <strong>of</strong>bog speciesThe main focus <strong>of</strong> raised-bog restoration initiatives isto pravi<strong>de</strong> conditions suitable for colonisation andgrowth <strong>of</strong> species typical <strong>of</strong> little-damaged bogs,especially species <strong>of</strong> Sphagnum. The broad requirementsfor this are usually to:• create, or maintain, permanently wet ombrotrophicconditions at the growing surface;• minimise water fluctuation at the growing surface;• prevent or reduce input <strong>of</strong> telluric water to the growingsurface.The establishment <strong>of</strong> Sphagnum-based vegetation is <strong>of</strong>great importance to raised-bog restoration, because (i)<strong>de</strong>velopment <strong>of</strong> a 'bog-Sphagnum' vegetation is aften aprime focus <strong>of</strong> restoration initiatives; (ii) it contributesto the regulation <strong>of</strong> surface wetness and to re-<strong>de</strong>velopment<strong>of</strong> a characteristic bog acrotelm; and (iii) growth<strong>of</strong> Sphagnum may help regulate the chemical environment<strong>of</strong> the <strong>de</strong>veloping mire by acidification (especiallyimportant to the <strong>de</strong>velopment <strong>of</strong> ombrotrophicnuclei within minerotrophic conditions).The exact conditions required for effective establishment<strong>of</strong> Sphagnum species on damaged peat (or other)surfaces are not well known and are likely to varysomewhat between species and sites f1.9, 9.21.Sphagna can colonise a quite wi<strong>de</strong> variety <strong>of</strong> situations,though a common feature <strong>of</strong> these is generally a highand fairly stable water level. This may be provi<strong>de</strong>d:• by high and frequent precipitation input (sorne c1imatespermit Sphagnum growth in a range <strong>of</strong> situations,including sloping ground);• by a mat <strong>of</strong> vegetation semi-floating within (shallow)water;• by a stable water table, at or just below the surface <strong>of</strong> thesubstratum.Bog plant species, inc\uding bog-Sphagl1um species,have sorne flexibility in their growth requirements andmay be able to grow in conditions that do not conformexactly to those characteristic <strong>of</strong> a little-damaged bogsurface. For example, many can grow well in weaklyminerotrophic conditions and sorne bog species cancolonise open water, fen peats, mineral soils andartificial habitats (floors <strong>of</strong> quarries, railway ballastetc.) when conditions are appropriate. Establishment <strong>of</strong>a Sphagnum cover in such situations does not meanthat bog will neeessarily <strong>de</strong>velop in these sites, but itdoes suggest that ombrotrophic vegetation can beregenerated from a range <strong>of</strong>possible starting points.Note that in sorne instances a stable, slightly subsurfaceminerotrophie water table in fen peat or mineral soilscan provi<strong>de</strong> a satisfactory basis for Sphagnum establishment.This is usually most suitable when base-richwater does not direct1y flood the surface; when theuppermost soil horizons are intrinsically acidic; and inregions <strong>of</strong> high precipitation input.3.4.3 Pathways<strong>of</strong> bog restorationReflecting the range <strong>of</strong> circumstances from whichraised bogs can naturally originate, restoration <strong>of</strong>damaged raised bogs can follow four main pathways.1. direct colonisation <strong>of</strong> bog peat by plants associated witht)'pical bog vegetation (MI8);20 colonisation <strong>of</strong> ombrotrophic water by p\ants anó mossesassociated with bog pools followed by successionalinvasion <strong>of</strong> other bog species;30 colonisation <strong>of</strong> fen peat (or wet mineral soils) by fenplants followed by successional <strong>de</strong>velopment to bog;40 colonisation <strong>of</strong> minerotrophic water to form fen andthence bogoThe first <strong>of</strong> these pathways can be consi<strong>de</strong>red to be aform<strong>of</strong>repair. The other three are forros <strong>of</strong>rebuilding.Of these, pathways (3) and (4) may represent themechanism by which the bog naturally <strong>de</strong>veloped,whilst pathway (2) is more artificial in these sense thatbogs are not normally initiated in ombrotrophic water(though they may subsequently <strong>de</strong>velop ombrotrophicflooding surfaces or bog lakes).3.4.4 Starting conditionsIn bog restoration initiatives, the pathway, speed an<strong>de</strong>xtent to which conditions suitable for the growth <strong>of</strong>typical bog species can be realised <strong>de</strong>pends strongly onthe starting conditions at each site (Table 3.2). Bogrestorers need to assess the conditions and problemsspecific to each site and, from these, <strong>de</strong>termine themost appropriate restoration possibilities andprocedures. In sorne cases it may be <strong>de</strong>sirable, ifpossible, to modify sorne starting conditions t<strong>of</strong>acilitate the restoration process. The principies andmethods by which this can be achieved form the mai<strong>of</strong>ocus <strong>of</strong>the remain<strong>de</strong>r <strong>of</strong>this reporto3.4.5 Suitability <strong>of</strong>sites for restorationVarious workers have pointed out that cut-overpeatlands may vary consi<strong>de</strong>rably io their potential forrestoration, <strong>de</strong>pending both upon their situatioo(especially c1imatic constraints) and their condition(see e.g. Rowell, 1988; Eggelsmann (in Heathwaite &


CHAPTER 3: AIMS AND GENERAL PRINCIPLES61Gottlich, 1993». In sorne cases 'difficult' restorationcircumstances (such as the effect <strong>of</strong> groundwater abstractionbeneath a bog) may prevent effective rewetting,or make it very cost1y, and it may then be appropriateto consi<strong>de</strong>r more feasible restoration objectives, or toallocate resources to more tractable sites. Similarly,there may be sorne situations in which rewetting maynot be feasible, for example on small or stronglysloping peat remnants.As the character and configuration <strong>of</strong> a cut-oversurface can have a critical influence upon successfulrecolonisation by bog plants, the best prospects forrestoration may result from active collaborationbetween conservation bodies and the peat companies ­which have the expertise and machinery for manipulatingcut-over surfaces - in implementing an agreedrestoration strategy. This would help to ensure thatwhen the peat workings are eventually abandoned, theyare in a conformation optimal for revegetation. Wheresorne workings have been abandoned without suchagreement, surface conditions may be such (e.g. veryirregular topography) that renaturation wil\ be almostimpossible, or at least impractical, without a great <strong>de</strong>al<strong>of</strong> manipulation. There are numerous examples <strong>of</strong> suchsites in which 'renaturation' has produced little morethan thickets <strong>of</strong>birch and swathes <strong>of</strong>bracken.Table 3.2 Summary <strong>of</strong> possible starting conditions on cut-over bogs.TopographyTopography may be very variable across an abandoned peal exlraclion complex, <strong>de</strong>pending on lhe melhod and exlenl <strong>of</strong> pealexlraclion. Two situalions can be dislinguished, al several scales [2.1]:MassifsDepressionsblocks wilh an overall convex or water shedding pr<strong>of</strong>ile.hollows wilh an overall concave or water holding pr<strong>of</strong>ile.Note that <strong>de</strong>pressions may occur within massifs.Block cutting <strong>of</strong>ien produces a regular system <strong>of</strong> baulks, f1ats and trenches, but can sometimes result in a largely nal surface.Miffing <strong>of</strong>ien produces a series <strong>of</strong> long peat fields, usually as cambered beds.Peat workings are <strong>of</strong>ien lower than adjoining refugium areas (which may be uncul remnants or revegetating cutlin!)s).Water conditionsPeal extraction and drainage modify or <strong>de</strong>stroy lypical bog vegetation and the characleristic bog acrotelm. They also typicallyinduce dry condilions in cul-over areas and may also affect adjoining upslanding remnanls eilher direclly or indirectly [Chapter 2].In consequence:• water levels are generally too low for growth <strong>of</strong> peat-building Sphagnum species (excepl perhaps in some hollows);• water levels tend to f1ucluate lo a greater extenl than in 'intacl' bog;• water storage capacity <strong>of</strong> the peal is lypically lower than in 'inlact' bog;• water loss may be exacerbated if lhe mineral subsoil is exposed.Physical and chemical conditionsThe peat surface <strong>of</strong> a little-damaged bog is typically acidic and nulrient poor. Peal extraction and drainage may lead to changes inthe physical and chemical characterislics <strong>of</strong> the peat available for recolonisation [Chapter 2]. For example:• rewetting dried peat may lead to release <strong>of</strong> nulrients;• rewetting dried peat may lead to further acidification;• peat extraction may expose fen peat or mineral ground;• bare, dry peal provi<strong>de</strong>s an inhospilable physical environmenl for vegetation eslablishment.VegetationThe vegetation <strong>of</strong> remnant peat surfaces and <strong>of</strong> abandoned peat workings can be extremely variable, <strong>de</strong>pending upon suchconslraints as <strong>de</strong>gree <strong>of</strong> damage, <strong>de</strong>pth <strong>of</strong> exlraction, lopography, base slalus, nulrient status, water level (and source) andlength <strong>of</strong> time since last worked [Chapter 4]. Areas lo be restored may lhus inelu<strong>de</strong> the following [see Box 3.1].• bog-Sphagnum vegetation • non-wetland vegetation;• para-bog-Sphagnum vegelation; • complelely bare surfaces• 'dry' bog vegetation; • open water• fen vegetalion;


Chapter 4Recolonisation <strong>of</strong> peat workings4.1 IntroductionThe most obvious feature <strong>of</strong> peat extraction is that itremoves the living vegetation from a bog to leave abare and <strong>of</strong>ien dry surface. Although natural,spontaneous colonisation by vegetation <strong>of</strong> sorne sortwill undoubtedly occur on such surfaces withoutfurther intervention, the aim <strong>of</strong> most restorationschemes will be to try to optimise conditions toencourage colonisation and establishment by speciesapptopriate to a specific restoration objective.The revegetation <strong>of</strong> cut-over bogs is consi<strong>de</strong>red heregiving attention to factors that may constrain orinfluence the renaturation processes. The techniquesavailable to facilitate recolonisation <strong>of</strong> vegetation areconsi<strong>de</strong>red in Chapter 9.Studies on the natural revegetation <strong>of</strong> cut-over siteshave indicated that the vegetation <strong>of</strong> such areas can bebroadly categorised into four groups [2.3.5; 3.2]:• bog-Sphagnum vegetation;• para-bog-Sphagnum vegetation;• vegetation typical <strong>of</strong>'dry' bogs;• vegetation typical <strong>of</strong>fens.In sorne instances, natural colonisation <strong>of</strong> abandonedhand-cut, or commercial block-cut, areas has inclu<strong>de</strong>dmany more bog species than spontaneous colonisation<strong>of</strong> a recently-abandoned, unmodified milled surface.This is due to factors such as topography, water levels,possible 'shoeing' I and availability <strong>of</strong> propagules andage (time since last cut). There is Iittle evi<strong>de</strong>nce tosuggest that vegetation typical <strong>of</strong> undamaged raisedbog, with a cover <strong>of</strong> actively growing Sphagnum. willspontaneously retum to extensive milled surfacewithout sorne <strong>de</strong>gree <strong>of</strong> intervention.Water regime appears to be the primary factor affectingrecolonisation by wetland plants, but both physical andchemical conditions <strong>of</strong> cut-over bog may differsignificantly from the undisturbed bog environment[Chapter 2]. On milled peat fields there are usuallyfewer areas where water is 'naturally' retained than inblock-cut areas, and abandoned areas are Iikely to bedrier (unless constructs are ma<strong>de</strong> to impound water).Spontaneous recolonisation <strong>of</strong>ien results in vegetationI Return <strong>of</strong>vegetation to the cuttingssimilar to that in the dry areas <strong>of</strong> block-cut sites, <strong>of</strong>ienwith few, if any bog species (e.g. E. vaginatum,Molinia) accompanied by a range <strong>of</strong> dry-Iand or'weed' species [see below].Preliminary botanical data (e.g. Shaw & Wheeler,1991) indicate that peat cuttings in fen peat support,overall, most <strong>of</strong> the characteristic fen plant species andmany distinctive fen vegetation-types occur wi<strong>de</strong>ly inrevegetated workings. Moreover, abandoned peatcuttings provi<strong>de</strong> the main reservoir for sorne speciesand vegetation-types, especially in England. This isbecause such peat cuttings help to provi<strong>de</strong> a wet fenand hydroseral environment in circumstances whichwould otherwise be comparatively dry and solid.Several <strong>of</strong> the species and communities which arerestricted, or almost restricted, to peat cuttings are rareand have high conservation importance, most notablythose in Broadland, Norfolk (GiIler & Wheeler, 1986,1988).The main factors affecting the revegetation <strong>of</strong> cut-overpeatlands can be i<strong>de</strong>ntified as:• availability <strong>of</strong> recolonist species;• physical and hydrochemical conditions, including type <strong>of</strong>peat;• water regime.These factors must be taken into account in consi<strong>de</strong>ringthe potential for revegetation <strong>of</strong> cut-over areas, andwhat, if any, measures should be taken in or<strong>de</strong>r t<strong>of</strong>acilitate the recolonisation by typical bog (or fen)species.4.2 Recolonisation <strong>of</strong> peatworkings by plantpropagules4.2.1 Seed banksRather little examination has been ma<strong>de</strong> <strong>of</strong> thecharacter <strong>of</strong> seed banks in undamaged ombrotrophicmires, but it is nonetheless clear that vadous bog plantspecies have a capacity to produce persistent seedbanks, and that various assemblages <strong>of</strong> viable seedshave been recovered from the uppermost peat <strong>of</strong> sorneSphagnum-dominated mires (e.g. McGraw, 1987;


64RESTORATION OF DAMAGED PEATLANDSPoschlod, 1988, 1990, 1995). Pennanent diasporebanks have also been found for many mosses andliverworts [Appendix 3].However, the characteristics <strong>of</strong> seed banks aresubstantialIy irrelevant to many peat extraction sites, asthe lower peat exposed by extraction does not retainviable seeds (Curran & MacNaeidhe, 1986; Salonen,1987a). In sorne circumstances, the top spit <strong>of</strong> peat canretain a viable bank <strong>of</strong> various bog species (Poschlod,1995), though this <strong>de</strong>pends upon its exact nature,origin and the conditions in which it has been kept.Seed banks may also have sorne significance in othercontexts. For example, the upper layers <strong>of</strong> uncutremnants may retain viable seed, which may respond torewetting initiatives. 'New' diaspore banks may also<strong>de</strong>velop in abandoned, revegetating peat cuttings, butvery <strong>of</strong>ten they are comprised <strong>of</strong> the seeds <strong>of</strong> various'weed' species, atypical <strong>of</strong> bogs, which have been<strong>de</strong>rived either from sources external to the bog or bythe spontaneous recolonisation <strong>of</strong> the abandoned cutoversurfaces. In many such cases the species concernedwill be unable to regenerate in a rewetted area, butthey may provi<strong>de</strong> a reservoir for a few species, such asJuncus effusus and Molinia caerulea, which may beconsi<strong>de</strong>red 'un<strong>de</strong>sirable', at least in large quantities.4.2.2 Diaspores and dispersa/distancesThe lack <strong>of</strong> a seed bank in the peat <strong>of</strong> newlyabandonedcut-over surfaces means that spontaneousrevegetation is <strong>de</strong>pen<strong>de</strong>nt upon the dispersal <strong>of</strong> viablediaspores from nearby sources. It has been suggested(Moore, 1982) that bog plant species are readilydispersed and can spontaneously recolonise sorne cutoverpeatlands in appropriate conditions. This may welIbe largely correct, though it is not supported by sornestudies (e.g., Poschlod, 1995). There is rather littlereliable infonnation on actual rates <strong>of</strong> dispersion formost bog species - in<strong>de</strong>ed, in sorne cases the dispersalagent is not conclusively known. It is likely that mostrapid colonisation would be selective towards specieswith wind-dispersed diaspores. Diaspores <strong>of</strong> variousbog species have been recor<strong>de</strong>d in the diaspore rainupon commercialIy-cut peatIands, though seed inputdoes not guarantee re-establishment (Salonen, 1987a,b). Sphagnum species may be welI adapted to longdistancedispersal by their minute spores, but effectivedispersal distances are not welI known, nor in<strong>de</strong>ed isthe ability <strong>of</strong> Sphagnum to establish onto bare peatfrom genninating spores. However, wind dispersal <strong>of</strong>Sphagnum is not necessarily restricted to its spores.Vegetation fragments <strong>of</strong> various bryophytes can bewind-dispersed to peat surfaces upon which they canregenerate (Poschlod, 1995).There is at least sorne evi<strong>de</strong>nce <strong>of</strong> the rapid colonisation<strong>of</strong> the wet floor <strong>of</strong> an abandoned sandstonequarry by bog species, including Sphagna, apparentlycolonised from a source sorne 14 km distant (Andreas& Host, 1983). However, the limits <strong>of</strong> dispersabilityare not realIy known and recolonisation <strong>of</strong> isolatedmires may possibly be constrained by this. Recolonisationrates will probably <strong>de</strong>pend upon the proximity<strong>of</strong> the worked-out areas to a source <strong>of</strong> propagules,though input <strong>of</strong>colonists from refugia may also <strong>de</strong>pendon the character <strong>of</strong>the intervening habitat, for example,the presence <strong>of</strong> woodland or scrub around a remnantmay reduce the influx <strong>of</strong> propagules <strong>of</strong> species usualIydispersed by wind. The importance <strong>of</strong> 'corridors' forwildlife conservation has received recent attention, butthe significance <strong>of</strong>these to bog plant species is unclear.It is important that, where possible, reservoirs <strong>of</strong>populations <strong>of</strong> bog species are maintained close to peatextraction sites as the presence 'on site' <strong>of</strong> typical bogspecies is likely to consi<strong>de</strong>rably enhance the rate and'quality' <strong>of</strong> natural recolonisation <strong>of</strong> bare surfaces orfloating rafts and increase the speed <strong>of</strong> <strong>de</strong>velopment <strong>of</strong>the more '<strong>de</strong>sirable' communities. Even where there isno uncut refugium for bog species, the survival <strong>of</strong>Sphagna in drainage ditches has been shown to be <strong>of</strong>value as a source for the spread <strong>of</strong> Sphagnum onto cutoversurfaces and the subsequent fonnation <strong>of</strong> floatingrafts. In sites lacking refugia, it may be necessary to reintroducespecies (see below).The availability <strong>of</strong>appropriate propagules is, <strong>of</strong>course,no guarantee <strong>of</strong> revegetation by these species withinabandoned peat workings as the conditions provi<strong>de</strong>dmay be unsuitable for their establishment (e.g. Salonen,1987a). Thus, for example, sites with dry, abandonedsurfaces may become colonised almost entirely by'weedy' species (Curran & MacNaeidhe, 1986), even ifthere is sorne remnant bog vegetation nearby, particularlywhere there is also adjoining fannland. Nonetheless,it is possible for a range <strong>of</strong> typical bog speciesultimately to establish on abandoned surfaces afterseveral years given suitable hydrochemical conditions.Dispersability obviously regulates colonisation by'weed' species as welI as by <strong>de</strong>sired ones. Anecdotalevi<strong>de</strong>nce from various workers has suggested that therate and extent <strong>of</strong> birch colonisation <strong>of</strong> bogs is relatedto the proximity <strong>of</strong> mature trees 1 , but that colonisationand establishment <strong>of</strong> 'un<strong>de</strong>sirable' species is reducedwhere water levels are sufficientIy high. However, theevi<strong>de</strong>nce suggests that it would be <strong>de</strong>sirable to controlpopulations <strong>of</strong> 'weed' species both within and aroundrevegetating mires to reduce the potential invasion <strong>of</strong>such species [see Chapter 10].1 Note that this is a problem on sorne Iittle-disturbed mires andmire remnants as well as in peat cuttings.


HAI'TER 4: RECOLONISATION OF PEAT WORKINGS 65Plate 4.1 Risley Moss, Cheshire: vegetation recolonisation c1early reflects the topography <strong>of</strong> the block peat cuttingsand relation to water level: baulks dominated by Molinia caerulea, the base <strong>of</strong> cuttings by Eliophorumangustifolium, and the trenches mainly open water. Sphagnum species (S. squarrosum, S. fimbliatum, S. palustre,S. recurvum) were recor<strong>de</strong>d in the base <strong>of</strong> the cuttings and trenches. (See also Plates 2.14 and 2.15]4.3 Effects <strong>of</strong> hydrologicalconditions on revegetation4.3.1 Significance <strong>of</strong> water levelThe importance <strong>of</strong> water level to the vegetationcomposition and structure <strong>of</strong> little-damaged raised bogsis outlined in Chapter 1, and discussed more fully inthe working document on which this report is based[see Background]. The hydrological regime is one <strong>of</strong>the main factors affecting the recoloni atíon <strong>of</strong> cutoverbogs by different plant species. Individual wetlandplant species may occupy rather dístinct zones withrespect to water level [1.9], although the actual waterlevel 'preferences' <strong>of</strong> mo t bog and fen plant species,(including bryophytes) have yet to be established withprecision. Thus, for example, sorne species areespecially tolerant <strong>of</strong> (and may 'prefer') quite <strong>de</strong>epwater conditions (e.g. Typha species); others seemtolerant <strong>of</strong> only shallow inundation (e.g. many forbs l );yet others may help form, or a least grow upon.tloating rafts <strong>of</strong> vegetation. Sphagnum specíes showtrends in mícrotopographical distribution with respectto water level [see Figure 1.1 O]. The <strong>de</strong>pth <strong>of</strong> water(above or below the surface) in abandoned cut-oversurfaces may therefore be expected to have animportant gross control upon the composition <strong>of</strong>recolonist vegetation [Plate 4.1], although any simpleprediction <strong>of</strong> likely <strong>de</strong>velopments <strong>of</strong> vegetation ingiven water level conditions is hampered by effects <strong>of</strong>the mechanism <strong>of</strong> recolonisation [4.3.2], and may beintluenced by the chemical conditions [44]. Optimal<strong>de</strong>pths <strong>of</strong> inundation are discussed in Chapter 5.The tability <strong>of</strong> the water table is also c1early importantin influencing which species may recolonise pealworkings. A strongly fluctuating water table may beinconducive to the colonisation <strong>of</strong> many typical bogspecies (and most importantly to Sphagna) and favourthe growth <strong>of</strong> less <strong>de</strong>sirable species as Molinia andbirch. Rewetting requires not just a high water table; italso requíres one that is relatively stable. This may bedifficult to achieve in practice, as the limited waterstorage capacity in the peat remaining in many peatextraction complexes can exacerbate water levelfluctuation. One solution is to try to stabilise the waterlevel relative lo lhe vegetation surface by creation <strong>of</strong>shaJlow lagoons, thereby helping to increase waterstorage, reduce water level fluctuations and to promotethe establishment <strong>of</strong> wetland species, particularlytloating Sphagnum rafts [see Chapters 5 & 9].I Forbs are non-graminoid herbs


Table 4.1 Vegetation recolonisation <strong>of</strong> cut-over surfaces by rooting (plants establish by attachment to the "solid" substratum) or rafting (growth <strong>of</strong> plants and vegetation, floatingin or on (sometimes shallow) water).Requirements:Water leveIsSurfaceconfigurationRootingSub-surface I shallow f100dingNo specific configuration required, other thanfor general retention <strong>of</strong> water; pools or pitsshould have gradually sloping si<strong>de</strong>s.RaftingDeep and persistent inundation (optimum <strong>de</strong>pth is probably c. 50 cm, unless supplementary f1otation mechanism available).Steep-si<strong>de</strong>d pools I pits; may be necessary to create sub-divisions <strong>of</strong> large peat fields using baulks to reduce potential fordamage to <strong>de</strong>veloping raft by wind or wave action.VegetationOccurrence <strong>of</strong> plants with sufficient buoyancy to f10at (either on the surface, or at least within the photic zone).Examples <strong>of</strong> possible colonising species in different conditions:········WeCbase~poo;:··T"Eriopiío;.üm·"ii¡.¡güsÜoiiüm:·E:·viigj";liiiüfii:·········T"Acjüaiic"Srihiig'nii:"Eiio¡;fioruin'angusiifo¡¡¡iin;"Drepanc;c;iidüs'-;¡üii"ii¡'¡s;"ói3'dic;podieiiii·;¡üiia·ns;··Menyanthes··iiifoiii3·ia··················· .! Erica tetralix, Rhynchospora alba, ¡¡ Sphagnum spp. ¡Wet, base-rich ¡ Typha spp., Scirpus lacustris, Phragmites ! Menyanthes trifoliata, Typha spp, Phragmites australis, Alisma plantago-aquatica, Carex pseudocyperus, Juncus effusus,! australis, Eleocharis palustris, Equisetum ¡ Glyceria maxima, Eriophorum angustifolium, Carex rostrata, Potentil/a palustris, Equisetum f1uviati/e¡ f1uviati/e, Glyceria maxima. ¡Ory, base-poor ¡ Molinia caerulea, birch, Cal/una vulgaris ¡ [not applicable]Ory, base-rich ¡ Holcus lanatus, Oactylis glomerata, Rubus ! [not applicable]¡ fruticosus, Ranunculus spp., Oeschampsia !¡ cespitosa, Carex nigra, C. <strong>de</strong>missa, Cirsium ¡Facilitation <strong>of</strong>recolonisationAdvantagesDisadvantages¡ spp., C. dissectum. ¡Inoculation with seed or rooted plant materialand 'seeding' with Sphagnum fragments.Does not require inundation.Existing '<strong>de</strong>sirable' vegetation (if present) isnot <strong>de</strong>stroyed.Vegetation change tends to be slow(e.g. birch may die gradually, but Moliniaremains dominant and species such asEriophorum vaginatum and Sphagna mayestablish and increase only slowly).Susceptible to water level f1uctuations; mayrequire management.'Seeding' with Sphagnum fragments, with subsequent inoculation with rooted plant material.Use <strong>of</strong> 'nurse' species such as Molinia caerulea or Eriophorum vaginatum to protect f10ating Sphagnum mats from wind andwave action. Water levels must be raised once Sphagnum has become established.May be possible to use birch brashings, floating <strong>de</strong>bris or an artificial material to accelerate recolonisation and reduce wind andwave action. Loose peat <strong>de</strong>bris ± existing vegetation may <strong>de</strong>tach from the bottom and f1oat.Inundation <strong>of</strong> the surface allows substantial water storage and may help to retard or even prevent establishment <strong>of</strong> speciessuch as birch, Molinia and Cal/una. Such species may also be killed by inundation.Vertical mobility <strong>of</strong> the raft allows the <strong>de</strong>veloping vegetation to accommodate some vertical flux in water levels. This isparticularly important in those situations where large seasonal f1uctuations in the mire water table are known to occur.May help to "short-circuit" the terrestrialisation process by forming a 'skin' <strong>of</strong> vegetation before cuttings have filled with peat,thereby allowing precocious invasion <strong>of</strong> species that will not grow in <strong>de</strong>ep water environments.Rafts may create conditions and support the vegetation that are known precursors <strong>of</strong> the natural <strong>de</strong>velopment <strong>of</strong> raised. bogs,e.g. lawn and hummock-forming Sphagna, even in base-rich conditions.Peat cuttings in fen peat have provi<strong>de</strong>d conditions for the <strong>de</strong>velopment <strong>of</strong> conservationally-<strong>de</strong>sirable plant communities.Requires a<strong>de</strong>quate control <strong>of</strong> water levels to ensure permanent inundation and to prevent "grounding" <strong>of</strong> the raft before thearea is self-sustaining; may require subdivision <strong>of</strong> large peat fields into smaller areas to avoid excessive damage to a fragile<strong>de</strong>veloping raft <strong>of</strong> vegetation by wind and wave action.Existing '<strong>de</strong>sirable' vegetation (if present) potentially <strong>de</strong>stroyed (although in some circumstances may become <strong>de</strong>tached fromthe bottom and f1oat, thus accelerating revegetation).


C1IAPTER 4: RECOLONISATlON OF PEAT WORKINGS67One potential problem in the creation <strong>of</strong> large floo<strong>de</strong>dlagoons is the possible attraction <strong>of</strong> certain birds(particularly gulIs and wildfowl), which may lead tonutrient enrichment through inputs <strong>of</strong> faeces, possiblygiving rise to the establishment <strong>of</strong> atypical vegetation,such as a dominance <strong>of</strong> the rush JUI7CUS ejfusus.However, the extent <strong>of</strong> the problem and the preciseconditions which may encourage such birds have yet tobe established, and there is at least sorne evi<strong>de</strong>nce thatbog vegetation can establish over 1. ejfusus at the sites<strong>of</strong> former gulI colonies (Baaijens, 1984, cit. Joosten &Bakker, 1987).lt is <strong>of</strong>ten suggested that an additional advantage <strong>of</strong>very wet conditions in recolonising peat workings isthat they help to suppress un<strong>de</strong>sirable species such asbirch or Molinia. Whilst in gross terms this is probablycorrect, both <strong>of</strong> these species can <strong>of</strong>ten show surprisingtenacity to survive, even in very wet conditions.However, consistently high water levels do seem to beable to restrain new colonisation by these species [seealso Chapter 10].4.3.2 Colonisation mechanismsIntroductionIn many situations, establishment <strong>of</strong> plant species uponpeat surfaces is by direct rooting l • but when thesurface is inundated another mechanism may operate ­rafting. in which the plants form a semi-floating raft,sometimes extending from, and anchored to, the si<strong>de</strong>s<strong>of</strong> the cuttings. Not alI wetland plants can form rafts,but many are able to grow upon rafts formed by otherspecies.In attempts to revegetate abandoned peat workings itmay be possible, <strong>de</strong>pending upon the local circumstances,to select a recolonisation mechanism. Inpractice this choice usualIy means either attempting tokeep the water table close to the peat surface to permitrooting, or attempting to have <strong>de</strong>eper flooding, topromote rafting. In sorne sites the possibility for evencru<strong>de</strong> control <strong>of</strong> the water levels may not exist, but inthose situations where it does, it becomes important toassess the merits <strong>of</strong> the two colonisation pathways.Salient features <strong>of</strong> rooting and rafting are summarisedin Table 4.1.RootingThe i<strong>de</strong>ntity <strong>of</strong> species colonising peat surfaces<strong>de</strong>pends upon the <strong>de</strong>pth and behaviour <strong>of</strong> the watertable (coupled with the chemical conditions) [4.3.1;4.4]. If the water table is substantialIy below thesurface <strong>of</strong> the peat for alI or part <strong>of</strong> the year, this wilIselect against species largely <strong>de</strong>pen<strong>de</strong>nt uponpermanently, consistently high water tables (such assorne SphagnulJ1 species) in favour <strong>of</strong> those that havemore drought tolerance (such as Eriophorumvaginatum). Conversely, if the water table remainshigh, either permanently or seasonalIy aboye the peatsurface, this may select against species that areintolerant <strong>of</strong> much flooding, in favour <strong>of</strong> emergentspecies (e.g. Eriophorum angustifolium). When thewater exceeds a certain <strong>de</strong>pth the water wilI becometoo <strong>de</strong>ep for most species to survive rooted to the peat,and colonisation wilI <strong>de</strong>pend on species able to floatand form rafts (see below). It is difficult to specify amean critical water <strong>de</strong>pth because:a) it varies between species;b) it differs for lhe new colonisalion <strong>of</strong> planls compared tothe persislence <strong>of</strong> established plants. In general, manywelland plants are able to survive, rooted, in consi<strong>de</strong>rably<strong>de</strong>eper water lhan that in which they would be able loestablish (from seed).Where pools <strong>of</strong> water are too <strong>de</strong>ep to pennit theinvasion <strong>of</strong> any given particular species by rooting,unless rafting takes place its establishment is <strong>de</strong>ferreduntil shalIower conditions prevai!. This may occurbecause <strong>of</strong> the gradual accumulation <strong>of</strong> organic mudsand peats within the pool, as part <strong>of</strong> autogenic 2terrestrialisation <strong>of</strong> the water (hydroseral infilling); byinputs <strong>of</strong> alIochthonous 3 sediments (e.g. wind-blownpeat); or through a sustained lowering <strong>of</strong> the waterleve!.RaftingThe term 'rafting' is used here to refer to the growth <strong>of</strong>plants and vegetation, floating in or on (sometimesshalIow) water. By <strong>de</strong>finition it requires some <strong>de</strong>gree<strong>of</strong> at least seasonal inundatíon. The i<strong>de</strong>ntity <strong>of</strong> speciesforming the rafts wilIlargely <strong>de</strong>pend upon the chemicalconditions; raft-forming species inclu<strong>de</strong> Menyanthestrifoliata, Phragmites australis, Typha spp.,Eriophorum angustifolium and aquatic Sphagnumspecies). Individual plants may be free-floating or theymay be attached to the margins <strong>of</strong> the pools, fromwhence they have expan<strong>de</strong>d across the water. WhenwelI <strong>de</strong>veloped, rafting may short-circuit the usualterrestrialisation process by producing a skin <strong>of</strong> vegetationat the water surface in <strong>de</strong>ep cuttings before theyhave filIed with peal. It therefore permits the earlyinvasion <strong>of</strong> plant species that will not grow in very wetconditions. The term 'rafting' also inclu<strong>de</strong>s the growth<strong>of</strong> loose mats <strong>of</strong>Sphagnum etc. within the water [PI ate4.2]. These may or may not ultimately form a surfacefloating raft, <strong>de</strong>pending on topographical and water1 Strictly speaking the term 'attachment' is more correct, asbryophyte species do not have roots.2 autogenic = 'self-ma<strong>de</strong>'3 allochthonous =externally <strong>de</strong>rived


68 RE TüRATlü üF DAMAGED PEATLANDPlate 4.2 Sphagnum cuspidatum forming a raft in a fioo<strong>de</strong>d lagoon within worked-out peat cutlings; AmsterdamscheVeld (Bargerveen, The Netherlands).e ndition , and in shallowly-floo<strong>de</strong>d sitegroun<strong>de</strong>d for at least part <strong>of</strong> the year.they may beWhere a raft <strong>of</strong> vegetation forms, it is usually initiallyfragile; <strong>de</strong>composing portion 111 a <strong>de</strong>tach and fall tothe floor <strong>of</strong> the pool and ontribute to upwardaccumulation <strong>of</strong> organic material. But rafts u uallyincrease in thickne , both b an increa e In livingplant material and by entrapment <strong>of</strong> mud and peal. Ins doing the raft will gradually tabilise and ultimatelywill be able to upport trees (see below).The occurrence <strong>of</strong> a rafting c loni ation pr ce doesnol mean thal colonisafon <strong>of</strong> the water b dy isin<strong>de</strong>pen<strong>de</strong>nt <strong>of</strong> its <strong>de</strong>pth. For example, ome f them re aquatic Sphagna (e.g. S. cllspidatllln) gro wellin fairly shallow open water bul less well in <strong>de</strong>epondition, p ibty becau e <strong>of</strong> limiled uppty <strong>of</strong>di olved carbon ource e.g. Baker & Boatman, 1990;Paffen & R el<strong>of</strong>s, 1991; .loo t n, 1992; Mon y, 1994).11 eems likely that lhe 'oplimum' inundation regimefor lhe promotion <strong>of</strong> aquatic Sphagna will usually be atra<strong>de</strong>-<strong>of</strong>f betw en a need to avoid <strong>de</strong>ep inundatíon tomaximise phagnum growth and a need to tore asmuch exce water as is nee<strong>de</strong>d to avoid <strong>de</strong>siccationd Iring dr period.. Depths grealer lhan .50 cm s emgenerally un uitable for good growth <strong>of</strong> aqualicphagna in bog water (e.g. Money, 1994) thoughexception also occur, ~ r e ample, S. auriclllatllnl isknown to grow in a lake at <strong>de</strong>pthZielone, Poland (pers. obs.).up to 10m at.le ioroAlthough rafting recolonisation may result in an initialeradication <strong>of</strong> 'un<strong>de</strong>sirable' pecie such as birch, raftsmay not be free from subsequenl c loni ation by these.Thi is becau e a the raft matures, although il mayink beneath it own weight, even before it has'groun<strong>de</strong>d' the urface may remain slightly proud <strong>of</strong>the water and may be suitable for e tablishment <strong>of</strong>eedling birche elc. The <strong>de</strong>gree to which this is aproblem may vary between ites. It i not diflicult t<strong>of</strong>ind floating rafts in which apling birche havebecome he Id in 'check' and show ¡ittle sub equentgrowth. Isewhere trees may progressively sinkthrough an lInslable raft as they become heavier and1I1timalely be ome moribund or die. lt cann t beconclu<strong>de</strong>d thal noaling raft <strong>of</strong> phagnllln will remainfree from woody cover, but this may, <strong>of</strong> course, be partf a natural I c s ional progres ion loward raisedbogo The problem is exacerbated when Ihe raft is only<strong>de</strong>veloped in hallow water, a 'grounding <strong>of</strong> the peatraft may lead t urface-dry conditions.Re torallon strategies aimed at Lhe production <strong>of</strong> rafts<strong>of</strong> vegetation seem to be particularly effectiveapproache lo the rewetting and revegetation <strong>of</strong> peatworking in both bog and fen peat in that (i) theyrequire inundalion <strong>of</strong> the mire surface (i.e. they permit


CCHAPTER 4: RE OLONl ATIO OF PEAT WORKING,69substantial water storage); (ii) they allow the<strong>de</strong>veloping vegetation to accommodate such vertical'water flux a may occur (at least within limits) by theirown vertical mobility and help to create permanentlywet urface conditions. In principie they seem a morepotent approach to mire re toration than strategies justaimed at keeping the water level close to the peatsurface, particllarly in those situation where largeseasonal fluctuations in the mire water table are knownto occur. Rafting is also a potentially importantmechanism for re-establishing Sphagnum vegetation in(former) bogs where substantial base-enrichment hasoccurred, as the hydrological stability and mobility <strong>of</strong>the raft prevents its inundation. However, the potentialimportance <strong>of</strong> rafting hould not just be seen in terms<strong>of</strong> the production <strong>of</strong> small-scale ombrotrophic tloatingrafts, important as the ma be, but also as afundamental strategy for regenerating an acrotelm-liketructure ayer large areas <strong>of</strong> <strong>de</strong>relict raised bogs. Insuch ituation the <strong>de</strong>velopment <strong>of</strong> floating rafts maybe the onl effective way <strong>of</strong> re-establishing mirevegetatíon, although there are sorne Iimitation .onversely, frost-heaving in winter is likely to affectseedling establishment on bare peat surfaces. Bare peatis also prone to erosion by wind 01' water, particularlywhere sloping (Tallis & Yal<strong>de</strong>n, 1983) [Plate 4.4].Such physical instability <strong>of</strong> the substratum is perhapsbest reduced by the <strong>de</strong>velopment <strong>of</strong> a vegctatíon cover,but it may sometimes be necessary to use artificialstabilants before this can be achieved.Dark, bare peat is likely to abso b heat - increasedtemperature will exacerbate moisture loss and mayaffect plant establishment A cover <strong>of</strong> vegetation canalso help to buffer against fluctuations in water contentand temperature <strong>of</strong> the surface peat, for example byreducing the drying effect <strong>of</strong> the wind, and providing amore favourable microclimate for the establishment <strong>of</strong>phagnum species (Grosvemier, Matthey & Buttler,1995). It may be possible to achieve similar results by'planting' the peat surface with plastic plants (Salonen,1992), but in general the <strong>de</strong>velopment <strong>of</strong> a naturalcover is to be preferred.4.4 Physical and chemicalinfluences on revegetation4.4.1 IntroductionDifferent plant pecie are adapted to grow un<strong>de</strong>rdifferent environmental conditions. The conditionsprevailing at a given site largely <strong>de</strong>termine whichavailable pecies are able to coloni e and establish. Themajor environmental influences upon the composition<strong>of</strong> mire vegetation are: water supply (rainfall amountand frequency, water <strong>de</strong>pth and flow); base status;nutrient status and (in a few cases) saJinity. There mayal o be physical constraints on revegetation,particllJarly <strong>of</strong> bare peat surfaces. The effects <strong>of</strong> sorne<strong>of</strong> these variables are i<strong>de</strong>ntified below. In addition toenvironmental variables, vegetation managementpractices have a critical role in controlling andmaintaining the character <strong>of</strong> many herbaceollsvegetation-types, particularly in fens - these areconsi<strong>de</strong>red further in Chapter 10.Plate 4.3 Bare peat surface created by surface milling,sparsely colonised by Narthecium ossifragum.4.4.2 Physical factorsBare peat surfaces are likely to provi<strong>de</strong> an inhospitableenvironment for establishment <strong>of</strong> plant propagules[Plate 4.3], although the 'difficult' environmentalconditions fOllnd on an expo ed peat surface mayometimes serve more to retard plant establishmentthan to prevent it (Salonen, 1987b). lImmer droughtmay not only have a directly adverse affect upon thesurvival <strong>of</strong> seedlings <strong>of</strong> bog plants, but may also leadto crust formation and cracking <strong>of</strong> the peal.Plate 4.4 Unstable and eroding, sloping peat surfaceremalnlllg after surface milling, partly colonised byEriophorum vaginatum. Wendlinger Filz (S. Germany).


70RE TORATINOFOAM GEOPEATLA oIf a peat surface is too un table for vegetation toe tabl"sh, it may be appropriate to use a surface mulch01' artificial stabilants, over small areas at least. lt is notpossible to make firm recommendatiolls <strong>of</strong> methods, asthese have not been wi<strong>de</strong>ly tested.4.4.3 Chemical factorsIn Britain, an important control on the attern <strong>of</strong>spatialand temporal variation in plant species distribution inombrotrophic mires is rainfall quantity and quality,itself controlled by factors sucb as proximity to the seaand <strong>de</strong>gree <strong>of</strong> atrno pheric poHution (Proctor, 1995).Two further major influences up n the peciecomposition <strong>of</strong> mire vegetarion are tbe ba e andnutrient status <strong>of</strong> the substratum.Plate 4.5 Polygonum amphibium and Typha latifoliacolonising peat cuttings in fen peat; Somerset Levels.Plate 4.6 Polygonum amphibium colonising refloo<strong>de</strong>d,marl-based peat workings at Turraun 80g (Ireland).(See also Plate 2.13]Base statusBase status exerts a primary influence upon thecomposition <strong>of</strong> fen and bog vegetation. The base status<strong>of</strong> the water in peat workings is <strong>de</strong>termined primarilyby the characteristics <strong>of</strong> the peat (and un<strong>de</strong>rlying subtrata)and the quality <strong>of</strong> any irrigating water inputs.These influences will substantially constrain thecharacter <strong>of</strong> the invading vegetation, though otherinfluence may modify ome <strong>of</strong> their effects fore ample whilst fen plant species are the typicalrecolonists <strong>of</strong> peat cuttings with base-rich water [PIates4.4 and 4.5], the <strong>de</strong>velopment <strong>of</strong> a semi-floating raft <strong>of</strong>vegetatian may facilitate the establishment <strong>of</strong>Sphagnum-dominated vegetatian even over the mostbase-rich water (Giller & Wheeler, 1988' Mallik,1989).Few chemical data exist for peat extracti n sites in theUK. Thos that are available for ombrotrophic peatworkings suggest that the concentration <strong>of</strong> most ions isgenerally higher in the water and peat frorn peatworkings than from less disturbed situations and sometimesprovi<strong>de</strong> chemical conditions more like those <strong>of</strong>pOOl' fens than ombrotrophic bogs [2.3.3]. There is alsoevi<strong>de</strong>nce to uggest that in ome circum tances,chemical change resulting from drainage <strong>of</strong> the peatand seasonal fluctuations in water levels can lead toincreases in acidity (pH


CHAPTER 4: RECOLONISAnON OF PEAT WORKINGS71<strong>de</strong>velopment into ombrotrophic bogo By contrast, if thepeat is f1oo<strong>de</strong>d, there is potential for <strong>de</strong>velopment <strong>of</strong> aseral, f10ating fen vegetation which may provi<strong>de</strong> atemplate for more rapid re<strong>de</strong>velopment <strong>of</strong> bogvegetation.It is possible that where only a small thickness <strong>of</strong> peatremains at the base <strong>of</strong> peat workings there may besorne chemical inf1uence from the un<strong>de</strong>rlying mineralground. The effect <strong>of</strong> this will <strong>de</strong>pend upon itscharacter - Sphagnum can recolonise base-poor sandsand gravels quite readily and sorne excellentSphagnum-based communities have <strong>de</strong>velopedhydroserally in small pits within glacial sands (e.g.Delamere Forest, Cheshire).Nutrient statusThe ombrotrophic bog environment is typicallynutrient poor and infertile. However, disturbance <strong>of</strong> thepeat through peat extraction operations or <strong>de</strong>hydrationcan lead to mineralisation <strong>of</strong> the drying peat andnutrient release [2.2.2; 2.3.3]. There is little evi<strong>de</strong>ncethat this is inimical to revegetation prospects bySphagnum species, but data are sparse. In many sites itis not obvious whether augmented N concentrations<strong>de</strong>rive from disturbance <strong>of</strong> the peat or atmosphericcontaminants (or both). More substantial nutrient (andbase) enrichment may occur when eutrophic waterfrom rivers or land drainage is allowed to enter peatworkings. Exposure <strong>of</strong> un<strong>de</strong>rlying fen peat or clayscan, in principie, also expose a substratum that is morenutrient-rich than was the overlying ombrotrophic peat.The quality <strong>of</strong> irrigating water inputs from sourcesother than precipitation should be carefully assessed,and ifnecessary, polluted water diverted away from thesite.A wi<strong>de</strong> range <strong>of</strong> fen communities have been recor<strong>de</strong>dfrom recolonised peat workings, <strong>de</strong>veloped either onsolid peat or hydroserally. As a general rule, thosewhich are particularly welcomed by conservationistsfor their intrinsic value are those which have <strong>de</strong>velopedin conditions <strong>of</strong> low fertility; such vegetation-types are<strong>of</strong>ien species-rich, frequently contain variousuncommon plant species and are themselves rare:Nutrient-enrichment <strong>of</strong> abandoned fen peat workings,particularly by nitrogen or phosphorus, is typicallyassociated with the <strong>de</strong>velopment <strong>of</strong> a vigorous, coarseand species-poor vegetation that has limited botanicalvalue, although it may still provi<strong>de</strong> an importanthabitat for other groups such as birds or invertebrates.4.4.4 Peat-typeThe nature <strong>of</strong> the peat surface presented for recolonisationmay <strong>de</strong>pend on the type <strong>of</strong> peat exposed [1.8;2.3]. Weakly-humified peat is thought to provi<strong>de</strong> betterconditions for revegetation than strongly-humified peat(e.g. Eigner & Schmatzler, 1980; Nick, 1985),apparently ref1ecting its physical properties, such aslooser structure, and, particularly, its greater waterstorage capacity (Schouwenaars & Vink, 1992;Ro<strong>de</strong>rfeld, 1992). It may be able to retain water betterthan strongly-humified peat, to the extent that it mayswell upon rewetting and thus take on sorne <strong>of</strong> thefunctional attributes <strong>of</strong> the original bog acrotelm.However, it has also been suggested that sorne littlehumifiedpeat is too <strong>de</strong>ficient in nutrients to sustaingood regrowth <strong>of</strong> sorne bog species (J. Blankenburg,pers. comm.), and there is little clear evi<strong>de</strong>nce tosuggest that the weakly-humified peat is necessari/ymore <strong>de</strong>sirable for encouraging revegetation <strong>of</strong> cutoversurfaces than is strongly-humified peat as this isalso related to the nature <strong>of</strong> the rewetting strategy[Chapter 5]. Evi<strong>de</strong>nce from The Netherlands (e.g.Joosten, 1992) suggests that weakly-humified peatthrown back into peat cuttings as a type <strong>of</strong> bunker<strong>de</strong>[9.5] may facilitate the formation <strong>of</strong> a f10ating rafi onwhich Sphagnum and other species could colonise.Exposure <strong>of</strong> fen peat will undoubtedly inf1uence thecomposition <strong>of</strong> the recolonist species, as the chemicalenvironment is likely to be more conducive to theestablishment <strong>of</strong> fen rather than bog vegetation (seeaboye).4.4.5 Depth o(residual peatIn broad terms, the effect <strong>of</strong> residual peat <strong>de</strong>pth uponthe prospects for rewetting and subsequent revegetationis likely to be important in two main ways:• the intrinsic characteristics <strong>of</strong> the peat-type that isexposed at a particular <strong>de</strong>pth;• the effect <strong>of</strong> the thickness <strong>of</strong> the residual peat layer as abuffer against un<strong>de</strong>rlying conditions and vertical waterloss by seepage.The intrinsic characteristics <strong>of</strong> the peat are related to,and partly <strong>de</strong>termined by, its position in the peat pr<strong>of</strong>ile[1.8]. The chemical composition may be <strong>of</strong> particularsignificance [4.4.3] but differences in physical propertiessuch as water storage capacity (if any) [2.3.2;4.4.4] may be overcome by inundation [Chapter 5].In peat cutting complexes, the <strong>de</strong>pth 01' residual peatthat is nee<strong>de</strong>d to minimise, to an acceptable level,downward seepage losses into the un<strong>de</strong>rlying mineralsubstrata in appropriate sites is likely to <strong>de</strong>pendstrongly on the permeability 01' the peat. Studies arehampered by difficulties <strong>of</strong> making an accurateestimate <strong>of</strong> vertical seepage. Schouwenaars,Amerongen & Boortink (1992) provi<strong>de</strong> evi<strong>de</strong>nce thatrates <strong>of</strong> downward loss are inversely related to residualpeat <strong>de</strong>pth. A 'critical <strong>de</strong>pth' against seepage has notbeen established, but Blankenburg & Kuntze (1987)suggest that at least 50 cm <strong>of</strong> a low permeability,


72RESTORATION OF DAMAGED PEATLANDSstrongly-humified peat is nee<strong>de</strong>d to keep downwardseepage losses below what they consi<strong>de</strong>red to be anacceptable rate <strong>of</strong> 60 mm a-l. Similarly, Schouwenaars(1993) suggests that at least 50 cm <strong>of</strong> stronglyhumifiedpeat (H ~ 7) is mostly sufficient to guaranteelimited water losses, whereas for less stronglyhumifiedpeat (H 5-7) a minimum thickness <strong>of</strong> I mmay be required, unless the water pressure in theun<strong>de</strong>rlying aquifer lies aboye the base <strong>of</strong>the peat. Suchpossible losses by vertical seepage may be largelyinconsequential to those many UK sites which are overimpermeable substrata, but there is a need for a morecareful evaluation <strong>of</strong> this water balance term in thosesites where this is a possibility; experience elsewheresuggests that it may have pr<strong>of</strong>ound repercussions forthe success <strong>of</strong>restoration initiatives.A minimum <strong>de</strong>pth <strong>of</strong> ombrotrophic peat may benee<strong>de</strong>d to help prevent enrichment from un<strong>de</strong>rlyingbase-rich substrata (fen peats or mineral ground), eitherdirectly or through plant roots being able to tap anyun<strong>de</strong>rlying enriched conditions. Again a critical <strong>de</strong>pthhas not been established, but various consi<strong>de</strong>rationspoint to a <strong>de</strong>pth <strong>of</strong> 50 cm as a <strong>de</strong>sirable minimum, aview shared by various workers (e.g. Eggelsmann,1980).Note also that the <strong>de</strong>pth <strong>of</strong> residual peat consi<strong>de</strong>redmust take into account the <strong>de</strong>pth beneath the f100r <strong>of</strong>drainage channels and the disposition <strong>of</strong> the peat fieldsin relation to the un<strong>de</strong>rlying topography <strong>of</strong> the mineralsub-soil [see also Chapter 6].4.5 External constraints onrevegetation4.5.1 IntroductionEarlier sections <strong>of</strong> this chapter have consi<strong>de</strong>red therelationship between sorne internal conditions <strong>of</strong> cutoversites to their revegetation prospects, for example,lack <strong>of</strong> recolonist species and hydrological andchemical factors. However, there are also sorneexternal processes which may inf1uence thecharacteristics <strong>of</strong> the site which it may not be possibleto manipulate directly.4.5.2 Effects <strong>of</strong>atmospheric pollutionIntroductionAs raised bogs are irrigated directly and more-or-Iessexclusively by precipitation inputs, and as theircomponent plant species may be well adapted to'scavenge' solutes from dilute solutions (as seenperhaps most notably in species <strong>of</strong>Sphagnum (Malmer,1988», they may be particularly susceptible toatmospheric contaminants [1.9.4]. These may inf1uencethe growing plant species either by sorne direct toxiceffects or by a more indirect perturbation <strong>of</strong> the'chemical balance' <strong>of</strong> the mire water, such asenrichment with nutrients that would normally begrowth-lirniting.Possible implications tor bog growth andrestorationThe assessrnent <strong>of</strong> the effects <strong>of</strong> atmospheric pollutantsand implications for growth <strong>of</strong> bog species is hamperedby lack <strong>of</strong> data and the difficulty <strong>of</strong> relating plantresponse to specific concentrations <strong>of</strong> different pollutants.However, it seems likely that in present circumstancesthe <strong>de</strong>position <strong>of</strong> nitrogen oxi<strong>de</strong>s and ammoniarnay have more significant effects on growth <strong>of</strong> bogspecies than sulphu'r dioxi<strong>de</strong>. Atmospheric pollutionhas probably inf1uenced the composition <strong>of</strong> thevegetation <strong>of</strong> sorne bogs in the past and it is possiblethat atrnospheric nitrogen enrichment may affectraised-bog vegetation in certain regions at present,though this is not c1early established. Threshold valuesfor the possible <strong>de</strong>trimental effects <strong>of</strong> nitrogenouscontaminants upon lowland bogs are not known, but itis possible that these may differ for the maintenance <strong>of</strong>existing bog vegetation compared to the recreation <strong>of</strong>bog comrnunities on cut-over sites, not least becausethe latter may be subject to additional sources <strong>of</strong>enrichment in consequence <strong>of</strong> disturbance,rnineralisation etc. [2.3.3]. Further work is required toprovi<strong>de</strong> critically <strong>de</strong>finitive evi<strong>de</strong>nce in or<strong>de</strong>r toestablish whether current levels <strong>of</strong> atmosphericpollution are disadvantageous to the prospects forregeneration <strong>of</strong>raised bogs.4.5.3 Lowering <strong>of</strong>regionalgroundwater levelsA <strong>de</strong>crease in regional groundwater tables mayinf1uence the water balance <strong>of</strong> sorne sites [2.3.2],although it rnay be possible to mitigate these effects byretaining a sufficient <strong>de</strong>pth <strong>of</strong> low permeability peat[4.4.5].4.5.4 Climatic constraintsThe clirnate at a given site may inf1uence theopportunities for revegetation by bog species, andhence the most appropriate restoration strategies. Aprecipitation input <strong>of</strong> 700 mm a- l has been suggestedas a threshold below which permanent moistureshortage will occur in North Germany and TheNetherlands (Casparie & Streefkerk, 1992) but it is notc1ear how accurately this has been established. It isdifficult to specify a universal threshold value as


CHAPTER 4: RECOLONISAnON OF PEAT WORKINGS73factors such as the amount and distribution <strong>of</strong> rainfall,temperature, humidity and evapotranspiration may allaffect the water balance <strong>of</strong> the mires and the potentialfor regeneration <strong>of</strong> bog vegetation. In the UK, the mostcrucial period for wetland vegetation is during thesummer months, when evaporation typically exceedsprecipitation. In addition, constraints imposed byspecific climatic regimes can sometimes beaccommodated by the rewetting strategy that is chosen.The conditions suitable for the maintenance <strong>of</strong> apeatland vegetation are Iikely to be different from thosenecessary for its establishment. For example, a c10sedcarpet <strong>of</strong> Sphagna is able to preserve moisture byforming a 'mulch' over the surface, and 'bleaching' <strong>of</strong>the Sphagna on <strong>de</strong>hydration helps to ref1ect inci<strong>de</strong>ntradiation, thereby helping to reduce the loss <strong>of</strong> waterfrom the peat surface / acrotelm (Schouwenaars, 1990).However, until a c10sed carpet is achieved, theindividual plants are more likely to be susceptible to<strong>de</strong>siccation during periods <strong>of</strong> low rainfall andhumidity.4.6 Recolonisation <strong>of</strong> peatworkings by invertebratesVery little is known <strong>of</strong> the colonising abilities <strong>of</strong>raised-bog invertebrates, but it is Iikely that dispersalwill be limited in flightless species or those havingreduced wings (as in the case <strong>of</strong> sorne beetles andbugs). However, the carabid beetle, Agonum ericeti isknown to be f1ightless in the UK and in<strong>de</strong>ed over much<strong>of</strong> its range (Thiele, 1977: 291; Lindroth, 1985) but itis nevertheless wi<strong>de</strong>ly distributed in suitableoligotrophic mires. In sorne species mobility may beeffected by methods other than flight, though it mayalso ref1ect in part, a greater contiguity <strong>of</strong> raised-bogareas in the past.The importance to dispersal <strong>of</strong>the habitat-type betweenthe refugium and areas to be colonised <strong>de</strong>pends greatIyon the mo<strong>de</strong> <strong>of</strong> dispersal <strong>of</strong> particular species. Forlarge, highly mobile and relatively strong-f1yingspecies such as dragonf1ies (Odonata) and sorne fliesand Lepidoptera, intervening habitat-type may berelatively unimportant. Sorne species <strong>of</strong> dragonflies,for example, are markedly migratory in their behaviour(though sorne notable raised-bog species are more-orlessse<strong>de</strong>ntary). At the other extreme, many flightlessspecies such as sorne beetles and bugs, may be unlikelyto enter areas <strong>of</strong> unsuitable habitat (i.e. areas that aretoo shady, dry, friable, alkaline, etc.); Thiele (1977:214) intimated that substratum type was probably animportant <strong>de</strong>terminant <strong>of</strong> movement in carabid beetles.Nevertheless, studies have shown that a surprisinglylarge number <strong>of</strong> invertebrate species are capable. <strong>of</strong>colonising even remote islands <strong>of</strong>suitable habitat givensufficient time.Rates <strong>of</strong> recolonisation <strong>of</strong> cut-over areas are likely tobe strongly inf1uenced by the character <strong>of</strong> thevegetation <strong>de</strong>veloped within the workings, and also bythe proximity <strong>of</strong> refugia for '<strong>de</strong>sirable' invertebratespecies - nothing is known about the potential toinoculate regenerating areas with appropriateinvertebrates in the absence <strong>of</strong> nearby refugia.Nevertheless, studies by Heaver & Eversham (1991) <strong>of</strong>extraction sites at Thorne Waste which had beenworked up to the 1970's but which were since largelyundisturbed and wet, show that colonisation <strong>of</strong> at leastsorne species can occur fairly rapidly (including in thiscase sorne 27 scarce or rare taxa). Such successfulrecolonisation was probably <strong>de</strong>pen<strong>de</strong>nt on thepersistence <strong>of</strong> the recolonising species in nearbyrefugia, but provi<strong>de</strong>s at least sorne evi<strong>de</strong>nce thatconservationally-worthwhile, more or less balancedinvertebrate communities can reassemble within c. 50­70 years given the presence <strong>of</strong> adjacent refugia,perhaps even less, although the communities that existat this time are undoubtedly still transitional. However,rates <strong>of</strong> recolonisation will c1early also <strong>de</strong>pend on theavailability and proximity <strong>of</strong> potential recolonistspeciesThere have been very few studies <strong>of</strong> the behavioural orphysiological selection processes that restrict peatlandinsect species to particular types <strong>of</strong> habitat, although ithas been suggested that factors such as pH and c1imatemay inf1uence distribution in sorne species (e.g. Paje &Mossakowski, 1984; Peus, 1932). Availability <strong>of</strong>specific food sources (plants, animals or <strong>de</strong>tritus),vegetation height and structure are also likely to beimportant <strong>de</strong>termining factors, as are the amount anddistribution <strong>of</strong> open water and hydrological regime(e.g. Key, 1991). For example, an increase in provision<strong>of</strong> open water habitat by management such as ditchblocking or creation <strong>of</strong> pits or scrapes, <strong>of</strong>ien leads to anincrease in dragonf1ies (e.g. Fox, 1986b). In general,dragonf1ies do better where there is sorne protectionfrom the wind and so are favoured by sites with peatwalls, adjacent scrub or at the edges <strong>of</strong> raised bogswhere woodland may act as a windbreak (R.G. Kemp,pers. comm.). It should be remembered that the habitatrequirements <strong>of</strong> a species will be govemed by both therequirements <strong>of</strong>the adult and also, the larva, pupa, etc.,and that these may be rather different, necessitating thepresence <strong>of</strong> two or more different and perhaps evenspatially separated features.


74RESTORATION OF DAMAGED PEATLANDS4.7 Recolonisation <strong>of</strong> peatworkings by birdsAlthough most birds show strong site fi<strong>de</strong>lity fornesting, roosting etc, ringing recoveries c1early showthat many species do not remain in the same area (oreven the same continent!) throughout the year. In view<strong>of</strong> such natural mobility it might be assumed that birdswould readily abandon a site following adverse habitatchange, or high levels <strong>of</strong> disturbance. Refugia may belocated far from a disturbed site, and may be eithertemporarily or permanently adopted by the displacedpopulations. However, where species are displacedfrom sites located close to the Iimit <strong>of</strong> their geographicalrange, the chances <strong>of</strong> recolonisation <strong>of</strong> the sitefollowing restoration measures would be consi<strong>de</strong>rablyreduced.A distinction can be recognised between areas whichhave previously been hand cut for peat and those whichhave been worked using current technology. In theformer, a mosaic <strong>of</strong> wet and dry habitats results over arelatively long timescale and colonisation fromadjacent intact or recently colonised areas can beexpected to be reasonably rapid if suitable habitatsresult. By contrast, extensive commercial extractiontechniques remove aH breeding birds from extensiveworking areas in the short termo No data are yetavailable on the colonisation characteristics <strong>of</strong>extensive cut surfaces in the longer termoDisturbance, lack <strong>of</strong> food sources and nest sites islikely to severely limit the use <strong>of</strong> expansive areas <strong>of</strong>newly cut-over bog by birds. As these areas becomerevegetated birds may readily colonise, although reestablishment<strong>of</strong> a community which is characteristic<strong>of</strong> little-damaged raised bog is unlikely in the shorttermo The species which colonise will largely <strong>de</strong>pendon the distribution and amount <strong>of</strong> open water and thetype <strong>of</strong> vegetation which <strong>de</strong>velops (as well as the site'sgeographical location), being influenced by suchfactors as suitability and availability <strong>of</strong> food sources,nesting sites, roosting sites, vegetation structure etc..For example, increased provision <strong>of</strong> open water hasbeen shown to attract breeding wa<strong>de</strong>rs and duck(including teal) which may be attributed to increasedfood availability (e.g. aquatic invertebrates, includingOdonata, Hemiptera, Coleoptera and Diptera) (Fox,1986a). The <strong>de</strong>velopment <strong>of</strong> birch scrub attractsspecies typical <strong>of</strong> woodland: willow warbler being themost characteristic species <strong>of</strong> pioneer birch woodland,with a number <strong>of</strong> other passerine species also beingrepresented. Where fen vegetation <strong>de</strong>velops in oId peatworkings, additional species such as sedge warbler,reed warbler, water rail, moorhen and coot can beattracted to breed. Conversely, loss <strong>of</strong> suitable habitatas a result <strong>of</strong> rewetting may reduce the numbers <strong>of</strong>such species as nightjar and skylark.


Chapter 5Rewetting damaged and cut-over peatlands5.1 IntroductionIn any project aimed at restoring or recreating wetlan<strong>de</strong>cosystems, long-term success <strong>de</strong>pends upon theprovision <strong>of</strong> a hydrological regime appropriate for theestablishment and maintenance <strong>of</strong> the target wetlandbiota. It is not possible to give a simple, or universal,prescriptive solution to the problems <strong>of</strong> rewetting peatextraction complexes as this will <strong>de</strong>pend critically uponsuch site-specific factors as topography, dispositionand character <strong>of</strong> the peat fields, peat type and climateas well as the objective <strong>of</strong> restoration. However, it ispossible to i<strong>de</strong>ntify sorne general principies, problemsand solutions, based upon attempts at restoration [seespecific references and Appendix 6J, and to discemsorne broad categories <strong>of</strong> context in which bogrestoration is likely to occur. In this chapter, the principies,potential and limitations <strong>of</strong> various rewettingprocedures are discussed. The adoption <strong>of</strong> these, inrelation to specific restoration objectives, is discussedfurther and summarised in Chapter 6. The primaryfocus is upon producing conditions appropriate for themaintenance or re-establishment <strong>of</strong> a typical,Sphagnum-rich, bog vegetation, but sorne altemativesare consi<strong>de</strong>red briefly.5.2 Establishment <strong>of</strong> suitablehydrological conditions forraised-bog restoration5.2.1 Principies <strong>of</strong> rewetting damagedand cut-over bogsThe exact character <strong>of</strong> water management in bogrestoration and conservation may <strong>de</strong>pend on whetherthe aim is to maintain an existing bog surface or torenature a damaged surface (i. e. one that may be ratherdry and which may have lost the original bog acrotelmlayer and most or all <strong>of</strong> its former species). It will also<strong>de</strong>pend upon the topography <strong>of</strong>the area (e.g. whether amassif. or a <strong>de</strong>pression [2.1 J) but in all such situationsthe primary problem <strong>of</strong> rewetting is that <strong>of</strong> retainingsufficient meteoric water so that the peat surfaceremains consistently wet year-round. A characteristicfeature <strong>of</strong> little-damaged bogs is that saturatedconditions are maintained close to the surface for much<strong>of</strong> the year, i.e. they have a cOllsistently high watertable. Although bog plants have sorne capacity totolerate occasional dry periods (<strong>de</strong>pending on theirduration and magnitu<strong>de</strong>), successful bog regenerationalso requires permanently wet conditions. Low waterlevels are not only unsuitable for the growth <strong>of</strong> manybog plant species but may also promote further oxidative<strong>de</strong>composition <strong>of</strong> the peal. On an ombrotrophicpeat surface, precipitation is the sole source <strong>of</strong> recharge,and hydrological management must seek to retainas high a proportion <strong>of</strong> this as is possible l to illitiatemire regeneration or to maintaill existing surfaces.Both the 'base-line' water level in raised bogs (Le. thelimit <strong>of</strong> permanent saturation) and the magnitu<strong>de</strong> <strong>of</strong>fluctuations aboye this, are regulated by similar(though not i<strong>de</strong>ntical) processes. The limit <strong>of</strong>permanent saturation is provi<strong>de</strong>d by the position <strong>of</strong> the'groundwater' mound surface in relation to the miresurface and is a reflection <strong>of</strong> the variables that<strong>de</strong>termine this [1.7J. In a damaged site it may belocated well below the peat surface.Water-Ievel fluctuations are restricted to the peathorizons aboye the limit <strong>of</strong> permanent saturation. Theyare essentially a reflection <strong>of</strong> the consistency <strong>of</strong>precipitation recharge, the capacity for water storage inthe upper layers (which is a function <strong>of</strong> the storagecapacity <strong>of</strong> the peat, fraction <strong>of</strong> open water etc.), thevegetation, climate and the regulation <strong>of</strong> water lossesthrough run-<strong>of</strong>f and evapotranspiration. In disturbedmires, drainage and peat extraction may reduce waterstorage capacity at or near the peat surface (Joosten,1992) relative to that <strong>of</strong> intact mires (Galvin, 1976;Eggelsmann, 1981, 1988a); removal <strong>of</strong> the acrotelm 2also removes sorne natural capacity for hydrologicalself-regulation; and recolonisation by plant speciessuch as Molinia or Betula may increase rates <strong>of</strong>1 while allowing for discharge <strong>of</strong> periodic water excess.2 The term 'acrotelm' refers to the surface layer <strong>of</strong>a peatland that isaboye the limit <strong>of</strong> permanent saturation. In this broad sense, cutoyerbogs also haye an acrotelm, but one which lacks some <strong>of</strong> thedistinctiye features <strong>of</strong> the acrotelm layers <strong>of</strong> a little-damaged bog'surface, such as its apparent capacity for hydrological self·regulation. In this report, unless qualified, the term 'acrotelm' isrestricted to refer to the 'fully-functional' surface layers such ascharacterise little-damaged bogs. [see Box 1.4]


76RESTORATION OF DAMAGED PEATLANDSevapotranspiration relative to a little-damagedSphagnum-dominated surface; and, in sorne cases peatfissures <strong>de</strong>velop which may create channels <strong>of</strong>preferential water flow and help to drain the surface. Incombination, these processes <strong>of</strong>ien result in damagedbog surfaces having a much greater amplitu<strong>de</strong> <strong>of</strong> waterlevel flux than is found in a little-damaged site (e.g.Streefkerk & Casparie, 1989; Beets, 1992; Schouwenaars& Vink, 1992; Money, 1994).5.2.2 Establishment o(an acrotelmcharacteristic o(little-damagedbogIn a little-damaged bog, the character, integrity and ongoinggrowth <strong>of</strong> the system is in consi<strong>de</strong>rable mea~uremaintained by the functional characteristics <strong>of</strong> theacrotelm [1.7]. This helps to maintain a 'stable state' atthe bog surface, by various feed-back mechanisms, sothat water level change is minimised and bog plants areable to grow, or at least survive, even during periods <strong>of</strong>drought. When the originiil acrotelm <strong>of</strong> a raised boghas been <strong>de</strong>stroyed (as by peat extraction), its capacityfor water storage and run-<strong>of</strong>f regulation is reduced andan altemative 'stable state', may <strong>de</strong>velop, but onewhich is essentially characterised by relative instability<strong>of</strong> various environmental variables, especially waterleve!. This condition is supported by various feed-backmechanisms, including the growth on a summer-drypeat surface <strong>of</strong> various <strong>de</strong>ep-rooted plant species withhigh rates <strong>of</strong> evapotranspirative water loss. Theimportance that loss <strong>of</strong> the original bog acrotelm hílS torenaturation <strong>of</strong> damaged sites is partly <strong>de</strong>termined bythe frequency and volume <strong>of</strong> recharge as well as by thewater storage characteristics <strong>of</strong> the 'new' acrotelm (i.e.the unsaturated zone formed by the upper layers <strong>of</strong> theremaining peat). However, in many situations the netresult is that whilst in wet (winter) conditions thesurface may become saturated, or even floo<strong>de</strong>d, in dry(summer) periods it dries consi<strong>de</strong>rably. In suchsituations, the water level fluctuations may be <strong>of</strong>sufficient magnitu<strong>de</strong> to prevent recolonisation <strong>of</strong> thepeat surface by bog (especially Sphagnum) species andhence to prevent re<strong>de</strong>velopment <strong>of</strong> an acrotelm whichhas the functional characteristics <strong>of</strong> a little-damagedbog acrotelm.As Bragg (1989) observed, in damaged bogs, "theacrotelm should be reinstated as soon as possible", butthe critical question is 'How 7'. The central problem <strong>of</strong>restoration <strong>of</strong> bog vegetation on a damaged ombrotrophicsurface is that <strong>of</strong> 'kicking' the system from the'damaged surface' stable state to a 'bog-acrotelmbased'stable state. The difficulty <strong>of</strong> this is that theconditions required to re<strong>de</strong>velop an acrotelm with theproperties typical <strong>of</strong>a little-damaged bog surface are inconsi<strong>de</strong>rable measure provi<strong>de</strong>d by this sort <strong>of</strong> acrotelmitself. A solution to this problem is to try to construct<strong>de</strong>vices that mimic sorne <strong>of</strong> the properties <strong>of</strong> theoriginal acrotelm and which permit its re<strong>de</strong>velopmentby sustaining the growth <strong>of</strong> typical bog species. Many<strong>of</strong> the different approaches to bog restorationessentially represent different ways <strong>of</strong> attempting tosolve this problem.5.2.3 Approaches to rewettingThe main aims <strong>of</strong>water management for the restoration<strong>of</strong> raised bog can be summarised:• i<strong>de</strong>ntify causes <strong>of</strong> dry conditions;• increase retention <strong>of</strong> nutrient-poor precipitation input;• eleyate level <strong>of</strong> permanent saturation as far as possible;• reduce water-level fluctuations;• prevent or reduce water inputs from other sources (e.g.mineral / nutrient-enriched or polluted water sources).Various approaches to rewetting damaged raised bogsare discussed below. They are mostly differentmethods <strong>of</strong> attempting to elevate the level <strong>of</strong>permanent saturation within the peat or <strong>of</strong> reducing theamplitu<strong>de</strong> <strong>of</strong> water level fluctuations near the surface,usually by increasing water storage (or both).Rewetting procedures <strong>de</strong>pend upon whether the aim is(i) to rewet a remnant <strong>of</strong> upstanding peat (or to retainits wetness); or (ii) to provi<strong>de</strong> appropriately wetconditions in extensive cut-over surfaces. Theseparation <strong>of</strong> these two situations - massifs and<strong>de</strong>pressions [2.1] - is sometimes rather arbitrary butthey provi<strong>de</strong> a simple conceptual basis on which toconsi<strong>de</strong>r different approaches to peatland restorationand help in the formulation <strong>of</strong> generalised restorationstrategies applicable to more than one site and fordifferent scales within an individual site.'Rewetting' <strong>of</strong> mires implies the creation <strong>of</strong> surfacewetconditions, but there is scope for variation in the<strong>de</strong>gree <strong>of</strong> wetness which may be <strong>de</strong>sired or that can beachieved. The following terms are used here withspecific connotations:Soaking:Flooding orinundation:5.3 Rewetting options for raisedbogmassifs5.3.1 IntroductionWater level is close to the surface <strong>of</strong> the peat(usually sub-surface) for much <strong>of</strong>the year.Water level is above the surface <strong>of</strong> the peatfor at least part <strong>of</strong> the year. The <strong>de</strong>gree <strong>of</strong>flooding can vary typically between shallow« c. 20 cm) and <strong>de</strong>ep « c. 50 cm).As used here, the term 'massif may comprise entirebogs (damaged or not), uncut remnants or upstanding


CHAPTER 5: PRINCIPLES OF REWETTlNG77blocks within peat extraction complexes [2.1]. In all <strong>of</strong>these situations, the retention <strong>of</strong> water is ultimately<strong>de</strong>pen<strong>de</strong>nt upon the maintenance <strong>of</strong> a water tableperched aboye that in the surrounding <strong>de</strong>pressions.'Groundwater' mound concepts [Box 1.5] are thusappropriate for consi<strong>de</strong>ring various conceptual optionsfor the rewetting <strong>of</strong> bog massifs.Various strategies for rewetting bog massifs arei<strong>de</strong>ntified below, based upon approaches that haveeither been used or proposed. Sorne cannot be regar<strong>de</strong>das well tried and tested and, where appropriate, theirIimitations are i<strong>de</strong>ntified. The choice, and effectiveness,<strong>of</strong> any <strong>of</strong> these options is likely to be inf1uencedstrongly by:• the causes and extent <strong>of</strong><strong>de</strong>hydration I darnage;• the nature <strong>of</strong>the peat;• the nature <strong>of</strong>the c1irnate;• the exact topography <strong>of</strong>the site.The choice <strong>of</strong> option wiII also be <strong>de</strong>termined bywhether the aim <strong>of</strong> rewetting is to mainlain an existingbog vegetation or to renalure a badly-damaged peatsurface [Chapter 6].The surfaces <strong>of</strong> residual bog massifs may be dry forseveral reasons [2.2.2], for example:• basal area is too srnall to rnaintain a perched waterrnound near the surface over sorne or aH <strong>of</strong>a site;• site has been drained;• excess vertical seepage occurs frorn the catotelrn into theun<strong>de</strong>rlying aquifer..Various feedback mechanisms' may exacerbate theseeffects:• <strong>de</strong>veloprnent <strong>of</strong> vegetation with greater rates <strong>of</strong>evapotranspiration than typical for a little-darnaged bogsurface;• <strong>de</strong>veJopment <strong>of</strong> fractures and fissures wilhin lhe pealconsequent upon drying;• loss <strong>of</strong> sorne <strong>of</strong>the attributes <strong>of</strong>the original acrotelrn.The concept <strong>of</strong> the basal area <strong>of</strong> a peatland being toosmall to maintain the perched water mound c10se to thepeat surface <strong>de</strong>rives from the 'groundwater' moundtheory, in whichthe height and shape <strong>of</strong> the watermound that <strong>de</strong>fines the upper Iimit <strong>of</strong> the catotelm isrelated to the basal area and plan <strong>of</strong> the mire. This isillustrated in Figure 2.3. However, it is not axiomaticthat a reduction <strong>of</strong> basal area will necessarily lead to areduction <strong>of</strong> the height <strong>of</strong> the water mound overall ormuch <strong>of</strong> the bogo This is because in sorne bogs,especially large ones, the actual height <strong>of</strong> the peatsurface is less than the hydrological maximumpredicted by 'groundwater' mound theory (eitherbecause it has not had sufficient time to accumulatepeat to the hydrological equilibrium position orbecause on-going peat <strong>de</strong>composition in the catotelmprevents the hydrological maximum being reached(Clymo, 1984)). Thus in large bogs it may be possibleto make a consi<strong>de</strong>rable reduction <strong>of</strong> the total areawithout lowering the height <strong>of</strong> the water mound overmuch <strong>of</strong> the remnant. However, when the remnant issmall, relative to its height, then it is likely that thewater mound may drop to a position that issubstantially subsurface.The effect <strong>of</strong> drains upon a bog surface will <strong>de</strong>pendupon their disposition, <strong>de</strong>pth and frequency. They arelikely to cause particularly marked water drawdown onthe acrotelm, as it has a higher hydraulic conductivitythan the catotelm. Indirect effects may also beimportant, for example through changes in waterstorage and species composition [2.2].Loss <strong>of</strong> water by vertical seepage downwards from thepeat into an un<strong>de</strong>rlying aquifer is only likely to occurin bogs that are located over permeable substrata(porous bedrocks, many glacial sands and tills) inwhich the groundwater head, which was once at, oraboye, the level <strong>of</strong> the bottom <strong>of</strong> the peat, has sincebeen reduced consequent upon groundwater abstractionele. This is consi<strong>de</strong>red to be an important source <strong>of</strong>water loss in many bog remnants in The Netherlandsand N Germany (e.g. Schouwenaars el al., 1992). Itsimportance in the UK is not known, though it may wellaffect both Thome and Hatfield Moors. The possiblesignificance <strong>of</strong> this for restoration in relation toresidual <strong>de</strong>pths <strong>of</strong>peat is discussed in section 4.4.5.The potential water drawdown induced by marginaldamage upon a mire massif is iIIustrated conceptuallyin Figure 2.3. Whatever the actual position <strong>of</strong> thereduced perched water mound, one main object <strong>of</strong>rewetting is to bring it back to an 'appropriate' positionwith respect to the peat surface over all or part <strong>of</strong> themire. Deciding what is 'appropriate' may be animportant subsidiary issue [3.2]. The second mainobject is to reduce water level f1uctuations aboye thepermanent perched water mound.A number <strong>of</strong> approaches for rewetting bog massifshave been i<strong>de</strong>ntified [see Box 5.1]. The salient features,Iimitations and appropriateness <strong>of</strong> these approaches fordifferent situations are consi<strong>de</strong>red below. Note thatthese approaches are not mutually exclusive. It is <strong>of</strong>ienpossible, and may be necessary, to combine differenttechniques to achieve optimum rewetting <strong>of</strong> massifs,due to the heterogeneous nature <strong>of</strong> many peatextraction complexes. AII <strong>of</strong> the approaches assumethat drainage ditches are blocked. For one, this is theonly requirement. Three main types <strong>of</strong> bund have beeni<strong>de</strong>ntified - these are iIIustrated in Figure 5.1.


78RESTORATION OF DAMAGED PEATLANDSBox 5.1Potential approaches to rewetting bog massifs[see Figures 5.1 to 5.4].Procedures based mainly on soaking:(a)(b)(e)(d)(e)Elevation <strong>of</strong>the water level by ditch blockingNon-intervention - natural subsi<strong>de</strong>nce <strong>of</strong>peat to the position <strong>of</strong>the perched water moundSculpting <strong>of</strong> the peat surface to the position <strong>of</strong> the perched water moundElevation <strong>of</strong> the water level by containment within wall bundsElevation <strong>of</strong> water level by increasing water le veIs in the surrounding areaProcedures based mainly on inundalion:(f) Inundation using parapet bunds(g)Inundation by reduction <strong>of</strong> the level o, the peat surface to form lagoonsOlher proeedures(h)Provision <strong>of</strong> supplementary water5.3.2 Methods(a) Elevation <strong>of</strong> water level by ditch blockingFundamental to aH rewetting options <strong>of</strong> peat massifs isblockage <strong>of</strong> any ditches that drain them [Figure 5.2 (i)],and this is the main focus <strong>of</strong> many restoration projects[Appendix 6]. Ditch blocking is essentially a soakingstrategy. Its likely efficacy as the sole rewettíngstrategy for massifs (and cut-over bogs) wil1 <strong>de</strong>pend onthe factors contributing to their dryness (including thehydraulic conductivity <strong>of</strong> the peat and un<strong>de</strong>rlyingsubstrata) (see, for example, Schouwenaars, 1995). Insorne cases where superficial ditches provi<strong>de</strong> more-orlessthe only reason for <strong>de</strong>hydration, ditch-blockingalone may be sufficient to provi<strong>de</strong> effective rewetting<strong>of</strong> the mire surface, or, particularly, to maintain theexisting interest <strong>of</strong> a little-damaged mire surface.In<strong>de</strong>ed, in sorne little-damaged sites spontaneousSurface bundsWall..bundocclusion <strong>of</strong>(small) ditches has occurred.Limitations• The prime limitation is that in sorne sites periodicsurface dryness may be a consequence <strong>of</strong> factorsother than drains. Where dryness has been inducedby an overall shift in the height <strong>of</strong> the water moundconsequent upon a reduction <strong>of</strong>the basal area <strong>of</strong>themire, it is unlikely that ditch blocking willeffectively rewet the massif, though it may lead towet conditions in and along the ditches.• Where ditches have been particularIy <strong>de</strong>ep an<strong>de</strong>xtensive, slumping and wastage may have causedconsi<strong>de</strong>rable change in the topography <strong>of</strong> parts <strong>of</strong>the massif. In this situation the topographicalposition <strong>of</strong> such ditches may mean that even whenfull <strong>of</strong> water they have little effect upon impedingdrainage from sorne higher parts <strong>of</strong> the bogo InParapet bund..weakly-humified peatstrongly-humified peatopen waterbundFigure 5.1 The three main types <strong>of</strong> bund which have been i<strong>de</strong>ntified as being used in bog restoration projects.Surface bunds restrict lateral run-<strong>of</strong>f through the upper horizons <strong>of</strong> weakly-humified peat; parapet bunds extendaboye the level <strong>of</strong> the adjoining peat massif, to form a long, low surface dam against which water may beimpoun<strong>de</strong>d; wall bunds aim to elevate the water mound within the peat massif by reducing water losses due tomarginal seepage and f10w around some, or all, <strong>of</strong> its periphery.


CHAPTER 5: PRINCIPLE OF REWEITl G 79sorne circumstances a stepped casca<strong>de</strong> <strong>of</strong> dams maybe used to circumvent this difficulty.• In damaged massifs without an acrotelm characteristic<strong>of</strong> a little-damaged bog, ditch-blocking maynot be a<strong>de</strong>quate to ensure a water table that issufficiently stable close to the peat surfac~ to permitthe extensive establishment <strong>of</strong> Sphagnum species.This is mainly because evapotranspirative waterloss, coupled with dry episo<strong>de</strong>s lead to a reduction[~OCklng •••In,(ii)Use <strong>of</strong> wall bunds around margins~ ~- ._--~;Resoaked peatWallbund,J.(iii) Raise water level in surroundings <strong>of</strong> bog(a) Water level al surface o,surrounding land.~ Unsaturated~ peat(b) Water level ffooding surrounding landl<strong>of</strong>water leve!. The extent to which this limitation isimportant <strong>de</strong>pends upon the topography <strong>of</strong> themassif and its climatic situation. It is especiallyimportant on surfaces with limited water storageand in regions that experience periodic andsustained droughts.Possíble applicatíon• Blocking <strong>of</strong> active ditches is essential in anyrewetting initiative.• Ditch bJocking is likely to be particularly effectivein rewetting large bogs, with shallow slopes, whereditches are the principal cause <strong>of</strong> surface dryness.• lt is likely to be particularly effective inmain/aining an existing bog vegetation but less wellsuited to rena/ura/ion, especially in drier parts <strong>of</strong>Britain.Potentíal for vegetatíon restoratíonIn appropriate conditions, ditch blocking has beenshown to help maintain existing bog vegetation, and toimprove lhe condition <strong>of</strong> somewhat <strong>de</strong>gra<strong>de</strong>dvegetation (e.g. Roudsea Moss, Cumbria). We know <strong>of</strong>no examples where ditch-blocking alone has led to thewi<strong>de</strong>spread regeneration <strong>of</strong> an Ml8-type vegetation ona badly-damaged massif, thollgh it seems likely thatthis process could occur on a small scale in badlydrainedhollows within a massif. Ditch-blocking <strong>of</strong> abadly-damaged massif surface may sometimes createcondjfons suitable for sorne individual bog species. Inthe cooler and wetter parts <strong>of</strong> Britain, these mayinelu<strong>de</strong> sorne species <strong>of</strong> Sphagnum. In other situations,it is more likely to produce wet heath or, whereparticularly ineffective, a 'dry bog' community.(b) Non-intervention - 'natural' reconformation<strong>of</strong> peat to position <strong>of</strong> perched water moundPerhaps the simplest approach suggested for therewetting <strong>of</strong> bog massifs where the peat surface iselevated above the position <strong>of</strong> the water mound over allor part <strong>of</strong> the site is one <strong>of</strong> non-intervention, i.e. topermit natural processes <strong>of</strong> water drawdown, wastageand subsi<strong>de</strong>nce to OCCllr. Its un<strong>de</strong>rlying presllmption isthat upstanding peat blocks will, by oxidation,slumping e/c., eventually reconform to the position <strong>of</strong>the 'new' groundwater mound within the massif. Insuch a process, increased humification <strong>of</strong> thesuperficial peats may help form a partial seal to thecollapsing mire (Schneebeli, 1989; Joosten, 1992). Jt isessentially a soaking strategy.LimítatíonsFigure 5.2 Approaches to rewetting badly-damagedremnant peal massifs based on resoaking.There is little, if any, evi<strong>de</strong>nce for the efficacy <strong>of</strong> thi~process in badly damaged massifs, but there is st r : ..reason to believe that it has been important in a d~r'


80RESTORATION OF DAMAGED PEATLANDS<strong>of</strong> 'accommodation' <strong>of</strong> the effects <strong>of</strong> marginal damageon otherwise little-damaged bogs (e.g. WedholmeFlow, Cumbria; Clara Bog, Ireland). Its potential valueprobably <strong>de</strong>pends very strongly upon the startingconditions, in particular the prevailing c1imate. Twoextreme starting conditions are consi<strong>de</strong>red below.A: Site with badly-damaged surface with water moundwell below surfaceThis situation is typical <strong>of</strong> a number <strong>of</strong> dry remnantmassifs, where the surface is fairly dry over much <strong>of</strong>the expanse, supporting heath, Molinia, bracken, birchetc. and perhaps a few bog species that are relativelytolerant <strong>of</strong> drier conditions (e.g. Eriophorumvaginatum). In this situation the limitations to a passiverestoration procedure based on wasting processes are:• the wastage process may be protracted (measured in<strong>de</strong>ca<strong>de</strong>s and possibly centuries, <strong>de</strong>pending on theheight difference between the peat surface and theposition <strong>of</strong> the surface <strong>of</strong> the perched watermound);• during this period part, or all, <strong>of</strong>the surface may berather dry and incapable <strong>of</strong> sustaining a bogvegetation, and the value as even a temporary'refugium' for bog species may be diminished;• even when sorne bog species persist the site mayneed sustained management (birch removal etc.) tomaintain the surface against invasive species; treegrowth on damaged mires can lead to a loss <strong>of</strong> theircharacteristic fauna and flora, and sometimesinduce consi<strong>de</strong>rable loss <strong>of</strong> hydrological integrity<strong>of</strong> the peat by fissuring;• the presumption that the wasting peat surface willequilibrate at sorne stage at the zone <strong>of</strong> permanentsaturation is questionable [see Figure 5.3]. In adiplotelmic mire an important role <strong>of</strong> the acrotelmis to supply water to the catotelm and hencemaintain the zone <strong>of</strong> permanent saturation. Bycontrast, when a badly-damaged peat surface haswasted (Iet it be assumed) to the position <strong>of</strong> theperched water mound, other than in climaticregions where there is a near-constant input <strong>of</strong>meteoric water, the position <strong>of</strong> the water moundwill continue to sink periodically below the peatsurface in response to periods <strong>of</strong> dryness. Hence asthe peat surface subsi<strong>de</strong>s, the zone <strong>of</strong> permanentsaturation will also sink beneath it. Such periods <strong>of</strong>surface dryness may not only constrain the reestablishment<strong>of</strong> bog species; they may also permitongoing wastage. It is then possible that theeventual consequence <strong>of</strong> a 'natural wastage'scenario will be the loss <strong>of</strong> the entire ombrotrophicpeat <strong>de</strong>posit. This process is likely to beexacerbated if the subsiding surface is rather dryand supports a vegetation with high rates <strong>of</strong> evapotranspiration(e.g. dominance <strong>of</strong> Molinia or birch);• even when peat has wasted to a position proximateto the perched water mound, the water table maynot be sufficientIy stable c10se to the peat surface topermit the establishment <strong>of</strong> bog (especially peatforming,Sphagnum-based) vegetation except,perhaps, in c1imatically-favoured localities.B: Site with well-<strong>de</strong>veloped bog vegetation subject tominor marginal water drawdownThis situation is representative <strong>of</strong> a site which hassuffered sorne marginal damage (for example, by peatextraction) and water drawdown, but where a well<strong>de</strong>velopedbog vegetation exists over much <strong>of</strong> thesurface and where the water-mound remains near thesurface over much <strong>of</strong> the mire. In this situation theeffect <strong>of</strong> marginal damage may have Iimited impactupon the rest <strong>of</strong> the mire, or processes <strong>of</strong> small-scalereconsolidation and slumping may permit rapidreconformation <strong>of</strong>the affected part <strong>of</strong>the surface to thesurface <strong>of</strong> the new position <strong>of</strong> the perched watermound. The main limitations <strong>of</strong> non-intervention maythen just be:• drying <strong>of</strong> the margins <strong>of</strong> the massif will occur, theamount being <strong>de</strong>termined by the <strong>de</strong>gree <strong>of</strong> waterdrawdown;• the edges may gradually conform to the edge <strong>of</strong> thewater mound by slumping, oxidation etc.; theymay, however, not rewet, and may continue tooxidise.Possible applicationThere is little evi<strong>de</strong>nce to suggest that naturalreconformation <strong>of</strong> the peat surface <strong>of</strong> a badly-damagedbog massif to the perched water mound will occur orwill produce suitable rewetting <strong>of</strong> the peat surface,other than in a few specific cases.• A non-intervention approach is unlikely to restoresurface wet conditions in the foreseeable term tosites that have been badly damaged and where thewater table is strongly sub-surface.• A non-intervention approach is unlikely to preservethe character <strong>of</strong> 'good' quality bog vegetation whenthe mire is subject to an extensive reduction in theheight <strong>of</strong>the perched water mound.Situations where a non-interventionist approach to'rewetting' may be acceptable are likely to be oneswhere the effects <strong>of</strong>drying will be small or where otherrewetting strategies are not feasible, for example:• in a mire site which supports 'good' quality bogvegetation over much <strong>of</strong> its area and where only themarginal areas are dry, if it is consi<strong>de</strong>red that driermargins are acceptable, and no lowering <strong>of</strong> thewater table is anticipated;• in sites where there has been a relatively small dropin the water level which has affected only a rather


CHAPTER 5: PRINCIPLES OF REWETTING 81Original mire~-=-r--.~=¡7=-7=:F5=~/ / / / / / // (Pennanentfy saturated peatr/ ; ; , ; , ; , ; , ; I /A This represents the original undamaged bog, with apermanently-saturated catotelm and a thin acrotelm.Unsaturated peat/ / / / / / / / / // / / / / / / / / / // / / / / / / / / / /8 The margins <strong>of</strong> the bog have been removed (throu!~h peatextraction or conversion to agriculture). The water moundsinks to a position <strong>de</strong>termined by the new dimensions <strong>of</strong> themassif, so that permanently saturated conditions are nowwell sub-surface. A new zone <strong>of</strong> peat that is not permanentlysaturated becomes established in the upper part <strong>of</strong> theformer catotelm./ / / / / / / / / // / / / / / / / / / / // / / / / / / / / / / / /~CPeat oxidation and <strong>de</strong>composition occurs in the periodicallydry upper part <strong>of</strong> the former catotelm. Coupled with othercauses <strong>of</strong> subsi<strong>de</strong>nce (slumping, <strong>de</strong>flation etc.), theunsaturated surface <strong>of</strong> the mire gradually wastes towardsthe zone <strong>of</strong> permanent saturation./ / / / / // / / / / / / // / /l/ / / / / / // / / / / / / /•II•F./ / / / /oContinued wastage in oxic conditions brings the surface <strong>of</strong>the mire increasingly into closer conformation with thesurface <strong>of</strong> the new water mound. However:E During periodic dry periods, lack <strong>of</strong> precipitation inputcoupled with evapotranspiration causes the water table tosink below the surface. Thus the zone <strong>of</strong> permanentsaturation (the water mound) becomes yet smaller. Theupper peat which had previously been permanentlysaturated is now only temporarily saturated and becomesmore susceptible to oxidation and <strong>de</strong>composition.The sequence <strong>of</strong> events C-E is repeated and the watermounds gets yet smaller, followed by a further loss <strong>of</strong>surface peal. This process may continue until theombrotrophic peat largely disappears (though it may <strong>of</strong>ienbe very slow). It could be arrested or retar<strong>de</strong>d (a) by theestablishment <strong>of</strong> permanently saturated conditions on thesurface (by inundation ?); and (b) by the associated<strong>de</strong>velopment <strong>of</strong> a peat-forming bog vegetation.Figure 5.3 Suggested scenario for the likely changes in badly-damaged peat remnants subject to naturalprocesses <strong>of</strong> peat wastage. It is relevant to suggestions for rewetting <strong>of</strong> peat massifs by just allowing wastage totake place and to proposals to remove upper peat down to the predicted position <strong>of</strong> the water mound. The scenarioassumes that seasonal dry periods regularly occur; the suggested changes are likely to take place more slowly inregions characterised by consistently high precipitation.


82RESTORATION OF DAMAGED PEATLANDSsmall area <strong>of</strong> the bog remnant; where the bogremnant is large and peripheral damage has beensustained gradually, or where the water drawdownat the edge <strong>of</strong> the massif affects only a narrowmarginal zone (e.g. because the height differencebetween the surface <strong>of</strong> the massif and adjoiningareas is small or because the peat is <strong>of</strong> lowpermeability);• in situations where re<strong>de</strong>velopment <strong>of</strong> a Sphagnumrichbog vegetation is not <strong>de</strong>sired or is unlikely tobe feasible for other reasons;• where the surface configuration (e.g. hollows orblock pea! cuttings) <strong>of</strong> the massif permits theretention <strong>of</strong> locally wet conditions <strong>de</strong>spite sorne<strong>de</strong>gree <strong>of</strong>drying <strong>of</strong>more elevated parts;• where 'good quality' bog vegetation towards thecentre <strong>of</strong> the massif is already separated from themargins by a zone <strong>of</strong> damaged surface, whichcontains the drawdown and functions as a 'bufferzone'.Non-intervention may be inevitable, for purelypractical reasons, in peat-extraction complexes wherethere are numerous small block remnants at differentlevels.Furlherconsí<strong>de</strong>rationsAs isolated peat massifs left to reconform by wastagemay be rather dry, over sorne or all <strong>of</strong> their surface,and are perhaps colonised by large stands <strong>of</strong> birch andbracken, they may be vulnerable to incendiary ev~nts.Severe fires, which ignite the dry peat, may sometlmesaccelerate the restoration process by causingconsi<strong>de</strong>rable loss <strong>of</strong> peat mass. At Thome Waste,severe fires are thought to have caused a loss <strong>of</strong> sorne30-40 cm <strong>of</strong> pea! on sorne dry baulks (R. Mea<strong>de</strong>, pers.comm.) and to have ma<strong>de</strong> them more conformable withthe adjoining wet cuttings. Such 'combustion levelling'may, for several reasons, not be seen as a <strong>de</strong>sirablemanagement tool, but there can be no doubt <strong>of</strong> itsefficacy in accelerating peat wastage. Nonetheless,wastage induced by this mechanism is likely to besubject to the same limitations as natural wastage ifused as the sole restoration 'strategy'.Potentíal for vegetatíon restoratíonIn sorne situations, sorne natural wastage may becompatible with the maintenance <strong>of</strong> existingSphagnum-rich bog vegetation. However, where badlydamagedbog surfaces have been left to waste, there<strong>de</strong>veloping vegetation is, in the short term at least,usually Molinia, bracken, birch scrub or heathland.Sorne <strong>of</strong> the more drought-tolerant bog species (e.g.Eriophorum vaginatum) may recolonise suchsituations. It is possible, particularly in the wetterregions <strong>of</strong> the UK, that a wi<strong>de</strong>r range <strong>of</strong> bog speciesmay ultimately establish on 'wasting bogs', but wehave no evi<strong>de</strong>nce to support this.(c) Sculpting <strong>of</strong> the peat surface to the position<strong>of</strong> the perched water moundA more interventionist version <strong>of</strong> the 'natural wastage'approach is provi<strong>de</strong>d by the interesting suggestion <strong>of</strong>Bragg (1989) that peat could be removed to form apr<strong>of</strong>ile which, <strong>de</strong>rived from 'groundwater' moun<strong>de</strong>quations, would conform to the predicted position <strong>of</strong>the perched water mound in a peat remnant. Such anapproach would reduce the potentialIy long time-spaninvolved in natural wastage processes. Like naturalwastage, it is essentialIy a soaking strategy.LimítatíonsThe fundamental limitations <strong>of</strong> this approach are thesame as for the 'natural wastage' approach, especiallythat the zone <strong>of</strong> permanent saturation is likely to sinkbeneath the position <strong>of</strong> the sculpted surface during dryperiods [Figure 5.3]; in addition:• it may be difficult to predict the ultimate position <strong>of</strong>the perched water mound;• it may be difficult (and costly) to sculpt the peatmound with the exactitu<strong>de</strong> that is required;• the surface thus produced may not be amenable togood renaturation due to water level fluctuations.Possíble applicatíon• An innovative small trial restoration projectun<strong>de</strong>rtaken by the Somerset Trust for NatureConservation is currently in progress, in which asmall area <strong>of</strong> peat (Getty's Mire) was contoured tothe predicted shape <strong>of</strong> the 'groundwater' mound[Plate 5.1]. Water level measurements have shownthat the water table was convex in the winter,folIowing quite well the shape <strong>of</strong> the mound, butbecame concave during the summer. This corroboratessorne <strong>of</strong>the limitations i<strong>de</strong>ntified aboye.• Sculpturing <strong>of</strong> the peat surface in the way proposedmay provi<strong>de</strong> suitable conditions for the establishment<strong>of</strong> sorne bog species in sorne situations, but itis difficult to see what practical benefits thisapproach confers in comparison with sorne <strong>of</strong> theother, technically more simple, approachesdiscussed below.Potentíal for vegetatíon restoratíonAs this approach has been little tried, few factualcomments on its efficacy can be ma<strong>de</strong>. It seems likelythat it would be possible for sorne '<strong>of</strong>the more droughttolerantbog species to establish on sorne surfaces andin appropriate c1imatic regimes, even that sorneSphagnum species could colonise. However, we haveno supporting evi<strong>de</strong>nce for this.


CHAPTER 5: PRINCIPLES üF REWETIING83(d) Elevation <strong>of</strong> the water level by containmentwithin wall bundsAn alternative, more elaborate approach to reducingthe peat surface to the position <strong>of</strong> the perched watermound, is to elevate the water mound within the peatmassif by reducing water los es due to marginalseepage and flow around sorne, or al!, <strong>of</strong> its periphery[Figure 5.2 (ii)]. This can be achieved using a wal!bund, ma<strong>de</strong> <strong>of</strong> low-permeability peat or, if this isunavailable, <strong>of</strong> inert materials such as plastic (or both)[8.2]. In effect, this raises the impermeable base <strong>of</strong> thebog and elevates the position <strong>of</strong> the perched watermound. In the simple form <strong>de</strong>scribed here, this isessentially a soaking strategy, but can be modified to. fonn aflooding strategy (see below).Limitations• It is relatively expensive to bund aH or part <strong>of</strong> abog, particularly if it is done weH [7.3].• As this approach involves elevation <strong>of</strong> the watermound aboye its natural position, it is potentiallyunstable. The bunds have to be substantial, wellma<strong>de</strong> and maintained to retain the water; weakbunds may be susceptible to collapse (for example,through a build-up <strong>of</strong> pre sure behind the bund). Itis possible that, in the long term, bunds maydisintegrate through oxidative <strong>de</strong>composition. Asyet there is little direct evi<strong>de</strong>nce for this, but sorneaHowance for on-going maintenance <strong>of</strong> at least themarginal bund may need to be ma<strong>de</strong>. Provisionmust also be ma<strong>de</strong> for the control <strong>of</strong> water levels toal!ow discharge <strong>of</strong> excess water during periods <strong>of</strong>high rainfall.• In steeply convex, or irregular, massifs it may benecessary to have two or even more concentricbunds if wet conditions are to be maintained at thesummit; as well as being very costly these willinevitably cause local damage and interrupt thenatural appearance <strong>of</strong> the massif.• The water table may not be sufficiently stable closeto the peat surface, particularly on badly-damagedsurfaces. This may mean that the surface is notnecessarily amenabl to'good' renaturation withSphagnum-rich bog vegetation.Note that most sites where substantial bunding hasbeen used to retain water on a remnant massif are thosewith a consi<strong>de</strong>rable thickness <strong>of</strong> weakly-humified peat(e.g. Meerstalblok and Engbertsdijksvenen, TheNetherlands). The relatively high permeability <strong>of</strong> thistype <strong>of</strong> peat means that such massifs are particularlyprone to water loss at the cut margins. In suchsituations waH bunds need not extend to the bottom <strong>of</strong>the peat <strong>de</strong>posit; it may be sllfficient just to insert aplug <strong>of</strong> strongly-humified peat (or other lowpermeabilitymaterial) into a trench within the weaklyhllmifiedpeat [see below and Figure 8.1].Possible application• This approach has been used, with some success, inrewetting raised-bog remnants in The Netherlandsand Gennany, for example at the Meerstalblok.• This is an appropriate strategy for maintaininggood quality bog surfaces on bogs where lateralwater loss 'threatens survival. It may be lesseffective as asole method forrenaturation <strong>of</strong>badlydamagedmassifs, particularly in drier c1imates, as itis essential!y a soaking approach.• This approach is appropriate for maintaining goodquality bog vegetation upon massifs adjoining (orwithin) peat extraction sites. In principie, it ispossible to maintain a wet surface across aconsi<strong>de</strong>rable height differential between the top <strong>of</strong>the wal! bund and the level <strong>of</strong> the adjoining ground,but very tall bunds are likely to be unstable and,where the height difference is great (>2 m) a series<strong>of</strong> stepped bunds would be <strong>de</strong>sirable (or the surfacefrom which peat is being removed should be gra<strong>de</strong>dup to the remnant).• Even where long-term stability cannot beguaranteed, this approach may be important insustaining bog refugia during peat extraction fromits surroundings.• Note that in principie it may also be possible tocreate a 'wet bund' by maintaining artiftcially highwater levels near the edge <strong>of</strong> a peat remnant usingpumped water. Nonetheless, a UK attempt at thisapproach by Heathwaite (1995) (the Ditch Rechargesystem at Thorne Waste) was unsuccessful.Plate 5.1 Getty's Mire, Somerset Levels. Former peatworkings mechanically contoured to the predictedshape <strong>of</strong> the 'groundwater' mound [see te"xt].


84RESTORATlON OF DAMAGED PEATLANDSPotential for vegetation restorationThis approach has been used with sorne success tomaintain, and improve the quality <strong>of</strong>, existing bogvegetation (e.g. Meerstalblok, The Netherlands). Itsefficacy as a starting point for renaturation <strong>of</strong> a badlydamagedmassif surface is less cIear; it seems likelythat fluctuations <strong>of</strong> the water table may be inimical tothe establishment <strong>of</strong> a Sphagnum-based vegetation, indrier regions at leasl.(e) Elevation <strong>of</strong> the mire water level byincreasing water levels in the surroundingareaA further possible method for elevating the surface <strong>of</strong>the water mound in a residual peat massif is by raisingthe water level in the surrounding land (peat-workings,farmland etc.) [Figure 5.2 (iii)]. In situations where a<strong>de</strong>eply sub-surface water mound in a peat massif hasresulted [rom a reduction <strong>of</strong> the basal area <strong>of</strong> the mire,sorne hydrological control <strong>of</strong> the surrounding land,particularly that which once formed part <strong>of</strong> the originalbog, may help to stabilise water in the mire remnant,for example by helping to reduce water loss toagricultural drains. However, it is far from certain thatmere control <strong>of</strong> the drainage <strong>of</strong> the surrounding peatworkings or cIaimed land will be sufficient to soelevate the water mound within the remnant massif asto rewet its surface a<strong>de</strong>quately. The nature andmagnitu<strong>de</strong> <strong>of</strong>any such effects will <strong>de</strong>pend primarily onthe topography and relative heights (hydraulic head), aswell as the amount <strong>of</strong> recharge to the catotelm andhydraulic conductivity <strong>of</strong> the peal. However, if it ispossible to increase the water level on the landsurrounding the remnant sufficiently (i.e. by floodingit) this could provi<strong>de</strong> an effective method for resoakingthe remnant massif.Limitations• The main problem with this approach is itspracticality and Iikely cosl.• In sorne cases it would require the flooding <strong>of</strong>adjoining agricultural land.• It may <strong>of</strong>ten be difficult to elevate the water tableover the adjoining land sufficiently to re-soak themassif. This largely <strong>de</strong>pends upon topography.Where the bog is in a cIosed basin it maysometimes be relatively easy to flood thesurrounding land within the basin confines.However, many bog massifs are on floodplains orflat valley bottoms, and elevation <strong>of</strong> thesurrounding water table would probably require acomplex series <strong>of</strong> lagoons to impound the water.• The water table may not be sufficiently stable cIoseto the peat surface, particularly on badly-damagedsurfaces. This may mean that the surface is notnecessarily amenable to 'good' renaturation withSphagnum-rich bog vegetation. It is Iikely thatinundation around the periphery <strong>of</strong>the massifmightdamp water level fluctuations, though thesignificance <strong>of</strong> this would partly <strong>de</strong>pend upon theconfiguration <strong>of</strong>adjoining inundated areas.Possible application• This approach could possibly be used to help rewetbog massifs in small basins.• It could be used as part <strong>of</strong> a co-ordinated strategyfor the restoration <strong>of</strong> a remnant massif andsurrounding peat workings. [This is discussedfurther below.]• This approach could also be used if it was thought<strong>de</strong>sirable that agricultural land once cIaimed fromthe bog should be retumed to a form <strong>of</strong>wetIand.Box 5.2 Efficacy <strong>of</strong> re-soaking approaches to rewettingRe-soaking approaches (i.e. approaches aimed at elevating lhe surface <strong>of</strong> lhe perched waler mound c10se lo lhe peal surface)have achieved variable success in bog resloralion. <strong>de</strong>pending upon lheir silualion and climalic conlext. We have noled lhefollowing, from field observations and reports:(i)(ii)(iii)lhey can be very effeclive in maintaining or even enhancing a massif surface which is slill in quile good condilion (i.e. wilh a'reasonable' <strong>de</strong>velopment <strong>of</strong> bog vegetation and an acrolelm characlerislic <strong>of</strong> little-damaged raised bog);lhey are reported as being appropriale for siles which are damaged bul which retain a thick horizon <strong>of</strong> fresh, weakly-humifiedpeat, which can slore water well and, in appropriale condilions, even swell in response lo lhis, thus taking on some <strong>of</strong> theproperties <strong>of</strong> the original acrotelm; this may be particularly lhe case in wetter, cooler climales bul lhere seems lo be litt/ecritical informalion;lhey do nol seem lo provi<strong>de</strong> an a<strong>de</strong>quale basis for rewetting siles where lhe peal has high humificalion and low walerstorage characlerislics.Where re-soaking approaches do nol lead to successful renaluralion, the main limitalions seem lo be eilher lhal they do noladdress lhe rool cause <strong>of</strong> dryness (as is lhe case wilh some dilch blocking procedures); or lhal lhey do nol provi<strong>de</strong> a slable walerlable that remains sufficienlly close lo lhe peat surface year round, in part because lhey do nol necessarily increase walerslorage capacily al or near lhe bog surface. This is a particular problem in siles where lhe exposed peal has low waler sloragecharaclerislics or in regions subjecl lo long dry periods. In lhese cases lhe only realislic way <strong>of</strong> minimising the effecls <strong>of</strong>f1uclualing water levels may be by inundalion slralegies. These are nol Iikely lo be provi<strong>de</strong>d jusI by a 'groundwaler' mound pr<strong>of</strong>ilewhich, al besl, is Iikely lo be al lhe surface for only part <strong>of</strong> lhe year.


CHAPTER 5: PRI CIPLES OF REWETTI G 85• As this is potentially an expensive restorationoption, it is only likely to be appropriate forprestige projects where the aim is to protect a miremassif <strong>of</strong> much existing conservation value and torenature adjoining peat workings etc.• There is tittle evi<strong>de</strong>nce to suggest that a retum <strong>of</strong>the entire former area <strong>of</strong> a raised bog to a wetlandcondition is necessarily es ential to maintainhydrologic stability in a remnant massif. This isbecause (a) in large sites the actual height <strong>of</strong> thepeat surface may be consi<strong>de</strong>rably lower than thepredicted hydrological maximum, i.e. the watermound can be sustained at this level with a bogbasal area consi<strong>de</strong>rably less than that <strong>of</strong> the originalm¡re; and (b) the construction <strong>of</strong> any lagoons thatmay be necessary to elevate the water level acrossthe adjoining land may be a less stable approachthan is the construction <strong>of</strong> wall or parapet bundsaround massifs. Nonetheless, sorne control <strong>of</strong>drainage in the surrounding land (as in'hydrological buffer zones' [8.3]) may well in sornecircumstances ameliorate sorne difficulties <strong>of</strong>rewetting the peatland.• This approach may be useful as part <strong>of</strong> an overallrestoration strategy in situations where Ioss <strong>of</strong> waterthrough downward seepage is thought to be aproblem.Patential far vegetatian restaratianElevation <strong>of</strong> water tables over peat workings around aremnant massif has been used with consi<strong>de</strong>rablesuccess at the Bargerveen reserve in The Netherlandsand is discussed more fully below.(f) Inundatian using parapet bundsThe use <strong>of</strong> parapet bunds for rewetting [Figure 5.4 (i)]represents a <strong>de</strong>velopment <strong>of</strong> the bunding approachdiscussed aboye [5.3.2(d)]. Both approaches, in effect,raise the impermeable ba e <strong>of</strong> the bog and elevate theposition <strong>of</strong> the perched water mound. The difference isthat with parapet bunds the bunds extend aboye thelevel <strong>of</strong> the adjoining peat massif, to form a long, lowsurface dam against which water may be impoun<strong>de</strong>d,and it is possible to accumulate water on the top <strong>of</strong> thepeat massif. The extent to which this is possible will<strong>de</strong>pend upon the topography <strong>of</strong>the massif. If it is domedthen the effect will be to produce a moat <strong>of</strong> water; ifflatter, it may be possible to inundate larger areas.Limitatians• The limitations <strong>of</strong> this approach are similar to thatdiscussed un<strong>de</strong>r 'wall bunding' [5.3.2(d)]. However,because this approach provi<strong>de</strong>s for somesurface inundation, it effectively increases waterstorage in the vicinity <strong>of</strong> the peat surface. This may(i) Partial inundation using parapet bundsResoakedpeat(ii) Removal o, peat to form lagoonsUnsaturatedpeat/;--__-----1/L Safurated peat \ParapetBundFigure 5.4 Approaches to rewetting badly-damagedremnant peat massifs based on reflooding.reduce the amplitu<strong>de</strong> <strong>of</strong> water-Ievel flux andprovi<strong>de</strong> an environment more conducive to theestablishment <strong>of</strong> typical bog species on <strong>de</strong>gra<strong>de</strong>dbog surfaces.• One <strong>of</strong> the main problems with the use <strong>of</strong> thisapproach is that on sloping massifs it may not bepossible to rewet more than a small proportion <strong>of</strong>the surface. In strongly domed bogs it may benecessary to have a series <strong>of</strong> concentric bunds ifmore wi<strong>de</strong>spread surface inundation is required.Passible applicatians• This approach has been used to rewet some bogmassifs in The Netherlands. In some instances ithas been adopted in consequence <strong>of</strong> the failure <strong>of</strong>other, more simple, procedures to produce the<strong>de</strong>sired goals. For example, parapet bunding hasbeen constructed in part <strong>of</strong> the Engbertsdijksveen[Plate 5.2], in recognition <strong>of</strong> the failure <strong>of</strong> ditchblocking to rewet the mire remnant. In other sites(e.g. Meerstalblok), previous wall bunding has beenexten<strong>de</strong>d upwards to form a parapet to permitflooding <strong>of</strong> parts <strong>of</strong> the mire surface.


86RE TORATION 01' DAMAGEO PEATLAOSwi<strong>de</strong>ly used lo maintain wet conditions within peatmassifs, as in sorne mires old peat workings withinupstanding bJocks <strong>of</strong> peat provi<strong>de</strong> wet conditions withregenerating bog vegetation. This approach mayprovi<strong>de</strong> a more stable olution to rewetting than doeseJevation <strong>of</strong> the water level using wall bunds, in that itis Jess <strong>de</strong>pen<strong>de</strong>nt upon bunding for ils success, and alsobecause it involv s reducin the height <strong>of</strong> much <strong>of</strong> thepeat surface to a position where the lagoons will holdwater. lt also <strong>of</strong>ien leads to larger fl o<strong>de</strong>d areas thandoes inundation using parapet bunds [Figure 5.4 (i)];note that the construction illustrated in Figure 5.4 (ii) ispurely conceptual; in practice it would <strong>of</strong>ien be<strong>de</strong>sirable to subdivi<strong>de</strong> the main lagoon into a series <strong>of</strong>smaller compartments.Plate 5.2 'Parapet' bund, causing flooding at themargin <strong>of</strong> an upstanding peat remnant; Engbertsdijksveen(The Netherlands).• This is an expensive restoration procedure, but isone that may be more suited to the renaturation <strong>of</strong>badly-damaged surfaces than i wall-bunding. Insorne instances it may be the only practicable wayto rewet massifs within peat extraction complexes.lt would, for example, be appropriate for sorne <strong>of</strong>the elevated massifs at Thome Waste which arecurrently difficult to keep wet. In view <strong>of</strong> its likelycost, it is particularly appropriate to apply thisapproach to areas which already have a known andimportant biological interest.• Where the vegetation <strong>of</strong> the massif is already <strong>of</strong>'good' quality, there may be little to be gained byusing parapet bunds compared to wall bunds, unlessthere is a perceived need to increase the water leve!.Potentíal for vegetatíon restoratíonThis approach has been used with sorne success tomaintain and improve the qualily <strong>of</strong>, existing bogvegetation. It has also been used with sorne uccess torewe <strong>de</strong>gra<strong>de</strong>d bog surfaces, though as these initiativesa -e mostly recent, it is difficult to judge their long-termpotential for renaturation.(9) Inundation by reduction <strong>of</strong> the level <strong>of</strong> thepeat suñace to form la900n5An alternative restoration option attempts to resolve therewetting problem not by elevating the water level butby <strong>de</strong>creasing the elevation <strong>of</strong> the peat surface to forma lagoon [Figure 5.4 (ii)]. It differs from the approach<strong>of</strong> sculpting the peat surface to the water mound[5.3.2(c)] in that it aims to produce a series <strong>of</strong> hollowsthat can store water. The inundated areas may beconfigured to act as growth lagoons for direct plantcolonisation 01' as fee<strong>de</strong>r tanks to help soak adjoiningbaulks <strong>of</strong> peal. This approach has, inadvertently, beenLimítatíons• Depending on its scale, this approach may involvesubstantial peat extraction, with attendant practicaJ,conservational and palaeoecological problems.• It i directly damaging to peat surfaces and wouldbe <strong>de</strong>trimental to any e isting wildlife interest.• It is obviously artificial and is most likely tocontribute to a specie -cent ed conservation strategy(aimed at the preservation <strong>of</strong> bog species) thana mire-centred one (regeneration <strong>of</strong> an entire,growing mire), particularly if only small-scalehollows are excavated.• It cannot be a slImed that hollows excavated on amassif surface will nece sarily relain water' thiswill be <strong>de</strong>termined by the hydrodynamics <strong>of</strong> themassif. Moreover, ongoing wastage <strong>of</strong> the driersurroundings may mean that this is not sustainablein the very long termoPossíble applicatíonsoThis type <strong>of</strong> renaturalion has occurred, inadvertently,al many rai ed-bog sites, where hollows andlagoons currently provi<strong>de</strong> some <strong>of</strong> the mainreservoirs for bog specie and Sphagnum-richvegetation e.g. Thorne Moor , S. Yorks.). [SeeChapter 2].• It is particularly well suited lo renaturation <strong>of</strong>badly-damaged bogs in drier regions as it canreadily provi<strong>de</strong> the floo<strong>de</strong>d conditions appropriatefor the <strong>de</strong>velopment <strong>of</strong> semi-floating rafts <strong>of</strong>Sphagnum.• It is likely to be an effective rewetting strategy forpeat massifs comprised largely <strong>of</strong> stronglyhumifiedpeal.• It is particularly appropriate for surfaces that havelimited existing biological interest.• If con tructed as part <strong>of</strong> an agreed commercial peatextraction process it would be consi<strong>de</strong>rably cheaper


CHAPTER 5: PRINCIPLES OF REWETTING87than most other restoration strategies that are likelyto be effective in comparable situations.Potentíal for vegetatíon restoratíonNumerous examples ilIustrate that peat cuttings canprovi<strong>de</strong> the main repository <strong>of</strong> typical bog species insorne massifs and that they have potential to <strong>de</strong>velopinto examples <strong>of</strong> Sphagnum-rich vegetation comparableto M18 communities.Further consi<strong>de</strong>rationsThe value <strong>of</strong> excavation <strong>of</strong> pits to optimise water levelconditions in mires has long been recognised byconservationists; shalIow scrapes 01' <strong>de</strong>eper excavationshave been dug for various purposes. The evi<strong>de</strong>nt value<strong>of</strong> topographical <strong>de</strong>pressions is seen in a number <strong>of</strong>mires that are otherwise rather dry, where peat cuttings,01' other holIows provi<strong>de</strong> the only reservoir <strong>of</strong> bogspecies. Even where extensive ditch blocking 01'bunding operations are being consi<strong>de</strong>red to raise waterlevels, smalI scale cuttings may help to provi<strong>de</strong> atemporary habitat for Sphagna, to act as foei fromwhere the Sphagnum can expand across the surfaceonce an a<strong>de</strong>quate water regime has been reinstated 1Clearly the scale <strong>of</strong> any peat excavation operations wiIIalso <strong>de</strong>pend on other management being consi<strong>de</strong>redand the <strong>de</strong>sired end-point, and, <strong>of</strong> course, the condition<strong>of</strong>the existing vegetation (ifany).Removal <strong>of</strong> a layer <strong>of</strong> surface peat on sorne drainedsites prior to rewetting may have other potentialbenefits. It may remove dry mineralised surface layers<strong>of</strong> peat, which may be enriched (Eigner & Schmatzler,1980; Jortay & Schumacker, 1989), though it is farfrom clear if this is an important consi<strong>de</strong>ration. It canalso remove short-term seedbanks <strong>of</strong> potentiallyun~esirable species such as Molinia 'and, <strong>of</strong> course,physicalIy removes any unwanted speeies as well.This restoration approach, <strong>de</strong>liberate 01' spontaneous,can be very effective at creating a series <strong>of</strong> 'boggar<strong>de</strong>ns' within damaged massifs. These may support alarge reservoir <strong>of</strong>typical bog species, but this approachis more' obviously 'artificial' than are sorne otherrewetting strategies. The perceived suitability <strong>of</strong> thisapproach thus <strong>de</strong>pends strongly upon the objectivesformulated for restoration. One <strong>of</strong> its features is thatparts <strong>of</strong> the massif surface are not rewetted and areparticularly' susceptible to ongoing oxidation andwastage, which may threaten the long-term stability <strong>of</strong>the 'bog gar<strong>de</strong>n'. Of course, this constraint applies toalI rewetting approaches where part <strong>of</strong> the surface isaerobic for much <strong>of</strong> the year and does not support peatproducingplants.(h) Provision <strong>of</strong> supplementary waterAn alternative approach to the problems <strong>of</strong> waterretention is to directly irrigate peat massifs (01' in<strong>de</strong>edpeat workings) with water. This is generally onlyappropriate for smalI peat remnants because <strong>of</strong> thelarge volume <strong>of</strong> water and resources that are required.This approach has also been little tried (examplesinelu<strong>de</strong> Dosenmoor, Germany (Müller, 1980); ShapwickHeath, Somerset; Thorne Waste, S. Yorkshire).Clearly, the original causes <strong>of</strong> <strong>de</strong>hydration and currentwater losses also need to be carefully investigated (andremedied as far as possible) in or<strong>de</strong>r to assess thefeasibility <strong>of</strong> providing supplementary water through apumping scheme.Possíble applicatíonsFor most situations, the use <strong>of</strong> elaborate pumpingschemes should be avoi<strong>de</strong>d as they are non-sustainable.However, pumping may be consi<strong>de</strong>red in certaincircumstances, for example:• to 'kick-start' the system - i.e. to provi<strong>de</strong> an initialinput <strong>of</strong> water to 'prime' the system;• to preserve archaeological artefacts and palaeoecologicalvalues;• to maintain water levels in boundary ditches toreduce outputs from the site;• to keep specific areas wet as a temporary measurebefore fulI remedial action can be taken due toongoing peat extraction;• to maintain water levels as a temporary measureduring periods <strong>of</strong> drought.Clearly, ifthis approach is consi<strong>de</strong>red, then to maintainan ombrotrophic vegetation it is important that onlyombrotrophic water should be introduced, as theconsequence <strong>of</strong> introducing minerotrophic water is topromote the <strong>de</strong>velopment <strong>of</strong> fen vegetation. Whereonly nutrient-enriched minerotrophic water isavailable, it may be possible to achieve sorne improvementin water quality by passing the water first througha 'buffer zone', for example, using a reed bed.Limítatíons• This approach is generalIy only appropriate forsmall peat remnants because <strong>of</strong> the large volume <strong>of</strong>water and resources that are required.• Unless provision has been ma<strong>de</strong> to store largevolumes <strong>of</strong> meteoric water, in many cases the onlysupplementary water available is likely to beminerotrophic.• Oxygenation and movement <strong>of</strong> the water maystimulate <strong>de</strong>composition <strong>of</strong> peat and archaeologicalartefacts by micro-organisms.1 In sorne sites this role rnay in faet be played by the water in thedarnrned ditehes, or borrow pits.


88RESTORATlON OF DAMAGED PEATLANDSBox 5.3Approaches to rewetting based on surlace inundationMany <strong>of</strong> the approaches to rewetting <strong>de</strong>scribed here are basedupon resoaking <strong>of</strong> the peat rather than inundation. Resoakingstrategies may help to elevate the level <strong>of</strong> permanentsaturation within a massif, but the water table may still showconsi<strong>de</strong>rable f1uctuation and may not provi<strong>de</strong> the consistentlywet peat surface that is required for renaturation. <strong>Restoration</strong>based upon surface inundation thus provi<strong>de</strong>s a reweltingapproach, which, on the basis <strong>of</strong> field evi<strong>de</strong>nce, can provi<strong>de</strong> avery satisfactory basis for the <strong>de</strong>velopment <strong>of</strong> Sphagnumdominatedvegetation, particularly in drier regions(Schouwenaars & Vink, 1992). This has been observed invarious restoration schemes on the near-Continent and byexperimental studies on Sphagnum re-establishment (Money,1994, 1995). It is corroborated by the occurrence, in manybogs, <strong>of</strong> well-<strong>de</strong>veJoped Sphagnum vegetation (M 18a) inabandoned, f100<strong>de</strong>d peat cultings coupled with an absence <strong>of</strong>such vegetation on adjoining uncut surfaces. Such cutlingsinitially <strong>de</strong>velop loose rafts composed <strong>of</strong> the more 'aquatic'Sphagnum species, but species such as S. capillifolium, S.magellanicum and S. papillosum can subsequently establish.The value <strong>of</strong> some surface inundation is primarily (a) that itincreases the water storage at the surface <strong>of</strong> the bog; (b) thatany <strong>de</strong>crease in water levels will be less relative to the peatsurface when the area starts inundated with water than wouldbe the case for a similar drop where the maximum water levelis at the peat surfaee; (e) it provi<strong>de</strong>s a good medium foreolonisation by some Sphagnum speeies and (d) it iseondueive to the <strong>de</strong>velopment <strong>of</strong> floating rafts <strong>of</strong> vegetation,whieh can remain wet even with consi<strong>de</strong>rable water-Ievelf1uetuatións. This approaeh does, however, have its ownlimitations, in particular that optimal inundation eonditions foreffeetive reeolonisation are not known with eertainty. They are<strong>de</strong>termined inter afia by sueh eonsi<strong>de</strong>rations as: (i) optimalwater eonditions for growth <strong>of</strong> some Sphagnum speeies; (ii)meehanisms <strong>of</strong> rafting; (iii) problems <strong>of</strong> wave damage; (iv)problems <strong>of</strong> damage by wildfowl altraeted to open water.Potential for vegetation restorationAt Shapwick Heath, Somerset, an elaborate pumpingscheme is operated to maintain wet conditions aroundan ancient woo<strong>de</strong>n trackway (The Sweet Track, seePlate 1.7). As the only water supply available wasminerotrophic, this has unfortunately lead to the<strong>de</strong>velopment <strong>of</strong> fen woodland on the Sphagnum peat.At Thome Waste, water has been pumped from drainsin the area <strong>of</strong> active peat workings into sorneabandoned cuttings. As this has only been carried outrecently, it is too early to comment on the success <strong>of</strong>this approach, although there is preliminary evi<strong>de</strong>ncethat flooding has retar<strong>de</strong>d the previously-vigorousgrowth <strong>of</strong>sorne birches.5.4 Rewetting options forextensive peat workings inbog peat5.4.1 IntroductionPeat workings most <strong>of</strong>ien represent topographical<strong>de</strong>pressions with respect to any adjoining peat massifand rewetting may <strong>of</strong>ien be easier to achieve than on amassif. This is because problems <strong>of</strong> lateral water lossmay be less acute; because the workings may serve assumps which collect water from adjoining slopes andhigher peat ground and because the hydraulic head issmaller than for an upstanding remnant. They alsoprovi<strong>de</strong> the opportunity <strong>of</strong> conforming the peat surfaceto maximise its potential for water storage. I<strong>de</strong>ally,agreement on final <strong>de</strong>sired conformations would bereached by negotiation between conservationists andthe peat industry.The two main problems <strong>of</strong> rewetting peat extractioncomplexes are related: (i) providing a<strong>de</strong>quate waterstorage; and (ii) preventing lateral (and possiblyvertical) water loss. The solutions to these problemswill <strong>de</strong>pend upon (a) the topography and disposition <strong>of</strong>the peat fields; (b) the nature <strong>of</strong> the remaining peatexposed; and (c) the climatic contextoSituation, topography and rewettingApproaches suitable for rewetting abandoned peatworkings <strong>de</strong>pend very much upon their situation andcharacter. Workings can occur as large complexesclearly distinct from remnant massifs, but also as<strong>de</strong>pressions within massifs. In sorne cases, such aswhere there are small peat cuttings within a dome <strong>of</strong>raised peat, or where only a limited amount <strong>of</strong> peat hasbeen removed, so as to leave a damaged but stillupstanding dome, the problems <strong>of</strong> maintaining apositive water balance and the options for rewettingmay be much the same as those for the mire massifs, asdiscussed above l . In<strong>de</strong>ed, in sorne cases former peatextraction has inadvertently produced a conditionsimilar to that suggested as an option for rewetting <strong>of</strong>sorne raised-bog remnants [Figure 5.4].In other cases extraction <strong>of</strong> peat has progressed so faras to remove most traces <strong>of</strong> the original peat dome andto leave a sometimes complex arrangement <strong>of</strong> peatfields, ditches and baulks largely unrelated to theformer topography <strong>of</strong> the mire. In this situation therewetting strategy need take little direct account <strong>of</strong> theformer disposition <strong>of</strong> the peatland as the solutionbecomes essentially one <strong>of</strong> engineering. This mayinclu<strong>de</strong> artificial manipulation <strong>of</strong> the water table andconstruction <strong>of</strong> lagoons etc.1 Note, however, that this will ín sorne consi<strong>de</strong>rable rneasure<strong>de</strong>pend upon the character <strong>of</strong>the residual peal.


CHAPTER 5: PRINCIPLES OF REWETII G89Even in sites that have been largely cut-over, theconsi<strong>de</strong>rations advanced for the rewetting <strong>of</strong>upstanding blocks still sometimes apply. This isbecause in sorne cases the cut-over complex may stillform a massif with respect to the surroundinglandscape and thus shares the problems <strong>of</strong> rewetting <strong>of</strong>a massif.The approach adopted to rewetting peat workings islikely to be <strong>de</strong>termined primarily by the topography <strong>of</strong>the residual peat, or <strong>of</strong> the un<strong>de</strong>rlying mineralsubstrata. The surface topography <strong>of</strong> abandoned peatextraction complexes is sometimes not well suited foreasy restoration. Cut-over surfaces may sometimesoccur at various levels which can mean that it isdifficult to achieve a wi<strong>de</strong>-scale rewetting by simpleprocedures. The peat fields may also sometimes bequite steeply sloping, which not only causes problems<strong>of</strong> water retention, but may also induce sorne measure<strong>of</strong>surface gullying and erosionoWater levelsThe critical question <strong>of</strong> '<strong>de</strong>sirable' water levels inrenaturation strategies may need to be addressed evenmore for peat extraction areas than with the upstandingremnant peat massifs. In particular, whereas with thelatter the question <strong>of</strong> what is <strong>de</strong>sirable may becomesubsumed by the practicalities <strong>of</strong> what is possible(<strong>de</strong>pending on the rewetting strategy), in abandonedpeat fields there may be a much greater opportunity tospecify <strong>de</strong>sired conditions, by engineering etc.On flattish peat surfaces (such as are produced by peatmilling) it is usually difficult to maintain a fairly stablewater table at around the peat surface without sorneengineering. In such situations the lack <strong>of</strong> waterprovision within the peat needs to be compensated bysorne other supplementation mechanism, especiallyretention <strong>of</strong> surface water (i.e. inundation). In thiscircumstance, the rewetting <strong>of</strong> peat extractioncomplexes becomes a question <strong>of</strong> how water can beimpoun<strong>de</strong>d (which is largely a function <strong>of</strong> topography)and to what appropriate <strong>de</strong>pth.Areas <strong>of</strong> open water can function (i) as growth lagoons(i.e. to provi<strong>de</strong> an aqueous matrix for pioneer bogvegetation); or as (ii) fee<strong>de</strong>r tanks (to rewet adjoiningblocks <strong>of</strong> solid peat by water seepage). Experience hasshown the importance <strong>of</strong> the former approach in the<strong>de</strong>velopment <strong>of</strong> floating rafts <strong>of</strong> vegetation [4.3], andthe use <strong>of</strong> open water as a growth lagoon is thereforeconsi<strong>de</strong>red as being <strong>of</strong> primary importance. This is notnecessarily incompatible with their use asfee<strong>de</strong>r tanks,<strong>de</strong>pending on the water balance.oWhere peat has been removed c10se to the base <strong>of</strong> themire, the lowered surface may be increasinglysusceptible to inputs <strong>of</strong> minerotrophic water from thesurrounding landscape. Unless it is thought <strong>de</strong>sirable torecreate fen vegetation (or such water is base-poor),such supplementary water is un<strong>de</strong>sirable and it isnecessary to ensure that a sufficiently impermeablestrip <strong>of</strong> peat remains around the mire as a buffer zone,to prevent ingress <strong>of</strong> groundwater [8.3]. For this samereason, <strong>de</strong>liberate pumping <strong>of</strong> groundwater into theworkings to help maintain a high water level would besimilarly un<strong>de</strong>sirable [5.3.2(h)]. Removal <strong>of</strong> peat c10seto the base <strong>of</strong> the mire is also likely to increase rates <strong>of</strong>vertical seepage downwards, in situations where thisprocess can occur (e.g. Schouwenaars, 1993).5.4.2 Block cuttingsIntroductionExtraction <strong>of</strong> peat using the block-cutting method <strong>of</strong>tenproduces a regular system <strong>of</strong> baulks, flats andtrenches l [2.3.1]. The disposition <strong>of</strong> these is importantto restoration options, as they can be used to increasewater retention. Block cut sites are sometimes thoughtto be particularly amenable to restoration. This isusually because the peat cuttings may already be'bun<strong>de</strong>d', in whole or in part, by baulks which confersorne hydraulic integrity upon the cutting. Blockcuttings are also <strong>of</strong>ten quite small and this, with itsassociated high edge:area ratio, may provi<strong>de</strong> bothprotection from wind and wave action in inundatedsites and facilitate colonisation by plants and animals.Many re-floo<strong>de</strong>d block cuttings have beenspontaneously colonised by Sphagnum-based bogvegetation (sometimes referable to M 18) and in sornesites sustain a rich biological resource. The c10sejuxtaposition <strong>of</strong> wet cuttings with contrasting habitats(e.g. heathland on separating baulks), and the interfacebetween them, may contribute to the high biodiversityand natural history interest <strong>of</strong> such sites. However, itnot axiomatic that block-cutting sites are richrepositories <strong>of</strong> bog species, nor that they are alwaysreadily rewetted.It is sometimes suggested that block cuttings are moreamenable to recolonisation than, say, milling fieldsbecause <strong>of</strong> plants and animals that have survived upon(or have recolonised) the intervening baulks <strong>of</strong> peat (orwithin the trenches). This is very likely to be correctwith comparatively small-scale peat operations, but it isnot a universal feature <strong>of</strong> block-cutting procedures. Insorne block-cutting complexes, the environment andvegetation <strong>of</strong> the baulks has been so modified (e.g. bydamage and <strong>de</strong>hydration) as to permit few bog speciesto survive, even where there is a long period betweensuccessive cuts. In other cases, the block-cutting cycle1 Note that this is not always the case: extensive block-cutting caneventually produce a largely !lal surface comparable lo a millingfield.


90RESTORATlO OF DAMAGED PEATLA os<strong>of</strong> has been <strong>of</strong> such short duration a to 'sterilise' thesurface <strong>of</strong> the baulks as effectively as any millingoperations.Ditch-blocking is likely to be a prerequisite for therewetting <strong>of</strong> block-cut sites, and in some situati ns itmay also be necessary to reduce rates <strong>of</strong> vertical waterloss into the subsoil by completely filling the drainageditches. The presence and functioning <strong>of</strong> tile or moledrains across the peat fields should also be a sessed,and drains blocked as necessary. However, the effectiveness<strong>of</strong> ditch-blocking alone for rewetting willlargely <strong>de</strong>pend on the topography <strong>of</strong> the site. [See also5.4.3]Effects <strong>of</strong> topographyIn an appropriate topographical context (e.g whereblock cuttings fonn natural sumps), it may be sufficientto ensure that the cuttings are sealed for them to rewet(ditch blocking alone may be sufficient (Mea<strong>de</strong>,1992». They partly then function as tanks that store(winter) rainfa!\. This may buffer them againstexcessive water-table drop during dry periods, and theycan serve either as growth lagoons or as fe er tanks.In sorne situations rewetting <strong>of</strong> block cuttings may bedifficull. For example, when the cuttings are locatedupon a residual peat massif the water level in thecuttings may be dominated by the behaviour <strong>of</strong> theperched water mound in the massif as a whole, andrewetting <strong>of</strong> the cuttings will be <strong>de</strong>pen<strong>de</strong>nt uponrewetting strategies for the massif (see aboye). Cuttingssituated within weakly humified peat may beparticularly influenced by the behaviour <strong>of</strong> the watertable in a surrounding peat mas if and in circumstanceswhere the perched water is low they may beparticularly susceptible to <strong>de</strong>hydration, <strong>de</strong>spite anygreater storage properties <strong>of</strong> such peal. However, manyabandoned commercial cuttings are within quitestrongly-humified peal.Some block-cutting sites possess a very uneventopography, with various states <strong>of</strong> revegetation [seeFigure 5.5]. Where cuttings have been ma<strong>de</strong> at verydifferent levels, it may be possible to rewet individualcuttings, but mor difficult to integrate this into anoverall rewetting strategy. Particularly intractableproblems may be presented where there are residualmassifs <strong>of</strong> strongly-humified peat within a cuttingcomplex. In this situation it may be difficult to <strong>de</strong>vise arewetting strategy that provi<strong>de</strong>s optimal water levelconditions for a large number <strong>of</strong> cuttings, at leastwithout a large amount <strong>of</strong> earthworks. Here, it may benecessary to consi<strong>de</strong>r an integrated approach usingditch blocking and parapet bunding (possibly in additionto and extending existing baulks) together withsome removal <strong>of</strong>peat to produce a more level field.The problem <strong>of</strong> baulksAlthough the network <strong>of</strong> baulks in a block-cutting sitemay be beneficial, for example, in helping to retainwater in cuttings and for access the baulks themselvesmay be difficult to rewet pennanently. This frequentlygives rise to a characteristic pattemed landscape <strong>of</strong> wet,revegetated cuttings separated by strips <strong>of</strong> heath or,Floating raftFigure 5.5 Revegetation <strong>of</strong> re-wetled block-cut peatland. In this configuration <strong>of</strong> cutting surfáce, the shallow poolsperiodically dry out and support only vegetation with purple moor-grass and cotton grass. The <strong>de</strong>eper pools showsimilar water level flux but have <strong>de</strong>ve10ped a floating raft <strong>of</strong> Sphagnum which accommodates this change. Theuneven topography permits good revegetation <strong>of</strong> some individual cuttings, but is less well-suited to re-wetting <strong>of</strong> theentire complex.


CHAI'TER 5: PRINCII'LES OF REWETTING91where continued management i not possible, by scrubor woodland (e.g. Risley Moss, Cheshire; CrowleMoor, Lincs.). Where the cuttings are themselvesnarrow, <strong>de</strong>velopment <strong>of</strong> scrub, or even vigorousEriophorum vaginatum, on the baulks may eventuallysha<strong>de</strong> l11uch <strong>of</strong> the cuttings as well as the baulks [Plate5.3]. Moreover, as long as the baulks rel11ain SUl11l11er-Plate 5.3 Revegetated block cuttings at Lichtenmoor(Germany). Dense growth <strong>of</strong> Eriophorum vaginatum onthe f100r <strong>of</strong> the cuttings sha<strong>de</strong>s growth <strong>of</strong> Sphagna inthe ditches. Baulks are ddminated by Molinia caerulea.Plate 5.4 Block peat cuttings f100<strong>de</strong>d to the level <strong>of</strong> thetop <strong>of</strong> the baulks; Fenns Moss (Clywd).dry they will effectively ensure that bog regeneration isconfined to the cuttings.One solution to this difficulty, in those situations whereit is possible, is to try to elevate the water table in thecuttings to be level with the surface <strong>of</strong> the baulks [Plate5.4], so that they can be more effective as fee<strong>de</strong>r tanks.However, there is little current evi<strong>de</strong>nce that it ispossible, just by maintaining high water levels in thecuttings, to rewet peat baulks sufficiently so that treegrowth will be prevented (though it may be reduced) orso that a wi<strong>de</strong> range <strong>of</strong> bog species will establish. Thisis not least because water tables tend to drop during thesummer months, though the magnitu<strong>de</strong> <strong>of</strong> this willpartly <strong>de</strong>pend upon the climate. One suggested solutionmay be to promote irrigation <strong>of</strong> the baulks by a network<strong>of</strong> grips extending from the cuttings, but we havenot seen this employed in practice. This would also<strong>de</strong>pend on maintaining water levels so that the gripsdid not act as drains in periods <strong>of</strong> low water supply.An additional consi<strong>de</strong>ration with regard to raising thewater level in the cuttings is the height di fferencebetween the base <strong>of</strong> the cutting and the surface <strong>of</strong> theadjoining baulk, when this is great (> 50 cm). Theresultant <strong>de</strong>ep water in the cuttings may not be optilllalfor growth <strong>of</strong> even aquatic Sphagnul11 species r5.4.I;5.4.4].AItemative approaches to the problem <strong>of</strong> too Illanybaulks are to reduce their height, total area orfrequency (especially where the cuttings comprise alarge number <strong>of</strong> thin, parallel baulks), as carried out at<strong>Peatlands</strong> Park (Arrnagh) [Plate 5.5]. Such operationsall require the removal <strong>of</strong> peat which Illay be expensivewhen peat extraction at a site has ceased, although itIllay be possible to use the peat to help fill in theditches. It is also difficult to carry out once rewettinghas started. Where manipulation is possible, carefulconsi<strong>de</strong>ration should be given to the most <strong>de</strong>sirableratio <strong>of</strong> baulk to cuttings in terms <strong>of</strong> achievingrewetting objectives and to the height <strong>of</strong> the baulks.Increases in the ratio <strong>of</strong> open water to baulk (bylevelling selected baulks) may help to reduce waterlevel fluctuations as open water has a higher waterstorage coefficient than peat (it would also be feasibleto use the peat frOIll the 'redundant' baulks to blocktrenches and drains). If the baulks around the openwater area are too thin « c. 5 m), a sufficiently stablewater table may not be maintained owing to leakageand slul11ping <strong>of</strong> the baulk, and the water balance l11ayshow greater losses than gains (Beets, 1992).If it is impractical to reduce the height or area <strong>of</strong>baulks, and where high water tables in the adjoiningcuttings do not a<strong>de</strong>quately rewet their surface, consi<strong>de</strong>rationmay be given to inundation <strong>of</strong> the baulks byelevated water levels across part or all <strong>of</strong> the cuttingcomplex. The feasibility <strong>of</strong> this will <strong>de</strong>pend largely on


92RE TORATION OF DAMAGED PEATLADSPlate 5.5 Recolonisation <strong>of</strong> former block peat cuttings;<strong>Peatlands</strong> Park (Armagh). Lowering baulk heights andraising water levels resulted in extensive colonisationby Sphagnum cuspidafum. The area is normallyf100<strong>de</strong>d in winter.the topographical situation <strong>of</strong> specific sites. Where thecutting form a large topographical bowl, it may bepo sible to achieve this just by blocking outfall ditches.However, where this is not the case (for example,where the cuttings are located upon a peat massit) thenit will be neces ary to create an artificial seal aroundthe cutting complex for e ample using a parapet bund[Figure 5.4; Plate 5.6].ConclusionIt may be conclu<strong>de</strong>d that, in ertain circumstances,block-cut urfaces may provi<strong>de</strong> a good template forrevegetation, but that this i not an invariable property.Also, even where ucces fui revegetation has occurredwithin block-cutting, he <strong>de</strong>veloping pockets <strong>of</strong> m 'revegetation may not readily spread from the cuttings tocoalesce across baulks. Approaches to the restoration<strong>of</strong> block-cutting complexes may therefore need to bephased to consi<strong>de</strong>r (i) the water rnanagement andrevegetation f individual cuttings (i.e. the nucleation<strong>of</strong> bog regrowth and ii) the wi<strong>de</strong>r issue <strong>of</strong> watermanagement and revegetation <strong>of</strong> the entire peat-cuttingcomplex. It shou Id be noted that once ubstantial parts<strong>of</strong> the ite are wet and regenerating, options forub equent human interventioh engineering ele.become progres ively more limited.5.4.3 Milled-peat workingsIntroductionMany current peat operations use some forrn <strong>of</strong> surfacemilling [2.3]. In this, a succession <strong>of</strong> thin layers <strong>of</strong> peatare shaved from the surface <strong>of</strong> cambered beds duringeach harvesting season. The fields are usually large,and are typically drained by a serie <strong>of</strong> <strong>de</strong>ep drains,sometimes fed by mole or tile drains beneath the peatsurface. The urfaces remaining after peat extractionceases are usually bare and dry, and when abandoned,Plate 5.6 Extensive bunding around former peat cuttings; SE 80g, Cors Caron (Dyfed) [Photo: J. Davis] [See alsoPlate 8.2]


C1IAI'TER 5: PRINClI'LES OF REWErnNG93the fields may have only a shallow <strong>de</strong>pth <strong>of</strong> typicallystrongly-humified, compressed peaL The surfacc maybe flat or sloping. Sometimes the fields may beconfined within un-worked peat banks, usually at veryinfrequent intervals.Milled peat fields are sometimes thought to be sorne <strong>of</strong>the most difficult peat surfaces to restore, apparently onaccount <strong>of</strong> their extensive area and featureless, andsometimes sloping, topography. Where they haveexposed strongly-humified peat they may beinconducive to a<strong>de</strong>quate water storage and retention.Water retention is particularly problematic on slopingfields, which normally suffer rapid run<strong>of</strong>f and,sometimes, erosiono Nonetheless, there is little reasonto suppose that milled fields are necessarily moredifficult to rewet than would be block cuttings ma<strong>de</strong> ona similar scale. This is because milling fields canthemselves be sculpted to provi<strong>de</strong> a topographyanalogous to block cuttings, or can be bun<strong>de</strong>d to retainwater. Both <strong>of</strong> these activities require investment <strong>of</strong>resources into surface preparation for restoration.There are currently few examples <strong>of</strong> long-termrestoration projects on milled surfaces, but it is likelythat restoration will only be possible if successfulattempts are ma<strong>de</strong> to retain precipitation, to preventerosion and to accelerate vegetation colonisation bymanipulating the surface relief (Pfa<strong>de</strong>nhauer, 1989).(a) Ditch blockingBlocking <strong>of</strong> drainage ditches is essential to preventwater loss from milled peat fields. As for blockcuttings,in sorne situations it may also be necessary toreduce rates <strong>of</strong> vertical water loss into the subsoil bycompletely filling the drain'age ditches and to take intoaccount the effects <strong>of</strong> any mole or tile drains across (hepeat fields.Limítatíons• The effectiveness <strong>of</strong> ditch blocking in rewettingmilled surfaces will <strong>de</strong>pend largely upon thetopography <strong>of</strong> the site. Where the milled fields aresloping, ditch blocking is unlikely to retain water ator near the surface <strong>of</strong> the peat, though it maymaintain high water levels in and along the ditches(as at Breitenmoos, Germany). [n flatter sites, ditchblockingmay retain water levels c10se to the peatsurface for at least part <strong>of</strong> the year.• Even on flat sites, ditch b[ocking alone is unlikelyto produce a water regime conducive to the reestablishment<strong>of</strong> a full complement <strong>of</strong> bog species.This is because there is <strong>of</strong>ien consi<strong>de</strong>rable flux <strong>of</strong>the water tableo In dry periods, the water tabletypically sinks sorne consi<strong>de</strong>rable distance belowthe surface. This may not be so great a problem inregions that are consistently wet, but generallymilled peat extraction is impractical in suchrcgions.• Exccpt in favoured topographical situations, ditchblocking alone is unlikely to provi<strong>de</strong> much surfaceinundation. [t thus <strong>of</strong>fers little potential forincreasing storage <strong>of</strong> surplus precipitation water,nor provi<strong>de</strong>s conditions for establishment <strong>of</strong> bogspecies other than those which are most tolerant <strong>of</strong>periodic dryness.Possíble applicatíans• Ditch-blocking is likely to be a prerequisite for therewetting <strong>of</strong> all milled surfaces.• [n most cases ditch-blocking is unlikely to besufficient for regeneration <strong>of</strong> a bog vegetation onmilled peat fields. An exception to this is wheremilled fields are surroun<strong>de</strong>d by high peat baulkswhich permit inundation just by blocking the mainditch outflow through the baulks. Even here, it islikely that some more complex constructs would bebeneficial to revegetation (see below).Patentíal far vegetatían restoratíanExcept in situations which are in some way confined,ditch blocking by itself is unlikely to supportregeneration <strong>of</strong> bog vegetation, except perhaps verylocally in shallow <strong>de</strong>pressions. Usual observed<strong>de</strong>velopments are species-poor Molinia grassland,birch scrub e/c. Where the milling fields are topographicallyconfined, so that surface inundation ispossible, it should be possible to encourage there<strong>de</strong>velopment <strong>of</strong>Sphagnum-rich bog vegetation.(b) Impaundment <strong>of</strong> water in lagoon5One approach to rewetting milled peat surfaces is tocreate a series <strong>of</strong> lagoons which impound meteoricwater [Plate 5.7]. These not only prevent, or reduce,lateral water run-<strong>of</strong>f but also serve to store water. Thishelps to prevent the occurrence <strong>of</strong> low sub-surfacewater levels during prolonged dry periods and alsoprovi<strong>de</strong>s an appropriate growing medium for pioneer,aquatic species <strong>of</strong>Sphagnum. Such lagoons provi<strong>de</strong> thesame sort <strong>of</strong> habitat as do the cuttings <strong>of</strong> block-cutpeatlands. They can be created either by leaving baulks<strong>of</strong> peat in si/u during extraction (unless these havebecome too dry to be effective) or by building walls <strong>of</strong>peat after operations have been completed. They areessential if water is to be retained on sloping surfacesand are probably also beneficial on flat surfaces, bysubdividing what would otherwise be extensivestre/ches <strong>of</strong> water, subject to consi<strong>de</strong>rable wind andwave action e/c.On sloping surfaces problems <strong>of</strong> rapid run<strong>of</strong>fexacerbate lack <strong>of</strong> water storage. In this situationlagoons can be constructed as a paddy-field-like


94 RESTORATIO OF DAMAGEO PEATLANDSPlate 5.7 Experimental restoration project in former milled peat workings, involving impoundment <strong>of</strong> water inconstructed lagoons; Gardrum Moss (Falkirk). [Photo: C. Turner]casca<strong>de</strong> [Figure 5.6] (see Nick, 1993). These reduceerosion on slopes to a minimum, hold precipitationwater on to the area and regulate discharge <strong>of</strong> surpluswater, i<strong>de</strong>ally to retain sufficient water to be favourablefor Sphagnul17 growth. Lagoon casca<strong>de</strong>s can also beused, in principIe at least, for gradient feeding (Joosten& Bakker, 1987). This is appropriate for sites that areparticu lady subject to summer drought and uses theupper lagoons as reservoirs to store winter water tohelp top-up lower lagoons during dry periods, anapproach which may help to ensure hydrologicalstability in at least part <strong>of</strong>the site.The dimensions and disposition <strong>of</strong> the lagoons will<strong>de</strong>pend on the fall in height across the surface <strong>of</strong> thearea to be rewetted, but areas <strong>of</strong> 1-10 ha have beensuggested. The size may also <strong>de</strong>pend on the disposition<strong>of</strong> the proposed lagoons in relation to the surroundingland, as in sOllle situations, the creation <strong>of</strong> such Jagoonsmay come un<strong>de</strong>r the provisions <strong>of</strong> the Reservoirs Act,if permanently tloo<strong>de</strong>d [Appendix 2]. The naturaldisposition and accumulation <strong>of</strong> water across thesurface should be studied and the information utilisedin any <strong>de</strong>sign solution. Each lagoon should have anoutlet at the bottom to allow excess water to escapeafter heavy rain 01' snow to avoid damage to the peatwalls. However, it is thought that these walls need notbe cOlllpletely water tight, as water will seep into thelagoons Jower down in the series.Limitations• Construction <strong>of</strong> lagoons is more expensive thanditch blocking.•••Construction requires an a<strong>de</strong>quate availability <strong>of</strong> arelatively impermeable construction material(i<strong>de</strong>ally strongly-humified peat) if the walls are tobe built rather than being created from peat left insitu (which may have become too dry to beeffective). In some cases, dark peat at the bottom<strong>of</strong> a bog may be suitable. In this case it isimportant to ensure that a sufficient thickness <strong>of</strong>peat remains to supply material for wall buildingas well as to limit any downward seepage, withoutpenetrating to un<strong>de</strong>rlymg fen peat 01' mineral soilin those sites where this would disadvantage the<strong>de</strong>sired renaturation.Lagoon walls may require some maintenance forlong-term stability. In practice this Illay be <strong>of</strong>consequence only for the outer peripheral walls a ,i<strong>de</strong>ally, renaturation should be well advanced bythe time that internal walls <strong>de</strong>teriorate. Nonetheless,it is always possible that heavy stonnscould cause premature dalllage to internal walls.On flat surfaces at least, the lagoons are likely toprovi<strong>de</strong> a rather uniform water <strong>de</strong>pth which mayrestrict, at least initially, colonisation just to thosespecies that are well adapted to those specific


CHAPTER 5: PRINCIPLES OF R WElTl G95(a)bundlagoonr1(b)bundFigure 5.6 Terraced casca<strong>de</strong> re-wetting <strong>of</strong> sloping cut-over peat surfaces. Overflow water from the upper lagoonscan be used to augment water in the lower ones.conditions (e.g. aquatic Sphagna). However, inpractice, even ostensibly 'flat' lagoons may showsome topographical variation; moreover, thisapparent limitation may actually be beneficial,becau e if the surfaces are not flat, any relativelydry areas with lagoons ma be subject to invasionby birch etc.• Smal1-scale topographical manipulation andheterogeneity may assist the establishment <strong>of</strong> agreater variety <strong>of</strong> species, but these may weJlinelu<strong>de</strong> birches and Molinia on the drier places.• Areas <strong>of</strong> open water may be attractive to wildfowl.Possible applications• This appears to be the single most useful techniquefor rewetting e tensive mil1ed surfaces, when theaim is to regenerate a Sphagnum-rich vegetation.• A technique such as this is essential to rewetsloping surfaces• This rewetting technique could also be used onmiJled fen peat surfaces and would provi<strong>de</strong>consi<strong>de</strong>rable opportunity to influence the character<strong>of</strong> the recolonist vegetationwater levels.Potential for vegetation restorationby manipulation <strong>of</strong>This rewetting technique has been uscd effectively torewet abandoned peat surfaces in The Netherlands andNW Germany (e.g. Lichtenmoor and Leegmoor,Germany; Amsterdamsche Veld, The Netherlands), andhas led to the establishment <strong>of</strong> extensive carpets <strong>of</strong>Sphagnum clIspidatum, <strong>of</strong>ien with species such asMolinia caerulea and Juncus effusus [Appendix 6]. Insome cases, these latter seem to encourage growth <strong>of</strong>Sphagnum species [9.2]. Peat stratigraphical studieshave shown that in numerous rai ed bogs the<strong>de</strong>velopment <strong>of</strong>a bog-building vegetation (with speciessuch as Sphagnum magellanicum, S. papillosum) hasarisen from a et phase <strong>of</strong> Sphagnum cuspidatum.Thus, whilst most examples <strong>of</strong> this restoration strategyare still in their infancy and have not progressed muchbeyond the S. cllspidatum phase, it is to be expectedthat, providing a positive water balance is maintained,they will foJlow a comparable <strong>de</strong>velopmental pathway(as has occurred in some ol<strong>de</strong>r, block-cut sites). Giventhe isolation <strong>of</strong> some sites it may be necessary to re-


96RE TORATlON OF OAMAGEO PEATLAOSintroduce some species that have been lost from thenear vicinity. Tí is also possible that atmosphericcontaminants (especially NH 4 ) may inhibit the reestablishment<strong>of</strong> some Sphagnum species, or othelwiseinnuence the <strong>de</strong>velopment <strong>of</strong> the vegetation.(e) Impoundment <strong>of</strong> water in sculpted hollowsAnother approach to the rewetting <strong>of</strong> extensive milledftelds would be to scrape large, shallow hollows in thepeat, to produce a scalloped surface which stores waterin the <strong>de</strong>pressions. [n principie, this is similar to theconstruction <strong>of</strong> lagoons, but relies upon the excavation<strong>of</strong> peat rather ti an the construction <strong>of</strong> walls. It has beensuggested that sculpted hollows may appear more'natural' and be intrinsically more stable than a lagoonbaed approach.Limitations• This approach may be better suited to flat surfacesrather than sloping ones.• If the hollows are to be exten ive and <strong>de</strong>ep enoughto store much water (to c. 50 cm <strong>de</strong>pth) thisapproach would require substantial excavation andmovement <strong>of</strong> peat.• In ites which have retained only a thin layer <strong>of</strong>ombrotrophic peat, substantial excavation may beimpractical, or is likely to ex pose un<strong>de</strong>rlying fenpeat or mineral soiJ. The effect this would haveupon revegetation will <strong>de</strong>pend upon the exactcharacter <strong>of</strong> these materials.• The sloping si<strong>de</strong>s <strong>of</strong> the scallops provi<strong>de</strong> asubstantial hydrological gradient from floo<strong>de</strong>d t<strong>of</strong>airly dry. Whilst this may well increase the range<strong>of</strong> specie that can quickly establish on the peatsurface, it is also likely to provi<strong>de</strong> consi<strong>de</strong>rableopportunity for the ma ive establishment <strong>of</strong>'un<strong>de</strong>sirable' species such as Molinia and birch inthe drier areas.ConelusionIn some sites, milling ha produced natural hollows andbasins within the peat, which may provi<strong>de</strong> a focus forwater storage but these may be small. In others, anentire milling lield may form a very large basinboun<strong>de</strong>d by walls <strong>of</strong> uncut peat and in this situation itma be possible to keep the floor suitably wet with fewadditionaJ constructions just by blocking the maindrains (as at the Amste damsche Veld, The Nether­Jands). In this situation sorne small-scale sculpting <strong>of</strong>the surface, as a series <strong>of</strong> <strong>de</strong>pressions and hummocks(Eggelsmann, 1987, 1988b - see also Nick, 1993;J-Iealhwaite & Gottlich, 1993), may help o increasestorage [Plate 5.8]; and subdivision <strong>of</strong> the field bybaulks may help to reduce damage to <strong>de</strong>velopingvegetation by wind turbulence and wave action (thoughthe evi<strong>de</strong>nce that this is necessarily <strong>de</strong>sirable isinconsistent). A further benefit <strong>of</strong> small-scale topographicalmanipula ion is that the heterogeneity mayassist recolonisation and establishment <strong>of</strong> variousspecies. Unfortunately, sorne <strong>of</strong> these latter mayinclu<strong>de</strong> birches and Molinia on the drier spots and insome instances such approaches to rewetting take onmore the appearance <strong>of</strong> the cambered beds used byforesters to plant conifers in waterlogged soils than that<strong>of</strong> an exercise in mire restoration!The optimal strategy for rewetting and restoring milledsurfaces will partly <strong>de</strong>pend upon particular sitecircumstances. [n general the approach adopted inNorth Germany (e.g. Leegmoor) has much tocommend it, with the construction <strong>of</strong> paddy-field likelagoons (1-10 ha may be an appr priate size), thoughpossibly with a slightly greater <strong>de</strong>gree <strong>of</strong> inundation(see below). Thi appears to be the only effectivestrategy where the milling fields are sloping - <strong>de</strong>sign <strong>of</strong>the restoration <strong>of</strong> the mire will be strongly <strong>de</strong>pen<strong>de</strong>ntPossible applications• [n principIe this approach could be used in many <strong>of</strong>the same situations as lagoon . The choice betweenthe two methods is Iikely to rest mainly upon <strong>de</strong>pth<strong>of</strong> residual peat, engineering convenience, slope <strong>of</strong>the site and on whether it is <strong>de</strong>sired to regeneratebog across most <strong>of</strong> the milling field surface or justwithin excavated hollows.• We know <strong>of</strong> no site where this approach has beenused on more than a very limited scale (viz. byexcavation <strong>of</strong> surface scrapes) (e.g. SomersetLevels).Plate 5.8 An attempt to increase microtopographicalvariation by small-scale sculpting <strong>of</strong> the peat surface asa series <strong>of</strong> <strong>de</strong>pressions and hummocks; Leegmoor (N.Germany).


I-IAPTER 5: PRI IPLE OF RE~ ETTI G97upon topography. This will be not just to usetopographical features to help retain water, but al o, inlow rainfall circum tances, to <strong>de</strong>vise configurationsthat can benefit, if neces ary from 'gradient feeding' orsome other form <strong>of</strong> water supplementation. Where thesurface is flat and confined, few earthworks may benecessary, but even here sorne <strong>de</strong>gree <strong>of</strong> compartmentalisationmay be <strong>de</strong> irable. If there is next-to-notopographical variation within the lagoon thu created,some minor topographical manipulation <strong>of</strong> the peatsurface could be countenanced but it is not evi<strong>de</strong>nt thatthis <strong>of</strong>fers much material advantage. As an alternativeto formal lagoons, excavation <strong>of</strong> shallow <strong>de</strong>pressionsscraped within the milling fields could be tried.It has been suggested that peat extraction could beplanned so as to leave, at completion, a residual surfacec nfigured a a dome <strong>of</strong> peat approximating to thepredicted position <strong>of</strong> the 'groundwater' mound (Bragg,1989). However, there appear to be inherent practicalproblems with this approach, and it cannot berecommen<strong>de</strong>d until there is further evi<strong>de</strong>nce that it mayprove to be an appropriate strategy [5.3.2(c)].5.4.4 Depth <strong>of</strong> inundationAs within peat extraction complexes there isconsi<strong>de</strong>rable opportunity to <strong>de</strong>termine and manipulatethe maximum height <strong>of</strong> the water table by engineering,it is necessary to i<strong>de</strong>ntify an appropriate water level.Various consi<strong>de</strong>rations will influence this.Approaches to rewetting based on just soaking the peatare likely to be unsuccessful due to excessive waterloss during dry periods. This is a particular problem insiles on peat with limited storage capacity (e.g.Blankenburg, 1992) and in summer-dry climates. Thussuch soaking may not provi<strong>de</strong> an a<strong>de</strong>quate basis forrevegetation <strong>of</strong> uch sites, except where somesupplementary water (such as is provi<strong>de</strong>d by gradientfeeding) is available to help maintain water level inthe cut-over peats. By contrast, sorne <strong>de</strong>gree <strong>of</strong> urfaceinundation increa es water storage, provi<strong>de</strong>s a suitablegrowth medium for pioneer species <strong>of</strong> Sphagnum andpermits the <strong>de</strong>velopment <strong>of</strong> tloating mats <strong>of</strong> vegetationwhich can better accommodate water level flux thancan plants growing on solid peat surfaces [Figure 5.7].It may also help to control the growth <strong>of</strong> 'un<strong>de</strong>sirable'plant species, such a Molinia caerulea [Plate 5.9] andbirch [see Plates 10.2 and 10.3].The <strong>de</strong>pth <strong>of</strong> water impoun<strong>de</strong>d within lagoons ele. maynot always be easily regulated - the <strong>de</strong>pth will reflectwater availability, topographical or constructionalfeasibility rather than ecological <strong>de</strong>sirability. However,choice <strong>of</strong> an 'i<strong>de</strong>al' water <strong>de</strong>pth is influenced byseveral consi<strong>de</strong>rations:• In a block-cut peatland, <strong>de</strong>ep filling <strong>of</strong> the (bun<strong>de</strong>d)cuttings may be <strong>de</strong>sired, to help rewet the adjoininguncut peal. The feasibility and suitability <strong>of</strong> thiswill <strong>de</strong>pend upon the height difference between thetop <strong>of</strong> the uncut peat and the bottom <strong>of</strong> Ihe cutting.• In any cut-over peatland, the <strong>de</strong>pth <strong>of</strong> winter(a) Not floo<strong>de</strong>d(b) Floo<strong>de</strong>dwater level fluxFigure 5.7 <strong>Restoration</strong> <strong>of</strong> peat excavations by inundation. In (a) the maximum water level only reache to aboutthe level <strong>of</strong> the cutting surface. Thus in dry periods the <strong>de</strong>clining water level leaves the cutting sUrface relativelydry. Fluctuations in water level <strong>of</strong> this sort are mainly conducive to the growth <strong>of</strong> a small number <strong>of</strong> species such ascotton grass and purple IT'0or grass. In (b) the cutting surface is relatively lower, so that for most <strong>of</strong> the year it isinundated. In dry periods the water level may sink slightly below the cutting surface, but it does not become dry.The relatively <strong>de</strong>ep water may preclu<strong>de</strong> grawth <strong>of</strong> raoted species, but will permit rafting by species such asSphagnum. The floating mats rise and fall with water level flux and thus experience relative hydrological stability.


98RE TORATlO OF O 1 ED PEATLA Dtlooding will be partly <strong>de</strong>termined by water lossduring the ummer - i.e. it needs to provi<strong>de</strong>ufficient storage to prevent water levels going to<strong>of</strong>ar below the urface for long period during thesummer. Depths <strong>of</strong> winter inundation <strong>of</strong> some 0.2­0.6 m have been calculated to be appropriate (e.g.chouwenaar ] 995).• Growth o pioneer Sphagnllm pecies (especiallySphagnllm clIspidatllm) is promoted by watel<strong>de</strong>pths that are continuously supra-surface, but nottoo <strong>de</strong>ep (50 cm summer <strong>de</strong>pth seems to be anoptimal maximum value, unless there i someadditional aid to tlotation).• Sorne <strong>of</strong> the 'bes' examples oC revegetation seenwas as floating rafts on <strong>de</strong>ep (c. I m <strong>de</strong>pth) water(e.g. Meerstalblok and Haaksbergeveen, TheNetherland ; Wieninger Filz, . Germany), but themechal1lsm <strong>of</strong> raft formation in such circumstancesis not always well estabJished.The approach <strong>of</strong> hallow-water flooding used in somenorth-German peatlands (e.g. Leegmoor - Plate 5.10)has been very successful in permitting the colonisation<strong>of</strong> extensive bare peat surfaces b Sphagnum speciesand may provi<strong>de</strong> an appropriate way forward. It stillremain subject to consi<strong>de</strong>rable water level fluctuation,though it may be expected that this effect will diminishas a thicker mat <strong>of</strong>Sphagnum accumulates.In situations where it is readily possible to have <strong>de</strong>eperwater tlooding (as in cutting bays within a block-cutcomple ) one revegetation strategy w uld be to have aphased inundation: (a) to initially establish a base <strong>of</strong>ombrotrophic vegetation in shallow tloo<strong>de</strong>d conditions;and then (b) to impose <strong>de</strong>eper inundation upon this.There is some evi<strong>de</strong> ce that the established vegetationmay lin to fonn a tloating raft when floo<strong>de</strong>d.Attention should also be given to inoculation <strong>of</strong>rewetted areas with plant material (includingSphagnllm pecies), the use <strong>of</strong> artificial aids to raftingand the po sibility <strong>of</strong> enhancing recolonisation by suchtreatments as fertilisation [9.6]. These have alreadyshown some potential value on a small scale (Money,J994, 1995) but they ill eed to be scaled up before afirm conclusion on their potential benefit can bereached.5.5 Rewetting extensive peatworkings in fen peatPlate 5.9 Tussocks <strong>of</strong> Molinia caerulea, killed byflooding; Fochteloerveen (The Netherlands).Plate 5.10 Extensive colonisation <strong>of</strong> former bare peatsurfaces by Sphagnum cuspidatum and Moliniacaerulea, within shallowly-floo<strong>de</strong>d lagoon; Lichtenmoor(N. Germany).5.5.1 IntroductionIn Britain commercial extraction <strong>of</strong> fen peat (bothwithin and without former raised-bog sites) is practisednow only in the Somerset Levels. However, extraction<strong>of</strong> fen peat once occurred much more wi<strong>de</strong>ly, andformer excavation <strong>of</strong> bog peat has led to the exposure<strong>of</strong> un<strong>de</strong>rlying fen <strong>de</strong>posits in numerous mire sites.The topography <strong>of</strong> fen peat workings shows internalva iation (retlecting excavation techniques) andvariation with respect to the urrounding landscape,reflecting events both in th mire and the wi<strong>de</strong>rlandscape. Some <strong>de</strong>posit form massifs slightlyelevated aboye the surrounding land cape, much aswith bog peat massif. This configuration may arisebecause <strong>of</strong> drainage and shrinkage <strong>of</strong> the surroundingland. In other sites, the exposed peat surface may bemore-or-less level with the urrounding land, or peatremovaJ may have produced <strong>de</strong>pressions below thegeneral ground leve!. When abandoned, thesesometimes readily tlood with telluric water.In broad terms the rewetting <strong>of</strong> fen peat surfaces issubject to many <strong>of</strong> the same constraints as those <strong>of</strong> bogpeat surfaces <strong>of</strong> comparable topography, and similarrewetting strategie may be appropriate. llowever, anadditional consi<strong>de</strong>ration is possible inputs <strong>of</strong> telluric


CHAPTER 5: PRINCIPLES OF REWETTING99water. The fact that fen peat has formed indicates thatat one time this horizon <strong>of</strong> the <strong>de</strong>veloping mire hadbeen irrigated by telluric water. This may have originatedfrom various sources (springs, river inundationetc.) which today are not always readily i<strong>de</strong>ntifiable(and may no longer exist), on account <strong>of</strong> natural orman-ma<strong>de</strong> changes to the hydrology <strong>of</strong> the mire'scatchment (e.g. embankment <strong>of</strong> rivers, construction <strong>of</strong>drains etc.). In consequence, possible telluric presentdaywater sources (and waterquality) available torewet fen peat workings may bear little relationship tothose un<strong>de</strong>r which the fen peat was laid down.Because there are various possible sources <strong>of</strong> telluricwater input into cut-over fen peat (and sometimes thepossibility <strong>of</strong> no obvious source at all) it iscorrespondingly difficult to make generalisations aboutwater management options applicable to many fen peatworkings.The restoration significance <strong>of</strong>any telluric water inputsto the rewetting <strong>of</strong> cut-over fen surfaces <strong>de</strong>pends uponthe <strong>de</strong>sired objective <strong>of</strong> restoration. On the one hand,such inputs may sometimes be instrumental in helpingto rewet the site; on the other, they promote there<strong>de</strong>velopment <strong>of</strong> fen vegetation. If this is not seen tobe a <strong>de</strong>sirable <strong>de</strong>velopment (i.e. if the restorationobjective is bog), it may sometimes be possible to buildperipheral bunds or dams both to impound meteoricwater and to exclu<strong>de</strong> telluric inputs. In this situation,revegetation wiII still re-commence upon minerotrophicpeat, but an absence <strong>of</strong> further telluric waterinputs should help to shorten the fen phase. Thesuccess <strong>of</strong>this approach will <strong>de</strong>pend consi<strong>de</strong>rably uponthe topography <strong>of</strong> the <strong>de</strong>posit, the character <strong>of</strong> telluricinputs (if any), and the quality <strong>of</strong> precipitationrecharge. Where the fen peat surface has only just beenexposed, and where the peat <strong>de</strong>posit stands proud <strong>of</strong>the surrounding land, precipitation can be the majorsource <strong>of</strong> water input, and rewetting consi<strong>de</strong>rations arethen much the same as with bog peal. However, wherepits have been dug into the fen peat, so that the peatsurface is below that <strong>of</strong> the surrounding landscape, it iscorrespondingly more difficuIt to excIu<strong>de</strong> telluricinputs. And whatever the topographical situation it maybe difficult to exclu<strong>de</strong> telluric inputs when these are<strong>de</strong>rived from upwelling groundwater springs.The outcome <strong>of</strong> rewetting strategies on fen peat<strong>de</strong>pends both upon the character <strong>of</strong> the irrigating waterand the level at which it is maintained. As a generalrule, assuming that sorne irrigating water isminerotrophic, a re-soaking strategy is likely to lead tothe re-<strong>de</strong>velopment <strong>of</strong>a fen vegetation which may haveonly a long-term potential to re-<strong>de</strong>velop into bogo Aflooding strategy (especially if with nutrient-poorwater) is likely to produce a seral, floating fenvegetation which may have great intrinsic value as wellas a potential for quite rapid (100-250 years) re-<strong>de</strong>velopment<strong>of</strong> bog vegetation (e.g. van Wirdum, 1995).5.5.2 Rewetting <strong>of</strong>f/at fen peatsurfacesThe following broad strategies can be adopted, eitherindividually or in combination:(a) Ditch blockingThe potential value <strong>of</strong> ditch-bJocking <strong>de</strong>pends upon thetopography <strong>of</strong> the site. Where the peat surface iselevated with respect to sorne or aH <strong>of</strong> the surroundingwater table, ditch blocking will help retain water on thesite and will usually be a prerequisite <strong>of</strong> restorationinitiatives. It may principally retain meteoric waterinputs, though retention <strong>of</strong> minerotrophic water mayalso occur in sorne situations.If adopted as the sole approach to rewetting, ditchblocking is liable to be subject to the same limitationsi<strong>de</strong>ntified aboye for bog peal. The main differences are(a) that it may be easier to maintain a permanently highwater table, <strong>de</strong>pending on the relationship <strong>of</strong> the peatworkings with the surrounding landscape and watertable and (b) that, even if periodically low water tablesoccur, the vegetation that re-<strong>de</strong>velops (sorne form <strong>of</strong>fen or fen meadow (if grazed or mown) or fen carr (ifunmanaged)) is more likely have higher conservationvalue than would the vegetation <strong>de</strong>veloped on bog peatin a similar situation. (This is because low-productivityvegetation on moist, base-rich peat is itself uncommonand <strong>of</strong>ien species rich.)In sorne topographical situations, ditch-blocking maybe nee<strong>de</strong>d, not to retain water on the site, but to preventthe ingress <strong>of</strong> minerotrophic water, should this beregar<strong>de</strong>d as un<strong>de</strong>sirable.(b) Irrigation by telluric water vía ditches or bysurface floodingMinerotrophic water from sources internal or externalto the peat <strong>de</strong>posit can be distributed around the cutoversurface by ditches, either with or without moregeneral surface flooding at times <strong>of</strong> water surplus.External water sources may incIu<strong>de</strong> adjoining riversand drains, but where the peat <strong>de</strong>posit is aboye thelevel <strong>of</strong> the adjoining land, external water may have tobe pumped into the mire. The cffects <strong>of</strong> theseprocedures <strong>de</strong>pends upon the topography <strong>of</strong> the site;slight <strong>de</strong>pressions may accumulate water whilstmounds may remain largely dry. Fen sites <strong>de</strong>pendingon river-flooding or ditch irrigation can showconsi<strong>de</strong>rable seasonal water flux. Much <strong>of</strong>the peat maybe waterlogged during the winter months, but duringthe summer there will be a ten<strong>de</strong>ncy for the water table


100RESTORAnON OF DAMAGED PEATLANDSto fal!. This occurs particularly in land parcels distantfrom the ditches. Care must also be taken to prevent theditches acting to remove water, especially during dryperiods.Rewetting by periodic tlooding or ditch irrigation canreinstate sorne form <strong>of</strong> fen vegetation upon the peatsurface, but its character <strong>de</strong>pends primarily upon the<strong>de</strong>gree and permanence <strong>of</strong> soil saturation, the chemicalcomposition <strong>of</strong> the peat and the irrigating water andtype <strong>of</strong> vegetation management (if any). The mostlikely <strong>de</strong>velopment is <strong>of</strong> a form <strong>of</strong> fen vegetationtypical <strong>of</strong> summer-dry fens (such as fen woodlandwhen unmanaged or fen meadow when mown orgrazed). This is likely to be rather coarse and speciespoorif the irrigating water is nutrient-rich. Thisapproach to restoration is in current use at WoodwaltonFen, Cambridgeshire (a former cut-over raised-bogsite).It is likely to be inconducive to the re-<strong>de</strong>velopment <strong>of</strong>bog, not least because <strong>of</strong> the inci<strong>de</strong>nce <strong>of</strong> low summerwater tables. It is most appropriate for situations wheremaintenance, or recreation <strong>of</strong> fen vegetation is arestoration objective, or as a specific, short-termmeasure.(e) Impoundment <strong>of</strong> water in lagoons orsculpted hollowsA fen peat surface can be engineered to producelagoons or sculpted hollows that retain water (as<strong>de</strong>scribed aboye for peat workings in bog peat [5.4]),as in the Somerset Levels, and Turraun Bog, Ireland[Appendix 6]. These can be used either primarily toimpound precipitation inputs or to hold minerotrophicwater (from various possible sources). Revegetation inthe first situation may be subject to much the sameconstraints as <strong>de</strong>scribed in section 5.4, with theadditional constraint that it may be necessary to takesteps to exclu<strong>de</strong> minerotrophic water when appropriate.However, proximity to minerotrophic water sourcescan also mean that a more stable water table is morereadily maintained. Where lagoons are <strong>de</strong>signed toproduce surfaces inundated with minerotrophic water,likely <strong>de</strong>veloprnents are as in 5.5.3.Note that sorne types <strong>of</strong> fen peat may be a less suitable(Iess cohesive and more permeable) constructionalmaterial than sorne bog peats.5.5.3 Rewetting <strong>of</strong>fen peat basinsPeat extraction in mires has sometimes created discretepits and basins, either dug in bog peat and tloored byfen peat, or excavated largely (or entirely) within fenpeat. These rnay occur at various scales, sornetirnes justas trenches produced by block-cutting or as rnuchlarger <strong>de</strong>pressions. Sorne former (now revegetated)peat excavations in fen peat have been large (> I6 ha).Such peat cuttings are very wi<strong>de</strong>spread in fens. Sornecurrent excavations in the Somerset Levels formcomparable basins.The water budget <strong>of</strong> cuttings in fen peat may be morecomplex than that <strong>of</strong> comparable examples in bog peatand water management options again will <strong>de</strong>pend upontopography, available water sources and restorationobjectives. In sorne sites drains which have been dug toevacuate water from the workings may need to beblocked to permit retlooding; in other situations suchdrains may provi<strong>de</strong> an important supply <strong>of</strong>minerotrophic water. In sorne cases it may be necessaryto install <strong>de</strong>vices that can regulate the water level to apre<strong>de</strong>termined maximum.Where such hollows are rewetted with rninerotrophicwater, fen vegetation can re<strong>de</strong>velop rapidly, itscharacter being <strong>de</strong>termined largely by water <strong>de</strong>pth andtluctuation, base-richness, nutrient-richness andmanagement regime (if any). Spontaneous rewetting <strong>of</strong>peat-cut basins within fen peat has occurred in a largenumber <strong>of</strong> mire sites in the UK (sorne <strong>of</strong> thern formerbog sites). When they are retloo<strong>de</strong>d, hydroseralrecolonisation can occur, <strong>of</strong>ien producing tloating mats<strong>of</strong> fen vegetation. These rafis, when irrigated by water<strong>of</strong> suitable quality (nutrient poor but relatively baserich)can provi<strong>de</strong> a suitable basis for spontaneoussuccession to bog, as well as having rnuch intrinsicvalue (sorne prime examples <strong>of</strong> fen vegetation inBritain occur in recolonised peat cuttings).In sorne instances it rnay be possible to exclu<strong>de</strong>minerotrophic water from fen peat basins by dammingintlow ditches etc., so that they are irrigated prirnarilyby meteoric water. This rnay be particularlyappropriate where the minerotrophie sourees are rieh innutrients and where it is <strong>de</strong>sired to recreate a nutrientpoorwetland.5.6 Integrated restoration <strong>of</strong>remnant massifs andcommercial peat fields5.6.1 IntroductionIn sorne commercial peat workings, peat extraetion hasoceurred across almost all <strong>of</strong> the surface, leaving anexpanse <strong>of</strong> peat fields with no remnant massifs..Inother sites the peat fields are interspersed withupstanding remnant massifs, <strong>of</strong> various dimensions.Remnant massifs may varyeonsi<strong>de</strong>rably in theireharaeteristics. Small remnants are <strong>of</strong>ien dry and mayhave rather Iittle biological interest. Other exarnples,particularly larger ones, may retain a wealth <strong>of</strong> typiealbog organisms, either as a surviving part <strong>of</strong> the original


CHAPTER 5: PIUNCIPLES OF REWETTING101bog surface (e.g. Wedholme Flow, Cumbria), or asspecies that have recolonised ol<strong>de</strong>r peat workings uponthe massif (e.g. Thorne Waste, S. Yorkshire). Theretention <strong>of</strong> the species complement <strong>of</strong> such sites isimportant both in its own right and because it provi<strong>de</strong>sa proximate source <strong>of</strong> recolonist species for theoperational peat workings [Chapter 2]. The peatstratigraphy and archive <strong>of</strong> the massifs may a\so beconsi<strong>de</strong>red important. Where


102RESTORATION OF DAMAGED PEATLANDSthey eventually naturally reeonform to a position inequilibrium with the water regime maintained in thesurrounding peat fields.Limitations• The limitations i<strong>de</strong>ntified aboye [5.3.2(b)] withrespeet to the possible rewetting <strong>of</strong> individualmassifs by 'natural wastage', <strong>of</strong> eourse, apply alsoin eomposite peatland sites, viz. that there is littlereason to suppose that the surfaee <strong>of</strong> damagedmassifs will neeessarily rewet satisfaetorily just inresponse to wastage. It is possible that the massifwould eompletely, if gradually, waste away to theposition <strong>of</strong> the water level maintained in the peatfields.• The feasibility <strong>of</strong> this approaeh for rewetting <strong>of</strong> themassif <strong>de</strong>pends upon the topography <strong>of</strong> the site andthe possibility <strong>of</strong> impounding water over the peatfields to a <strong>de</strong>pth suffieient to saturate a signifieantproportion <strong>of</strong>the massif (see below).Possible applicationsThis approaeh to integrated restoration may sometimesbe <strong>de</strong>termined by laek <strong>of</strong> resources for more elaborateapproaehes. It may be partieularly appropriate:• where the heíght dífferenee between the massifsurfaee and the peat field surfaee ís small;• where elevatíon <strong>of</strong> the water level withín thesurroundíng peat fields (usually ínundation)elevates the positíon <strong>of</strong> the perched water moundwíthín the massifto a posítíon close to the surfaee;• where the massif retaíns a 'good quality' bogvegetation and where ít ís aeeeptable to permitsorne drying <strong>of</strong> the margins (and probably loss <strong>of</strong>vegetatíon 'quality' at the períphery) either beeausethe total area <strong>of</strong> the 'good quality' vegetation islarge or beeause the amount <strong>of</strong> peripheral damageís predieted to be small;• where the climatie regime is suitable (i.e. eool an<strong>de</strong>onsistently wet) for the direet establishment <strong>of</strong>Sphagnum on damaged or wasting bog surfaces;• Where the massif is already badly-damaged so thatthere is likely to be little loss <strong>of</strong> biologieal interestupon wastage, whatever the outeome.(b) Reduction <strong>of</strong> the height <strong>of</strong> the massif bypeat removalAn altemative approaeh to permlttmg wastingproeesses etc. to ron their natural course is to substitutefor them by peat extraetion, to reduce the height <strong>of</strong> themassifto a level at which it can be a<strong>de</strong>quately rewettedintegral with water management <strong>of</strong> the adjoining peatfields.Limitations• Peat removal would remove the peat archive. [Thismay also eventually oeeur by proeesses <strong>of</strong> naturalwastage].• Peat removal would remove any biologieal valueassoeiated with the remnant. The extent to whichthis represents a eonstraint <strong>de</strong>pends upon (a) thenature <strong>of</strong> the biologieal resource <strong>of</strong> the remnantmassif; and (b) the likely long-term stability <strong>of</strong> thisresource in the absenee <strong>of</strong> other water managementmeasures.• Peat removal may <strong>de</strong>stroy the reservoir <strong>of</strong> speeiesfor reeolonisation <strong>of</strong> adjoining peat fields. [It ispossible that this could to sorne extent be mitigatedby transfer <strong>of</strong> the massif surfaee directly to the peatfields, provi<strong>de</strong>d that the latter had been rewettedinto an appropriate condition to reeeive it.]Possible applicationsAn exeeption to the aboye situations may be provi<strong>de</strong>dwhen the vegetation etc. is <strong>de</strong>monstrably not stable andwhere 'interest' is likely to be lost anyway. In thissituation a 'reseue' operation (i.e. transfer <strong>of</strong> sorne orall <strong>of</strong> the remnant surface to adjoining peat fields in asuitable receptor condition) eould be eontemplated.Peat removal from remnant massifs eould beeonsi<strong>de</strong>red when:• the massif has Iimited value as a reservoir for bogspecies or archaeology;• the massif is unlikely to become effectivelyrewetted by other proeedures, beeause <strong>of</strong> problems<strong>of</strong>'diffieult' topography or lack <strong>of</strong>resourees;• when the height difference between the surfaee <strong>of</strong>the massif and peat fields is great and when themassif area is smal!.Planned peat removal from remnant massifs may notseem an attraetive option to sorne conservationists.However, it should be reeognised that in sorne cases itseffeets may be similar to those that wilI be produeedmore slowly by natural processes <strong>of</strong> wastage etc.I<strong>de</strong>ally the potential for the rewetting <strong>of</strong> massifs shouldbe consi<strong>de</strong>red with respeet to the cessation <strong>of</strong> peatextraetion: there may be little to be gained if prematureeurtailment <strong>of</strong> peat extraetion results in a bogtopography that is particular\y diffieult to rewet.5.6.4 Elevation <strong>of</strong> the water table'around a remnant massif(a) Elevation <strong>of</strong> the water table in basinsAn altemative approaeh to an integrated restoration <strong>of</strong>remnant massifs and surrounding peat fields is toelevate the water table over the peat fields suffieiently


CHAPTER 5: PRINClPLEOF REWETIING103to effectively rewet the remnant massif. In suitabletopographical situations (such as a closed basin) it maybe possible to do this just by allowing the peat fields t<strong>of</strong>ill with water, confined by the basin topography[Figure 5.8(a)]. However, this approach is inappropriatefor many commercial peat workings, which are<strong>of</strong>ien on rather flat, unconfined sites. In this situationthe alternative approach, if possible, is to elevate the¡--I (a) Peal workings confined in basinFloo<strong>de</strong>dpeal field(b) Peal workings unconfined(i) Inundation <strong>of</strong> peal fields(ii) Reconslruclion <strong>of</strong> water moundFlal peal fieldSlepped peat fielḏ- ­ , -water mound around the residual massif by appropriatebunding. Note that in either case consi<strong>de</strong>ration must begiven to the <strong>de</strong>pth to which the peat fields will flood,both in terms <strong>of</strong> their potential for revegetation andconsi<strong>de</strong>rations <strong>of</strong> safety.(b) Reconstruction <strong>of</strong> the water mound arounda remnant massif on flat sitesOn flat surfaces, elevation <strong>of</strong> the water table on thepeat fields relative to the massif surface is moredifficult than in a basin and will inevitably entail theconstruction <strong>of</strong> bunds to impound water. In situationswhere the height difference between the surfaces <strong>of</strong> themassif and the peat fields is small, the construction <strong>of</strong>simple lagoons across the peal fields may be sufficientto maintain high water levels in the massif. However,when the difference is greater, this approach may beina<strong>de</strong>quate to maintain the surface <strong>of</strong> the massif in asuitably wet condition [Figure 5.8 (b,i)].A more elaborate approach, appropriate for thissituation, is to reconstruct the water mound around theremnant massif. The principie <strong>of</strong> this approach isillustrated in Figure 5.8 (b,ii). It differs from simpleinundation <strong>of</strong> the peat fields in that lagoons <strong>of</strong>increasing eJevation are used to build the water moundin a series <strong>of</strong> steps. On level surfaces this may beachieved by a series <strong>of</strong> bunds <strong>of</strong> varying height; onpeat surfaces which rise up to the massif, there will beless need for tall bunds and associated <strong>de</strong>ep lagoons.Limitations• This approach involves consi<strong>de</strong>rable bunding andmay be expensive, though the magnitu<strong>de</strong> <strong>of</strong> theoperation will <strong>de</strong>pend upon the height differencebetween the surface <strong>of</strong> the massif and the peatfields.• Where the surface <strong>of</strong> the peat fields is more-or-Iesslevel, bunds near the massif will be tall and theassociated lagoons will be <strong>de</strong>ep. Consi<strong>de</strong>rationmust be given both to the stability <strong>of</strong> lhe bunds andto the prospects for revegetation <strong>of</strong> <strong>de</strong>ep lagoons.• Where the surface <strong>of</strong> the peat fields rises up to themassif, shorter bunds will be nee<strong>de</strong>d, but the slopemay require bunds at frequent intervals.Figure 5.8fieldsRe-soaked peal Mineral subslratumSaturaled peal Open walerUnsoaked peal BundRewetling <strong>of</strong> remnant massifs and peatPossible application• This approach could be used for the integratedrestoralion <strong>of</strong> many composite peat workings.Where the height difference between lhe remnantmassif and the peat fields is not greal, il may belittle more expensive than the normal cost <strong>of</strong>creating lagoons on abandoned peat fields.• Where substantial peat engineering is required, thisapproach is perhaps best seen as a prestigeapproach, that may be used in sites where the


104RE TORATION 01' DAMAGED PEATLAND.residual massif has particularly great conservation·mpOltance.Potential tor vegetation restorationThis appr ach has been used with consi<strong>de</strong>rable successin the restoration <strong>of</strong> the Meerstalblok in the Bargerveenre erve (The Netherlands). Here, lagoons peripheral tothe remnant massif, over worked peat surfaces havehelped to rewet the massif, and have themselves revegetatedwell [Plate 5.1 J]. At this site, some adjoiningagricultural land is aloto be tloo<strong>de</strong>d to help maintainthe water balance <strong>of</strong> the area. [This stems partly [rom a<strong>de</strong>sire to prevent the po sible <strong>de</strong>velopment <strong>of</strong> oxidisingconditions beneath the peat mass as a result <strong>of</strong> loweringgroundwater table .]5.7 Maintenance <strong>of</strong> remnantmassifs during peatextractionoperations5.7.1 IntroductionIn sltes where peat extraction is taking place adja entto peat massi[s that sustain important populatio lS <strong>of</strong>bog species, it may be <strong>de</strong>sirable to protect these fromexcessive water loss, occurring in consequence <strong>of</strong> theextraction operations. Factors associated with peatextraction which may contribute to water loss inclu<strong>de</strong>'(a) direct drainage <strong>of</strong> the adjoining massif (either as a<strong>de</strong>liberate policy to drain t e massif, or as a consequence<strong>of</strong> ditches dug acro s the ma si[ to evacuatewater from the operational peat workings); (b)reduction <strong>of</strong> basal area <strong>of</strong> the massif; and (c) increasein hydraulic gradient between the urfaces <strong>of</strong> themassif and the peat fields The requirement to minimiseany water drawdown and loss in the massif induced byongoing peat removal will <strong>de</strong>pend largely on theimportan e <strong>of</strong> the massif for bog species. Where thebog massif alr ady supports few bog species, but ¡s, forexample, heathland, there may be little need to protectit against water los (alth ugh this does not necessarilymean that rewetting should not be attempted.) Wherethe massif supports 'high quality' bog vegetation, someform <strong>of</strong> protectlOn is likely to be necessary.Whilst peat operations are in progress, the priorityrequirement is likely to be to pr tect any existinginterest rather than lo attempt restoration <strong>of</strong> areaswhich are already badly-damaged [see Chapter 6],unless these can be incorporated into an integratedstrategy at an early tage. Thus, water managementstrategies will most <strong>of</strong>ien be those which aim tomaintain wet onditions rather than to restore wetcondition . For uch purpose, trategies which aim atre-soaking are likely lo be appropriate.Plate 5.11 . Floating rafts <strong>of</strong> vegetation (including Sphagnum euspidatum, S reeurvum, Enophorum angustifo/ium.Eriea tetra/Ix) <strong>de</strong>veloped in refloo<strong>de</strong>d, bun<strong>de</strong>d block-peat cuttings; .Meerstalblok (The Netherlands).


CHAPTER 5:. PRINCIPLES OF REWETTING(055.7.2 BundingPeat massifs can be protected from water loss by theconstruction <strong>of</strong> an impermeable bund around all or part<strong>of</strong> their periphery. Bunds can be constructed from lowpermeability peat or from an artificial, inert lowpermeabilitymaterial. Various arrangements <strong>of</strong> bundscan be used, as discussed in previous sections. Therequired character <strong>of</strong> the bunds wiJl <strong>de</strong>pend upon theheight difference between the massif surface and thepeat field surface and also upon the character <strong>of</strong> thepeat. When the <strong>de</strong>eper peat is <strong>of</strong> sufficiently lowpermeability, relatively shallow bunds may be used tocontain water in the upper, more transmissive peatsrather than needing complete wa/l bunds down theentire <strong>de</strong>pth <strong>of</strong>the massifedge [Figure 5.9].Limitations• Bunding is comparatively expensive.• Where the height difference between the surface <strong>of</strong>the massif and the cut-over peat is large, bunds willneed to be particular well constructed andmaintained. Altematively a series <strong>of</strong> stepped bundsmay be required [as in Figure 5.8].PossibJe applications• Bunding can be used in a large number <strong>of</strong> situationsto protect a remnant peat massif from excessivewater loss [5.3]..• In many situations it may be <strong>de</strong>sirable to configurethe peat excavation so that there is a series <strong>of</strong> stepsup to the base <strong>of</strong>the remnant [Figure 5.8]. This wiJlhelp to reduce the hydraulic gradient, be morestable and will permit shorter, less robust bunds tobe used.5.7.3 Non intervention (exeept ditehblocking)The main altemative to sorne form <strong>of</strong> bunding is apolicy <strong>of</strong> non-intervention, other than the blocking <strong>of</strong>any ditches that drain the remnant massif. Thisapproach has the advantage <strong>of</strong> being cheap and simple,but it is unlikely to be universaIly acceptable as, ingeneral, it is an approach based upon the accommoda/ionrather than preven/ion <strong>of</strong> damage associatedwith water loss [5.3.2(b)].Limitations• In many situations non-intervention may lead tosustained and increasing damage <strong>of</strong> the bog habitatsupported on the remnant massif.• The extent to which damage will occur will <strong>de</strong>pendupon the character <strong>of</strong> the massif biota and theextent to which water loss is induced by adjacentpeat extraction. This latter will be <strong>de</strong>termined interalia by the hydraulic gradient, the transmissivity <strong>of</strong>(a)(c)(b)(d)weakly-humified peat § strongly-humified peatIbundFigure 5.9 Protection <strong>of</strong> massifs alongsi<strong>de</strong> peat extraction by bunding. When the exposed massif is eomposed <strong>of</strong>permeable peat, a wall bund the height <strong>of</strong> the edge <strong>of</strong> the massif may be nee<strong>de</strong>d to retain water (a), although itsheight can be redueed to some extent by removing less peat immediately alongsi<strong>de</strong> the massif (b). When thepermeable peat is un<strong>de</strong>rlain by a low permeability peat, the wall bund need only proteet the edge <strong>of</strong> the permeablepeat (e). In some cases, it may be possible to maintain the surfaee-wet eonditions over mueh <strong>of</strong> the.massif just bythe use <strong>of</strong> surfaee bunds to prevent exeessive water loss through the aerotelm (d).


TABLE 6.1 Summary <strong>of</strong> the Iikely outcomes <strong>of</strong> different options <strong>of</strong> raised bog restoration, from a contrasting range <strong>of</strong>starting conditions.The starting conditions (represented in the table by headings in bold type and with a single number i<strong>de</strong>ntifier (e.g. 1)) have beenchosen as representative starting conditions that have been observed in a number <strong>of</strong> damaged sites. It should be recognisedthat variants <strong>of</strong> these may occur and that some sites will present a range <strong>of</strong> starting conditions - i.e. the options are not mutuallyexclusive.For each type <strong>of</strong> starting condition, various management options have been presented (<strong>de</strong>signated by a double numberi<strong>de</strong>ntifier (e.g. 1.1 )). These are not comprehensive but represent the main options that seem likely to be applicable. Variouspermutations <strong>of</strong> them can be ma<strong>de</strong>, for example to cover various different starting conditions present on one site. Because <strong>of</strong>this, to avoid excessive repetition not every option has been entered for every starting condition.It is assumed that in all options simple attempts will be ma<strong>de</strong> to retain water on the mire, i.e. that as a base-line minimum outfallsand ditches will be a<strong>de</strong>quately blocked. Thus the 'no bunding' option assumes that ditch blocking, but nothing else, will takeplace.Assessment <strong>of</strong> the probable effects on water tables, vegetation, revegetation and implications for conservation andmanagement are based on practical experiences <strong>of</strong> restoration together with current knowledge <strong>of</strong> bog and fen ecology outlinedin this reporto The suggested outcome is therefore not 'guaranteed', but presented as the most likely outcome in the givencircumstances.The implications <strong>of</strong> the different options for working practices and subsequent possibilities for restoration need to be carefullyconsi<strong>de</strong>red, as do the potential impacts <strong>of</strong> peat extraction on the uncut or abandoned areas and the viability <strong>of</strong> such areas in theabsence <strong>of</strong> positive management. In some cases, restoration <strong>of</strong> such areas may represent a 'value-ad<strong>de</strong>d' approach in that thebiological value may be enhanced by appropriate management techniques (for example, replacing a dry, birch-Molinia mix witha wet, Sphagnum-dominated system).


¡o::. theTable 6.1a <strong>Restoration</strong> options for uncut peat remnants (bog peat) (see text)--QStarting conditions Probable effects Other Probable effects on vegetation Conservational assessment Conservation I managementon water tables hydrological and revegetation implicationsManagementconsi<strong>de</strong>rationsPeat remnant large with respect to marginal damage; surface little-damaged (Sphagnum cover etc. retained);1.1 No bunding ¡ Drying near margins; Original surface maintained in centre. Original character and conservation¡ central area remains Development <strong>of</strong> heathland, Molinia interest retained, at least in centre.¡ wet; subsi<strong>de</strong>nce may grassland or birch scrub near margins Edges may become heathy and¡ occur to reconform unless surface reconformation occurs susceptible to birch encroachment.shape <strong>of</strong> the mire rapidly. They may provi<strong>de</strong> a habitat for someorganisms otherwise absent from thebogoBirch control may be necessary,particularly around margins............ .; .;..............................................•..........................................., ;. ~ .1.2 ¡ Surface bunding ¡ Drying near margins; ¡ Water mound similar ¡ Original surface maintained in centre ¡ Original character and conservation ¡ Birch control may be necessary,¡ <strong>of</strong> weakly- ¡ wetter central area ¡ to 1.1 but marginal ¡ to greater extent than 1.1. ¡ interest retained, at least in centre and ¡ particularly around margins.¡ humified peat on ¡ more extensive than ¡ damage has less ¡ Development <strong>of</strong> heathland, Molinia ¡ to a greater <strong>de</strong>gree than 1.1. Edges <strong>of</strong> ¡¡ remnant. ¡ 1.1; subsi<strong>de</strong>nce may ¡ effect upon acrote/m ¡ grassland or birch scrub near margins ¡ remnant (outsi<strong>de</strong> bunds) may become ¡¡ ¡ occur to reconform ¡ conditions because ¡ unless surface reconformation occurs ¡ heathy and susceptible to birch ¡i i the shape <strong>of</strong> the mire i <strong>of</strong> shallow bunding. ! rapidly. i encroachment. i2 Peat remnant small with respect to marginal damage; surface Iittle-damaged (Sphagnum cover etc. retained)2.1 No bunding Drying across most orUltimate loss <strong>of</strong> many components <strong>of</strong> Much original conservation interestall <strong>of</strong> site, especiallyoriginal surface, except, perhaps, likely to be lost. Replacement habitatnear marginssome more drought tolerant bog may have new conservation value asspecies (e.g. Eriophorum vaginatum). dry/wet heath. Birch encroachment aReplacement by wet heath, dry heath, problem across entire site.Vegetation management <strong>de</strong>pendson objectives for non-bog habitats.Peat may be subject to ongoingoxidative <strong>de</strong>composition.Mo/inia grassland, bracken etc. ¡•••••••••••; ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••~•••••••••••••••••••••••••••••••••••••••••• ,4 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••2.2 ¡ Surface bunding ¡ Drying across most or ¡ Surface bunding ¡ Ultimate loss <strong>of</strong> many components <strong>of</strong> ¡ Most original conservation interest lost. ¡ Vegetation management <strong>de</strong>pends¡ <strong>of</strong> acrotelm / ¡ all <strong>of</strong> site, especially ¡ has little effect on ¡ original surface except, perhaps, a few ¡ Replacement habitat may have new ¡ on objectives for non-bog habitats.¡ 'white' peat on ¡ near margins. ¡ the overall position ¡ drought tolerant bog species (e.g. ¡ conservation value as dry/wet heath. ¡ Peat may be subject to ongoing¡ remnant. ¡ Possibly localised wet ¡ <strong>of</strong> the water table. ¡ Eriophorum vaginatum). Replacement ¡ Birch encroachment a problem across ¡ oxidative <strong>de</strong>composition............I.. ..l..~~~~~~ .1 1.;r~;;I~;;~.~~~;.~~.;.~~!~: ..~~::~:~ .J..~.~~~~~.. ~~~~ ..1. .2.3 ¡ Wall bunding ¡ Retention <strong>of</strong> high ¡ Marginal bunds ¡ Retention <strong>of</strong> original surface and ¡ Original character and conservation Remnant left isolated aboye¡ around remnant ¡ water table over much ¡ have elevated base- ¡ species. ¡ interest is retained. Important per se generallevel <strong>of</strong> mire. Bunds needim",'oo !m"re i~j~~?gi~~:y 1 !~:~~:i~,~~N,:~~~:~~:~,""'O" ~g~~~:~~~~~:~~~~~¡ ¡ ¡ domed. ¡ ¡ domed.


3 Peat remnant with <strong>de</strong>hydrated and damaged surface (little or no Sphagnum cover remaining)3.1 No bunding Drying across most orall <strong>of</strong> site, especiallynear margins. Possiblylocalised wet areas(e.g. in blocked drains)Bog species reduced or lost3.4Parapet bundingaround remnantmarginsRetention <strong>of</strong> high watertable over some ormuch <strong>of</strong> site, with localinundation.Success <strong>of</strong>rewetting may<strong>de</strong>pend on original<strong>de</strong>gree <strong>of</strong><strong>de</strong>hydration /damage to peat andon dimensions <strong>of</strong>remnant.(<strong>de</strong>pending on climate and severity <strong>of</strong>damage). Prospects for unai<strong>de</strong>drecovery <strong>de</strong>pend on climate andnature and severity <strong>of</strong> damage. Inmany situations re<strong>de</strong>velopment <strong>of</strong>M18-type vegetation is unlikely, butmay be possible to retain a number <strong>of</strong>¡ species in wetter regions. Elsewhere,¡ replacement by wet heath, dry heath,¡ Molinia grassland, bracken, birch etc.Possible re<strong>de</strong>velopment <strong>of</strong> M18-typebog vegetation on rewetted surfaceand, particularly, in shallow-f1oo<strong>de</strong>dareas, even in drier climates.Replacement habitats may persist onhigher areas..Original character <strong>of</strong> mire surface lostand unlikely to re<strong>de</strong>velop readily. Insome regions, a number <strong>of</strong> bog speciesmay persist in reduced abundance.Elsewhere replacement habitat mayhave new conservation value as dry/wetheath. Birch encroachment a Iikelyproblem across entire site.Remaining bog species Iikely to surviveand some likelihood <strong>of</strong> re<strong>de</strong>velopment<strong>of</strong> 'good quality' (M 18) vegetation overat least part <strong>of</strong> remnant. May requireinoculation <strong>of</strong> vegetation. Birchencroachment a potential problem indrier places.Vegetation management <strong>de</strong>pendson condition <strong>of</strong> surface andobjectives for a 'damaged bog' or'non-bog' habitat. Peat likely to besubject to ongoing oxidative<strong>de</strong>composition.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• •..•••••••••••••••••••••....••••.••4.•••••••••••••• ···•••••••••••••••••··••••• 4••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••..••••••••••••••••.•.•••••••••••.••••••••.•••••••••••••••••.•••••••••••••••••••••••••••••••.•.•••••••••.•...••••••••••••••...•..•••••••••••••••••••••••••••••••••••••••3.2 ¡ Surface bunding ¡ As 3.1 ¡ ¡ As 3.1 ¡ As 3.1 ¡ As 3.1J~~;!:;r;~:t~~JLJLL3.3 ¡ Wall bunding ! Retention <strong>of</strong> high water ¡ Success <strong>of</strong> ¡ Possible re<strong>de</strong>velopment <strong>of</strong> M18-type ¡ Remaining bog species likely to survive ¡ Remnant left as isolated remnantaround remnant table over some or rewetting may i bog vegetation on rewetted surface <strong>of</strong> and some potential for increase bog aboye general level <strong>of</strong> mire. Bunds¡ margins ¡ much <strong>of</strong> site. ¡ <strong>de</strong>pend on original ¡ remnant, but unlikely in any areas with ¡ conservation interest over all or part <strong>of</strong> ¡ need to be well ma<strong>de</strong> if height<strong>de</strong>gree <strong>of</strong> protracted dry periods. Replacement remnant. May require inoculation <strong>of</strong> difference is great and may require<strong>de</strong>hydration / habitats may persist. vegetation. Birch encroachment a long-term maintenance. Series <strong>of</strong>damage to peat and potential problem. concentric bunds may be requiredon dimensions <strong>of</strong>if strongly domed. Removal <strong>of</strong>remnantexisting vegetation (e.g. birch)Iikely to be a problem.Remnant left as isolated remnantaboye generallevel <strong>of</strong> mire. Bundsneed to be well ma<strong>de</strong> if heightdifference is great and may requirelong-term maintenance. Series <strong>of</strong>concentric bunds may be requiredif strongly domed. Removal <strong>of</strong>existing vegetation (e.g. birch)Iikely to be a problem.contd-


.:::.!::::: drybracken,Table 6.1 b <strong>Restoration</strong> options for c'ut-over surfaces (bog peat) (see text)-NStarting conditions Probable effects on Other Probable effects on Conservational assessment Conservation I managementwater tables hydrological vegetation and revegetation implicationsManagementconsi<strong>de</strong>rations4 Cut-oyer peat massif with original suñace lost, exposure <strong>of</strong> <strong>de</strong>eper, more humified peats etc. Suñace relatiyely f1at.4.1 No bunding ¡ Surface shows strong Fluctuations in ¡ Liltle recolonisation by bog species Lil ~velopment <strong>of</strong> original Massif left as dry remnant aboye¡ fluctuations in wetness. 'wetness' created by ¡ except, perhaps, a few drought ce :ion interest <strong>of</strong> bogo generallevel <strong>of</strong> mire. Vegetationl May be very wet during lack <strong>of</strong> sufficient ¡ tolerant taxa (e.g. Eriophorum Replacement habitat may or may not management <strong>de</strong>pends on¡ winter rains but dries out water storage in ¡ vaginatum). Replacement by wet have conservation value as dry/wet objectives for non-bog habitats.¡ during summer dry residual peat ¡ heath, dry heath, Molinia heath. Birch encroachment a problem Peat likely to be subject to. ¡ periods ¡ ! grassland, bracken etc. across entire site . ongoing oxidative <strong>de</strong>composition"4·.·2"·["w~·li"b~~~f¡·~g"""""r··ü~·i~~~·¡;·~~d"¡~·~~t~~d'~d"T'M~y'h~~~'iiitl~'¡~'p~~i"'["L'ii'ii~';~~~i~'~¡~~i'i'~~'¡;'y'b~'g'~¡;~~¡~~'Túiii~";~d~~~i~'p~~'~t'~'i'~;i'g¡~~'I""""""'''''''rM'~~~¡f''l~ft'~';'d;Y'~~';;;~~~t'~b~~~''''''j around massif ! upwards into a parapet ¡ in reducing lateral ¡ except, perhaps, a few drought ¡ conservation interest <strong>of</strong> bogo ! generallevel <strong>of</strong> mire. Vegetation! margins ! (4.3) surface may still ¡ wallloss as residual ¡ tolerant taxa (e.g. Eriophorum ¡ Replacement habitat may or may not ! management <strong>de</strong>pends on¡ ¡ show strong fluctualions ¡ peat is Iikely to be <strong>of</strong> ¡ vaginatum). Replacement by wet j have conservation value as dry/wet ¡ objectives for non-bog habitats.¡ ¡ in wetness. ! inherently low j heath, dry heath, Molinia ! heath. Birch encroachment a problem ¡ Peat likely to be subject to¡ ¡ ¡ permeability. ¡ grassland, bracken etc. ¡ across enlire site ¡ ongoing oxidative <strong>de</strong>composition"4·.·3"rp~;~¡;~·i·b~·~d¡~g""c;~~i~~·~~·~~~·~·fi~;d¡~g""'["B~~d'i'~g'~~~'~~d"''''''''''''[''p~i~~ii~'I''i~;'~~~;~~'i¡~~"~i'iy'pi~~i""'''Tp~t~~t'i~i'f~;'~~'g~~'~~~ti'~~''~f'¡;'~g""""''''''''rM'~~~¡f''I~'ft'~';'i~~i~'i~d'';~~'~~'~'i''''''''''¡ over all or some <strong>of</strong> ¡ exposed edge <strong>of</strong> ¡ bog vegetation on rewetted surface ¡ conservation ¡nterest over aU or part <strong>of</strong> ¡ aboye generallevel <strong>of</strong> cut-over! massif. Still strong j massif nol required if ¡ <strong>of</strong> massif. May require inoculation j massif. ¡ mire. Periodic maintenance <strong>of</strong>! fluctuations in water level ! in situ dark peat has j <strong>of</strong>vegetation.! j parapet may be nee<strong>de</strong>d, but as¡ but surface water storage ¡ low permeability. ¡ ¡ ¡ most <strong>of</strong> impermeability is ai.~=~~~~~~~LLJJ;;1~e~:~;f~;:';~~:~~~4.4 ¡ Peat removal ¡ Creates conditions <strong>of</strong> 4.3 j Bunding around ¡ Potential for recreation <strong>of</strong> typical ¡ Potential for regeneration <strong>of</strong> bog j Massif (or parts <strong>of</strong> it) no longer! j by excavation <strong>of</strong> peat ! exposed edge <strong>of</strong> ¡ bog vegetation on rewetted surface j conservation interest over all or part <strong>of</strong> ¡ substantially elevated aboye¡ i from all or part <strong>of</strong> massif. 1 E:~~~~o~:~~f~r~~sif I~; :~:~:ii~n~y require ¡noculation . massif. . generallevel <strong>of</strong> cut-over mire.5 Block-cut suñaces in massif with only strongly-humified ('black' peat5.1 No bunding ¡ Peat cuttings / hollows If peat is low j Potential for regeneratíon <strong>of</strong> bog Mosaic <strong>of</strong> wet and dry habitats and Not uniform bogo Usuallyj tend to remain wet; permeability, wet ! vegetation within peat cuttings. their interface gives range <strong>of</strong> consi<strong>de</strong>rable birch <strong>de</strong>velopment onj intervening baulks show conditions can be j Baulks <strong>de</strong>velop a drier vegetation conservation interest, including ridges (= cambered beds <strong>of</strong>! strong fluctuations in maintained even in ! (wet heath, dry heath, Molinia, elements <strong>of</strong> bogo foresters). Potential for bog¡ water level and tend to hollows close to 1::::::::::. birch etc.}. expansion out <strong>of</strong> cultings ontoduring summer. margins <strong>of</strong> massif. baulks uncertain. Massif may beleft as isolated remnant aboyegenerallevel <strong>of</strong> cut-over mire. Drypeat Iíkely to be subject to ongoing. . . . ¡ . oxidative <strong>de</strong>compositíon......................................................................................................................................................................................................................................................................................................................................................................................


"'fú'TÍÑ~'II'¡;~~di~g"""""'Tif'd~';k'¡;~~t"h~~"I~~"""""TA~'5"1"""""""""""""""'T'A~'5·.·1·······················································T"A~··5:1·······························································rA~··5:1······················· .j around massif j permeabilily, Wall j ¡ ¡ ¡¡ margins ¡ bunding is unlikely lo ¡ ¡ j ¡j ¡ have many advanlages j ¡ ¡ ¡¡ ¡ upon 5.1. ¡ ¡ ¡ ¡•••••••••••; ••••••••••••••••••••.••••••••..•••••.. ~••••.•.••••••••••••••••..••••••••••••••••••••••••• ; ••••••••••••••••••••••••••••••••••••••••••••••~••••••.•••••••••••••..•••••••••••••..•••••••••••••••••••••••••••••••• ; ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••j •••••••••••••••••••••••••••••••••••••••••••••••••••••••••...••••••••••5.3 ¡ Parapel bunding ¡ Creales surface f100ding ¡ Wall bunding around ¡ Regeneralion <strong>of</strong> bog vegelalion ¡ Potenlial for regeneralion <strong>of</strong> bog ¡ Massif left as isolaled remnant¡ j upon lhe baulks over all ¡ exposed edge <strong>of</strong> ¡ wilhin peal cultings. Also bog j conservalion inleresl over all or part <strong>of</strong> ¡ above general level <strong>of</strong> cut-over¡ ¡ or some <strong>of</strong> lhe massif as j massif nol required if ¡ regeneralion on f100<strong>de</strong>d or wet ¡ massif. ¡ mire. Periodic mainlenance <strong>of</strong>: : well as in lhe peal ¡ in situ dark peat has ¡ conditions <strong>of</strong> baulks. May require ¡ ¡ parapet may be nee<strong>de</strong>d, bul as¡ ¡ cuttings. ¡ low permeabilily. ¡ inoculalion <strong>of</strong> vegetalion. ¡ ¡ mosl <strong>of</strong> impermeabilily is a producl¡ ¡ ¡ ¡ j ¡ <strong>of</strong> low permeabilily peat left in situ,..........,L l.. 1... ,L L. .L~X.~.~=~..~.~X.~~..~~.i~~.~~.~~~=: .5.4 ¡ Peal removal - as 4.4 !! ! ¡6 Block-cut surfaces in massif. with weakly-humified peal6.1 No bunding ¡ Peal cultings and ¡ Wet'condilions Polenlial for regeneralion <strong>of</strong> bog Mosaic <strong>of</strong> wel and dry habilals and¡ hollows wel; inlervening ¡ unlikely lo be vegelation wilhin peal cuttings. lheir inlerface gives range <strong>of</strong>Nol uniform bogo Usuallyconsi<strong>de</strong>rable birch <strong>de</strong>velopmenl¡ baulks show slrong ¡ mainlained in hollows Baulks <strong>de</strong>velop a drier vegelalion conservalion inleresl, including ¡ on ridges (= cambered beds <strong>of</strong>¡ f1uclualions in waler j close to margins <strong>of</strong> (wet healh, dry heath, Molinia, elements <strong>of</strong> bogo : foreslers). Polenlial for bog¡ level and lend lo dry '.::::::::::. massif. bracken, birch etc.). ¡ expansion oul <strong>of</strong> cuttings onlo!::::::.'::. during summer. ¡ baulks uncertain. Massif may be¡ left as isolaled remnanl abovej general level <strong>of</strong> cul-over mire. Dry¡ peal Iikely lo be subjecl lo ongoing...........; + ; .L.~~.i~.~~~~~..~=.~.~~?.~~~~!~.~.: .6.2 ¡ Wall bunding ¡ Unless bund is ¡ Marginal bunding may ¡ Polenlial for regeneralion <strong>of</strong> bog ¡ Mosaic <strong>of</strong> wel and dry habilals and ¡ Nol uniform bogo Birch¡ around massif j exten<strong>de</strong>d upwards inlo ¡ nol be nee<strong>de</strong>d lo ¡ vegelalion wilhin peal cullings. ¡ lheir inlerface gives range <strong>of</strong> ¡ encroachmenl on baulks likely lo¡ margins ¡ a parapel (6.3) surface ¡ prevenl waler loss ¡ Baulks <strong>de</strong>velop a drier vegelalion ¡ conservalion inleresl, including ¡ be a problem. Polenlial for bog¡ ¡ <strong>of</strong> baulks may slill show j lhrough lower peals <strong>of</strong> ¡ (wet healh, dry healh, Molinia, ¡ elemenls <strong>of</strong> bogo ¡ expansion oul <strong>of</strong> cullings onloj ¡ slrong f1uclualions in j small permeabilily. ¡ bracken, birch etc.). ¡ ¡ baulks uncertain. Massif may be! ! welness.! ¡ : ¡ left as isolaled remnant aboveIJLJIJ::;~~~,~~;~J;;~~¡~;t~::g~;~g6.3 ¡ Parapet bunding j Creales surface j Wall bunding around j Regeneralion <strong>of</strong> bog vegelalion ¡ Polenlial for regeneralion <strong>of</strong> bog j Massif left as isolaled remnanl¡ ! flooding upon lhe ! exposed edge <strong>of</strong> : within peat cullings. Also bog ¡ conservation interesl over all or part <strong>of</strong> ! above generallevel <strong>of</strong> cut-over¡ ¡ baulks over all or some ¡ massif nol required ¡ regeneralion on f100<strong>de</strong>d or wet j massif. ¡ mire. Periodic mainlenance <strong>of</strong>¡ j <strong>of</strong> lhe massif as well as ¡ where in situ dark ¡ conditions <strong>of</strong> baulks. May require ¡ ¡ parapel may be nee<strong>de</strong>d, bul as¡ ¡ in the peal cuttings. ¡ peal has low ¡ inoculalion <strong>of</strong> vegelalion. ¡ ¡ most <strong>of</strong> impermeabilily is a¡ ¡ ¡ permeabilily. ¡ j ¡ producl <strong>of</strong> low permeabilily peal64lp;;i;;;;;;;~;i~;;L¡L!¡;=~;~'tu:'y':==a~:q::'contd-t..l


Table 6.1 b (continued) [Options for cut-over surfaces (bog peat)]- ""Starting conditions Probable effects on Other Probable effects on Conservational assessment Conservation I managementManagement water tables hydrological vegetation and revegetation implicationsconsi<strong>de</strong>rations7 Milled surface <strong>of</strong> ombrotrophic peat: surface sloping7.1 No bunding i Surface does not retaini w.¡".Surface run-<strong>of</strong>f + lack ! Development <strong>of</strong> vegetation with few.! <strong>of</strong> storage means that ! if any bog species - heath. Molinia,! surface is dry except ! bracken. birch scrub.¡ during wet parts <strong>of</strong> ¡year. ¡Little re<strong>de</strong>velopment <strong>of</strong> originalconservation interest <strong>of</strong> bogoReplacement habitat may or may nothave conservation value. Birchencroachment a problem across entiresite.Vegetation management <strong>de</strong>pendson conservational objectives fornon-bog habitats. Likely to beongoing oxidative <strong>de</strong>composition<strong>of</strong> residual peat.":;·.·2···¡"T~~·~~~·d:·b·~~d·~d"·\~j~t~~"~~i~·i·~~d"i·~ .. ·············t··¿~·~t~~··~~;t~~~··········· .. ·t··p~i·~~ii~·i·i~;·d~~·~i~~·~~~t·~f·b~g· ...... ····¡··p~i·~~i¡~·i·i~;·~~·d~~~·i~~~·~~i··~f·b·~9·· ......····t.. M·~Y·~·I~·~·~~·~d·i·~·h~·~~·;;~~~i~~·I·· ..····1. lagoons lagoons. 1. f1ooding. Reduces i.: vegetation within wet areas in :. vegetation. Encroachment by birch and 1. bund (or residual baulk) to reducerun-<strong>of</strong>f. Still wi<strong>de</strong> lagoons. Possibly wet heath/Molinia some other species a problem on drier water loss from site margins and¡ ¡ f1uctuations in water ¡ in less wet higher areas. May j areas. ¡ to prevent ingress <strong>of</strong> enriched¡ ¡ level but surface ¡ require inoculation <strong>of</strong> vegetation. \ \ water. Birch encroachment <strong>of</strong> drier¡ ¡ water storage (and. in ¡ ¡ ¡ areas may need to be checked.¡ ¡ some situations. ¡ ¡ ¡ Likely to be ongoing oxidative¡ ¡ 'casca<strong>de</strong> feeding') ¡ j ¡ <strong>de</strong>composition <strong>of</strong> areas that are¡ ¡ reduces effects <strong>of</strong> ¡ j j not reweUed. Marginal bunds mayj ¡ summer droughts. ¡ j ¡ require periodic maintenance.8 Milled surface <strong>of</strong> ombrotrophic peat: surface ± flat8.1 No bunding j Surface shows strong ¡ Fluctuations in ¡ Little re<strong>de</strong>velopment <strong>of</strong> bog Little re<strong>de</strong>velopment <strong>of</strong> original¡ f1uctuations in wetness. j 'wetness' created by j vegetation excepto perhaps. for a conservation interest <strong>of</strong> bogoj May be very wet during j lack <strong>of</strong> sufficient ¡ few more drought tolerant bog Replacement habitat may or may not¡ winter rains but dries out ¡ water storage in j species (e.g. Eriophorum have conservation value. Birch¡ during summer dry 1:,':: residual peat. j vaginatum) and in sites in wet encroachment a problem across entirej periods. ¡ regions. Heath. Molinia, bracken. site.Vegetation management <strong>de</strong>pendson conservation objective for nonboghabitats. Likely to be ongoingoxidative <strong>de</strong>composition <strong>of</strong>residual peat...........; L l..~~~.~~.~~.~~~..~~~.~~~~~~.~.~~~.I~.?~.~~~~: , ; .8.2 ¡ Bun<strong>de</strong>d lagoons ¡ Water retained in j Creates surface j Development <strong>of</strong> bog vegetation ! Potential for re<strong>de</strong>velopment <strong>of</strong> bog ¡ May also need to have marginal¡ ¡ lagoons. j f1ooding. Reduces j within wet areas in lagoons. Wet ¡ vegetation. Encroachment by birch and : bund (or residual baulk) to reduce¡ : ¡ run-<strong>of</strong>f. Still wi<strong>de</strong> j heath/Molinia in less wet higher ¡ some other species a problem on drier j water loss from site margins and¡ : ! fluctuations in water ¡ areas. May require inoculation <strong>of</strong> ¡ areas. ! to prevent ingress <strong>of</strong> enriched: j ¡ level but surface ! vegetation.! ¡ water. Birch encroachment withinj j ! water storage ¡ j ¡ lagoons unless well inundated.j j j reduces effects <strong>of</strong> j j j Likely to be ongoing oxidative! ¡ ! summer droughts. ¡ ¡ : <strong>de</strong>composition <strong>of</strong> areas that are! j j not reweUed. Marginal bunds may¡ ¡ j ¡ ¡ ¡ require periodic maintenance.


9 Milled surface <strong>of</strong> ombrotrophic peal: surface scalloped or forming <strong>de</strong>pressions9.1 No bunding Water retained in Creates surface Development <strong>of</strong> bog vegetation Potential for re<strong>de</strong>velopment <strong>of</strong> bog May need a marginal bund (orhollows f1ooding. Reduces within wet areas in hollows. Wet vegetation. Encroachment by birch and residual baulk) to prevent ingressrun-<strong>of</strong>f. Still strong heath/Molinia in less wet upper some other species a problem on drier <strong>of</strong> enriched water. Birchf1uctuations in water areas. May require inocl,Jlation <strong>of</strong> areas. May be extensive, <strong>de</strong>pending on encroachment within lagoonslevel but surface vegetation. surface configuration. unless well inundated. Likely to bewater storageongoing oxidative <strong>de</strong>compositionreduces effects <strong>of</strong><strong>of</strong> areas that are not rewetted.summer droughts.10 Shallow peat <strong>de</strong>posits upon permeable substrata with lowered groundwater tables10.1 No bunding Effect <strong>of</strong> lowered If residual peat is too Development <strong>of</strong> heath, grassland Little re<strong>de</strong>velopment <strong>of</strong> original bog Vegetation management <strong>de</strong>pendsgroundwater tables upon thin rewetting <strong>of</strong> and scrub. No re<strong>de</strong>velopment <strong>of</strong> conservation interest. Replacement on conservation objective for nonbogsurface condition is surface is likely to be bogohabitat may or may not havehabitats. Likely to be ongoingpartly <strong>de</strong>pen<strong>de</strong>nt upon impossible. No form <strong>of</strong>conservation value. Birch encroachment oxidative <strong>de</strong>composition <strong>of</strong><strong>de</strong>pth <strong>of</strong> residual peal. remedial action isa problem across entire site.residual peal.50 cm <strong>of</strong> strongly- known. [Even withhumified ('black') bog sufficient peat <strong>de</strong>pth,peat seems theany ditches c10se to ormínimum nee<strong>de</strong>d to penetrating the subsoilreduce vertical seepage must be filled with lowto an acceptable level. permeability peal.].............;. ; o'··· .:. .:..........................................•...........................:. ~ .10.2 ¡ Intervention? ¡ It is likely that the only way this problem may be mitigated in sites with insufficient residual peat will be the management <strong>of</strong> landscape hydrology to re-elevate water levelsi i generally.contd-(JI


.j:::::.: quitestatusTable 6.1c <strong>Restoration</strong> options for fen peat surfaces (in peat cuttings) (see text)--Q\Starting conditions Probable effects on Other Probable effects on vegetation Conservational assessment Conservation Iwater tables hydrological and revegetation management implicationsManagementconsi<strong>de</strong>rations11 Flat surface <strong>of</strong> fen peat11.1 No action : Wetness <strong>of</strong> surface will Fluctuations in Development <strong>of</strong> wet grassland Developing vegetation can inclu<strong>de</strong> : Without management only a ranki <strong>de</strong>pend upon site 'wetness' created by vegetation, or some form <strong>of</strong> rough fen species-rich pastures or hay : species-poor herbaceous or wet! topography and the lack <strong>of</strong> sufficient water or fen carr, <strong>de</strong>pending upon water meadows when managed, and these i woodland vegetation will <strong>de</strong>velop.¡ intrinsic properties <strong>of</strong> storage in residual peat levels and management may have consi<strong>de</strong>rable conservation ¡ Likely to be ongoing oxidativei the local hydrological . coupled with absence value (e.g. Molinia-Cirsium fen ! <strong>de</strong>composition <strong>of</strong> residual peal.i environmenl. May be <strong>of</strong> water-retaining meadow). Elsewhere, rough or dry : This may contribute to nutrient¡~~~{~~~i~on:~~~etness, ::;~~~i~~~' ~:~~~~ may ~~r~~;;i::;~iu~:f:;;u~~~;~~~n 1:::::::::::::.! very wet (perhaps : be used to regulate woodland etc. is likely to <strong>de</strong>velop.i inundated) in winter but ~:::::::: water levels This may have Iimited conservationdry in summer.. . value as fen vegetation (unless in: exceptional hydrological situation).: but habitat may have 'generali wildlife' value.":¡';':2'T'D¡t~'h"bí~'~k'i'~g"""T"Eff~~t'd~'p~~'d~'~'~···········T·Wh·~~·~·~~d··t~·;~t~·i~········rA~··;·1·:·;·,··~~·~~Pt··(~)··~;;~·;~·~·~d~·;i~¡~··by·rA~··1"1":·;·<strong>of</strong> substratum... ·b~·t·p~·t~~t·i~i·f~·;·~;~~···············T"A~··1"1":·;··· .: : topography and water : meteoric water effects : stable groundwater table (which may i <strong>de</strong>velopment <strong>of</strong> wetter fen :: : source. Can be used to : are likely to be similar : then provi<strong>de</strong> a suitable basis for ¡ communities, at least locally :¡ ¡ retain meteoric water; ¡ to 11.1 , unless un<strong>de</strong>rl- ¡ various types <strong>of</strong> fen and possibly ¡ ¡: : to exclu<strong>de</strong> telluric : ain by high & stable : Sphagnum in climatically-suitable i ¡¡ : water; or to retain a mix : groundwater table. : areas); and (b) where used to retain : :¡ : <strong>of</strong> both water supplies j When used to retaín : minerotrophic water, in which case : :: : i telluric water, high : wi<strong>de</strong>r <strong>de</strong>velopment <strong>of</strong> fen vegetation : :i : i water levels can some- j may beexpected.: :i i i times be maintained i i i..................................................¿ , .Il•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• , •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••


· , .11.3 ¡ Ditch irrigation ¡ Effect <strong>de</strong>pends upon ¡ In dry episo<strong>de</strong>s there ¡ Ditch-irrigated sites can maintain fen ¡ Ditch irrigated systems can <strong>de</strong>velop ¡ Some form <strong>of</strong> management isor periodic topographyand ¡ will be a ten<strong>de</strong>ncy for ¡ vegetation (but not usually wet-fen ¡ fen vegetation <strong>of</strong> consi<strong>de</strong>rable ¡ Iikely to be required (summer¡ f100ding ¡ availability <strong>of</strong> water ¡ the fen to dry out away ¡ types). If there is no other water ¡ conservation interest (Phragmites- ¡ mowing or grazing) to help¡ ¡ source. If sufficient ¡ from irrigation ditches. source, sites irrigated by episodic ¡ Peucedanum, Phragmites- ¡ maintain a species-rich¡ ¡ supply <strong>of</strong> telluric water, ¡ Flooding will be ¡ flooding usually support dry, coarse ¡ Eupatorium fen, Molinia--Cirsium ¡ vegetation and to prevent¡ ¡ parts <strong>of</strong> fen can be kept ¡ episodic and may lead ¡ fen vegetation or fen grassland. ¡ dissectum fen meadow). Sites just ¡ successional <strong>de</strong>velopment <strong>of</strong>¡ ¡ permanently wet to periodic dryness ¡ Quality <strong>of</strong> water is also important, ¡ irrigated by episodic f100ding may scrub and woodland. May be¡ ¡ ¡ across much <strong>of</strong> the site ¡ especially in f100ding episo<strong>de</strong>s: input ¡ support low-quality vegetation (e.g. ¡ some ongoing oxidative¡ ¡ ¡ ¡ <strong>of</strong> high nutrient loadings typically lead ¡ Phragmites-Urtica or Phragmites- ¡ <strong>de</strong>composition <strong>of</strong> peat,¡ ¡ ¡ to impoverished vegetation. Flooding ¡ Eupatorium fen if unmanaged; wet <strong>de</strong>pending upon maintainednot suitable for bog regeneration but'if ¡ grassland if mown or grazed); ¡ water levels.¡ ¡ ¡ ¡ ditch irrigation can maintain ¡ however, these may have much ¡¡ ¡ ¡ permanently high subsurface ¡ ornithological value, especially during ¡¡ ¡ ¡ ¡ groundwater table it may provi<strong>de</strong> a ¡ winter f100ding episo<strong>de</strong>s. ¡¡ ¡ ¡ basis for local Sphagnum invasion, ¡ ¡¡ ¡ ¡ ¡ especially. in wetter, cooler regions. ¡ ¡··ú:4.. r~~~,~f;j·~·~ ....·.... ·rt~~~~~~~·~:~~:d ..i~··.. ···T~ii~:·~·~~~·~:il:~~:~··T~:;:;~i:~·~t;~~~~~~~~i~,~~·~ ..~f·f~~ ...... T~i~~~~~:~~~~~·~~~~~;~~~[~·~~:~~:···T~~~~~~~·~f~:~f~f;~~i~:~~~~~d"""I I~t~~~~~I~~~~~~:~;~~1 I~~t~~~~~ ~~::t~i~~~s I~h~~~::~~~~iu~~~;a~:~\~;~: ;~~tbe I~~t~~~~~~ ~~~:e~~~t~er~~~s~~:~:~~ I~:~~~~~li~~:g~~dn~)u~~ec;~~:I~! : water level but surface ! for lagoons is not well : Vegetation character <strong>de</strong>pen<strong>de</strong>nt on ! Sphagnum invasion into ! inundated. Dry areas may be! i water storage reduces ! known. i <strong>de</strong>pth, base-richness and nutrient ! terrestrialising lagoons ! subject to ongoing oxidative¡ ¡ effects <strong>of</strong> summer ¡ ¡ richness <strong>of</strong> water (see 12, below). ¡ ¡ <strong>de</strong>composition <strong>of</strong> peat.i !droughts.!! ! !: hollows : surface f1ooding. ¡ help impound telluric : characteristic <strong>of</strong> low-fertility : some management and (perhaps) : ingress <strong>of</strong> enriched water. Scrub12 Cuttings within fen peat¡ Wetness <strong>of</strong> cuttings will¡ <strong>de</strong>pend their topography¡ and the intrinsic¡ properties <strong>of</strong> the local12.1 No intervention(except blockoutfalls)Intrinsically morestable water table than11.1 because cuttingsFen community that <strong>de</strong>velops will<strong>de</strong>pend upon water sources andlevels.May generate conservation interest.Difficult to speculate on the largenumber <strong>of</strong> possible communities thatWithout management, vegetationwill <strong>de</strong>velop into a form <strong>of</strong> fenwoodland. Herbaceous fenhelp to retain watercould <strong>de</strong>velop in this condition. communities may have great¡ hydrologicalsurplus.conservation value.. ¡. environment."••••••••••••••••••••••••••••••••••••••••••••••••1"•••••············································1·········.......................................•............................................................................•.........................................................................•................................................................... .12.2 ¡ Soaking with ¡ Water near or just above ¡ Water level ¡ Potential for <strong>de</strong>velopment <strong>of</strong> species- ¡ Fen communities may inclu<strong>de</strong>: Carex ¡ Without management, vegetation¡ nutrient-poor ¡ water level ¡ manipulated by inflow ¡ rich fen vegetation. ¡ rostrata-Potentilla, Phragmites- ¡ will <strong>de</strong>velop into a form <strong>of</strong> fen¡ water ¡ ¡ ditches, sluices, pumps ¡ ¡ Peucedanum fen , Juncus-Cirsium, ¡ woodland. Herbaceous fen¡ (precipitation + ¡ ¡ etc. ¡ ¡ Molinia--Cirsium fen meadow and ¡ communities may have great¡ groundwater) ¡ ¡ ¡ ¡ various forms <strong>of</strong> fen woodland. ¡ conservation value..............•.......= ..:: :::~ ~- -.~~ ~ : -.: ~ ~=;..;.--.~..; ;.-;-.-;;-;;;-;-.; - - ,~.""=~••••F- ~~~~.-..--.--.--.- ...- ~~........ ..~_ _._._•••••••._••_ !~.--!_~!!.! •••••••••••__12.3 ! Soaking with Water near or just above ! Water level : Potential for <strong>de</strong>velopment <strong>of</strong> a coarse ! Fen communities may inclu<strong>de</strong>: ! Without management, vegetation! nutrient-rich water level ! manipulated by inflow ! fen vegetation. ! Phragmites- Eupatorium fen, ¡ will <strong>de</strong>velop into a form <strong>of</strong> fen¡ water ¡ ditches, sluices, pumps ¡ ¡ Phíagmites -Uítica fen, various ¡ wccdland. Heavy management1: w~na:et~e~r~)~:~l~;;~ .:1:e~.1:.:!: ~:;,~::'"he'"fi" 00' reo 1:.. T::~~r.~~"~~:~¿~:.::y" be<strong>of</strong> great interest. Such situations.¡ . !! ! ! may be best managed for birds.............._ : .: :. :. .:. .contd-..l


p"m",Table 6.1c (continued) [<strong>Restoration</strong> options for fen peat surfaces (in peat cuttings)]-ocStarting conditionsManagementProbable effectson water tablesOther hydrologicalconsi<strong>de</strong>rationsProbable effects onvegetationand revegetationConservational assessmentConservation Imanagement implications12.4 Shallow f100dingwith nutrientpoor water(precipitation +groundwater)Water level >0 SOcm ! Water level manipulated Formation <strong>of</strong> <strong>de</strong>ep-water emergent Potential communities inclu<strong>de</strong> Typha ! Management not required untilwith nutrient-rich Lby inflow ditches, sluices, swamp communities latifolia swamp and Phragmites ¡ substantial terrestriaHsation hasWw~:a7t;e~r~)~1~:~~ 1::::'elo.~~:"~~~d~~~y =ri;e~;~~'~ 1::::~iª~~~iff;?j;~~beperhaps best managed for othertaxonomic groups.


CHAPTER 6: RESTORATION OPTIONS AND PEAT-\VORKING I'RACTlCES 119In general, rewetting problems are <strong>of</strong>ien greater onmassifs (which are typically water-shedding areas) thanthey are in <strong>de</strong>pressions (which are typically waterholdingareas) [2.1]. Various approaches can be used torewet massifs [Table 6.1 a; 5.3], but particulardifficulties can be experienced with badly-damagedremnants. Likewise a series <strong>of</strong> upstanding blocks, atdifferent levels, which are found in sorne (usuallyabandoned) peat extraction complexes can presentparticularly intractable problems for restoration. Insorne situations it may have to be accepted thateffective rewetting <strong>of</strong> the whole complex is notfeasible, in which case the remnants may be lefi tosupport sorne replacement habitat, which may inclu<strong>de</strong>sorne bog species, though they are ultimately likely tobe wasting assets.Because <strong>of</strong> their situation, peat fields may ultimatelyprovi<strong>de</strong> a more satisfactory basis for bog restoration(especially 'whole-mire' regeneration) than sorne uncutmassifs. This is because they may provi<strong>de</strong> a lesstopographically-varied surface; because, when close tothe mineral ground, they may be intrinsically morestable, both in terms <strong>of</strong> water regime and peat wastage;and because their effective rewetting [Table 6.1 b] maybe technically less difficult than rewetting <strong>of</strong> massifs.Nonetheless, in many cases sorne technical interventionwill be required to produce structures that impoundwater against lateral flow and increase storage,although this will <strong>de</strong>pend upon the topography anddisposition <strong>of</strong> the abandoned surfaces. The flat orgently sloping surfaces <strong>of</strong> mo<strong>de</strong>m commercial peatfields may be quite well suited to rewetting overextensive areas.Nonetheless, rewetting <strong>of</strong> peat fields cannot bedivorced from that <strong>of</strong> peat massifs. This is partlybecause cut-over surfaces are themselves sometimeslocated on a massif well-elevated aboye thesurrounding land, in which case consi<strong>de</strong>rationspertinent to the rewetting <strong>of</strong> massifs become equallyapplicable to the peat fields (this is a lesserconsi<strong>de</strong>ration when peat has been removed nearer tothe base <strong>of</strong> the <strong>de</strong>posit). It is also because an obviouseffect <strong>of</strong> peat removal is to accentuate the heightdifference between the peat field surface and thesurface <strong>of</strong> adjoining peat massifs. In this situation itmay still be possible to maintain an in<strong>de</strong>pen<strong>de</strong>ntly highwater table in the massif, but is Iikely to be moreexpensive and difficult to do so (<strong>de</strong>pending upon thecharacteristics <strong>of</strong> the massit). An additional consi<strong>de</strong>rationis that <strong>of</strong> linking the regeneration <strong>of</strong> the peatfield surfaces to the maintenance <strong>of</strong> the massif,particularly when the aim is to regenerate a bog acrossthe whole site, integrating both peat fields and themassifs. This difficulty can be ameliorated in variousways. One option, in those situations where it ispossible, is to have the peat surface grading up to themassif, by removing less peat dose to the rnassif. [Thisdoes, <strong>of</strong> course, produce an inclined surface which,<strong>de</strong>pending on its slope, may be much more difficult torewet than a flat one.] Where the massifs are badlydamaged, <strong>of</strong> limited biologidll or palaeoecologicalinterest and difficult to rewet, an altemative approachwould be to remove peat from them so that they aremore conformable with the peat fields. In othersituations, where the massifs have consi<strong>de</strong>rableconservation value there may be little choice but toengineer in<strong>de</strong>pen<strong>de</strong>nt water management strategies forthe massifs and the peat workings.6.3 <strong>Restoration</strong> options forminerotrophic peat surfacesConsi<strong>de</strong>rably less attention has been directed towardsthe <strong>de</strong>liberate restoration <strong>of</strong> raised-bog sites where peatextraction has exposed un<strong>de</strong>rlying fen peat. In<strong>de</strong>ed, thefull occurrence <strong>of</strong> this circumstance is not even wellknown. This is because, whilst in sorne sites it isobvious that peat cutting <strong>of</strong> ombrotrophic peat hasuncovered fen peat (e.g. Brackagh Bog, Armagh), inothers bog peat has been removed so comprehensivelythat there is little evi<strong>de</strong>nce for the former existence <strong>of</strong>bog (e.g. Woodwalton Fen, Cambridgeshire).However, increasing evi<strong>de</strong>nce suggests that a number<strong>of</strong> sites that are now regar<strong>de</strong>d


120Rt:STORATlON OF DAMAGED PEATLANDSworkings ir1 fen peat is primarily a function <strong>of</strong> water<strong>de</strong>pth (and stabi\ity), waterqua\ity (particu\ar\y baserichnessand nutrient-richness) and managementregime (if any). Many herbaceous fen vegetation typesrequire regular management to maintain their characterand to prevent their colonisation by trees. Suchmanagement is <strong>of</strong>ten most feasible when it isassociated with sorne ecoJ1omic retum. Grazing orsummer mowing is possible in sorne circumstances andcan produce conservationaJly-<strong>de</strong>sirable communities,as with some <strong>of</strong> the fen meadows <strong>of</strong> the SomersetLevels. Such objectives, when coupled with summerdryconditions, are usually incompatible with there<strong>de</strong>velopment <strong>of</strong> bog, although in certain círcumstanees,mowing may enhance the initial <strong>de</strong>velopmenttowards bogoThe formulation <strong>of</strong> <strong>de</strong>sirable restoration options for fenpeat sites is <strong>of</strong>ten more difficult than for sites based onbog peat, because there is usual1y more scope forhabitat manipulation and renaturation. In someinstances circumstanees will dictate the most feasiblerestoration option, but in others it may be possible tochoose from several possibilíties. A primary <strong>de</strong>cision iswhether to focus on the recreation <strong>of</strong> bog or fen,though these options are not mutually exclusive,especially as some forms <strong>of</strong> fen can give rise to bogvegetation. If the fen option is selected, the choice thenbecomes the type <strong>of</strong> fen <strong>de</strong>sired. This can sometimesbe <strong>de</strong>termined by choice <strong>of</strong> water sources and levels.For examp\e, fen cuttings can be f\oo<strong>de</strong>d with nutrientrichwater from adjoining rivers, in which case theresulting vegetation (e.g. reedbeds) is likely to havelittle botanieal interest but, possibly, mueh omithologicalvalue; if, however, such sources are exclu<strong>de</strong>dand preeipitation inputs are a<strong>de</strong>quate to retlood thecuttings, then a vegetation <strong>of</strong> more botanica\ interestmay <strong>de</strong>velop, together with a greater likelihood <strong>of</strong> thesuccessional <strong>de</strong>velopment <strong>of</strong> bogo The choice <strong>of</strong>objectives is thus likely to be <strong>de</strong>termined bytopography, availability (and quality) <strong>of</strong> minerotrophiewater sourees and implications for on-goingmanagement and maintenance as weIl as byeonservational <strong>de</strong>sirability.In general, regeneration <strong>of</strong> bog within fens occurs mostreadily as a hydroseral <strong>de</strong>velopment from fenvegetation in peat workings tloo<strong>de</strong>d with nutrient-poor(but not necessarily base-poor) water\ . In appropriatecircumstances Sphagnum can grow rapidly and thicknesses<strong>of</strong> c. 1 m <strong>de</strong>pth <strong>of</strong> Sphagnum peat accumulatingwithin c. 100 years have been reported (van Wirdum,( It may a(so occur on solid fen peat where there is a stable, slightlysubsurface water table, especial\y in wetter regions. The potenti alfor raised bog <strong>de</strong>velopment from this starting point is not wellknown • it may be suspected that it will be slower initial\y than froma semi-floating origin and in sorne situations may not occur at al\.pers. COI/1I/l.).However, as the organisms associatedwith the fen ))hase <strong>of</strong> the 'i>ucce'i>'i>ion 'i\~e them'i>e~'1e'i><strong>of</strong>ten <strong>of</strong> great interest to conservationists, thisspontaneous process <strong>of</strong> 'ombrotrophication' may notbe universally welcomed.It is obvious that if cut-over surfaces in fen peat are tore<strong>de</strong>velop fen vegetation (and perhaps ultimately bog)they require water input, but because <strong>of</strong> the likely (aJ1dusually unknown) complexities <strong>of</strong> the hydrology <strong>of</strong>individual minerotrophic systems and, with tllecontribution and quality <strong>of</strong> possible water sources alsovarying amongst sites, it is difficult to specify tlleeffect'i> (lf 'i>pecif\c m\ne~ot~ophk 'Nater 'i>Q\lrceo¡; \lpCt1..the revegetation process. It is, however, possible toi<strong>de</strong>ntify broadly the likely effects <strong>of</strong> the irrigatiJ1gwater in terms <strong>of</strong> its quality (nutrient poor versUSnutrient rich) on restoration [Table 6.1 e]. In this table,the assumption has been ma<strong>de</strong> that tlle residual fen peatis intrinsicany not very fertik ihis assumption may beinapplicable to some sites. <strong>Restoration</strong> options for siteswith fertile residual peats will probably be similar tothose at sites where peat extraction has exposed fertilefreshwater clays [6.4].Re'Nett\ng, 'i>trateg,\e'i> fQ~ fen peat will <strong>de</strong>pend strot1..g,lyon the surrounding topography <strong>of</strong>the peat workings. Ingeneral, rewetting can be achieved most readily wherethe workings forro a closed <strong>de</strong>pression (within bogpeat, fen peat or mineral soil) or where they have been<strong>de</strong>liberately bun<strong>de</strong>d. In this situation it may be possibleto inundate the <strong>de</strong>pressions. 1n other situations cut-oveTfen surfaces are tlat and located at about the same levelas, or even higher than, surrounding farmland. In t!liscase attempts to maintain a permanentIy high watertable on the peat surface with minerotrophic water maybe difficult without causing (at least temporary) waterlogging<strong>of</strong> adjoining land. Bunding may be used tohelp hold water on the site, both to prevent flooding <strong>of</strong>adjoining land and to maintain a high water level in thefen peats.6.4 <strong>Restoration</strong> options tormineral substrataIn some sites peat has been extracted to expose largeareas <strong>of</strong> the un<strong>de</strong>rlying mineral substrata. Specification<strong>of</strong> restoration options for this may be subject 1.0 thesame problems as for fen peat with respect to variationin the character <strong>of</strong> water sources. It is further eomplicatedby the great variability <strong>of</strong> physico-chemicalcharacteristics <strong>of</strong> the substrata. For example, the pHrange <strong>of</strong> the substrata beneath ombrotrophic bogs isknown to vary between about 3.0 (acid sands andgravels) to 7.5 (calcareous marls). Where it has beenexposed, these characteristics <strong>of</strong> the substrataconsi<strong>de</strong>rably <strong>de</strong>termine restoration options and have


CHAPTER 6: RESTORATION OPTIONS AND PEAT-\VORKING PRACTICES 121obvious ramifications with respect to <strong>de</strong>sirable watersources etc. Growth <strong>of</strong> Sphagna and other bog speciesmay be just as good (if not better) on acid graveIs as itis on ombrotrophic peats. Clays are perhaps the mostwi<strong>de</strong>spread un<strong>de</strong>rlying substratum type and are afien(but not always) relatively base rich. Where theyrepresent sorne form <strong>of</strong> estuarine <strong>de</strong>posit they may alsobe brackish.Rather little is known about the recolonisation <strong>of</strong>rewetted mineral substrata in the peatland context, butthe outcomes <strong>of</strong> restoration initiatives upon base-rich,nutrient-poor substrata are probably similar to those onfen peat irrigated with nutrient-poor water; whereasthose upon base-rich, nutrient-rich substrata areprobably similar to those on fen peat irrigated withnutrient-rich water. There is even less informationabout revegetation pathways on rewetted brackishclays. In wet (inundated) sites characteristic colonistspecies are Phragmites allstralis, Scirplls tabernaemontanae,Typha angustifolia and T. fatifolia.6.5 Optimisation <strong>of</strong> peatworkingpractices andstarting conditions forrestoration6.5.1 IntroductionIt is not possible to set out universal gui<strong>de</strong>lines on<strong>de</strong>sirable working practices to optimise startingconditions for restoration following extraction, as thesewill partly <strong>de</strong>pend upon site-specific features:• conservation objectives;• character <strong>of</strong>the existing biological resource;• character and configuration <strong>of</strong> the remaining peat <strong>de</strong>posit(especially topography and peat properties);• environmental context <strong>of</strong>the sites (especially climate, butalso characteristics and use <strong>of</strong>the adjoining landscape).Here, sorne <strong>of</strong> the un<strong>de</strong>rlying principies are i<strong>de</strong>ntifiedand working practices suggested which facilitate therestoration process.6.5.2 General requirementsThe folIowing requirements are likely to be applicablein many restoration initiatives:• a scientific assessment <strong>of</strong> the character <strong>of</strong> the site, possiblyby in<strong>de</strong>pen<strong>de</strong>nt environmental scientists (Akkermann,1983), with particular regard to features importantin <strong>de</strong>termining <strong>de</strong>sirable and feasible restoration oplions,based on factors i<strong>de</strong>ntified in Chapler 7; 1• a resloration slratcgy should be <strong>de</strong>vised and agreed forlhc sitc, based On the scientific assessment andconservaUon objectives (Chapter 3J;• where feasible, peat extractors should optimise and phaseworking operations to facilitate the agreed restorationstrategy;• working practices should aim to minimise furlher damageto abandoned arcas and refugia, and, wherc feasiblc,enable restoration work (o commence un some workingareas as soon as possible;• at cessation <strong>of</strong> operations (in parts or all <strong>of</strong> the site), peatfields should be configured into an (agreed) conditionthat will optimise restoration (i.e. to maximise use <strong>of</strong> insi/u machinery, operators and infrastructure) (Chaplers 5& 8].6.5.3 Working practices fo,.restoration during peatextraction operationsOnce restoration options have been <strong>de</strong>fined for aparticular site ongoing peat operations should aim tominimise damage to remnants and refugia that havebeen agreed as having an important and sustainableconservation value or which are in sorne other waycritica! to restoration objectíves. They should also aimto optimise the conditions upon abandonment t<strong>of</strong>acilitate the realisation <strong>of</strong> the objectives. ThefolIowing principIes should be taken into consi<strong>de</strong>ration,and implemented where possible:• Importan! refugja (whkJ¡ may inclu<strong>de</strong> little-damagedareas <strong>of</strong> bog, as well as revegeü¡tcd cuttings or damagedareas with an important biological resource) should bei<strong>de</strong>ntified and sleps taken to preserve or enhance theirexisting conservation interesl. Such areas should not besubject to further peat extraction, unless as part <strong>of</strong> anagreed rolling programme <strong>of</strong> peat extraction andrestoration.• If feasible and necessary, a buffer zone should be<strong>de</strong>signated around the core part <strong>of</strong> any refugium areas,which should also remain uncul. (This requirement willpartly <strong>de</strong>pend upon the topographical circumstance andthe method used to protect the remnant massif; optimumwidths will be site-specific. See Chapter 8.]• Work should start on the restoration 01' abandoned areasand maintenance 01' refugia as soon as possible, so that<strong>de</strong>hydration is minimised.• Peat should be extracted in such a way as to leaveupstanding baulks to a specitied eventual height at agreedintervals. This height will be site-specific; 0.5-1 m islikely to be appropriate for many sites. It is recognisedthat in many existing workings, it would not be possibleto achieve the final configuration 01' baulks in this way asthe scale <strong>de</strong>sired would be too smal!. In this case, residualI These rnay inelu<strong>de</strong> sorne assessrnent <strong>of</strong>: existing biologicalresource; characteristics <strong>of</strong> the residual peat <strong>de</strong>posit (peattopography, type, <strong>de</strong>pth, permeability, storage coeflicient anuposition <strong>of</strong> water table); downward water loss inlo mineral grounu;character <strong>of</strong>minerotrophic water sources (irany).


122RESrORATION OF DAMAGED PEATLANDSbaulks may be supplemented by constructed baulks afteroperations have ceased.• If feasible, operations should be phased such that:(i) Contiguous areas are completed in sequence.(ii) Areas c10sest to refugia should be abandoned first,leaving agreed <strong>de</strong>pths <strong>of</strong> peal. [This would help to reducethe hydraulic gradient from the remnant across thecuttings, and may help to reduce drying-out. It will alsomake the <strong>de</strong>sign <strong>of</strong> a 'casca<strong>de</strong> paddy-field' system <strong>of</strong>lagoons more feasible. Note, however, lhal this fealurewill <strong>de</strong>pend upon the existing topography and agreedrestoration strategy for the site.]• If the aim is to recreate ombrolrophic bog directly, it isreeommen<strong>de</strong>d that as a general rule a minimum<strong>of</strong> 50 cm<strong>of</strong> ombrotrophic peat be left in situ. Sufficient peatshould also be left to allow for constructs to impoundwater (bunds or a scalloped surface). [This suggestedresidual <strong>de</strong>pth may vary aeeording to the nature <strong>of</strong> thepeat and the un<strong>de</strong>rlying substratum and its topographyand restoration objeetives. In sites subject to downwardsseepage <strong>of</strong> water into the mineral substratum, a greater<strong>de</strong>pth (> 1m) may be nee<strong>de</strong>d to seal to base <strong>of</strong>the bog, inothers, a <strong>de</strong>pth <strong>of</strong> 50 cm (or less) may be a<strong>de</strong>quate[4.4.5]. The differenee between a minimum <strong>de</strong>pth <strong>of</strong> 50em and an average <strong>de</strong>pth <strong>of</strong> 50 em should be noted.]• Orains should not be dug into mineral subsoil (unless thisis impermeable and unlikely to lead lo downward waterloss). [This may be impossible to achieve where theagreed <strong>de</strong>pth <strong>of</strong> peat to be left in situ is an averag.e <strong>of</strong> 50em.]• Where possible, 'nursery' pools for the 'farming' <strong>of</strong>Sphagnum should be initiated, to provi<strong>de</strong> an inoculum forabandoned areas [9.2].• Orainage operalions should be assessed, and wherepossible re<strong>de</strong>signed to minimise impacts on remnants andareas un<strong>de</strong>rgoing restoration. In low rainfall arcas it maybe <strong>de</strong>sirable to pump drainage water into abandoned peatworkings etc., although this will partly <strong>de</strong>pend on thequality <strong>of</strong>the pumped water [Chapter 5].6.5.4 Operations followingabandonmentOnce an area has been brought out <strong>of</strong> production,further operations should start as soon as practicable t<strong>of</strong>acilitate rewetting and revegetation. This should beplanned to ensure that rewetting initiatives do notpreclu<strong>de</strong> subsequent access or actions elsewhere on thesite. In sites where peat extraction is ongoing inadjoining areas, it will usually be most cost-effective tomake use <strong>of</strong> the machinery available on sile forrestoration work. More specific background and <strong>de</strong>tailsare given elsewhere in this volume [in particularChapters 5, 8, 9 & 10], but the main factors to beconsi<strong>de</strong>red are outlined below.Water managementAH ditches and outfa\ls should be blocked wherepossible to increase retention <strong>of</strong> rainfall and reducewater loss etc. It may be necessary to further seal / fillditches cut into mineral soil where these are thought tocontribute significantly to vertical water losses[Chapters 2 & 4] or to provi<strong>de</strong> un<strong>de</strong>sirable mineralenrichment.Topographical manipulationAttention should be given to the creation <strong>of</strong> optimumconditions for rewetting and revegetation, including thebuilding <strong>of</strong> constructs, such as bunds. Where possible,use should be ma<strong>de</strong> <strong>of</strong> the existing network <strong>of</strong>embankments etc., raising levels where necessary,although the permeability <strong>of</strong> the baulks should first be<strong>de</strong>termined to assess their efficacy. [The movement <strong>of</strong>peat and alteration <strong>of</strong> the configuration <strong>of</strong> abandonedpeat cuttings should be carried out as part <strong>of</strong> an agreedrestoration plan, usually in consultation with thestatutory conservation and archaeological bodies.]Milled surfacesIt may be necessary to subdivi<strong>de</strong> large peat fields tocreate lagoons to facilitate rewetting and renaturation.Block-cut surfacesDepending on the configuration remaining, it may be<strong>de</strong>sirable to flatten SOme <strong>of</strong> the baulks to achieve amore level area for rewetting, while utilising sornebaulks to retain water. It should be possible to usesome <strong>of</strong>the material from the 'redundant' baulks to fillthe ditches. .Control <strong>of</strong> vegetation invasionVegetation management should start as soon asproduction ceases in or<strong>de</strong>r to reduce the establishment<strong>of</strong> 'un<strong>de</strong>sirable' species, especially if it is not possibleto raise water levels within a short time [Chapter 101.Where 'abandoned' fields lie within the zone <strong>of</strong>ongoing peat extraction, it may be possible to achievethis by running rotovating machinery over the surfaceeach year to retard seedling establishment. Where thishas not been done, it may be necessary to removevegetation (e.g. birch and Molinia) froro abandonedareas prior to rewetting.6.5.5 MaintenanceFull renaturation and regeneration <strong>of</strong> rewetted peatfields is likely to be slow, partly on account <strong>of</strong> theimpoverished nature <strong>of</strong> the ombrotrophic environmentand the intrinsically low relative growth rates <strong>of</strong> bogplants. In consistently wet conditions, initial colonis-


CHAPTER 6: RESTORATION OPTlONS AND PEAT-\VORKING PRACTICES 123ation by pioneer Sphagnum species (e.g. S. cuspidatum)may occur rapidly, but subsequent <strong>de</strong>velopmentto a more diverse bog surface is likely to take longer,possibly several <strong>de</strong>ca<strong>de</strong>s [6.6]. There is seope forexploring possible means <strong>of</strong> artificial acceleration <strong>of</strong>colonisation by other bog species [Chapter 9]. As thecut-over areas regenerate into bog they may beexpected to become increasingly self-sustaining.However, some <strong>de</strong>gree <strong>of</strong> maintenance may be nee<strong>de</strong>din the early stages <strong>of</strong> rewetting and renaturation, suchas removal <strong>of</strong> scrub from dry sites within the peatfields (though the extent <strong>of</strong> this problem will <strong>de</strong>pendpartly on the success <strong>of</strong> the rewetting procedures). Thecondition <strong>of</strong> the peat bunds, especia11y the outer ones,will also require periodic inspection and, if nee<strong>de</strong>d,sorne rnaintenance. The expected intrinsically-slowrenaturation <strong>of</strong> the peat fields is likely to mean thatsorne (intennittent) maintenance rnay be required formuch longer than an after-care period <strong>of</strong> 5 years. Therestoration scherne should be <strong>de</strong>signed to minimise ongoingmanagernent requirements 1 but also to make itpracticable for thern to take place, ifnee<strong>de</strong>d.6.6 Prospects for restorationAn assessment <strong>of</strong> the prospects <strong>of</strong> restoration <strong>of</strong>lowland bogs damaged by peat extraction must besubject to the usual caveats <strong>of</strong> the precise objectives <strong>of</strong>restoration and the specific conditions <strong>of</strong> individualsites. Assessment <strong>of</strong> the <strong>de</strong>sirability and the perceivedsuccess <strong>of</strong> restoration options also needs to take intoaccount the condition <strong>of</strong> the sites prior to current peatextraction: sorne, but not all, sites were consi<strong>de</strong>rablydarnaged before current peat extraction operations (as aconsequence <strong>of</strong> drainage, repeated burning, partialagricultural conversion or an earlier phase <strong>of</strong> peatextraction). In such cases successful restoration rnayserve to enhance the conservation value <strong>of</strong>the site.6.6.1 Remnant peat massifsMany <strong>of</strong> the 'best' remaining raised bogs in Britainhave been subject to some <strong>de</strong>gree <strong>of</strong> marginal damageand reduction in area, either through peat extraction orconversion for agricuhure. The fact that they sti11provi<strong>de</strong> a 'good quality' bog habitat points to thecapacity <strong>of</strong> the systerns to accomrnodate, naturally,sorne <strong>de</strong>gree <strong>of</strong> marginal damage. The 'cost' <strong>of</strong> thiscapacity is usua11y some dryíng around the margins <strong>of</strong>the sites and the <strong>de</strong>gree to which this is regar<strong>de</strong>d as1 For example, by ensuring that the floors <strong>of</strong> lagoons can be keptinundated, to minimise opportunities for establishment <strong>of</strong>un<strong>de</strong>sirable speeies; a strongly undulating, or sloping, surface maycreate periodically dry arcas that are susceptible to birchencroaehment elc.acceptable will largely <strong>de</strong>pend upon the proportion <strong>of</strong>marginal damage relative to th~ area <strong>of</strong> Ettle-damagedbog and upon the consequential effects <strong>of</strong> the damage.In large sites, with just a small amount <strong>of</strong> marginalwater draw-down, some loss <strong>of</strong>area may be acceptabIe(although long-term effects may be unknown). Greaterproblems arise where only a small peat remnant is leftundamaged or where, perhaps because <strong>of</strong> a large heightdifference between the peat fields (etc.) and theremnant surface, marginal water drawdown affectsmost <strong>of</strong> the bogo Here the damage is likely to result in aloss or reduction <strong>of</strong> typical bog species over rnuch ora11 <strong>of</strong> the massif, unless constructive measures aretaken to prevent this. These may inelu<strong>de</strong> theconstruction <strong>of</strong> bunds around sorne or a11 <strong>of</strong> theperiphery <strong>of</strong> the rernnant, an approach whiCh has hadsome success in The Netherlands.It is undoubtedly possible to retain existing interestupon a bog massif with a little damaged surface,though this may require sorne engineering. It issimilarly possible to retain bog species upon a partlydamaged surface, though not necessarily in the sarneproportions as when in a little-damaged state, andperhaps requíring sorne periodic rnanagernent toremove 'un<strong>de</strong>sirable' colonists such as birch. In thissituatíon attempts to enhance the quality <strong>of</strong> thevegetation and habitat by further elevation <strong>of</strong> the waterlevel (where possible) may also meet with sornesuccess, <strong>de</strong>pending upon specific circumstances(though such procedures may not integrate we11 withattempts at restoration <strong>of</strong> adjoining cut-over surfaces).However, where a massif surface is badly darnaged (sothat it has lost many or mos! <strong>of</strong> its original species)effective rewetting may be mlich more difficult 2 and,whilst perhaps technically possible, may be irnpracticalor eost-ineffective, except perhaps in the case <strong>of</strong> largemassifs or sites located in particularly cool and wetregions. Elsewhere it rnay be more practical to pennitthe massif to <strong>de</strong>velop into a replacement habitat <strong>of</strong>some more general wildlife interest.6.6.2 Cut-over ombrotrophic surfacesIt is evi<strong>de</strong>nt from exarnination <strong>of</strong>old peat cuttings that,where they have been kept (<strong>of</strong>ien fortuitously) in asuitably wet eondition, recolonisation by typical bogspecies has occurred, to the extent that in sorneinstances the appearance and composition <strong>of</strong> thevegetation is little different to that found on some littledamagedbogs, including sorne <strong>de</strong>velopment <strong>of</strong> ahummock-hollow patterning. Such examples aretypically sorne 50-150 years old. Although sorne suchexamples are quite \arge (severa\ hectares) they are2 This will partly <strong>de</strong>pend upon the reason why the massif isdamaged and dry.


124RESTORAnON OF DAMAGED PEATLANDSusually on a much smaller scale than currentcommercial operations; moreover, the conditions <strong>of</strong>their restoration may have been rather different to that<strong>of</strong> sorne present operations (e.g. close juxtaposition tosources <strong>of</strong> recolonist species), though in manyinstances critical information is lacking.<strong>Restoration</strong> initiatives on large commercial cut-oversites are still in their infancy; moreover sorne <strong>of</strong> themhave been in sites where problems <strong>of</strong> watermanagement have been exacerbated by severalunusually dry summers and by vertical loss <strong>of</strong> waterdown into a permeable mineral substratum. Nonetheless,it is evi<strong>de</strong>nt (a) that a wi<strong>de</strong> range <strong>of</strong> bog plantspecies can inva<strong>de</strong> such surfaces (where there is aproximate inoculum source); and (b) that it is possibleto rewet the peat fields to the extent that (c) carpets <strong>of</strong>aquatic Sphagna can rapidly colonise extensive areas.This latter event permits consi<strong>de</strong>rable optimism forregeneration prospects as it is evi<strong>de</strong>nt (from studies onthe natural <strong>de</strong>velopment <strong>of</strong> bogs and <strong>of</strong> recolonisedpeat workings) that a wet Sphagnum cuspidatum phasehas provi<strong>de</strong>d a basis for spontaneous successional<strong>de</strong>velopment <strong>of</strong> a more diverse vegetation composed <strong>of</strong>more important bog-building species such asSphagnum papillosum and S. magellanicum (e.g.Joosten, 1995). It is difficult to see why this processshould not be repeated on commercialIy-cut over sites,provi<strong>de</strong>d that three conditions are satisfied:(i) that the site is accessible to potential recolonistspecies (if it is not, then re-introduction <strong>of</strong> specieswilI need to be consi<strong>de</strong>red) [Chapter 9];(ii) that the chemical composition <strong>of</strong> precipitationinputs will support the growth <strong>of</strong> recolonist bogspecies and(iii) that sufficient precipitation water can be retainedon site.If such conditions are not limiting, it seems likely thatcommercialIy-cut peat fields wilI re<strong>de</strong>velop acharacteristic bog vegetation and that peat accumulationwilI recommence in time. In<strong>de</strong>ed, the long-termstability <strong>of</strong> bog <strong>de</strong>velopment on flat peat-cuttingsurfaces may well be greater than that on upstandingbog remnants.6.6.3 Cut-over minerotrophic surfacesProspects for restoration <strong>of</strong> minerotrophic surfaces wilI<strong>de</strong>pend criticalIy upon the topography <strong>of</strong> the site, thewater level that can be maintained and the quality <strong>of</strong>the water used to achieve this. Fen vegetation <strong>of</strong>conservation value has spontaneously re<strong>de</strong>veloped onextensive cut-over fen peat surfaces, includingexamples that are flat and not floo<strong>de</strong>d (e.g.Woodwalton Fen, Cambridgeshire (Poore, 1956» an<strong>de</strong>xamples in large, floo<strong>de</strong>d cuttings (e.g. Catfield &Irstead Fens, Norfolk (uiller & Wheeler, 1986». Inboth cases revegetation has occurred over large areas(tens <strong>of</strong> hectares), but the nature <strong>of</strong> the vegetation thathas re<strong>de</strong>veloped in each is rather different. Sorneexamples <strong>of</strong> revegetation within floo<strong>de</strong>d peat workingshas produced sorne <strong>of</strong> the prime areas <strong>of</strong> lowland fenwithin the UK. Such hydroseral situations are alsosusceptible to Sphagnum establishment and in sornelocations consi<strong>de</strong>rable thicknesses <strong>of</strong> Sphagnum peathave accumulated (up to 1m <strong>de</strong>pth in c. 100-150years). By contrast, Sphagnum re-establishment onsol id fen surfaces is generally more limited, probablyon account <strong>of</strong> periodic dryness and irrigation withbase-rich water.For the most part, the particular conditions that wereoperative at the start <strong>of</strong> the spontaneous revegetation <strong>of</strong>cut-over fen peats are, not known. This makesgeneralisation from historical observations to presentdayworkings difficult, other than to recognise theimportance <strong>of</strong> wet, shallowly-inundated, conditions tothe prospects <strong>of</strong> re-establishment <strong>of</strong> specific types <strong>of</strong>fen and the <strong>de</strong>velopment <strong>of</strong> bogo In principie, givenappropriate water management, there seems littlereason why ombrotrophication processes should notrecur in fens sites which have formerly supportedraised bog, subject again to (i) the possible limitations<strong>of</strong> availability <strong>of</strong> suitable recolonist species; (ii)<strong>de</strong>position <strong>of</strong> atmospheric contaminants; and (iii) thestability <strong>of</strong>telIuric water supply to the fen peat.6.7 Holistic approaches toraised-bog restorationIn sorne situations the restoration <strong>of</strong> damaged peatlandscan be approached piecemeal. This approach is likelyto be most satisfactory when it is possible to provi<strong>de</strong>in<strong>de</strong>pen<strong>de</strong>nt hydrological control <strong>of</strong> particular landparcels. For example, in the fen peat basins <strong>of</strong>individual holdings in the Somerset Levels it may <strong>of</strong>ienbe possible to rewet and renature each peat workingin<strong>de</strong>pen<strong>de</strong>ntly <strong>of</strong> the others. Similarly, sorne sealed<strong>de</strong>pressions within ombrotrophic peat may be rewettedin<strong>de</strong>pen<strong>de</strong>ntly <strong>of</strong> their surroundings; in<strong>de</strong>ed, as notedaboye [6.2] such an approach may be the only practicalpossibility in sorne sites where cut-over surfaces havebeen lefi at wi<strong>de</strong>ly differing levels. Such an approachmay be very effective in maintaining populations <strong>of</strong>bog species within the landscape (i.e. production <strong>of</strong> aseries <strong>of</strong> 'bog gar<strong>de</strong>ns') but it is less suited to the coordinatedregeneration <strong>of</strong>a single mire [5.6].These observations notwithstanding, habitat continuityis <strong>of</strong>ien particularly important in the restoration <strong>of</strong>mires because <strong>of</strong> their <strong>de</strong>pen<strong>de</strong>nce upon a suitablewater source (and sink). Whilst lack <strong>of</strong> such continuitymay not prevent effective rewetting it may materialIy


CIIAPTER 6: RESTORATION OPTIONS AND I'EAT-WORKING I'RACTICES 125increase the complexity (and cost) <strong>of</strong> watermanagement. This problem is sometimes most evi<strong>de</strong>ntin attempts to restore fen ecosystems, where sorneseparate peat cuttings may have become isolated fromappropriate sources <strong>of</strong> minerotrophic water (inputs <strong>of</strong>river 01' seepage water). In principie, this problem ismuch less acute in ombrotrophic systems as the mainwater source (precipitation) is accessible across theentire site. However, even here, sorne surfaceconfiguration (e.g. a very varied block-cut topography)may require a mosaic <strong>of</strong> several individual rewettingschemes. In addition, rewetting <strong>of</strong> bogs in low rainfallregions may only be possible by sorne redistribution <strong>of</strong>water across the entire site (e.g. by a form <strong>of</strong> 'gradientfeeding' [5.4]). Unless continued pumping iscountenanced, this approach requires inputs from parts<strong>of</strong> the surrounding mire and hence an integrated watermanagement plan.An integrated approach to site restoration may a)soprovi<strong>de</strong> a rational basis for <strong>de</strong>cisions upon conservationpriorities in specific areas. For example, whereworkings in fen peat can only be rewetted by nutrientrichriver water, they may be appropriately managedfor birds (as reedbeds); where they can be kept wet bynutrient-poor seepage water, then management for aspecies-rich fen vegetation can be consi<strong>de</strong>red. Onombrotrophic peat, restoration to Sphagnum-richvegetation can be focused on those areas that are leastdifficult to maintain in a wet condition. This approachthereby avoids the problem that can accompanypiecemeal restoration, namely attempts to recreate aspecific habitat-type in circumstances that are not bestsuited to it.In most instances, restoration <strong>of</strong> a raised bog need not<strong>de</strong>mand the rewetting<strong>of</strong> adjoining land, even in thosecases where it once formed part <strong>of</strong> the original peatlandarea. However, in sorne instances localised rewettingmay be useful, for example, to enhance the coherence<strong>of</strong> the mire (e.g. at Wreaks and White Mosses(Duddon, Cumbria) where two massifs <strong>of</strong> peat are nowseparated by a narrow strip <strong>of</strong> agricultural land) 01' aspart <strong>of</strong> a co-ordinated strategy for the restoration <strong>of</strong> aremnantmassif and surrounding peat workings 01'drained land [5.6].In sorne cases, effective rewetting <strong>of</strong> a bog may onlybe possible by sorne manipulation <strong>of</strong> the drainage inthe surrounding land. This is likely to be the casewhere land-drainage systems directly (:1) drain the mire(e.g. Fenns and Whixall Moss) 01' (b) indirectly drainit, in situations where the water table in fen peat 01' anun<strong>de</strong>rlying aquifer would otherwise form the'impermeable' base to the perched water mound.Rewetting <strong>of</strong> peat workings in fen peat may havegreater repercussions upon the adjoining land as <strong>of</strong>ienthe ability to rewet the workings may <strong>de</strong>pend uponwater supply and retention that is <strong>de</strong>termined, directly01' indirectly, by adjoining land drainage systems.Such consi<strong>de</strong>rations suggest that the restoration 01'recreation <strong>of</strong> wetlands as substantial landscape featureswould benefit from the <strong>de</strong>velopment <strong>of</strong> a co-ordinatedpolicy <strong>of</strong> land management. This would requireintegration <strong>of</strong> the activities and interests <strong>of</strong> the peatindustry and the conservation bodies and also, inspecific situations, <strong>of</strong> the Internal Drainage Boards, theWater Authorities, the National River Authorities andagriculturalists. Integration <strong>of</strong> restoration activities intoan overall plan (and the available options) will also<strong>de</strong>pend upon the timing <strong>of</strong> peat extraction· in specificareas, particularly in those localities where there areseveral operators (e.g. Somerset Levels). In suchsituations the <strong>de</strong>velopment <strong>of</strong> a holistic scheme formire restoration would be enhanced if it was possiblefor the co-ordinating body to <strong>de</strong>velop a proactivestrategy for peat extraction rather than to just beresponsive to individual applications.It may also be noted that <strong>de</strong>cisions concerning the<strong>de</strong>sirability <strong>of</strong> the various wetland habitat-types thatcould form the most appropriate focus for wetlandrestoration schemes in different parts <strong>of</strong> the UK couldbenefit from the formulation <strong>of</strong> a 'national wetlandstrategy'. Amongst other things, this could helpi<strong>de</strong>ntify objective ground-rules for assessing prioritiesin wetland habitat recreation, based on such consi<strong>de</strong>rationsas the perceived 'value' <strong>of</strong> particular habitattypes,their national and regional scarcity and thefeasibility and appropriateness <strong>of</strong> their recreation inspecific locations. Such an approach would help toprovi<strong>de</strong> a rationale for wetland restoration optionsbased on assessed ecological and conservational meritand would thus reduce the chance <strong>of</strong> options beingchosen on a purely ad hoc basis 01' in response to theoverweening influence <strong>of</strong> a particular interest group.


PART 111Practical Aspects <strong>of</strong> <strong>Restoration</strong>


Chapter 7Planning a restoration strategy7.1 IntroductionThe occurrence <strong>of</strong> spontaneous and '<strong>de</strong>sirable' revegetation<strong>of</strong> some abandoned peat workings shows that insorne instances a measure <strong>of</strong> bog 'restoration' can beachieved wíthout intervention or planning. However,the existence <strong>of</strong> large areas <strong>of</strong> rather dry cut-oversurfaces dominated by birch, bracken or heather showsthat this is by no means always the case. In mostdamaged peatland sites, particularly those subject toextensive commercial peat extraction, it will beimportant to <strong>de</strong>velop a strategy in or<strong>de</strong>r to optimise. restoration procedures to achieve specific objectives.This is required to ensure that:• areas <strong>of</strong> existing natural history interest that will not besubject to further peat extraction are safeguar<strong>de</strong>d;• peat workíngs are left in a condition optímal forrestoration;• restoration practices and objectives for specific areas arewe\! phased and integrated with one another;• techniques appropriate to achieve specific restorationobjectives are i<strong>de</strong>ntified.Formulation <strong>of</strong> a restoration plan for a cut·over bogsite requires the acquisition <strong>of</strong> sorne information aboutthe site in question (e.g. Turchenek, Ted<strong>de</strong>r &Kranowski, 1993; Famous, el al. 1995; Ward, Hirons& Self, 1995). Information (environmental andbiological) is required particularly: (i) to help selectappropriate restoration options; (ji) to i<strong>de</strong>ntify theconstraints upon the chosen options and to enableinformed <strong>de</strong>cisions to be ma<strong>de</strong> on the most appropriateways to achieve specific objectives; and (jii) to provi<strong>de</strong>base-line data for monitoring purposes.Consultation with various statutory and non-statutorybodies will form an important part <strong>of</strong> the planningphase <strong>of</strong> restoration. These inelu<strong>de</strong> the local mineralplanning authority, heritage, conservation and waterresources bodies. It may also be necessary to engagespecialists in or<strong>de</strong>r, for example, to carry out surveywork; interpret the results; assist in the preparation <strong>of</strong>an appropríate restoration scheme with <strong>de</strong>tailedspecifications; and to provi<strong>de</strong> legal advice.The variability <strong>of</strong> starting conditions amongst damagedlowland peatlands means that a universal statement <strong>of</strong>'data required' for formulating a restoration plancannot be ma<strong>de</strong>. However, it is possible to i<strong>de</strong>ntifysome <strong>of</strong> the main types <strong>of</strong> information that may benee<strong>de</strong>d, the objectives <strong>of</strong> restoration and the way inwhích restoration may be planned, although specificrequirements are Iikely to vary between sites,<strong>de</strong>pending upon their exact conditions.7.2 Planning for restoration7.2.1 Approaches to restorationplanningThere are at least three broad approaches to peatlandrestoration in relation to the nature <strong>of</strong> informationrequired.Unplanned approachThe 'unplanned approach' is one in which, forexample, spontaneouS changes are aJlowed to takeplace in a way which it is hoped will produce a satisfactoryresult. Although several important conservationsites are a product <strong>of</strong> unplanned restoration, this cannotbe commen<strong>de</strong>d as a reliable approach to realise aspecific restoratíon goal. Nonetheless, in manyrestoration schemes, some events and responses arelikely to be both unplanned and unexpected.Empirical approachThe 'empirical approach' is one in which restoration issubstantially based upon an intuitive appraisal <strong>of</strong> therequirements for habitat manipu\ation, rather than upondata acquisition and prediction. This approach has bothmerits and limitations:• some successful restoration initiatives have procee<strong>de</strong>d inthis way;• ignorance <strong>of</strong> actual site conditions may mean that thisapproach involves a good <strong>de</strong>al <strong>of</strong> 'trial-and·error' inwhich certain options are tried and then, if necessary,modified; some errors may be acceptable ¡fthey are nottoo costly or irreversible;• it is strongly <strong>de</strong>pen<strong>de</strong>nt upon the personnel involved;some individuals have a c1ear intuitive appraisal <strong>of</strong>controls on particular conditions within peat\ands withwhich they are familiar; others do not;• this approach is <strong>of</strong>ten not readily communicable, nor arereasons for failure or success always easily i<strong>de</strong>ntified;


130RESTORATION OF DAMAGED PEATLANDS• it is particularly suitable for repair <strong>of</strong> relatively minordamage lo bog siles, where lhe oplions are fairly weJlcircumseribed, where the operations are comparativelysmalJ-scalc and can be reverscd or replaced ifunsuccessful;• it is less suitable for the rebui/ding <strong>of</strong> extensivelydamaged sites, where larger-scale and innovative habitatmanipulation may be nee<strong>de</strong>d;• even in extensivcly damaged sites this approach mayhave sorne contribution to makc; for example, peatworkers <strong>of</strong>ten have a good insight into the drains thathave most control <strong>of</strong> the water balance <strong>of</strong> the bog, or <strong>of</strong>arcas where water naturally accumulates; thei<strong>de</strong>ntificatíon <strong>of</strong> wet conditions to nucleate restorationmay be more easily and accurately assessed byexamining the natural accumulation <strong>of</strong> water than byattempting to predict ít using topographical andhydrological measurements.Measured approachThe 'measured approach' is one in which numerousdata conceming site conditions are collected andanalysed predictively to <strong>de</strong>vise a well-researched, wellthought-out restoration plan. This is <strong>of</strong>ien consi<strong>de</strong>red tobe the 'best' approach. Nonetheless, it may have anumber <strong>of</strong> limitations both in principie and,particularly, in practice:• there is sometímes a ten<strong>de</strong>ncy for data acquisition not tobe focused upon specific questions, but to be part <strong>of</strong> a'wish-list' <strong>of</strong> 'useful' information, or to be seen as away <strong>of</strong> i<strong>de</strong>ntifying the specific questions that need to beanswered; sometimes the aequisition <strong>of</strong> such data,although <strong>of</strong> interest, may have Iittle direct relevance tothe <strong>de</strong>velopment <strong>of</strong> a restoratíon plan and may even becounter-productive because:• data acquisition is frequently expensive and in mostcases this constrains the amount <strong>of</strong> information that canbe callected; Ihis usually results either in ina<strong>de</strong>quatesample replication or ina<strong>de</strong>quate site coveragc. Thclatter may be <strong>of</strong> particular importance in large raisedbogsites and can lead to lack <strong>of</strong> information about quitelarge parts <strong>of</strong> the mire; it is quite common experiencethat even elaborate investigations do not generate thelevel <strong>of</strong><strong>de</strong>tail required for sorne restoration purposes;• data interpretatíon may sometimes be difficult. Thisreflects both lack <strong>of</strong> knowledge and un<strong>de</strong>rstandingspecific to sorne areas <strong>of</strong> peatland ecology together withthe more general problems <strong>of</strong> data interpretatíon. Forexample, it is simple to, measure high concentrations <strong>of</strong>ammonium in the peat <strong>of</strong> sorne peat extraction surfacesbut it is much more difficult to predict the thresholdconcentrations that may constrain re-invasion by typicalbog plant specíes;• measurements and analyses may not provi<strong>de</strong> the level <strong>of</strong>predictive accuracy required for the exact formulation <strong>of</strong>restoration objectives. For example, there are variousprocedures available for mo<strong>de</strong>lling the behavíour <strong>of</strong>water table in peatlands, but they may have limitedcapacity to predict accurately the position <strong>of</strong> the watertable with respect to the peat surface, especially in peatcuttingsites. This is because <strong>of</strong> intrínsíc límitations <strong>of</strong>sorne mo<strong>de</strong>ls; because the more sophisticated mo<strong>de</strong>ls are'data-hungry'; and beeause <strong>of</strong>the difficulty afobtaíningmeaningful estimates <strong>of</strong> certain parameters for themo<strong>de</strong>ls. <strong>Restoration</strong> initiatives may, <strong>of</strong>course, provi<strong>de</strong> avaluable opportuníty to <strong>de</strong>velop and refine variousecological techniques, but there are obvious limítationsin using methods with unknown propensitics to studypeatland siles with unknown properlíes.In practice, many restoration schemes will rely on asensitive ínteraction between the empírical andmeasured approaches. In most cases, empiricalprocedures require some 'hard' data to help ensure(and monitor) their success, but equally, the empíricalapproach may provi<strong>de</strong> the only realist option when dataacquisition is ina<strong>de</strong>quate or <strong>of</strong> limited predictivereliability. To yield maximum benefits for restoration,data acquisition should be: (a) focused upon answeringspecific, <strong>de</strong>fined questions that are critical to particularaspeets <strong>of</strong> restoration; (b) sufficientIy well resourced toensure that reliable and usable data are col1ected; and(c) performed by experienced practitioners who areaware <strong>of</strong>the inherent problems and likely límitations <strong>of</strong>their studies. These comments are not ¡nten<strong>de</strong>d todiscourage acquisition <strong>of</strong>site data, but to emphasise theneed for relevant and reliable data and for a eonsi<strong>de</strong>redappraisal, at the outset <strong>of</strong> planning a restorationstrategy, <strong>of</strong>the salient questions and data that are likelyto be required to answer them. The acquisition <strong>of</strong>information <strong>of</strong> limited relevance or reliability (e.g.because <strong>of</strong> ina<strong>de</strong>quate replication) may ultimatelyprovi<strong>de</strong> little more than a loss <strong>of</strong>money17.2.2 Feasibility studyIn view <strong>of</strong> the various sources <strong>of</strong> informationpotentially available and varying conditions at differentsites, it is recommen<strong>de</strong>d that the formulation <strong>of</strong>restoration schemes should be prece<strong>de</strong>d by a feasibilitystudy which will provi<strong>de</strong> the basis for choice <strong>of</strong>specific objectives for a site and the nature <strong>of</strong> anyrestoration work required. For sites currently un<strong>de</strong>rextraetion, a restoration scheme should be formulatedas soon as possible, before extraction ceases, eventhough this wiIJ involve an element <strong>of</strong> prediction (e.g.final topography, peat <strong>de</strong>pths etc.).The primary functions <strong>of</strong> the feasibility study are:(i)(ii)lo <strong>de</strong>termine lhe practica! and financia! feasibility <strong>of</strong>restoration;to <strong>de</strong>termine the most suitable techniques for rctainingand enhancing any existing wildlífe or archaeologicalinterest within or on a site (in particular raised-bogelements);(iii) (o <strong>de</strong>termine the most suitable techniques for recreatingan appropriate habitat (in particular, the raised-boghabitat) on a cut-over or otherwise damaged site, payingdue regard to (i),


CHAPTER 7: RESTORATION PLANNING131In sorne sites it may also be appropriate to consi<strong>de</strong>r thepotential <strong>of</strong> the site for education and research and itspotential for interpretation and public access.Assessments will be based on information <strong>de</strong>rived from(a) a preliminary '<strong>de</strong>sk study' by collation <strong>of</strong> existinginformation and (b) from on-site investigations. Thelatter, together with interpretation <strong>of</strong> the information,may require the expertise <strong>of</strong> specialists from severaldisciplines, although an indication <strong>of</strong> the importanceand usefulness <strong>of</strong> the information is given in theappropriate sections below. Collection <strong>of</strong> supertluousinformation should be minimised by careful scoping <strong>of</strong>the site assessment programme; a reasonable balancemust be achieved between collection <strong>of</strong> a<strong>de</strong>quate datato facilitate informed <strong>de</strong>cisions and the cost <strong>of</strong>collecting such data. The latter is likely to be a majorlimiting factor in peatland restoration. An example <strong>of</strong>the potential scope <strong>of</strong> a feasibility study is given inTable 7. I.It is essential that accurate maps are prepared for use inconsultations and survey work ifnot already available.7.2.3 Consu/tationConsultations should begin as early as possible in theplanning stages <strong>of</strong> a restoration scheme. They relateboth to the process <strong>of</strong> choosing the most appropriaterestoration objectives for each site and the realisation<strong>of</strong> the specified objective. It will particularly help toi<strong>de</strong>ntify at an early stage· any known potentialconstraints on <strong>de</strong>velopment. The main interestedparties are given in Table 7.2. Key consultees inclu<strong>de</strong>the statutory bodies, peat extraction companies andland or mineral owners involved with the site oradjacent land. There are also numerous non-statutoryorganisations who may be able to provi<strong>de</strong> advice orinformation on various aspects <strong>of</strong> the site and proposedrestoration schemes, sorne <strong>of</strong> whom may wish to bedirectly involved. Some <strong>of</strong>these are Iisted in Table 7.3.Table 7.1 Potential scope <strong>of</strong> a feasibility study concerning the restoration <strong>of</strong> a cut-over or damaged peatland site.1. Site <strong>de</strong>scription1.1 Site location, landscape selling, and boundary information1.2 Soils and geology (including peat types and <strong>de</strong>pths)1.3 General topography (within site, and in relation to surroundings)1.4 Flora and fauna (past, present and potential) (including features <strong>of</strong> special interest or conservalion value)1.5 Hydrology (including climate, regional and local water resources, 'un<strong>de</strong>sirable' water inputs)1.6 Current and past management1.7 Archaeology I historie landscape I industrial landscape2. Peat workings2.1 Extent, type, age, planning permissions (current and future)2.2 Topography and relationship to uncut areas2.3 Integration into restoration strategy3. Ownership I Tenancies3.1 Details <strong>of</strong> land and minerals ownership <strong>of</strong> site and adjoining land which may be affected by any restoration scheme4. <strong>Restoration</strong> options4.1 Objectives4.2 Constraints and opportunities4.2.1 Potentiallegal and land-use constraints on <strong>de</strong>velopment (e.g. physical, legal, financial, wildlife, manpower,timescales, archaeology, adjoining land-use)4.2.2 Options available, and potential for financiar and practicar assistance4.3 Specification <strong>of</strong> restoralion work including:4.3.1 Conservalion <strong>of</strong> existing features <strong>of</strong> importance4.3.2 Optimisation <strong>of</strong> working practices to achi€we optimal starting conditions for restoration4.3.3 Work nee<strong>de</strong>d to improve hydrological water balance (and water quality, if appropriate)4.3.4 Reconfiguration <strong>of</strong> topography4.3.5 Proposed schedule <strong>of</strong> restoration work (including phasing <strong>of</strong> the work, taking climatic, management and practicalconstraints .into consi<strong>de</strong>ration)4.3.6 Proposals for on-going maintenance and management4.3.7 Proposals for monitoring progress6. Costed options


132RESTORATION OF DAMAGED PEATLANDSThe focus <strong>of</strong> the consultations may <strong>de</strong>pend upon the¡nitiator <strong>of</strong>the restoration scheme, for example a natureconservation body attempting to restore former peatworkings or a peat company putting forward a planwhen applying to a Mineral Planning Authority (MPA)for an updated or new planning permission. Theguidance is also <strong>of</strong> relevance to MPA's in assessing theinformation provi<strong>de</strong>d in any applications submitted.7.3 Financial consi<strong>de</strong>rations7.3.1 IntroductionThe feasibility <strong>of</strong> the various restoration options may<strong>de</strong>pend on financial Iimitations, as well as practical andlegal constraints. Unless funding for restoration workhas been agreed in advance, an important part <strong>of</strong> theinitial feasibility study will be to <strong>de</strong>termine thepotential for financial or practical assistance that maybe available from different sources, including bothstatutory and non-statutory conservation bodies. Thelatter may be able to provi<strong>de</strong> help with past records forthe site, reconnaissance and recording. The costs <strong>of</strong>restoration are inevitably site specific, <strong>de</strong>pending onsuch factors as the size <strong>of</strong> the site, the <strong>de</strong>gree <strong>of</strong>damage, the extent <strong>of</strong> the remedial action necessary toachieve the stated management objectives (includingarchaeological mitigation), availability <strong>of</strong> materials,and the technical difficulties in carrying out the work.Sorne typical ranges <strong>of</strong> costs for different techniquesare given in Table 7.4.Table 7.2 Primary interested parties* in the formulation <strong>of</strong> a restoration scheme.OrganisationPeat extraction companiesLand and mineral owners involved with the siteor adjacent land (if different from aboye)Mineral Planning AuthorityEnglish Nature, Countrysi<strong>de</strong> Council for Wales.Scottish Natural Heritage, DoE(NI), Countrysi<strong>de</strong>Commission.National Rivers Authority (NRA) and InternalDrainage Boards (IDB); River PurificationBoards (Scotland) ; DoE(NI).The Ministry <strong>of</strong> Agriculture Fisheries and Food(MAFF), Department <strong>of</strong> Agriculture NorthernIreland (DANI), Scottish Office Agriculture andFisheries Department (SOAFD), ForestryAuthorityEnglish Heritage, Cadw, Historic Scotland, DoE(NI), County Archaeological OfficersTopieInvolvement and co-operation in restoration schemes, advice on methods,use <strong>of</strong> machinery etc.Details <strong>of</strong> peat extraction history.Future plans for land when extraction completed.Possible financial support tor restoration work.Involvement and co-operation in restoration schemes.Legal aspects <strong>of</strong> site leases.Future plans for land following cessation <strong>of</strong> extraction.Guidance on planning and conservation issues (e.g. in <strong>de</strong>velopment plans)Planning constraints relating to the site (e.g. existing conditions, rights <strong>of</strong>way); Site history (planning).Statutory <strong>de</strong>signations, e.g. Local Nature Reserves (LNR), common land,Scheduled Ancient Monuments (SAM).Non-Statutory <strong>de</strong>signations e.g. Local Nature Reserves.Possible financial support for restoration work.Statutory <strong>de</strong>signations e.g. National Nature Reserves, Sites <strong>of</strong> SpecialScientific Interest (SSSI's), Areas <strong>of</strong> Special Scientific Interest (ASSI's),Areas <strong>of</strong> Outstanding Natural Beauty (AONB), National Parks, SpecialProtection Areas (SPA's) and Ramsar sites.Occurrence or likely occurrence <strong>of</strong> scheduled species e.g. ad<strong>de</strong>r, badger,great crested newt.Wildlife value <strong>of</strong> the site and existing records.Advice on species introductions and peatland restoration methods.Possible practical and I or financial support for restoration work.Consent requirements for water abstraction, water impoundment, waterdischarge, works affecting drainage or flood <strong>de</strong>fences.Location <strong>of</strong> any nearby water abstraction points.Pollution potential <strong>of</strong> dischargesPossible collaboration with, practical or financial support for and advice onrestoration work.Water quality information I data relating to catchment water supply Iadjacent water courses I regional water resources etc.Catchment management.Current usage and possible effects on adjacent land.Designations <strong>of</strong> Environmentally Sensitive Areas (ESA's)Agriculturalland quality (<strong>of</strong> site and/or surrounding areas)Advice on archaeological interest and survey.Location and <strong>de</strong>tails <strong>of</strong> Scheduled Ancient Monuments (SAM).Possible practical and I or financial support for restoration work.The relevant participants will <strong>de</strong>pend on the party initiating or assessing the restoration scheme.


CHAPTER 7: RESTORATION PLANNING133As with mueh eonservation work, there is unlikely tobe mueh tangible eeonomie retum on the investment,unless (a) the raised-bog objeetive is subsumed bymore remunerative objeetives sueh as provision <strong>of</strong> afishing lake; (b) eompensation payments are ma<strong>de</strong>; or(e) publie aeeess and finaneial eontribution iseneouraged. The major investments are likely to oeeurat the start <strong>of</strong> a projeet, but ongoing maintenaneemanagement may be essential for a long time. It iselear that the most eost-effeetive means <strong>of</strong> earrying outthe work will be earried out by or in eo-operation withthe Peat Industry, where the maehinery and expertiseare already on site. Sorne <strong>of</strong> the most reliable gui<strong>de</strong>s toeosting come from NW Germany, where a number <strong>of</strong>bogs have now been prepared for restoration. Thesesuggest that preparation eosts <strong>of</strong> eut-over surfaees arein the region <strong>of</strong> f 200-400 ha- I when appropriateequipment exists on site and f 800-1250 hao! when ithas to be brought in.The eosts assoeiated with restoration can be brokendown un<strong>de</strong>r the following headings:• Land - e.g. purchase <strong>of</strong>site or adjacent land.• <strong>Restoration</strong> procedures and management:(a)(b)(e)personnel;specialist advice;management operations;Table 7.3 Useful consultees in the formulation <strong>of</strong> a restoration scheme (in addition to those given in Table 7.2).SourceLocal Authority Record Office.Local Authority archaeologists or ArchaeologicalTrust; Council for British Arehaeology; localarehaeologieal organisations; wetland arehaeologiealspeeialistsRoyal Commission on Historieal Monuments <strong>of</strong>England; Royal Commission on Historieal Monuments<strong>of</strong> Wales; Royal Commission on Historical Monuments<strong>of</strong> Seotland; Historie SeotlandJoint Nature Conservation CommitleeThe Wildlife Trust Partnership RSNC; Seotlish WildlifeTrust; Ulster Wildlife TrustCouneil for the Proteetion <strong>of</strong> Rural England; Couneilfor the Proteetion <strong>of</strong> Rural Wales.Royal Society for the Proteelion <strong>of</strong> Birds (RSPB),British Trust for Ornithology (BTO) and other nationaland local speeialist bird groupsNational and local specialist invertebrate groups (e.g.Royal Entomological Society; British Entomology andNatural History Society; Balfour-Browne Club; BritishAraehnological Society; British Dragonfly Society;British Butterfly Society; Bees, Wasps and AntsRecording Scheme.)Various other national and local conservation Ispecialist species groupsBiological Records CentreHealth and Safety ExecutiveUtilitiesMeteorological OfficeInstitute <strong>of</strong> HydrologyScientific literature, local journals etc.Local schools and colleges etc.Nature <strong>of</strong> informationCounty Series Ordnance Survey maps. Estate plans. Earlydocuments relating to peat extraction.Site history.Statutory <strong>de</strong>signations e.g. Scheduled Ancient Monuments.Information and advice on archaeological interest and value <strong>of</strong> thesite.Possible practical support for survey and restoration work.Hold the National Archaeological Record, which contains informationon archaeological sites, and the National Building Record, which¡nclu<strong>de</strong>s the National Record <strong>of</strong> Industrial Monuments.Existing records for specific sites (including Invertebrate SiteRegister).Advice on conservation and management for specific speciesExisting records for specific sites.Amenity and wildlife value <strong>of</strong> sites.Advice on restoration methods used in existing restoration schemeson Trust reserves.Landscape, wildlife, and historical <strong>de</strong>tails relating to local sites.Ornithological records for specific local sites.Advice on conservation and management for specific species.Invertebrate records for speeific local sites.Advice on invertebrate conservation and management.Records for specific sites.Wildlife information covering a wi<strong>de</strong> range <strong>of</strong> groups. Speciesevaluation.Health and safety issues <strong>of</strong> the site.Location <strong>of</strong> gas, telephone, electricity, water supply and surface andfoul drainage.Climatic records and information.Information and advice on hydrological aspects.General and specific information on various aspects <strong>of</strong> peatlands,restoration, conservation, site I county records etc. In some cases,such information may be held by conservation I historicallarchaeological groups etc.If a site has been used as an educational resource, unpublishedrecords may be held.


134RESTüRATIüN üF DAMAGED PEATLANDS(d)(e)monitoring and maintenance;archaeological survey and mitigationThese are consi<strong>de</strong>red further below. In sorne instances,financial assistance with the costs may be availablethrough various schemes and organisations [see Table7.5].7.3.2 Land costsThe costs <strong>of</strong> purchasing or leasing land has been amajor consi<strong>de</strong>ration in the conservation <strong>of</strong> several <strong>of</strong>the raised-bog sites in England and Wales, althoughobviously this wil1 not be a consi<strong>de</strong>ration where thework is to be carried out by existing owners oroccupiers, unless the scheme requires control <strong>of</strong>additional land. For example, the National NatureReserve at Fenns and Whixal1 was bought in 1990 at acost <strong>of</strong> f 1.7m (for 137 ha) and f 20,000 is spentannual1yl on rent for the leased land (302.3 ha). Costs<strong>of</strong> land purchase in the Somerset Levels were estimatedto vary from c. f 2,800 to f 10,700 ha-¡ <strong>de</strong>pending onthe amount <strong>of</strong> peat remaining (Hancock, 1991).7.3.3 <strong>Restoration</strong> procedures andmanagement(a) PersonnelMost <strong>of</strong> the major restoration projects in the UKcurrently un<strong>de</strong>rtaken by the statutory conservationagencies involve a full time war<strong>de</strong>n (site manager),with assistance from varying numbers <strong>of</strong> estateworkers. Sorne sites are managed as nature reserves bythe local Wildlife Trusts. Volunteer labour is <strong>of</strong>ienused but it is general1y consi<strong>de</strong>red to be most costeffectiveto leave tasks such as ditch blocking tocontractors or permanent staff using mechanicalmethods, particularly where large scale operations areinvolved. However, even with experienced contractors,consi<strong>de</strong>rable time investment by site managers isusual1y nee<strong>de</strong>d to supervise the work to ensure that it iscarried out to the required specifications and in theright place.(b) Specialist adviceIt is likely to be necessary to involve specialists inor<strong>de</strong>r, for example, to carry out survey work(topographical, biological, hydrologicaI, archaeological);perform chemical analyses <strong>of</strong> water, peat ormineral substrata; interpret the results; assist in thepreparation <strong>of</strong> an appropriate restoration scheme with<strong>de</strong>tailed specifications, and perhaps occasionally toprovi<strong>de</strong> legal advice. This is likely to be relativelyI To be reviewed every three years.expensive; typical consultancy fees may range from< f 100 to f 1000 per day, <strong>de</strong>pending on the type <strong>of</strong>work, and experience necessary to carry it out. Theinformation required should therefore be careful1yi<strong>de</strong>ntified before any such work is commissioned.(e) Management operationsApproximate ranges <strong>of</strong> costs have been summarised fordifferent management operations [Table 7.4], based oninfonnation provi<strong>de</strong>d by site managers, the peatindustry and published information (e.g. Beets, 1993;Edgar, 1993). From these, the approximate potentialcosts <strong>of</strong>sorne restoration measures have been estimatedfor a hypothetical situation <strong>of</strong> a cut-over bog with anadjacent remnant, which could amount to around f140,000-200,000, excluding supervision, survey,monitoring etc. However, it should be recognised thatcosts wil1 inevitably <strong>de</strong>pend heavily on the extent <strong>of</strong>the remedial action required.Machinery, equipment and materialsA variety <strong>of</strong> specialist machinery, adapted for work onboggy terrain (i.e. with low ground pressure) is likelyto be required to carry out the various operationsrequired for restoration (e.g. scrub c1earance, ditchblocking, bunding, surface configuration). The choice<strong>of</strong> machine <strong>de</strong>pends on the task and the operatingconditions. Advice can be appropriately sought fromthe peat industry and the statutory conservationagencies with experience in restoration. It will be mostcost-effective if the work can be carried out as a rol1ingprogramme <strong>of</strong> restoration alongsi<strong>de</strong> ongoing peatextraction, while the machinery is on site. In theabsence <strong>of</strong> appropriate equipment on site, it willusual1y be necessary to hire the machines (and perhapsoperators) from contractors; this is generally moreexpensive than standard agricultural contracting rates.Use <strong>of</strong> inexperienced contractors, although sometimescheaper, is not recommen<strong>de</strong>d as practical experiencesuggests that these lack appropriate expertise andrequire more supervision.For construction <strong>of</strong> peat dams and bunds, the mostcost-effective option is to use the peat in situ, wherethis is available and judged to be sufficiently wel1<strong>de</strong>composed. Excavation and transport <strong>of</strong> peat fromone area to another substantial1y increases costs. It mayalso be necessary to reinforce the dams with animpermeable care, either <strong>of</strong> polythene, plastic-coatedmetal or wood.Irrigation using pumps and piping requires purchase <strong>of</strong>hardware, plus instal1ation and running costs.It may be appropriate to provi<strong>de</strong> boardwalks at sornesites, for example, to facilitate management andmonitoring or to provi<strong>de</strong> public access.


CHAPTER 7: RESTORATION PLANNING135Vegetatíon managementScrub control is <strong>of</strong>ien a major problem <strong>of</strong> vegetationmanagement, either on bog remnants that have driedout, or on abandoned surfaces [10.2]. Depending onstaff and machine availability, this can either be carriedout 'in house' or by using contractors. Costs quotedvaried from c. f. 400 to f. 2,500 ha- I , <strong>de</strong>pending on theamount <strong>of</strong>scrub.Grazing is only practised rarely in bog restorationprojects in the UK, and is not generally consi<strong>de</strong>red tobe economical (i.e. it costs more to maintain andsupervise the tlock than is recouped from sale <strong>of</strong> thewool or meat) although it could be consi<strong>de</strong>red to be acost-effective management tool in certain circumstances,for example, in helping to control scrubinvasion until water levels are sufficiently raised.The active revegetation <strong>of</strong> cut-over areas, by transplantation<strong>of</strong> vegetation etc. [see Chapter 9] should beinclu<strong>de</strong>d in any costed options. This would mainlyinvolve transport and labour costs, but may be as muchas f. 2,000 per ha. Obviously, such procedures requirecareful planning and targetting.(d) Monitoring and maintenanceThe costs <strong>of</strong> monitoring and maintenance will mainlyconsist <strong>of</strong> personnel time, in terms <strong>of</strong> establishing an<strong>de</strong>xecuting the work and taking appropriate remedialaction (which may involve sorne machinery). The costswill <strong>de</strong>pend on the options taken and methods used,and whether the work can be carried out 'in house' ornecessitates the engagement <strong>of</strong> suitably qualifiedspecialists. Assessment <strong>of</strong> monitoring costs shouldinelu<strong>de</strong> provision for regular data analysis andinterpretation. [see also Chapter 11].7.3.4 Financial assistanceFinancial assistance with the costs <strong>of</strong> restoration <strong>of</strong> cutoverbogs may be available from a variety <strong>of</strong> sources.These should be investigated as part <strong>of</strong> the feasibilitystudy, as they may have consi<strong>de</strong>rable bearing on whatis financially practicable. Eligibility for assistance<strong>de</strong>pends on such factors as ownership; <strong>de</strong>tails <strong>of</strong>planning conditions; conservation status (whether SSSIetc.); proximity to water or impact on water resources;presence <strong>of</strong> specially-protected species or habitats;whether located within <strong>de</strong>signated areas etc. The applicability<strong>of</strong> each scheme will <strong>de</strong>pend on the precise circumstances,and will usually be consi<strong>de</strong>red on merit.Specific <strong>de</strong>tails and qualifying conditions are availablefrom the organisations concerned [see Table 7.5].In certain cases it has been, or may prove, necessary tocompensate owners for loss <strong>of</strong> revenue from a site, forexample as a consequence <strong>of</strong> terminating peatextraction before a previously agreed limit; orprevention <strong>of</strong> land improvements, either on the siteitself, or on adjacent land (as on certain SSSI's). Thistranslates into income for the owners concerned.Table 7.4 Approximate ranges <strong>of</strong> costs for selected restoration techniques used on lowland peatlands. These aremainly based on examples from a survey carried out in 1991-1992, using information provi<strong>de</strong>d by site managersand the peat industry.Operation Methods Range <strong>of</strong> costs Example potential costs for50 ha site with 45 ha cutover(milled) + 5 ha remnant*Bunding <strong>of</strong> remnant Peat embankments (in situ peal) f. 1.8-6 m- 1 f. 2,160 - 7,200Peal embankmenls (imported peal) f. 2-40 m- 1 f. 2,400 - 48,000Peat + plaslic membrane f. 15-45 m- 1 f. 18,000-54,000Ditch blocking (inclu<strong>de</strong>s Wi<strong>de</strong>, palisa<strong>de</strong> limber dams < f. 380 each as approprialeoperator I inslallalion steel sheel dams c. f. 2.50 each as approprialecosls etc.) peat dams f. 9-12 each f. 9,000-12,000 (for 1000 dams)dilch infilling f. 0.67- c. f. 30 m- 1 as appropriateSurface configuralions Surface levelling, forming shallow f. 200-1,250 ha- 1 f. 9,000-56,250bunds <strong>of</strong> peal and compacling,(may inclu<strong>de</strong> transport <strong>of</strong> peal)Scrub conlrol By hand or machine (may inclu<strong>de</strong> f. 400-2,500 ha- 1 as approprialechemicallrealments)Transplanlalion <strong>of</strong> < f. 2,000 ha- 1 < f. 100,000vegetation• Assuming division <strong>of</strong> lhe cul-over ¡nlo 9 pol<strong>de</strong>rs <strong>of</strong> 5 ha, and 1200 m perimeler <strong>of</strong> remnanl; wilh some damming <strong>of</strong> drainagedilches.


136 RESTORATlüN 01' DAMAGED PEATLANDSTable 7.5 Possible sources <strong>of</strong> financial or practical assistance for restoration schemes.OrganisationStatutory nature conservation agenciesWater resources bodies (NRA etc.)English Heritage I Historic Scotland ICadw/local authority archaeologistNon-governmental conservation bodies(e.g. RSNC I RSPB I BTO)Local community groups I BTCVPeat Industry Iland ownersCountrysi<strong>de</strong> CommissionMAFF I DANII DAFSEuropean UnionType <strong>of</strong> assistance possibly availableManagement agreements (on SSSl's I ASSl's)Grant aid (un<strong>de</strong>r the Wildlife and Countrysi<strong>de</strong> Act I Town and Country Planning Act)for restoration work through schemes such as Wildlife Enhancement Scheme orSpecies Recovery Programme. Potential for co-operative venturesPractical assistance with machinery etc.Practical assistance with e.g. archaeological survey and mitigation.May provi<strong>de</strong> help with specific projects, for example survey and monitoring.May provi<strong>de</strong> help with specific projects (including volunteer labour)Potential for co-operative ventures, help with machinery etc.Possibility <strong>of</strong> contributions from <strong>de</strong>velopers to longer-term management throughSection 106 obligations un<strong>de</strong>r the Town and Country Planning Act, 1990.Countrysi<strong>de</strong> Stewardship Scheme-<strong>of</strong>fers incentives for positive conservationmanagement in selected landscapes, including watersi<strong>de</strong> landscapes. May beapplicable to enhancement <strong>of</strong> existing vegetated areas (on and <strong>of</strong>f site), but wouldnot be applicable to restoration un<strong>de</strong>r planning conditions. Individual casesconsi<strong>de</strong>red on merit.Environmentally Sensitive Areas scheme (ESA). The <strong>de</strong>signation is <strong>de</strong>signed toensure that traditional farming practices are continued within the area concerned,with financial incentives <strong>of</strong>fered to farmers not to intensify their agricultural practice.Although not directly applicable to restoration <strong>of</strong> recently cut-over bog, the schemecould inclu<strong>de</strong> the raising <strong>of</strong> water levels on adjacent agriculturalland.Funding may be available for selected restoration projects; relevant schemes mayvary annually.·7.4 Preliminary collation <strong>of</strong>information (<strong>de</strong>sk studies)7.4.1 Cartographic <strong>de</strong>tailsExamination <strong>of</strong> maps will help to put a peatland siteinto its overall topographical, historical, industrial,geological and land-drainage setting. Features whichmay be <strong>de</strong>termined by examination <strong>of</strong> various mapsinelu<strong>de</strong> the following:• geology and soils;• topography;• main land drainage pattems and water courses(<strong>de</strong>tailed site drainage will not normally be shown);• infrastructure, buildings, access roads etc.;• information on the historic and industrial landscapeand structures;• natural features <strong>of</strong>the site boundary.Sources inclu<strong>de</strong> Ordnance Survey, Soil Survey andGeological Survey maps.Examination <strong>of</strong> a series <strong>of</strong> maps <strong>of</strong> different ages canbe valuable in helping to establish the history <strong>of</strong> thesite, particularly with respect to land-use changes.These inclu<strong>de</strong> Tithe Maps, 1st edition OrdnanceSurvey, Enelosure Maps, Manorial Maps. 1t should,however, be noted that cartographers have not alwayssurveyed peatland areas in <strong>de</strong>tail and sorne maps <strong>of</strong>peatlands may have limited accuracy. Moreover,successive Ordnance Survey revisions do not alwaysinelu<strong>de</strong> changes to the character <strong>of</strong>sorne peatland sites.Soil and geology maps may help to put the site in aregional and local context, for example, in establishingthe original extent <strong>of</strong> the peat body, <strong>of</strong> which the sitemay form only a small parto This may influence<strong>de</strong>cisions on the best restoration strategy, for examplewhether it would be <strong>de</strong>sirable or feasible to try tomanage the entire peat area as a whole. At sorne sites,information shown on these maps may proveinsufficiently <strong>de</strong>tailed, and, if required, plotting aprecise boundary <strong>of</strong> the peat body is likely to requirefurther investigation in the field.The amount <strong>of</strong> information that can be obtained frommaps with direct value to peatland restoration is <strong>of</strong>ienstrictly limited. For example, geological and soil mapsmay provi<strong>de</strong> some useful background information onpossible factors that may influence restorationmanagement (e.g. . type <strong>of</strong> bedrock surrounding andun<strong>de</strong>rlying the site), but in general do not provi<strong>de</strong>information concerning, for example, the nature <strong>of</strong> thesubstratum beneath the bogo In these situations it isimportant to substantiate the information <strong>de</strong>rived frommaps with chemical analyses <strong>of</strong> the soils (see below)


CHAPTER 7: RESTORATION PLANNING137and, in most cases, any important influences will needto be substantiated by appropriate field investigations.7.4.2 Use <strong>of</strong>aerial photographsAerial photographs are important aids to sitecharacterisation and, when time-series photographs areavailable, may perrnit <strong>de</strong>termination <strong>of</strong> the effects <strong>of</strong>recent activities on site. They are also useful inupdating cartographic information and for locatingfeatures not readily evi<strong>de</strong>nt on the ground, such as oldpeat cuttings and forrner drainage ditches, whichalthough occlu<strong>de</strong>d, may still retain sorne drainagefunction. Aerial photographs are also useful ini<strong>de</strong>ntifying vegetational features and boundaries. Forexample they may help to locate open areas otherwisehid<strong>de</strong>n within <strong>de</strong>nse scrub. They thereby provi<strong>de</strong> animportant aid to ground survey work and if possiblerecent photographs should be ma<strong>de</strong> available to fieldworkers.7.4.3 Ownerships and tenanciesLocal occupants <strong>of</strong> the site and adjoining land shouldbe consulted and involved at an early stage in theplanning <strong>of</strong> any restoration project, particularIy wheretheir land may be affected by the restoration scheme.They may also provi<strong>de</strong> a valuable source <strong>of</strong> localinforrnation. ]n addition, in sorne sites, it may benecessary to obtain perrnission to cross land, forexample for vehicular access to the site duringrestoration procedures. It is therefore important that therelevant <strong>de</strong>tails (e.g. name, address, land affected) arecollated.7.4.4 Current management regimesand general site historyWhen possible, inforrnation should be gathered fromsite occupants on the current land-use and managementpractices on different areas <strong>of</strong> the site so that these canbe incorporated into the restoration strategy, whereappropriate, or possible constraints on <strong>de</strong>velopmenti<strong>de</strong>ntified.Inforrnation on the land use history <strong>of</strong> a site, includingprevious management regimes, can sometimes begleaned by examination <strong>of</strong> maps, aerial photographs,literature and local sources etc. Although not criticalfor assessing restoration options, the inforrnation canprovi<strong>de</strong> valuable insights into the site. For example itcan be used to chart the changing layouts <strong>of</strong> peatextraction operations, and help to date different cutoverareas. Such data are crucial to the archaeological,historical or industrial background <strong>of</strong>a site.7.4.5 Hydro/ogical informationAvailable existing information relating to climate,regional and local water resources, 'un<strong>de</strong>sirable' waterinputs etc. should be collated and assessed.Climatic data can be obtained from the MeteorologicalOffice and from published sources and maps (e.g.Sm ith, 1976). The most important factors are rainfalland potential evapotranspiration, particularIy duringthe summer. The presumed relevance <strong>of</strong> meteorologicaldata to individual bog sites is related to theproximity <strong>of</strong> the recording station, but in many cases itwill be a<strong>de</strong>quate to provi<strong>de</strong> a broad outline <strong>of</strong>the Iikelyc1imatic conditions, although it is not possible tospecify critical threshold amounts [see Chapter ]].It is important to set each site in its local and regionalhydrological context, in terrns <strong>of</strong> potential effects onboth water inputs and outputs, for example,consi<strong>de</strong>ring availability <strong>of</strong> water for supplementarysupply, possible constraints imposed by flood <strong>de</strong>fenceor water abstraction. This is particularly important inareas such as the Somerset Levels where peat workingsmay be below regional groundwater levels, and areaswhere it is thought that there may be sorne connectivitybetween the perched water mound in the bog andregional groundwater levels. ]nformation and adviceconcerning local and regional water resources will beavailable from the water resources bodies (e.g. NRA).7.4.6 Wildlife conservation andarchaeo/ogical interestExisting records concerning the wildlife conservation,archaeological and palaeoecological interest <strong>of</strong>peatland sites can be collated from the sourcesi<strong>de</strong>ntified in Tables 7.2 and 7.3. Available data arelikely to vary consi<strong>de</strong>rably in quantity and quality, butmay provi<strong>de</strong> sorne useful background inforrnation andinsights, for example concerning former conditions orspecies on the site.7.4.7 PotentiaI legal and land-useconstraints on <strong>de</strong>ve/opmentThe relevant legislation (international, national andlocal) which may affect <strong>de</strong>velopment should beinvestigated and its implications for restoration optionsset down. The most important areas to be consi<strong>de</strong>redconcern legislation relating to planning, conservationand water resources. Further <strong>de</strong>tails are provi<strong>de</strong>d inAppendix 2.Planning legislationPeat is classed as a mineral un<strong>de</strong>r planning law and issubject to the same planning requirements as any other


138RESTORATION OF DAMAGED PEATLANDSextracted mineral. Peat extraction requires planningpermission, which may place conditions on workingpractices and specify after-use and after-care. It isimportant therefore that the <strong>de</strong>tails <strong>of</strong> any planningpermissions are known, including the preciseboundaries <strong>of</strong> the area affected and the implications <strong>of</strong>any specified conditions.Wildlife and conservation legislationAlthough one <strong>of</strong> the main aims <strong>of</strong> the restorationschemes consi<strong>de</strong>red in this document will usually be tomaintain and enhance the conservation 'value' <strong>of</strong> asite, it should be recognised that aH operations must becarried out with due regard to current conservationlegislation. For example, there may be certain restrictionson the work that can be carried out withoutconsent from the statutory conservation agencies andthere may be circumstances where a cont1ict <strong>of</strong>conservational interest needs to be resolved (forexample, where a statutorily-protected species <strong>of</strong> birdoccurs in an area which would be disturbed throughrestoration operations). It is important that the relevantagencies are consulted about these aspects beforecarrying out any work.Particular care should be taken where operations beingcarried out may directly or indirectly affect any <strong>of</strong> thefollowing:• Species specially protected un<strong>de</strong>r the Wildlife andCountrysi<strong>de</strong> Act 1981 (as updated and amen<strong>de</strong>d);• National Nature Reserves;• Sites or Areas <strong>of</strong> Special Scientific Interest (SSSI /ASSI);• SpeciaI Areas <strong>of</strong>Conservation (SAC sites)• Ramsar sites;• Special Protection Areas (SPA's);• Environmentally Sensitive Areas (ESA's);• National Parks;• . Areas <strong>of</strong> Outstanding Natural Beauty;• Heritage Coasts;• Public Rights OfWay;• Scheduled Ancient Monuments;• Listed Buildings;• Local Nature Reserves;• Any further sites <strong>of</strong> environmental, archaeologicaI orgeological interest, such as those i<strong>de</strong>ntified by LocalAuthorities and those owned/managed by the NationalTrust or voluntary conservation bodies.Legislation relating to water resourcesFor any proposed restoration schemes which mayimpact upon water resources (e.g. blocking or divertingwater courses; impounding, discharging or pumpingwater), the bodies with responsibility for thoseresources (e.g. National Rivers Authority, InternalDrainage Boards, River Purification Boards, DoE-NI)must be consulted at an early stage in the planningprocess, as there are several areas in which they mustbe specifically involved:(a) Impoundment <strong>of</strong> water; bloeking or divertingwater eoursesA water impoundment licence is required to impoundwater, for example if 'on-stream' water is impoun<strong>de</strong>dor an existing water course is blocked or diverted toprovi<strong>de</strong> water for an impoundment.Regulations also impose safety provisions on reservoirsor artificial lakes not used for water supply purposesthat retain more than 25,000 m 3 <strong>of</strong> water aboye the'natural level' <strong>of</strong>any part <strong>of</strong>the adjoining land or havea dam higher than 4.5 m. The intention <strong>of</strong> this is toensure that there is no potential danger to Jife orproperty through the sud<strong>de</strong>n release <strong>of</strong> water due to thecatastrophic failure <strong>of</strong> the retaining structures. Thevolume <strong>of</strong> water specified is equivalent to c. 4.5 hat100<strong>de</strong>d to 50 cm <strong>de</strong>pth. lt is therefore possible thatparts <strong>of</strong> sorne restoration schemes may fall un<strong>de</strong>r theprovisions <strong>of</strong> the legislation, where the intention is tocreate large lagoons, in which case it is recommen<strong>de</strong>dthat advice is sought from a qualified engineer.(b) Abstraetion <strong>of</strong>waterConsent is nee<strong>de</strong>d to abstract water either from water .courses or groundwater.(e) Diseharge <strong>of</strong> waterIn sorne circumstances it will be necessary to makeprovision for the discharge <strong>of</strong> water from a bogo Thiswill usually require a certificate giving the Consen! !oDischarge, unless drainage rights already exist.Situations where this may apply inclu<strong>de</strong> the provision<strong>of</strong> specific outfalls from a bog and pumping <strong>of</strong>enriched water from a lagoon. It is necessary to provi<strong>de</strong><strong>de</strong>tails <strong>of</strong>the quality <strong>of</strong>the water to be discharged.(d) Works affeeting land drainageAny works which interfere with existing drainagerequire Land Drainage Consent. This inclu<strong>de</strong>s thebuilding <strong>of</strong> any constructs on or adjacent to watercourses, the diversion <strong>of</strong> any streams around a bog andthe potential for causíng t100ding <strong>of</strong> land not within thesite. Details <strong>of</strong> the proposed work must be notified tothe water resource bodies, who, before issuingconsents, mustbe satisfied that either the works willnot adversely affect drainage on land owned by thirdparties or that those third parties agree to accepting theconsequences <strong>of</strong>the proposals.


CHAPTER 7: RESTORATION PLANNING139Miscellaneous legislationAdherence to health and safety legislation should forrnpart <strong>of</strong> the requirements for any work carried out inconnection with restoration works.Searches should also be ma<strong>de</strong> for possible constraintssuch as cO,mmon land, turbary rights, rights <strong>of</strong> way,riparian rights, mineral rights, shooting rights, grazingrights, location <strong>of</strong> public utilities such as gas pipes,electricity pylons etc. The implications <strong>of</strong> any suchconstraints for the project should be assessed.7.4.8 SummaryA preliminary examination and summary assessmentshould be ma<strong>de</strong> <strong>of</strong> the inforrnation gathered by the<strong>de</strong>sk study in or<strong>de</strong>r to i<strong>de</strong>ntify its nature and usefulnessand where further <strong>de</strong>tails are nee<strong>de</strong>d, in or<strong>de</strong>r t<strong>of</strong>acilitate the planning <strong>of</strong>further work.7.5 Field investigations7.5.1 IntroductionThe aim <strong>of</strong> field investigations is to build on datagathered in the preliminary <strong>de</strong>sk-study, enabling aH therelevant options to be consi<strong>de</strong>red in the forrnulation <strong>of</strong>an appropriate restoration strategy. Suggestions <strong>of</strong> thetype <strong>of</strong> inforrnation which may be gathered is outlinedin Table 7.1 and consi<strong>de</strong>red in further <strong>de</strong>tail below.This is inten<strong>de</strong>d as a gui<strong>de</strong> to possible field investigationsthat may be nee<strong>de</strong>d at sorne sites, rather than aprescriptive list. It is recommen<strong>de</strong>d that 'hard' dataacquisition is focused upon inforrnation that is specificaHynee<strong>de</strong>d, rather than upon a general 'wish-Iist' <strong>of</strong>inforrnation that may be <strong>of</strong> interest, and that it issufficiently well resourced and perforrned byexperienced practitioners who, when appropriate, areaware <strong>of</strong>the likely limitations <strong>of</strong>their studies [see 7.2].Appropriate field investigations are an essentialrequirement <strong>of</strong> site assessment and may require theservices <strong>of</strong> various specialists. On-site investigationwiH allow the various specialists to familiarisethemselves with the site and, when appropriate, to mapdata which they collect. AH field workers should workwith the same base maps if possible and preferablyrecord data on topographical survey plans <strong>of</strong> the site.Locations <strong>of</strong> aH transects, sample points etc. should berecor<strong>de</strong>d on the base maps. Assessments <strong>of</strong> any healthand safety measures which need to be taken should bema<strong>de</strong> and action implemented to protect field workersprior to field work commencing.Surveys <strong>of</strong> the site must necessarily gather inforrnationon a wi<strong>de</strong> range <strong>of</strong> topics, but these inter-relate to alarge extent. For example, inforrnation on thetopography <strong>of</strong> the site would be required to assess thecurrent and future hydrological regimes; in theplanning <strong>of</strong> any earth-works and as an archaeologicalrecord. It is thus <strong>de</strong>sirable to co-ordinate the efforts <strong>of</strong>different interested parties into an integrated approachto the site investigation. The advantages <strong>of</strong> this inclu<strong>de</strong>the foHowing:• avoids unnecessary duplication and overlap (andtherefore reduces costs);• optimises the information gathered by each survey team,to provi<strong>de</strong> input for other specialisms;• minimises disturbance or damage to sensitive areas <strong>of</strong> thesite;• promotes on-site discussions between various specialists<strong>of</strong> the various restoration options and means <strong>of</strong>achievement;• allows the early i<strong>de</strong>ntification <strong>of</strong> any potential problemsor areas <strong>of</strong>conflict <strong>of</strong> interests.7.5.2 Site physical characteristicsA broad survey <strong>of</strong> the topography and physicalcharacteristics <strong>of</strong> the site should be carried out toobtain inforrnation on the following factors, whenconsi<strong>de</strong>red necessary and if not already -available insufficient <strong>de</strong>tail from existing documentation:• general size and shape; extent <strong>of</strong> site in relation to wholepeat body;• surface and subsurface topography; peat <strong>de</strong>pths;• geology and soils un<strong>de</strong>rlying and surrounding the site;• access for machinery and equipment;• location <strong>of</strong> existing tracks, pathways, boundaries,buildings and other structures; location <strong>of</strong> potentialhaúrds (e.g. rubbish tips).These aspects are discussed below. A general plan <strong>of</strong>the site should be ma<strong>de</strong>, and relevant features mapped.General size and shape; extent <strong>of</strong> site inrelation to whole peat body.In most cases the exact boundaries <strong>of</strong> the site un<strong>de</strong>rconsi<strong>de</strong>ration will have already been established, butoccasionaHy there may be a need for sorne verificationand accurate mapping. The establishment <strong>of</strong> at least theapproximate boundaries <strong>of</strong>the peat body wiH allow thesite to be put into context [7.4.1]. In most cases it willbe necessary to supplement information from existingmaps with at least sorne field investigation to enablethe plotting and provision <strong>of</strong> reasonably accurate maps<strong>of</strong> the site boundaries for further reconnaissance work.The potential for buffer zones can also be assessed atthis stage.


140RESTORATION OF DAMAGED PEATLANDSSuñace and sub-suñace topography; peat<strong>de</strong>pths(a) Disposition <strong>of</strong>peat fie/ds in re/ation to eaehother and any upstanding areasI<strong>de</strong>ally, the <strong>de</strong>tailed topography <strong>of</strong> the peat fields andany uncut areas should be carefully mapped andlevelled to Ordnance Datum to facilitate the planning<strong>of</strong> a <strong>de</strong>tailed restoration scheme. For example, it willhelp to i<strong>de</strong>ntify any 'massif areas [2.1]; i<strong>de</strong>ntify theneed and potential for any buffer zones [8.3]; allowpredictions to be ma<strong>de</strong> <strong>of</strong> the movement or collection<strong>of</strong> water; facilitate the optimal siting <strong>of</strong> water controlmeasures such as dams and bunds and provi<strong>de</strong> a record<strong>of</strong> the historical and industrial land surface. Thepotential value <strong>of</strong> existing baulks etc. as water-holdingstructures should be assessed l .It may also be important to <strong>de</strong>termine subsurfacecontours, as this can have implications for therewetting strategy, for. example, when there is morethan one basin, or when the subsoil slopes in aparticular direction. In most cases the surface contourscan be measured using standard pr<strong>of</strong>essional surveyingtechniques. Subsurface contours can be measured inrelation to the surface with peat coring equipment,augers or ground-penetrating radar. Sampling shouldbe carried out using a combination <strong>of</strong> Iíne transects andgrids, plus examination <strong>of</strong> pr<strong>of</strong>iles where, for exampledrains have already been cut into the sub-soil. This willalso provi<strong>de</strong> the necessary information on peat <strong>de</strong>pths.(b) Re/ationship to surroundingsThe general disposition <strong>of</strong> the site in relation to thesurrounding land is important in assessing possibleimpacts both from and on the adjoining land. Forexample, the potential for inputs <strong>of</strong> minerotrophic orpolluted water is greater if any <strong>of</strong> the exposed peatsurfaces líe below the level <strong>of</strong>the surrounding land, butit may be easier to retain water on the site. Conversely,if the site forms an upstanding block in relation to itssurroundings, it will increase the problems <strong>of</strong> waterretention, and potential for flooding <strong>of</strong> adjoining land,but ensure that the only water inputs are atmospheric.(e) Peat <strong>de</strong>pthsThe data available from the survey <strong>of</strong> the surface andsubsurface contours will allow i<strong>de</strong>ntification andassessment <strong>of</strong>:• <strong>de</strong>pth <strong>of</strong>peat remaining;• areas with the most complete peat stratigraphical andpalaeoenvironmental record;I The efficacy <strong>of</strong> the baulks as bunds will <strong>de</strong>pend on their size,intactness, <strong>de</strong>gree <strong>of</strong> <strong>de</strong>hydration and humification <strong>of</strong> the peat, andits bulk <strong>de</strong>nsity.• areas where drains or peat extraction has exposed mineralsoil;• potential availability <strong>of</strong> peat for bunding, ditch blockingetc.Where possible the recording <strong>of</strong> peat <strong>de</strong>pths should beaccompanied by sorne assessment <strong>of</strong> the peat types[7.5.5].Geology and soils un<strong>de</strong>rlying and surroundingthe sitePublished geology (solid and drift) and soil mapsprovi<strong>de</strong> sorne information to put a site into its regionaland local context [7.4.1] but <strong>of</strong>ten the amount <strong>of</strong>information <strong>of</strong> direct value to restoration is strictIylimited and, in those situations where it is consi<strong>de</strong>redimportant, it may be necessary to supplement theinformation <strong>de</strong>rived from maps by on-site survey.Consi<strong>de</strong>ration <strong>of</strong> the geology may be particularIyimportant when it is suspected that otherwiseunexplained water losses may be caused by verticalseepage through the peat into a permeable substratum.If this is suspected, expert hydrogeological adviceshould be sought to assess the likely impact onrestoration measures.More <strong>de</strong>tailed survey may also help to indicate thepotential for mineral enrichment <strong>of</strong> water supplies(although this should also be substantiated by chemicalanalyses <strong>of</strong> the soils) and provi<strong>de</strong> locational information<strong>of</strong> palaeochannels for palaeoenvironmentalanalysis.Access for machinery and equipmentFor most restoration schemes it will be necessary tomaximise the use <strong>of</strong> machinery and equipment incarrying out management operations such as ditchblocking, bund building and scrub clearance. The fieldreconnaissance should therefore:• i<strong>de</strong>ntify access routes for machinery <strong>of</strong> different types (atleast those potentially available) including light railways;• i<strong>de</strong>ntify areas where passage <strong>of</strong> machinery would bedamaging to biological interest.The strategy adopted should take into account theaccessibilíty <strong>of</strong> different areas <strong>of</strong> a site to differentequipment, both before and after rewetting. Theplanning <strong>of</strong> operations will also need to take intoaccount the possible climatic constraints on the use <strong>of</strong>machinery at different times <strong>of</strong>the yearLocation <strong>of</strong> existing featuresFeatures such as tracks, pathways, boundaries,buildings and other structures, location <strong>of</strong> potentialhazards (e.g. rubbish tips) should be carefulIy recor<strong>de</strong>don the base maps, where not already documented.


CHAPTER 7: RESTORATION PLANNING1417.5.3 Land useWhere information has not been available from thepreliminary '<strong>de</strong>sk study', or proves insufficient, the siteand adjacent land should be surveyed to assess:• current management activities (e.g. grazing) which mayaffect the options for restoration;• risk <strong>of</strong> nutrient enrichment from agricultural actívitíes(either through water or air) and assessment <strong>of</strong> possibleremedial action that may be necessary (e.g. catch·waterdrains, shelter belts, diversion <strong>of</strong> polluted streams);• potential damage to adjoining land caused by raisingwater levels in the bog;• possible constraints on restoration options and potentialfor change <strong>of</strong> land-use in adjacent areas to onesympathetic to wetland conservation and restoration, orthe provision <strong>of</strong> buffer zones (through purchase,management agreements, ESA schemes etc.).7.5.4 HydrologyIntroductionThe maintenance <strong>of</strong> an ombrotrophic environmentrequires that the input <strong>of</strong> water from precipitation mustequal or exceed the water losses (at least on an annualbasis). The major problem for the restoration <strong>of</strong> mostdamaged raised bogs is the lack <strong>of</strong> an a<strong>de</strong>quate andconsistent ombrotrophic water supply at or near thepeat surface to sustain the growth <strong>of</strong> peat-buildingSphagna.In sorne situations a mainly empirical approach torestoration <strong>of</strong> suitable hydrological conditions may besufficient for effective restoration [7.2]. However, inor<strong>de</strong>r to formulate the most appropriate and costeffectiveremedial strategy it is important to <strong>de</strong>terminethe main causes <strong>of</strong> dry conditions [see Chapter 2], toi<strong>de</strong>ntify the main factors which affect the water inputsand outputs in different areas <strong>of</strong>the mire and to put thesite into its local and regional hydrological context.Available information collated as part <strong>of</strong> the <strong>de</strong>sk study(see aboye) can be supplemented as required by furtherinvestigations and measurements, as outlined below.It is recommen<strong>de</strong>d that expert hydrological advice issought on the level <strong>of</strong> <strong>de</strong>tail required for an a<strong>de</strong>quatehydrological assessment <strong>of</strong> a site. Information whichmay be required could inclu<strong>de</strong> the following (at leastthose items marked * are likely to be nee<strong>de</strong>d for mostprojects):• c1imatic information*;• <strong>de</strong>tails <strong>of</strong>water courses* (type, distribution, slope, <strong>de</strong>gree<strong>of</strong>functíoning);• water outputs*;• topographical disposition <strong>of</strong> peat fields*and remnants*;peat <strong>de</strong>pths* and sub-surface contours;• peat hydraulic conductivity;• vegetation characteristics;• distribution and stability <strong>of</strong> open water*;• potential for water supply;• local and regional context <strong>of</strong>the site.(i) Climatic informationConstruction <strong>of</strong> <strong>de</strong>tailed water budgets for a site orhydrological mo<strong>de</strong>lling may require more localisedinformation than that available from publishedmeteorological records, as conditions on site may varyfrom those recor<strong>de</strong>d sorne distance away, particularlyin situations <strong>of</strong> varying topography. The most relevantdata inclu<strong>de</strong>seasonal variations in rainfall, temperatureand evapotranspiration.(U)Reconnaissance <strong>of</strong> drains and watercourses. A reconnaissance survey should be carried out <strong>of</strong> alldrains and water courses impacting upon the site(including those outwith the site), and a map producedshowing direction <strong>of</strong> flow; slope; <strong>de</strong>gree <strong>of</strong>functioning; main outfalls and inputs; whether cutthrough to mineral subsoil and whether thought to beintroducing minerotrophic or polluted water on to thesite. This should inclu<strong>de</strong> drains which are apparentlyalready occlu<strong>de</strong>d by vegetation and also a generalassessment <strong>of</strong> any 'buried' cross drains (usually slitdrains or mole drains) across peat fields or cuttings.Aerial photographs can be an invaluable source <strong>of</strong><strong>de</strong>tail, particularly when trying to trace old drains andwater courses. Potential impacts <strong>of</strong> external drains andwater courses on the site should be noted, in terms <strong>of</strong>both water outputs and as potential sources <strong>of</strong> inputs(where appropriate).This information can be used to prioritise ditchblocking operations and, at least in the initial stages,may be useful for achieving the optimum dispersion <strong>of</strong>water around the site. Note, however, that operatives <strong>of</strong>the peat industry <strong>of</strong>ten have a good workingknowledge <strong>of</strong>the characteristics <strong>of</strong> the drainage systemand consultation may be advantageous.Measurement <strong>of</strong>the mean altitu<strong>de</strong> <strong>of</strong>the water levels inthe main drains and around the margins <strong>of</strong> the site canhelp to predict possible water draw-down effects.(iii) Water outputsReconnaissance <strong>of</strong> water cour.ses (see aboye) shouldprovi<strong>de</strong> information conceming the most obvious waterlosses from the sites. However, where appropriate, andpossible, more indirect causes <strong>of</strong> <strong>de</strong>hydration shouldalso be i<strong>de</strong>ntified and assessed. This inclu<strong>de</strong>s possibleconnectivity between the perched water mound andregional water tables; leakage through the base <strong>of</strong> themire; losses through cut edges etc.


142RESTORATION OF DAMAGED PEATLANDSFor sites cUlíently being pllmp-drained, valuableinformation catl be obtained from the pumping records.It may be useful to carry out sorne simple pump testsun<strong>de</strong>r different conditions.(iv) Dispositíon <strong>of</strong>peat fields and remnants,peat <strong>de</strong>pths and subsurface contoursThese features should be i<strong>de</strong>ntified by the topographicsurvey (see aboye) and will be useful in <strong>de</strong>tennininglikely pattems <strong>of</strong>water distribution across the mire andpotential for increasing water retention. For example,in any damaged peatland, particularly where thesurface topography is uneven, it is probab\e that therewill be areas where water naturally collects. Theseareas should be i<strong>de</strong>ntified and the infonnationincorporated into the <strong>de</strong>sign <strong>of</strong> any 'engineering'works (constrllction <strong>of</strong> bunds etc.). Although suchareas may be i<strong>de</strong>ntified from the topographical survey,if carried out in sufficient détail, an empirical approachwiII confirm whether the areas do in fact hold water.The areas are likely to be most evi<strong>de</strong>nt after a period <strong>of</strong>heavy rainfal!.(v) Peat hydraufic conductivityMeasurements <strong>of</strong> peat hydraulic conductivity can beuseful in several different contexts associated withhydrological mo<strong>de</strong>lling [Box 7.1]:• prediction <strong>of</strong> (potential) perched water mounds withinrellllively 'inlact' peat remnanls [Chapter 1];• prediction <strong>of</strong> the rates at which water is lost tllrough peatin different areas (e.g. edges <strong>of</strong> remnants, through baulksor lhe basallayer <strong>of</strong>peal);• prediction <strong>of</strong> the draw-down in potential buffer zones,and hence calculation <strong>of</strong>an appropriate buffer zone width[8.3];• prediction <strong>of</strong> the effects <strong>of</strong> different peat extraction ormanagement operations.For such measurements and predictive hydrologicalmo<strong>de</strong>Iling [Box 7.1], it will usually be necessary toemploy the services <strong>of</strong> a competent hydrologist. Itshould, however, be recognised that good-qualityhydrological data (such as meaningflll estimates <strong>of</strong>actual values <strong>of</strong> hydraulic conductivity) may be bothdifficlllt and expensive to obtain.(vi) Vegetation characteristics anddistribution <strong>of</strong> open waterA field survey <strong>of</strong> the vegetation [7.5.6] wiII provi<strong>de</strong>infonnation on the distribution <strong>of</strong> different vegetationtypes across the site, together with open water and bareground. This may facilitate some assessment <strong>of</strong> likelyevapotranspirative losses and water storage characteristicsin different areas should the information berequired for hydrological studies. It is known, forexample, that summer evapotranspirative losses areBox 7.1Hydrological mo<strong>de</strong>llingVarious hydrological mo<strong>de</strong>ls are available which can be usedto explore the hydrodynamics <strong>of</strong> peatlands, including: anassessment <strong>of</strong> the hydrological relationships between bogremnants and their surroundings; hydrological relationshipsbetween different areas on a site; inler-relalionships belween.the hydrodynamics <strong>of</strong> the bog and local and regional walertables; calculation <strong>of</strong> the appropriate width <strong>of</strong> buffer zones andprediclion <strong>of</strong> lhe outcome <strong>of</strong> various operations (including peatextraction and management techniques) bolh on sile and onadjacent land.Sorne <strong>of</strong> lhe available hydrological mo<strong>de</strong>ls are mostappropriate to relatively simple, uniform bog sites such aslhose which retain much <strong>of</strong> lheir original dome. In suchsituations 'simple' 'groundwater mound' mO<strong>de</strong>ls can, subject lovarious constraints, help to predict, for example (a) the effectsthat reduction <strong>of</strong> the area <strong>of</strong> a raised bog will have upon thewater level in the remnant; or, conversely, (b) to estimate thebasal area required to sustain a given 'groundwaler' moundheighl. However, many damaged raised-bog sites are veryheterogeneous in character, with cuttings, baulks, remnantsand ditches etc., <strong>of</strong>ten at various altitu<strong>de</strong>s and perhaps withvarying (and usually unknown) hydraulic conduclivilies). Hereapplication <strong>of</strong> 'simple' mo<strong>de</strong>ls is particularly difficull, nol leastbecause the assumptions <strong>of</strong> sorne mo<strong>de</strong>ls are inapplicable orbecause 'calibration' <strong>of</strong> sorne <strong>of</strong> their parameters may nol befeasible. In such circumslances, finile element groundwalermo<strong>de</strong>ls may potenlially be more useful than lhe simpler'groundwater mound' mo<strong>de</strong>ls, as they are more flexible, canlake into accounl more easily variabilily in paramelers andmay be able to predict changes as a result <strong>of</strong> differentdisturbance or management activities. In addition, sorne canconsi<strong>de</strong>r variables such as the acrolelm properties and, inparticular, run-<strong>of</strong>f and overland-f1ow elements that representlarge losses lo raised-bog syslems in winter. Such mo<strong>de</strong>ls are,however, very 'dala hungry' and have not been wi<strong>de</strong>ly testedin peatlands.11 is beyond the scope <strong>of</strong> this report to provi<strong>de</strong> gui<strong>de</strong>lines onthe most appropriale mo<strong>de</strong>ls and methods, not least becauselhese are still being refined. The choice <strong>of</strong> mo<strong>de</strong>l largely<strong>de</strong>pends on the purpose <strong>of</strong> lhe mo<strong>de</strong>lling, lhe level <strong>of</strong> <strong>de</strong>tailrequired, lhe resources available and the amount (and quality)<strong>of</strong> data available (Schouwenaars, 1995; Bromley & Robinson,1995). In general, jI may be suggested thal al present theapplication <strong>of</strong> hydrological mo<strong>de</strong>ls is Iimited more by thedifficulties <strong>of</strong> obtaining sufficient and accurale field estimates<strong>of</strong> sorne <strong>of</strong> lheir parameters than by <strong>de</strong>ficiencies <strong>of</strong> lhe mo<strong>de</strong>lsthemselves.There can be little doubt thal, in principie, hydrological mo<strong>de</strong>lsmay be able to provi<strong>de</strong> exact solutions to sorne critical aspects<strong>of</strong> lhe hyorooynamics ano rewet\ing <strong>of</strong> pea\\am:ls, bu\,<strong>de</strong>pending on lhe questions asked, at present there is Iittlereason lo suppose lhal lhey necessarily have sufficienlprediclíve accuracy lo provi<strong>de</strong> more Ihan a broad basis forpraclical peatland resloration and that empírícal solutjons willconlinue to be important. Nonetheless, further <strong>de</strong>velopment <strong>of</strong>hydrological mo<strong>de</strong>ls, and <strong>of</strong> techniques for better estimatingsorne <strong>of</strong> their terms, may be expected to make an importantfulure contribution to peatland restoralion.Specific advice on lhe use <strong>of</strong> hydrological mo<strong>de</strong>ls should besought from hydrological specialisls.


CHAPTER 7: RESTORATION PLANNING143higher from Mo/inia-dominated vegetation than fromSphagnum-dominated vegetation (Schouwenaars,1990), but in general there is only a limited amount <strong>of</strong>comparative information currently available.l<strong>de</strong>ntification <strong>of</strong> areas which are permanentlyinundated will also be useful in assessing approaches torevegetation, for example where there ís exístíngpotential for establishment <strong>of</strong>floating rafts.(vii) Potential for water supplyThe potential for supplementary water supply tospecific areas may be an important consi<strong>de</strong>ration insorne sÍtes. The quality <strong>of</strong> such supplíes is <strong>of</strong> criticalimportance [4.4.3] and needs to be established at anearly stage ifthis approach is consi<strong>de</strong>red <strong>de</strong>sírable.7.5.5 Substratum characteristics andwater qualityThe chemical properties <strong>of</strong> water and peat wíll have apr<strong>of</strong>ound influence on the plants that will colonise agiven area <strong>of</strong> peatland, and on the likely course <strong>of</strong>subsequent succession [1.9; 4.4]. They may also affectthe long-term preservation <strong>of</strong> sorne archaeologicalstructures. Thus sorne basic chemical data may benee<strong>de</strong>d to make <strong>de</strong>cisions on the most appropriatestrategies and outcomes.Simple measurements <strong>of</strong> pH and the conductivity(corrected for pH) <strong>of</strong> water inputs, including rainfall,ma<strong>de</strong> in a representative selection <strong>of</strong> peat fields canprovi<strong>de</strong> valuable ínformation. Comparison betweenresults (and with published values) will allowi<strong>de</strong>ntification <strong>of</strong> anomalous values [see also Table 2.1].Where sorne pollution or inappropriate minerotrophícinput is suspected, it may be necessary to carry outfurther analyses to i<strong>de</strong>ntify the nature and source <strong>of</strong> theproblem. Analysis <strong>of</strong> the water (including the common'heavy' metals), followed by comparison <strong>of</strong> theproportions <strong>of</strong>various ions with those in localrainwater inputs will give an indication <strong>of</strong> which ionsmight be coming in from sources other than rainfall.It will also be important to establish the water quality<strong>of</strong>any potential supplementary water supplies [4.4.3].Knowledge <strong>of</strong>the type <strong>of</strong> peat that is, or will be,present when restoration management commences isvery important in assessing the potential and optionsfor restoration. One <strong>of</strong> the most important consi<strong>de</strong>ratíonsis whether the exposed peat is ombrotrophic(bog) peat or minerotrophic (fen) peat. Usually, thiscan be easily <strong>de</strong>termined by simple measurement <strong>of</strong>pH, or by examination <strong>of</strong> the plant remains preservedin the peat (macr<strong>of</strong>ossils) [see Chapter 1]. The <strong>de</strong>gree<strong>of</strong> <strong>de</strong>composition <strong>of</strong> the peat is also <strong>of</strong> importance asthis will help to <strong>de</strong>termine the water storagecapabilities and permeability <strong>of</strong> the peat, and itssuitability for use in the construction <strong>of</strong> dams andbunds etc. Table 1.3 gives the basic <strong>de</strong>tails <strong>of</strong> the vonPost scale <strong>of</strong> hum ification.7.5.6 Survey and assessment <strong>of</strong>biological interest - flora andfaunaIntroductionA survey and assessment <strong>of</strong> the existing biologicalinterest <strong>of</strong> any site is an important component in theformulation <strong>of</strong> a restoration strategy. Where possible,field survey should build on the information collatedduring the initial <strong>de</strong>sk study [7.4].The aíms <strong>of</strong> the survey should i<strong>de</strong>ally inclu<strong>de</strong> thefollowing:• i<strong>de</strong>ntification and assessrnent <strong>of</strong> any areas with existingbiological interest;• i<strong>de</strong>ntification <strong>of</strong> any species or cornrnunities with specialconservation status (e.g. statutory protection) eitherpresent on, or using the site; for the less cornrnon species,sorne assessrnent <strong>of</strong>the population size should be ma<strong>de</strong>;• i<strong>de</strong>ntification <strong>of</strong> any potential conflicts between existingconservation interest and airns <strong>of</strong> restoration strategy;• assessrnent <strong>of</strong> the potential for 'natural' and 'assisted'recolonisation <strong>of</strong> darnaged or rewetted areas (i.e. theavailability <strong>of</strong> inoculurn etc.);• i<strong>de</strong>ntification <strong>of</strong> areas with 'un<strong>de</strong>sirable' species orcornrnunities (e.g. scrub etc.);• i<strong>de</strong>ntification <strong>of</strong> potential 'threats' to the existing floraand fauna;• provision <strong>of</strong>base-line data for rnonitoring.FloraA broad survey <strong>of</strong> the vegetation and main habitattypespresent should be carried out. Various surveymethodologies are available, but it is recommen<strong>de</strong>dthat the survey should at least conform to the Phase 1habitat mapping used by the statutory natureconservation bodies (Nature Conservancy Council,1990». The survey should also i<strong>de</strong>ntify the specificfeatures outlined aboye. It is particularly important toi<strong>de</strong>ntify species and areas <strong>of</strong> existing conservationinterest, and those areas which may provi<strong>de</strong> a reservoir<strong>of</strong> bog species for recolonisation <strong>of</strong> the cut-over areas.These species and specific areas should form the focus<strong>of</strong>the restoration scheme for the whole site.An extensive cover <strong>of</strong> Sphagna, with a variety <strong>of</strong>Sphagnum species (including semi-aquatic species,lawn and hummock species) may help to i<strong>de</strong>ntify arefugium as providing a good reservoir <strong>of</strong> bog specíes.However, good refugium areas need not necessarilytake the form <strong>of</strong> a residual, uncut block <strong>of</strong> peat; old,


144RESTORATION OF DAMAGED PEATLANDSrevegetated peat cuttings can fulfil a similar role. Thepresence <strong>of</strong> a cover <strong>of</strong> birch should not be consi<strong>de</strong>red<strong>de</strong>trimental to the assessment <strong>of</strong> interest, providing theground layer is still relatively Sphagnum-rich.In sorne sites, existing wildlife interest <strong>of</strong> certain areasmay not be as a refugium for bog species but forspeejes <strong>of</strong> replaeement habitats (dry heath, fen, birehwoodland etc.). The róle and future <strong>of</strong> sueh areas mustbe elosely consi<strong>de</strong>red in relation to the strategy for thewhole site; adviee should be sought from the statutorynature eonservation bodies.As part <strong>of</strong> the field investigations, it would be <strong>de</strong>sirableto initiate sorne fixed point photography, to illustratekey features, both as an aid to <strong>of</strong>f-site diseussions andas the basis <strong>of</strong> a monitoring programme [Chapter 11].FaunaInvertebratesAssessment <strong>of</strong> the invertebrate interest <strong>of</strong> a site willi<strong>de</strong>ally eomprise referenee to existing reeords, speeieslists, etc., supplemented as neeessary by field survey,together with expert appraisal <strong>of</strong> the likely habitatrequirements <strong>of</strong>any rare or notable taxa.Given the diversity <strong>of</strong> invertebrates and the diffieultyand expense that would be assoeiated with i<strong>de</strong>ntifyingall speeimens in any reasonably-sized sample, fieldsurvey work will neeessitate restrietion to a limitednumber <strong>of</strong> groups and the partieipation <strong>of</strong> expertseapable <strong>of</strong> aeeurately i<strong>de</strong>ntifying material and <strong>of</strong>reeognising notable and rare groups. Survey work <strong>of</strong>this sort is very prone to adverse effects <strong>of</strong> weathereonditions and sampling technique. To overeome suchbias, surveys should employ several samplingprocedures and be carried out on several occasions.Methodologieal problems inclu<strong>de</strong> the difficulties <strong>of</strong>accurately censusing the populations <strong>of</strong> different types<strong>of</strong> invertebrates (Beukeboom, 1986). The larger,actively flying, diurnal species such as dragonflies andbutterflies are usually counted along line transects, an<strong>de</strong>rrant ground dwellers are usually sampled using pitfalltraps. Undoubtedly a major problem with interpretingthe abundance and distribution <strong>of</strong> invertebrates inraised bogs, and in particular in intact Sphagnumcarpets, are practical difficulties <strong>of</strong> sampling fromthese low vegetation types. Nearly al1 studies haverelied heavily on pitfall trapping ancl/or water pan trapsand net sampling <strong>of</strong> water beetles [see Table 7.6].These wil1 undoubtedly tend to be biased in favour <strong>of</strong>errant species sueh as carnivorous beetles (e.g.Carabidae, Staphylinidae) and spi<strong>de</strong>rs, and will tend toun<strong>de</strong>restimate more se<strong>de</strong>ntary, phytophagous and sapsuekinggroups (Coulson & Butterfield, 1985). ThusKirby (1992a) notes that several species <strong>of</strong> <strong>de</strong>lphacidbugs occurring in bogs seem to be difficult to find (andhence record), and though they may be caught in pitfalltraps, these will undoubtedly miss many <strong>of</strong> thesespecies unless very intensive sampling is carried outand quantifying more se<strong>de</strong>ntary species such as manybugs has yet to be applied accurately to bog situations(Nelson, 1983/4; Kirby, 1992a). Even relativelyeommon bog speeies such as the Iygaeid bugPachybrachius fracticollis may be overlooked unlessTable 7.6 Standard survey methods applicable to survey <strong>of</strong> invertebrates on cut-over peatlands.Survey methodAquatic nettingTransect walks with visualcountingWaterpan trappingPilfall trappingU.V. Iight trappingSweep-nettingHand searchingExtraction <strong>of</strong> soil samplesVacuum samplingCommentsWater beetles and water bugsButterflies, diurnal moths (Lepidoptera) and dragonflies (Odonata)Mainly for low-flying insects, may be useful for water beetles and bugs on Sphagnumcarpet; floating waterpans can be used on water surfacesErrant ground invertebrales, nolably beetles (especially Carabidae, Slaphylinidae), variousbugs (Heleroplera) and spi<strong>de</strong>rs; perhaps lhe besl melhod for sampling from lowvegetalion siles though lhey may show certain biases (Southwood, 1978; Coulson &Butterfield, 1985)Molhs (Lepidoplera) and several olher or<strong>de</strong>rs (e.g. Neuroplera, Trichoplera)Insecls may be attracled from a dislance and therefore <strong>de</strong>rive from habilals olher thanwhere the trap is localedAppropriate for a wi<strong>de</strong> range <strong>of</strong> errant and more se<strong>de</strong>ntary insects and spi<strong>de</strong>rs <strong>of</strong> the herband scrub layer; can be difficult un<strong>de</strong>r wet or windy condilions (Coulson & Butterfield,1985)Particularly importanl for locating some bugs (Heteroptera) that frequent the ground layer(Kirby, 1992a)Perhaps lhe most accurate way <strong>of</strong> surveying soil fauna though it may un<strong>de</strong>restimate moreerrant taxaDifficult to apply to wel vegelation (Coulson & Butterfield, 1985)


CHAPTER 7: RESTORATION PLANNING145its population level is very high and the weatherconditions are particu\ar\y suitab\e (Kirby, 1992a).Given the aboye, however, most standard surveymethods for invertebrates are applícable to raised-bogsíte invertebrate communities, though to date, a Iimitedsubset have been most wi<strong>de</strong>ly employed. These aresummarised in Table 7.6. No one sampling method isIikely to be a<strong>de</strong>quate to make a thorough and usefulassessment <strong>of</strong> the invertebrate interest <strong>of</strong> a site. Themethods selected will no doubt normally reflect theavailability <strong>of</strong> taxonomic expertise. However, pitfalltrapping and.UV light trapping should be used ifpossib\e as they have been the two most wi<strong>de</strong>\y usedtechniques in past studies and therefore data obtainedfrom these are likely to be more readily interpretable.Given that most lowland raised-bog sites in the UKinclu<strong>de</strong> a mosaic <strong>of</strong> habitats, it is important thatinvertebrate records for any site can be attributed totheir particular habitats. In the past, many studies havefailed to do so with the result that it is <strong>of</strong>ien unc1earwhat aspects <strong>of</strong> the bog system may need to beprotected in or<strong>de</strong>r to favour particular species. This isparticularly important with lowland raised bogs, whichin their undamaged state have few rare species that arespecific to this habitat type, but at various stages <strong>of</strong>recovery from certain forms <strong>of</strong> peat extraction, notablyfrom traditional hand-cutting, do provi<strong>de</strong> importantsites for a number <strong>of</strong> species <strong>of</strong> high conservationpriority. Taxa which fall into this category inelu<strong>de</strong> thetwo rare beetles Bembidion humerale and Curimopsisnigrita. Given this, it may be preferable to sample eachparticular habitat type intensively rather thanattempting long transects that cover more than onedistinct type <strong>of</strong>habitat.BírdsAssessment <strong>of</strong> the omithological status <strong>of</strong> a site mayrequire field survey to supplement the information<strong>de</strong>rived from the collation <strong>of</strong> existing records, togetherwith expert appraisal <strong>of</strong> the Iikely habitat requirements<strong>of</strong>any rare or notable species.A survey <strong>of</strong> breeding birds could be carried out usingthe method used in the British Trust for Omithology'snew Breeding Bird Survey (BBS). There is, as yet, nostandard method for un<strong>de</strong>rtaking an assessment <strong>of</strong>popu\ations <strong>of</strong> wintering birds, but methods involvingtransects, point counts or grid surveys may beappropriate. Basic <strong>de</strong>tails are provi<strong>de</strong>d by Bibby,Burgess and HiIl (1992). However, bird censustechniques are currently receiving much attention, andit is recornrnen<strong>de</strong>d that the British Trust forOmithology (BTO) are contacted for up to dateinformation on preferred methods.Assessrnent <strong>of</strong> breeding and wintering birds will needto be carried out over a mihimum <strong>of</strong> one year andshould aim to provi<strong>de</strong> an assessment <strong>of</strong> bird habitatsnot only within but also surrounding the site in or<strong>de</strong>r toput the site into its local context..Non-avían vertebratesNon-avian vertebrates (mammals, amphibians, reptiles)usually form a relatively minar part <strong>of</strong>the conservationinterest <strong>of</strong> raised-bog sites, but efforts should be ma<strong>de</strong>to collate and review existing records so that thepotential impact <strong>of</strong> restoration measures can beassessed. Records from raised-bog sites have inc1u<strong>de</strong>dsuch species as otter, mountain hare, <strong>de</strong>er and ad<strong>de</strong>r.Bogs roay a\so constitute important feeding areas forbats, especially around marginal habitats.Assessment <strong>of</strong> wildlife 'value'Following the reconnaissance surveys, an overalleva\uation <strong>of</strong> the wildlife <strong>of</strong> the site shou\d be carriedout, in consultation with the statutory conservationagencies, in particular to i<strong>de</strong>ntify key areas or specieswhich require special protection. This should becoupled with an assessment <strong>of</strong> how such areas can bestbe maintained and, where possible, the ecologicalrequirements <strong>of</strong> the relevant species.Sites may be conservationalIy valuable either throughthe presence <strong>of</strong> notable or rare organisms or becausethey represent communities that are themselvesinteresting and/or vulnerable even if the species theycomprise are not particu\arly rare (or specificto bogs).Conservationists and site managers may at times needto consi<strong>de</strong>r which sort <strong>of</strong> interest they consi<strong>de</strong>r to bemore important [see Chapter 3].7.5.7 Survey <strong>of</strong> archaeological andpalaeoecological interestThe palaeoecological record contained within peat(pollen, plant macr<strong>of</strong>ossils, fossil beetles etc.) can beused to reconstruct vegetation history, landscape<strong>de</strong>ve\opment, climatic change, human activity. etc.Organic and inorganic artefacts may also be found,giving further useful information on human activities.The historical and industrial landscape and buildingson a cut-over site may also be <strong>of</strong> interest, and maywarrant recording before remedial action is un<strong>de</strong>rtaken.There roa)' be existing docuroentation for individualsites in the literature or heId by the bodies Iisted inTables 7.2 and 7.3. Recent activities may have hid<strong>de</strong>nor <strong>de</strong>stroyed artefacts or may have exposed features notpreviously recor<strong>de</strong>d. Contact should be ma<strong>de</strong> at leastwith the local authority or county archaeologists andthe statutory archaeological bodies to seek advice onthe potential archaeological interest <strong>of</strong>the site.


146RESTORATION OF DAMAGED PEATLANDSWhere further evaluation is consi<strong>de</strong>red <strong>de</strong>sirable,assessments <strong>of</strong> archival value can be ma<strong>de</strong> by wetlandarchaeologists or palaeoecologists. Archaeologicalinvestigations can inclu<strong>de</strong> topographical and structuralsurvey, palaeo-environmental analyses and siteinspection, coupled with evaluation and mitigation.Sorne exploratory excavations may be required.Specific points which should be consi<strong>de</strong>red during anarchaeological investigation inclu<strong>de</strong>:• the 'value' <strong>of</strong> the site both in terms <strong>of</strong> the individualstructures and artefacts and the site as a whole;• the importance <strong>of</strong> the site in the context <strong>of</strong> others in thearea;• the historical and industrial landscape;• the palaeoenvironmental record contained in the peat(pollen and macr<strong>of</strong>ossil stratigraphy);• the conservation needs <strong>of</strong> any finds and sites, and thepotential for conflict with wildlife conservation aims (andrestoration methods).In sorne sites it may also be appropriate to consi<strong>de</strong>r thepotential <strong>of</strong> the site for education and research and itsthe potential for interpretation and public access.Following the archival work, survey and siteinspection, further investigation may be nee<strong>de</strong>d,particularly where there is evi<strong>de</strong>nce <strong>of</strong> extensivearchaeological interest or conflicts are i<strong>de</strong>ntifiedbetween the archaeological and biological conservationneeds. Any areas which would be affected byrestoration proposals may need to be properly recor<strong>de</strong>dprior to the works being carried out - advice should besought from the Local Authority and otherarchaeologists (e.g. English Heritage).7.5.8 Potential for control <strong>of</strong>fireFire is a potential hazard on any bog, and can causeextensive damage if uncontrolled. Provision should bema<strong>de</strong> for the prevention and control <strong>of</strong> fires in theformulation <strong>of</strong> any site plan, concentrating particularlyon areas that dry out in the summer. Access routes forvehicles carrying fire-fighting equipment, potentialwater sources and firebreaks should be i<strong>de</strong>ntified.Where these are consi<strong>de</strong>red to be ina<strong>de</strong>quate, it may benecessary to increase such provisions [see 10.5].Advice may be sought from the statutory conservationagencies and the local Fire Authorities.7.5.9 Engineering assessmentWhere it is inten<strong>de</strong>d to carry out restoration workthrough the building <strong>of</strong> bunds, movement <strong>of</strong>consi<strong>de</strong>rable amounts <strong>of</strong> peat etc., it may be advisableto carry out an engineering assessment <strong>of</strong> the site, aspart <strong>of</strong> the feasibility study for any particularrestoration strategy. This would centre on the natureand properties <strong>of</strong> the materials available on site, theexisting topography, the condition <strong>of</strong> structures, thepotential for building water-retaining constructs andthe movement <strong>of</strong>water through the site.Particular attention should be paid to the followingpoints:• acccss for machinery - existing availability vsrequirements;• hydrology;• impoundment <strong>of</strong> water may bring the constructs un<strong>de</strong>rthe provisions <strong>of</strong> the Reservoirs Act 1975 and thus besubject to inspections and remedial works [Appendix 2];• <strong>de</strong>sign <strong>of</strong> 'new' landforms must take into accountstability consi<strong>de</strong>rations.7.5.10 SafetyassessmentSafety assessments should consi<strong>de</strong>r:(a)(b)physical hazards;chemical hazards.Physical hazards will be principally related to old orcurrent peat workings and structures, and should berecor<strong>de</strong>d during the field reconnaissance surveys. Theymay inclu<strong>de</strong>:• old peat cuttings with unstable, floating rafts <strong>of</strong>vegetation;• unstable or unsafe buildings;• drainage ditches - both extant and occlu<strong>de</strong>d;• peat works machinery, light railway etc;• <strong>de</strong>bris from tipping.Chemical hazards may be encountered where the sitehas been used for tipping (either <strong>of</strong>ficial1y or for flytipping).Where a potential problem is i<strong>de</strong>ntified, theLocal Authority should be contacted for guidance ondisposal.Consi<strong>de</strong>ration will need to be given to the safety <strong>of</strong>workers on site and the general public (if applicable,e.g. if rights <strong>of</strong> way exist). Adherence to other healthand safety legislation should form part <strong>of</strong> therequirements <strong>of</strong> any contracts to be let in connectionwith restoration works.7.5.11 Landscape assessmentMost cut-over raised bogs are found in a rural setting,but sorne occur in c10se proximity to housing orindustry. Sorne have been used for waste disposal. Oneobjective <strong>of</strong> a restoration scheme is therefore Iikely tobe to produce a site in harmony with its landscapesetting, reducing its prominence as a disturbed areawith large expanses <strong>of</strong> bare ground, and to blend withits surroundings.


CHAPTER 7: RESTORATION PLANNING147Where a site is c10se to housing, potential <strong>de</strong>trimentaleffects <strong>of</strong> rewetting to househol<strong>de</strong>rs should beconsi<strong>de</strong>red. For example, in at least one instance in TheNetherlands,increased populations <strong>of</strong> biting insects, asa consequence <strong>of</strong> peatland rewetting, have led to anadverse reaction amongst the nearby inhabitants torestoration initiatives.


Chapter 8Water management8.1 IntroductionAs discussed in Chapter 5, the three main problems <strong>of</strong>rewetting peat extraction complexes in the UK arerelated: (i) maintaining a consistently high water levelin the peat; (ii) providing a<strong>de</strong>quate water storage; and(iii) preventing lateral water loss. The solutions to theseproblems will <strong>de</strong>pend upon the topography anddisposition <strong>of</strong> the peat fields, the nature <strong>of</strong> the exposedpeat; and the climatic context.The retention <strong>of</strong> water in peat extraction complexes ispartly a function <strong>of</strong> their topography and capacity forwater storage. The latter is a property <strong>of</strong> the peat type[2.3.2]. Where the exposed peat has limited storagecapacity, increase <strong>of</strong> storage may be possible only bystoring water above-ground, by creating sorne form <strong>of</strong>reservoir on part or all <strong>of</strong> the cut-over fields (Chapter5]. Such reservoirs can be used directly as the basis forrecolonisation by rafting, or, in sorne situations, to infiltratewater into adjoining peat. Lateral water loss canbe reduced by dammingdrains and, where necessary,by creating bunds across extensive peat surfaces.The nature <strong>of</strong> water management operations is partly<strong>de</strong>termined by c1imatic consi<strong>de</strong>rations - in areas <strong>of</strong>high rainfall the <strong>de</strong>sired water level control may bereached and maintained more easily than in drier areas- the main principie being to ensure a positive waterbalance. There will also be climatic constraints on thephasing <strong>of</strong> operations, for example there may beperiods when access by machinery is not possible.All water management operations should be carried outwith due regard to the legislation relating to waterresources (e.g. impoundment, abstraction or discharges<strong>of</strong> water), and to conservation interests (includingarchaeological or palaeoecological interest in theresidual peat <strong>de</strong>posit). Possible constraints should bei<strong>de</strong>ntified and resolved at an early stage in the planning<strong>of</strong>any restoration scheme [Chapter 7].Sorne reconfiguration <strong>of</strong> the peat surfaces prior torewetting may be nee<strong>de</strong>d to optimise the conditionsprovi<strong>de</strong>d for water retention and recolonisation, forexample removal <strong>of</strong> existing vegetation; manipulation<strong>of</strong> the macro- or micro-topography through reductionor increase in the number or height <strong>of</strong> baulks, creation<strong>of</strong> lagoons for retention <strong>of</strong> water etc. [see Chapter 5].8.2 Constructs for waterretention8.2.1 IntroductionBecause the rewetting necessary to regenerate raisedbogs can only be achieved by retaining the incomingprecipitation, aH drains, trenches and outfalls must bedammed (although it is recognised that there may becircumstances in which this is not possible due toexternal constraints). However, any measures used forreduction in outflow from the bog must have thecapacity to <strong>de</strong>liver peak discharges from the bog otherwiseerosion <strong>of</strong> the regenerating peat surface, damageto the dam network and bunds or to the recolonistvegetation may occur. Even in undisturbed raised bogs,high run-<strong>of</strong>f occurs in autumn through to spring whenprecipitation exceeds evaporation. In <strong>de</strong>signing thewater level control system for a regenerating mire, highwater flows must therefore be catered for and this mayinvolve the installation <strong>of</strong>weirs or sluices.Rowell (1988) <strong>de</strong>als with the general principies andpractical aspects <strong>of</strong> control <strong>of</strong> water in peatlands.Brooks (1981) also gives practical advice, particularlyon the building <strong>of</strong> dams and sluices or weirs. Thetechniques available to reduce hydrological changewithin refugia and rewetting cut-over sites inclu<strong>de</strong>:• ditch blocking;• bunding;• provision <strong>of</strong>supplernentary water;• buffer zones.In most situations, it may be necessary to utilise morethan one technique to optimise rewetting.8.2.2 Ditch blockingThe following principies should be applied:• all possible ditches should be blocked, including old,occlu<strong>de</strong>d ones as these rnay retain sorne function, even ifapparently choked with vegetation;• existing vegetation should be cleared out where dams areto be built, to ensure a good seal;• a phased approach rnay be necessary, to integrate withother rnanagernent operations, such as scrub rernoval;• if required, particular care should be taken to seal ditches


150RESTüRATlüN üF DAMAGED PEATLANDScut into mineral soil, particularly where the latter is <strong>of</strong>high permeability;• slit drains or mole drains in abandoned cut-over areasmust be i<strong>de</strong>ntified, and blocked if thought to befunctioning (in sorne cases they will be effectivelyblocked by retention <strong>of</strong> water in the main drains);• for large scale operations it is necessary to use machinery(rather than hand methods) to build the dams, butconsi<strong>de</strong>ration must be given to potential damage toexisting vegetation;• in most cases, peat dams will be a<strong>de</strong>quate if buiUcorrectly, but they may need to have an impermeablecore <strong>of</strong> plastic, metal sheeting, wood etc.• careful attention should be paid to the re-routing <strong>of</strong> drainscarrying enriched or polluted water across a site;• careful attention must be paid to legal constraints andpotential effects on adjacent land;• the number and spacing <strong>of</strong> dams will largely <strong>de</strong>pend onthe size, fall and orientation <strong>of</strong>the drain;• on-going maintenance <strong>of</strong> dams is essential to correet assoon as possible any damage through faetors sueh asshrinkage, slumping and erosion;• a<strong>de</strong>quate provision must be ma<strong>de</strong> for overflow.Once blocked by dams, open ditches should beencouraged to infill as rapidly as possible, particularlywith Sphagnum species. However, in some situations, itmay be <strong>de</strong>sirable to prevent too much vegetation colonisationand preserve the linear pools created by blockingditches at intervals, which can provi<strong>de</strong> an attractivehabitat for wetland fauna (e.g. Fox, 1986a, b) and mayhelp to temporarily provi<strong>de</strong> increased water storage.Damming and ditch-blocking techniques used inrewetting damaged bogs are illustrated in Plate 8.1.8.2.3 BundingBunds may be used to seal the edges <strong>of</strong> upstanding bogremnants, to reduce run-<strong>of</strong>f from remnants, to impoundwater within existing peat cuttings or to create newlagoons. Depending on location and availability <strong>of</strong>source material, these may be constructed frommaterials such as c1ay, peat and plastic membranes, andusually involve the use <strong>of</strong> machinery. Note that c1aybunds may help to enrich the mire water, although thesignificance <strong>of</strong> this to bog restoration is not wellknown. The construction material may be won in si/u,or brought in from outsi<strong>de</strong>. The latter may only beappropriate in sites with existing infra-structure frompeat cutting operations, for example tramways orroadways that permit the transport <strong>of</strong> materials insufficient quantities, and would substantially increasecosts. In many cases, existing tramways and roadwaysmay act as bunds, and can be utilised or exten<strong>de</strong>d,although they may not necessarily be watertight. Theefficacy <strong>of</strong> the baulks as bunds will <strong>de</strong>pend on theirsize, intactness and <strong>de</strong>gree <strong>of</strong> <strong>de</strong>hydration <strong>of</strong> the peat.Use <strong>of</strong> bunding techniques is illustrated in Plates 8.2and 8.3.PeatThe construction <strong>of</strong> bunds raises several problems fromthe engineering point <strong>of</strong> view, as, although manyembankments have been constructed from, and on,peat, there is still no accepted procedure for<strong>de</strong>termining the engineering properties <strong>of</strong> these types<strong>of</strong> structure or standard engineering criteria on whichto base a <strong>de</strong>signo However, unless a major project withparticularly large bunds is planned, an empiricalapproach would seem to be satisfactory, taking intoaccount experience from other restoration projects. Itshould, however, be noted that the Reservoirs Act 1975imposes safety provisions on reservoirs or artificiallakes not used for water supply purposes that retainmore than 25,000 cubic metres <strong>of</strong> water aboye the'natural level' <strong>of</strong> any part <strong>of</strong> the adjoining land or havea dam higher than 4.5 m; requiring that theconstruction be un<strong>de</strong>rtaken in accordance with the<strong>de</strong>sign and un<strong>de</strong>r the supervision <strong>of</strong> a qualified civil.engineer [see Appendix 2].For an effective bund, the peat recommen<strong>de</strong>d by mostpractitioners is wet, strongly-humified peat, although itshould retain some fibrous structure (for example, peat<strong>of</strong> humification value H6-H8\). Where sufficientquantities <strong>of</strong> this are not available, it may be necessaryto use less strongly-humified peat, in which case it willusually be necessary to insert a plastic membrane (seebelow). The main principIe is to ensure a good seal <strong>of</strong>wet black peat to wet black peat. Thus any remainingweakly-humified or dry peat should be removed beforethe main bund construction (the former may bereplaced on top <strong>of</strong> the strongly-humified peat once thisis in place [Figure 8.la]). It is not normally necessaryto excavate down into the mineral subsoil if there is ana<strong>de</strong>quate layer <strong>of</strong> strongly-humified, wet peat. Suchbunds may be used to seal the edges <strong>of</strong> uncut remnantsor constructed 'within' the remnant using thistechnique, although clearly potential damage to thevegetation needs to be taken into account.An altemative approach for bunding within remnantsused on some German sites (e.g. Hahnenmoor) is toexcavate a trench down into the strongly-humifiedpeat, then replace the weakly-humified peat first,followed by the strongly-humified peat on top [Figure8.1 b]. This has the effect <strong>of</strong> creating an impermeableseal within the weakly-humified peat, thus reducingseepage losses through the more permeable peats.Where the bunding is based on existing baulks ortramways <strong>of</strong>peat, the drier surface peat and vegetation\ von Post humification scale [see Table 1.3].


CHAPTER 8: WATER MA AGEMENT151(a) Peat dams blocking narrow drainage ditch; AstleyMoss (Lancashire)(b) Peat dams across wi<strong>de</strong> drainage ditch; WedholmeFlow (Cumbria).(e) Sheet-metal dam across narrow drainage ditch,Glasson Moss (Cumbria).(d) Sheet metal dam across wi<strong>de</strong> fire-break;Moss (Cheshire).Risley(e) Simple plywood-sheet dam across narrow ditch;Danes Moss (Cheshire).(f) Palisa<strong>de</strong> timber dam across broad erosion gully;Blawhorn Moss (Lothian).Plate 8.1Rewetting using damming and ditch-blocking techniques.


152RESTORATION 01' DAMAGED PEATLANDS(a)(b)lirledpe~_- -:::::::----- ---~-----+ -+ ::::::-::::::::::-::::- ~Qweakly-humified peata strongly-humified peatFigure 8.1 Construction <strong>of</strong> shallow, internal bunds: (a) by replacement <strong>of</strong> upper, weakly-humified peat with importedstrongly-humified peat 1 ; (b) by interchange <strong>of</strong> strongly- and weakly-humified peat horizons in trenches.will usually need to be removed, unless sufficientquantities are available to create a good seal throughthe weight <strong>of</strong> peat itself (as suggested at Cors Caron,Dyfed). Where new lagoons are to be created on cutoversurfaces, the peat may be bulldozed into position,if sufficient <strong>de</strong>pth remains. Sorne compaction <strong>of</strong> thepeat in the construction <strong>of</strong> dams and bunds is usuallyachieved by driving machinery across the surface. Thismay help to consolidate the peat so that subsequentslumping and erosion are minimised.For bunds around lagoons, it may be necessary initiallyto provi<strong>de</strong> sorne protection from erosion through windand waves using woo<strong>de</strong>n baffles. Provision <strong>of</strong> a 'shelfarea would aIso help to dissipate the wave energy, thusprotecting the main bund, and may help to provi<strong>de</strong> aplatform for the initiation <strong>of</strong> rafting vegetation.Plastic membranesThese have been used in situations where there is somedoubt about the permeability <strong>of</strong> the peat available forbunding. The plastic used is a heavy duty polythene(such as is available from buil<strong>de</strong>rs meq:hants) which isinserted vertically into a narrow slit cut into the peatwall. This approach has been used in extensive bundingaround massifs at sites such as Wicken Fen (Cambridgeshire),Corlea (Ireland; Plate 8.3) and Fochteloerveen(The Netherlands). Such bunds are probably mostappropriately used for 'externa!' bunding <strong>of</strong> massifs, asexpense may prohibit their extensive use within peatcutting complexes. However, the material can also beused to improve the water retention <strong>of</strong> existingstructures (dams or bunds) which are thought to beleaking.Plastic membranes are non-bio<strong>de</strong>gradable and have anin<strong>de</strong>finite (although unknown) life-span. The mainpotential problems suggested inclu<strong>de</strong> damage by1 The source <strong>of</strong> the strongly-humified peat may be from clsewhereon the site, or from a treneh dug along the insi<strong>de</strong> <strong>of</strong> the position <strong>of</strong>the proposed bund.burrowing animaIs, in particular rats and moles, andthe potential formation <strong>of</strong> a vertical 'slip plane' downthe outer face <strong>of</strong> the plastic membrane, particularly ifthe peat on the 'outsi<strong>de</strong>' becomes dry. Neither problemseems to have happened so far, although the possibilitycannot be exclu<strong>de</strong>d. The plastic does not necessarilyneed to go down to the base <strong>of</strong> the peat, althoughshould penetrate into the most highly humified peat ifpossible. Some seepage across the bund at a low-levelmay help to reduce the build-up <strong>of</strong> pressure behind themembrane, although this should be monitored. lt maybe possible to reduce the potential for a zone <strong>of</strong>enhanced water movement at the base <strong>of</strong> themembrane, which could lead to leakage and weakening<strong>of</strong> the bund structure, by inserting lengths <strong>of</strong> the plasticto different <strong>de</strong>pths.Mineral substrataEmbankments on peat or estuarine clay for river floodcontrolare usually constructed from peat or sandymaterials around a c1ay coreo Sorne <strong>of</strong> these have beenreported to have problems due to weak foundations,piping, instability and leakage (Harris, 1979; A.Bullivant, pers. comm.). Such problems may be relatedto construction <strong>de</strong>sign and methods, and size. Wheremineral materials are used, attention must also be givento the potential problem <strong>of</strong> leaching <strong>of</strong> bases andnutrients from the bund into an ombrotrophic system.General cornrnentsBunds should be kept as wet as possible. To protect abog remnant, Rowell (1988) suggests the construction<strong>of</strong> a trench on the remnant si<strong>de</strong> <strong>of</strong> the bund to ensurethere is a supply <strong>of</strong> water to keep the bund wet. Insorne sites this function may be carried out by thetrench from which the peat used in the bund has beenexcavated (borrow-trench). At Corlea (Eire), in or<strong>de</strong>rto help counteract drying, part <strong>of</strong> the length <strong>of</strong>the bundhas been constructed with a water trap half-way downthe outsi<strong>de</strong>-slope, inten<strong>de</strong>d to contain water and release


CHAPTER 8: WATER MANAGEME T 153Construction <strong>of</strong> a bund around old peat cuttings on the SE bog at Cors Caron (Dyfed). The lines <strong>of</strong> dams acrossditches on the remaining 'dome' <strong>of</strong>the bog can also be seen. [Photo: lE. Davis]. [see also Plate 5.6]Shallow peat bunds forming lagoons within former peat workings at (left) Esterwege Dose (Germany) and (right)Kendlmühlfilze (Germany).Plate 8.2 Rewetting using bunding techniques. [see also Plate 8.3]


SER\1CES LEGENDTD..ECOW EIREA,NNCAl< PAlU: UG!fTl: lo, SE"O"ER LC>"E~ ~nn~.O,:,, ~. ',..",~",">­'" < QZ:> Q=::=::::-:::=::==:::::::: '::::::::-:-=-=====-= =-=-=========-=---¡Scale O ::¡;¡¡S¡;;O===;i;'O¡¡O 'SO ....


CHAPTER 8: WATER MANAGEMENT155it slowly in times <strong>of</strong> water <strong>de</strong>ficit (Wynne & O'Oonnell,1993) [Plate 8.3]. As this project is new, there hasbeen no opportunity to assess the effectiveness <strong>of</strong> thisapproach. Vegetation growth should be encouraged, tohelp bind the surface peat together and reduce erosion,but tree growth should be prevented, as this mayincrease drying and cracking.There must be sorne provision for water-Ievel controlto prevent damage by excess water flowing over thetop surface <strong>of</strong> the bunds. An adjustable collar-overflowpipe system laid through the bund, or a sluice can beused for this. An overflow system also has theadvantage <strong>of</strong> providing specific discharge points forthe water, whether into another lagoon or externaldrainage system as appropriate. The latter will help toavoid any potentially un<strong>de</strong>sirable impacts on adjoiningland. Careful consi<strong>de</strong>ration must be given to thematerials and methods used for over-flow provision, sothat lines <strong>of</strong> weakness are not created, and regularchecks ma<strong>de</strong> for correct functioning.On-going management <strong>of</strong> the bunds is necessary toensure that any problems are <strong>de</strong>alt with promptly, forexample rectifying slumping and removal <strong>of</strong> shrubseedlings. The height <strong>of</strong> the bunds around bogremnants may need to be increased periodically as thepeat within swells. Maintenance <strong>of</strong> 'internal' bundswhich subdivi<strong>de</strong> peat fields in less important, once thecuttings have started to renature.8.2.4 Provision <strong>of</strong>supplementarywaterSupplementary water provision should only beconsi<strong>de</strong>red in certain circumstances, for example to'prime' the system, as in general it is time-consumingand costly to run [see 5.3(h)]. Sites where this approachhas been used inelu<strong>de</strong> Shapwick Heath (Somerset) andThorne Waste (S. Yorkshire).8.3 Buffer zonesOn the European mainland an attempt has been ma<strong>de</strong>,in sorne cases, to surround uncut remnants, and regeneratingcut-over areas with 'buffer zones', <strong>de</strong>signed tohelp protect the sites against adverse influences <strong>of</strong>surrounding land use. Buffer zones may have varyingfunctions:A. Buffer ZOlles Oll or adjoillillg the peat body:• A buffer zone on adjoining land within which waterlevels can be raised. This may (a) help to reduce lateralwater losses by redueing the hydraulie gradient betweenthe bog and its surroundings; (b) help to preventdownward leakage <strong>of</strong> water from the bottom <strong>of</strong> the bog;or (e) reduce oxidation <strong>of</strong> un<strong>de</strong>rlying impermeable layersor <strong>of</strong> the basal peats that might oeeur should anunsaturated zone <strong>de</strong>velop beneath the bogo Note that (b)and (e) are likely to be important only in bogs subjeet tovertical water seepage [4.4.5] (See also Sehouwenaars,1995).• An 'agricultura\' buffer zone in whieh agrieulturalaetivities are eontrolled in or<strong>de</strong>r to reduce drainage andwater abstraetion and to prevent enriehed water fromentering the bogo Spray from agro-ehemicals may also bea problem; to help ameliorate this, a shelter belt <strong>of</strong> trees(a non-invasive speeies) may be ineorporated into thebuffer zone.• A buffer zone to provi<strong>de</strong> an impermeable barrier aroundthe margins <strong>of</strong> a peat-extraetion eomplex to preventingress <strong>of</strong> enriehed or polluted water into the cut-overareas, if these are situated at a lower topographieal levelthan the surrounding land.• A 'eonservation' buffer zone - zone <strong>of</strong> semi-naturalvegetation adjoining the bogoB. Buffer zone Oll the peat body:• A buffer zone whieh eorresponds to the maximum width<strong>of</strong> the water drawdown zone at the margin <strong>of</strong> anupstanding peat block.The principIe <strong>of</strong> the establishment <strong>of</strong> buffer zonesaround both uncut remnants and cut-over mires ise1early an important one. The width <strong>of</strong> the buffer zone<strong>de</strong>pends on such factors as climate, hydraulicconductivity <strong>of</strong> the peat, height differences and thedistance to (and <strong>de</strong>pth ot) active drains. However,although the width <strong>of</strong> buffer zone required in differentsituations can be calculated using standardhydrological data and equations (see e.g. Eggelsmann,1982; van <strong>de</strong>r Molen, 1981; Robinson el al, 1992; vanWalsum, 1992), the accuracy and value <strong>of</strong> such<strong>de</strong>terminations have been little tested in practice, andmay be limited by difficulties <strong>of</strong> obtaining meaningfulestimates <strong>of</strong> sorne key hydrological variables. Moreresearch is nee<strong>de</strong>d to refine the mo<strong>de</strong>lling approach tocalculate the appropriate buffer zone widths fordifferent situations before it is possible to provi<strong>de</strong>precise gui<strong>de</strong>lines by such methods.Widths <strong>of</strong> between 30 m and 100 m have beensuggested to provi<strong>de</strong> a sufficient hydrological buffer.However, work by Robinson el al (1992) suggestedthat in sorne circumstances, a buffer zone <strong>of</strong> 500 mmight be nee<strong>de</strong>d to minimise the effect <strong>of</strong> peatextraction on an adjacent upstanding peat block, unlesshydrological management measures were taken (e.g.ditch blocking or installation <strong>of</strong> an impermeablebarrier).Raising <strong>of</strong> water levels in a buffer zone within theadjoining land, while probably not sufficient in itselftoeffect much rewetting <strong>of</strong> an upstanding bog remnant(unless there is a very low hydraulic gradient) mayprovi<strong>de</strong> the opportunity for the establishment <strong>of</strong>sympathetic management, for example in the creation


156RESTORATION OF DAMAGED PEATLANDS<strong>of</strong> wet meadows. Thís would have the addítionalbenefit <strong>of</strong> reducíng the potentíal for agriculturalpolIutíon impinging on the site, either from watercourses or aeríal sources.8.4 Practical implications <strong>of</strong>rewetting for adjoining landAs the major aim <strong>of</strong> most restoration strategies ís toreduce water losses from the bog remnants, ít may bethought that the measures taken to achieve thís neednot have an undue adverse effect on adjoining ground.However, this wiII <strong>de</strong>pend on such factors as thehydraulic conductivity <strong>of</strong> the peat, the difference inheight between site and surroundings, distance todrains, permeability <strong>of</strong>the un<strong>de</strong>rlying substratum etc.Use <strong>of</strong> bunds should alIow relatively ín<strong>de</strong>pen<strong>de</strong>ntcontrol <strong>of</strong> water levels 'insi<strong>de</strong>' the bogo In manycircumstances, however, it may be necessary tomaintain a marginal ditch to ensure the surplus water iscarried away, as in a natural lagg. It would bepreferable to keep the water level in the marginal ditchas high as possible to reduce the hydraulic gradíentfrom the bog, but this could make it difficult to drainadjacent land. Where thís ís likely to cause a problem(for example on agriculturalland) it may be possible tocreate a buffer zone extending away from the edge <strong>of</strong>the bog and boun<strong>de</strong>d by a second ditch within whichwater levels can be lowered. The width <strong>of</strong> buffer zonenecessary would <strong>de</strong>pend largely on the permeabiJity <strong>of</strong>the substratum and the required drainage capacity <strong>of</strong>the outer ditch. However, clearly thís could haveímplications in terms <strong>of</strong> loss <strong>of</strong> the land for agriculture,and requires further investigatíon.There is sorne evi<strong>de</strong>nce to suggest that in certain mires,partjcularly those un<strong>de</strong>rlain by a mineral subsoil whichhas a high permeability:a) there may be sorne connectivity with the regional andlocal water tables, such that raising water levels in thebog may affeet water levels in the surrounding land, or,conversely, drainage in the surrounding land willinf1uence the hydrology <strong>of</strong> the bag (e.g. Paelman &loosten, 1992);b) the role <strong>of</strong> ground water recharge cannot be ignored,especially where the mire has been extensively cut-overand a relatively thin veneer <strong>of</strong> peat remains above themineral subsoil.The rewetting options that wjJJ have the most iropacton adjoining land are those which require the waterlevels in this land to be raised [see Chapter 5] an<strong>de</strong>ither elevated aboye or retumed to formergroundwater levels. 5uch strategies may involvefurther substantial infrastructural works, which, besi<strong>de</strong>sdirect costs <strong>of</strong>construction and maintenance, may alsohave obvious financialimplications in terms <strong>of</strong> landpurchase or compensation etc. Consi<strong>de</strong>rable problemsin achíeving such rewetting are Iikely to beencountered where the adjoining land is un<strong>de</strong>r multipleownership or where land-uses other than agricultureand structures such as roads, railways and buildings areinvolved in former wetland areas where water levelsare currently controlled by drainage schemes.When surrounding farmland has been rewetted, it isimportant that base- or nutrient-rich or polluted wateris prevented from reaching the site. In sites wheredrains enteríng or crossing the cut-over areas carryenriched draínage water from adjoining agriculturalland, the water should be diverted away from the site assoon as possible.The potential <strong>of</strong>the restoration measures for increasíngthe buffering capacity <strong>of</strong> the mire in terrns <strong>of</strong> fioodcontrol <strong>of</strong> adjoining land should be consí<strong>de</strong>red as thismay be perceived as beneficial by the water resourcesagencíes and would enhance the 'value' <strong>of</strong> therestoration scheme. However, there is conflictingevi<strong>de</strong>nce in the literature conceming the role <strong>of</strong>undamaged, drained and rewetted peatlands in the'dampíng' <strong>of</strong>peak fiows folJowing storms.


Chapter. 9Facilitation <strong>of</strong>revegetation9.1 IntroductionNatural recolonisation <strong>of</strong> cut-over bogs by plants maytake place quite readily where there are local refugia <strong>of</strong>typical bog species. However, where these do not exist,or have a sparse range <strong>of</strong> species, or where sites areparticularly large, it may be necessary to consi<strong>de</strong>r'inoculation' <strong>of</strong> damaged areas with suitable plantspecies, either by transplantation or by seeding.Before areas are inoculated, it is important that otherstages <strong>of</strong>the restoration scheme have been successfullycarried out, and that any remedial work can beun<strong>de</strong>rtaken without damage to the vegetation. Forexample, if appropriate vegetation is to re-establish, itis important that the hydrological conditions, in terms<strong>of</strong> quality, quantity and stability <strong>of</strong> water supply, areappropriate [see Chapters 4 and 5]. Conversely, therestoration scheme <strong>de</strong>veloped should take into accountthe availability <strong>of</strong>plant inoculum.9.2 Inoculation with Sphagnumspecies9.2.1 IntroductionThe main feature <strong>of</strong> the vegetation <strong>of</strong> an undamagedraised bog is the extent <strong>of</strong> the Sphagnum cover, which,besi<strong>de</strong>s being characteristic, may play various importantroles in the functioning <strong>of</strong>the mire [1.7]. The restoration<strong>of</strong> a mire to a self-sustaining system requiresthe reinstatement <strong>of</strong> an acrcJíelm which is comparableto that <strong>of</strong>a little-damaged bbg surface. Thus, one <strong>of</strong>themost important consi<strong>de</strong>rations in the restoration <strong>of</strong> adamaged bog is the question <strong>of</strong> how to regain theSphagnum cover. A characteristic <strong>of</strong> many damag\j.dbogs is the lack <strong>of</strong> or limited areas <strong>of</strong> Sphagnum-richrefugia, which may hin<strong>de</strong>r recolonisation.In sorne sites, it is possible to inoculate damaged areaswith plant material, such as Sphagnum, either as wholeplants or fragments. For relatively small operationsSphagnum plants could be collected from areas indonor sites consi<strong>de</strong>red least 'sensitive', ensuring thatdamage is minimised. Donor sites should preferably bein the same geographic area to avoid un<strong>de</strong>sirabletranslocation <strong>of</strong> non-local species or gene pools [seealso 9.4], particularly if the donor site is likely, orknown to support scarce bog species. In sites whereSphagna do survive, for example in a mire remnant,old peat cuttings or in ditches, it may be possible toinoculate rewetted areas with Sphagna by hand. Manysite managers have successfully spread S. ..:uspidatumin this way and it has been suggested that Sphagnumfuscum, S. capillifolium, S. magellanicum, S. cuspidatumand S. recurvum can all be transplanted in sods(Nilsson et al., 1990). However, trials by Money(1994) suggest that hummock and lawn species <strong>of</strong>Sphagnum will regenerate more readily if a template <strong>of</strong>aquatic Sphagna is first created, than from direct'broadcasting' <strong>of</strong>plants into open water pools.For larger scale restoration, removal <strong>of</strong> large quantities<strong>of</strong> Sphagnum from donor sites is likely to beinappropriate. In these situations the availability <strong>of</strong>propagules may be increased by Sphagnum 'farming'.9.2.2 Sphagnum 'farming'AII Sphagnum species can reproduce vegetatively andtechniques have been investigated to increase theamount <strong>of</strong> Sphagnum plants available using 'nursery'pools (Money, 1994, 1995). Aquatic Sphagna (such asS. cuspidatum) can be farmed readily and are likely tobe more suitable for this treatment than hummockforming species (such as S. papillosum), which mayrequire a 'template' <strong>of</strong> aquatic Sphagna on which toregenerate [9.2.3]. Further work is nee<strong>de</strong>d to formulatea<strong>de</strong>quate gui<strong>de</strong>lines for optimal conditions for sustainablefarming <strong>of</strong> Sphagna to allow for harvesting on aregular, rotational basis. It may be recommen<strong>de</strong>d that'nursery' poois'are established as soon as possible in arestoration programme (if possible alongsi<strong>de</strong> ongoingextraction), so that inoc.m is available as required.9~2.3 Propagation <strong>of</strong>Sphagnum fromsma/l vegetative fragments~ ~Effective inoculation <strong>of</strong> the extensive areas presentedby commercial peat workings with whole Sphagnumplants would require large amounts <strong>of</strong> source material.Techniques have therefore been investigated foroptimising the use <strong>of</strong> available plant material. It is


158RESTORATION 01' DAMAGED PEATLANDSknown from numerous observations that S. cuspidatumregenerates remarkably well from fragments and alsothat the growth <strong>of</strong> lateral buds <strong>of</strong> Sphagnum can bestimulated by damage to the plant apex, for example,by <strong>de</strong>capitation. Small-scale trials have shown goodregeneration <strong>of</strong> S. cuspidatum plants in pools intowhich fragments <strong>of</strong> plants in a suspension <strong>of</strong> waterwere 'broadcast' (Money, 1994, 1995). Regenerationfrom fragments will <strong>de</strong>pend on provision <strong>of</strong> a suitablewater regime as periodic <strong>de</strong>siccation on a dry peatsurface inhibits regeneration, while regeneration alsoseems to be inhibited if fragments are introduced into<strong>de</strong>ep water (>50 cm), unless sorne provision is ma<strong>de</strong> toassist flotation [9.2.5]. Colonisation <strong>of</strong><strong>de</strong>ep water by S.cuspidatum tends to occur by lateral spread from plantsanchored to the edges <strong>of</strong> pools, thus regeneration islikely to be most successful initially at the peat-waterinterface and in shallow water (Money, 1994, 1995).The regenerative capacities <strong>of</strong> other Sphagna are lessc1ear (Money, 1994). Hummock and lawn fonningSphagna hav~ been grown successfully from fragmentsin carefully controlled laboratory conditions (Sabotka,1976; Baker & Macklon, 1987; Poschlod & Pfa<strong>de</strong>nhauer,1989; Rochefort, Gauthier & Lequéré, 1995)and viable vegetative fragments may sometimes persistin upper peat layers or be dispersed by water and air.However, growth from fragments <strong>of</strong> these Sphagna isgeneralIy less prolific than for S. cuspidatum and mayrequire more precise conditions (such as permanentlymoist, rather than saturated conditions) for successfulestablishment. It may be necessary to consi<strong>de</strong>rinoculation as whole plants in c1umps, to the edges <strong>of</strong>pools, or on to artificial rafts.9.2.4 Regeneration <strong>of</strong>Sphagnum fromsporesRegeneration <strong>of</strong> Sphagnum from spores is potentiallyan important process for recolonisation <strong>of</strong> damagedpeatland as it would enable long-distance inoculation<strong>of</strong> areas <strong>de</strong>void <strong>of</strong> a local source <strong>of</strong> propagules forcertain species. However, the contribution to dispersalma<strong>de</strong> by sexual reproduction <strong>of</strong> Sphagnum is poorIyun<strong>de</strong>rstood. Spores have regenerated successfullyun<strong>de</strong>r laboratory conditions (e.g. Boatman & Lark,1971; Sabotka, 1976; Baker & Boatman, 1985; Clymo& Duckett, 1986), but un<strong>de</strong>r nutrient poor conditions inthe field it would appear that regeneration from sporesmay be less important than vegetative reproduction.9.2.5 Facilitation <strong>of</strong>Sphagnumestablishment and raftingThere is evi<strong>de</strong>nce that the establishment and spread <strong>of</strong>Sphagnum within embryonic bogs may be facilitated insorne situations by the presence <strong>of</strong> 'nurse species' suchas Molinia caerulea, Eriophorum vaginatum andJuncus ejJusus (Joosten, 1992; Mea<strong>de</strong>, 1992; Grosvernieret al. 1995). These may (i) afford protectionagainst wind and wave action in floo<strong>de</strong>d sites; (ii)provi<strong>de</strong> a 'climbing frame' for Sphagnum; and (iii)provi<strong>de</strong> a more suitable microclimate for Sphagnum.Joosten (1992) refers to this as 'tussock buffering'.However, a possible limitation <strong>of</strong> this approach is thata critical balance may exist between conditions thatfavour extreme dominance <strong>of</strong> species such as E.vaginatum and M caerulea and those which pennitthese species to act as nurse species to Sphagnum.The provision <strong>of</strong> 'artificial' constructs within the watersuch as birch brashings may also perform functions (i)and (ii). Rafting may also be encouraged by loose peatfragments (e.g. bunker<strong>de</strong> - see 9.6) or particles floatingin the pools, either washed in from the si<strong>de</strong>s, or<strong>de</strong>tached and lifted from the base <strong>of</strong> the cuttings(probably due to the formation <strong>of</strong> gas bubbles).9.3 Inoculation with vascularplantsCommercial supply <strong>of</strong> seed <strong>of</strong> bog species is unlikelyto be available, although seed mixtures are availablefrom specialist seed merchants which could be used forthe creation <strong>of</strong> 'wet meadows' at the margins <strong>of</strong> sites.SimilarIy, few bog plant species are Iikely to becommercially available in sufficient quantities forinoculation. Species not occurring naturally in the areashould not be introduced. Where possible, transplantationfrom 'natural' sources is preferable, as theinoculum may contain propagules <strong>of</strong> a range <strong>of</strong> plantspecies, as well as invertebrates, which would beabsent from specially raised sources.There is little information available on the Iikelysuccess <strong>of</strong> transplanting vascular bog species, but it isunlikely to be too problematic un<strong>de</strong>r a suitablehydrological regime and could be consi<strong>de</strong>red wherethere is no nearby source <strong>of</strong> propagules. However, it islikely to be practicable only over small areas, usualIybeing restricted by the availability <strong>of</strong> suitable plantmaterial and intensity <strong>of</strong> ¡abour input required,although once established, plants will be able to spread.Turves, whole plants or individual tillers may be usedas transplants, either collected from another site, orgrown and established from seed in the greenhouse. Onblanket bog 'live mulching' (i.e. spreading materialcollected by machinery from an 'intact' surface) hasbeen used to provi<strong>de</strong> fragments <strong>of</strong> vascular plants andmosses, and a seed source (Bayfield et al., 1991),although this technique is likely to be <strong>of</strong> use at only afew sites, as it presumably severely damages thesurfaces from which the mulch is taken. These authorsalso suggest that turf transplanting at a <strong>de</strong>nsity <strong>of</strong> 2-4


CJlAPTER 9: FACILlTATION OF REVEGETATIO159turves m- 2 can be used to provi<strong>de</strong> a good source <strong>of</strong>inoculum (at least on blanket bog).Some <strong>of</strong> the techniques for revegetation suggested byBrooks (1981) and Hammer (1992) may also beapplicable to raised-bog restoration, although mainlyaimed at minerotrophic wetland restoration. Forexample, suggestions to overcome some <strong>of</strong> theproblems <strong>of</strong> transplanting into open water such asusing log or board baffles to help break the force <strong>of</strong>any waves and using bio-<strong>de</strong>gradable cotton mesh ornetting to hold the plants in position until established.Planting should i<strong>de</strong>ally be carried out in the autumn orearly spring so that vegetation can establish before anyonset <strong>of</strong> dry periods in summer. Plant material shouldbe transplanted as soon as possible after collection ­drying out in transit must be avoi<strong>de</strong>d. Maintenance <strong>of</strong>high and stable water levels are crucial for thesuccessful establishment <strong>of</strong> bog species. It should beapparent after only one growing season whether transplantationhas been successful. Any failures should benoted, the reasons for failure assessed and remedialaction taken, before any replacements are ma<strong>de</strong>.9.4 Legal aspects <strong>of</strong>transplantationConcem is sometimes expressed about the use <strong>of</strong> intersitetransplants, as disturbance <strong>of</strong> regional gene pools isconsi<strong>de</strong>red un<strong>de</strong>sirable, as is the possible introduction<strong>of</strong> non-local plants and invertebrates. However, whilstintra-site transplants would be preferable, there may beinsufficient materiallocally to make this possible and achoice has to be ma<strong>de</strong> as to whether or not such speciesare a <strong>de</strong>sired component <strong>of</strong> restoration (this is partly<strong>de</strong>terrnined by the restoration objectives for the site).While there is no specific legislation which coverstransplantation, un<strong>de</strong>r the Wildlife and Countrysi<strong>de</strong> Act(1981) it is illegal to uproot any plant without theowners' consent and consent is required from thestatutory conservation agencies for the removal <strong>of</strong>organisms from, or introduction to a Site (or Area) <strong>of</strong>Special Scientific Interest as this may be consi<strong>de</strong>red apotentially damaging operation. It is recommen<strong>de</strong>d thatguidance on intra-site translocations <strong>of</strong> both flora andfauna is sought from these agencies, as the generalgui<strong>de</strong>lines are currently un<strong>de</strong>r review.9.5 Mitigation <strong>of</strong> adversechemical effects9.5.1 Phosphorus fertilisationIn some circumstances, the chemical conditions prevailingin peat cuttings or on bare, milled surfaces, maynot be conducive to the rapid establishment <strong>of</strong> 'typical'bog species, due to particularIy high acidity or lownutrient availability. The use <strong>of</strong> phosphorus has beenshown experimentally to assist in the short-term establishment<strong>of</strong> certain Sphagnum species in peat cuttings(applied at arate <strong>of</strong> 30 g NaH 2 P0 4 in c. 4m 3 <strong>of</strong> water)(Money, 1995). However, to date, this has only beencarried out on a very small scale; large scale trials areundoubtedly nee<strong>de</strong>d before firm guidance andrecommendations can be ma<strong>de</strong> as to the use <strong>of</strong> fertiliserin facilitating revegetation. Any application <strong>of</strong> fertilisershould be regar<strong>de</strong>d as experimental, and the resultscarefully documented. There is likely to be a finedividing line between the stimulation <strong>of</strong> the growth <strong>of</strong>'<strong>de</strong>sirable' vegetation and the encouragement <strong>of</strong>'un<strong>de</strong>sirable' species, including algae. The potential forthe stimulation <strong>of</strong> the microbiota and henceacceleration <strong>of</strong> peat <strong>de</strong>composition must also be takeninto account. The latter is an important consi<strong>de</strong>ration interms <strong>of</strong> the preservation <strong>of</strong> the pollen record andarchaeological artefacts. Note that similar commentsapply to the use <strong>of</strong> some water sources for rewetting asite. Where water is pumped onto a site, it is also likelyto be aerated to some extent, which may also help toaccelerate <strong>de</strong>composition.9.5.2 Base- or nutrient-enrichmentExcess inputs <strong>of</strong> bases or nutrients (from telluric water,bird droppings etc.) may have an adverse impact uponre<strong>de</strong>velopment <strong>of</strong> bog vegetation, <strong>de</strong>pending on theloadings in question. In most situations, the onlymethod <strong>of</strong> mitigating any adverse effects will be toi<strong>de</strong>ntify the source(s) and attempt to stop or reduceinputs, for example by diversion <strong>of</strong> polluted streams,providing flood-protection banks, scaring <strong>of</strong>f birds etc.Once the inputs have been reduced, it may be possibleto further reduce the nutrients cycling within thesystem by harvesting and removing the vegetation regularIy,although this may involve reducing water levelsto unacceptable levels to allow access by machinery.Where it is possible to maintain water levelspermanently aboye the peat surface, the promotion <strong>of</strong>vegetation rafting can help to initiate the hydrosere,and provi<strong>de</strong> a buffer against the influence <strong>of</strong> poorqualitywater [4.3].9.6 Importance <strong>of</strong> 'bunker<strong>de</strong>' torevegetation'Bunker<strong>de</strong>' is a Gerrnan terrn for the surface layer <strong>of</strong>vegetation and peat which is removed prior to peatcutting, and is probably roughly equivalent to the Irish'scragh' and the English 'riddings'. The word issometimes translated into English as 'top-spit'. It has


160RESTORAno OF DAMAGEO PE TLA OSno standard'recipe', and its character and compositioncan be variously based upon the uppermost layer <strong>of</strong>'natural' vegetation, or upon such recolonist vegetationthat ha re<strong>de</strong>veloped between cutting ep