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Restoration of Damaged Peatlands - Biblioteca digital de CIREN

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Department of the EnvironmentRestoration of DamagedPeatlands


DEPARTMENT OF THE ENVIRONMENTRestoration oC Damaged Peatlandswith 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 made to HMSOFirst published 1995ISBN 011 7529788Enquiries relating to this publication should be addressed to:Minerals DivisionDepartment ofthe Environment2 Marsham StreetLondonSWIP 3EBorEnvironmental Consultancy, University ofSheffield (ECUS)343 Fulwood RoadSheffieldSlO 3BQMain cover photograph: Solway Moss (Cumbria). [Air Images, Haltwistle, Northumberland(Tel: 034-320798), courtesy ofB. Henderson & 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 of Animal and Plant Sciences, University of Sheffield(APS» and S.C. Shaw (Environmental Consultancy, University of Sheffield (ECUS», based partly on contributionsfrom:T.R. BirkheadP. BradleyG. FosterA.L. HeathwaiteMiss L. BinnieMr D.M. Ellis(APS)(ECUS)(Balfour-Browne Club)(Department ofdeography,University ofSheffield)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 (Acadernic ComputingServices, University ofSheffield); S.Ball (Department ofLaw, University of Sheffield).The research was funded by the Department ofthe Environment (Minerals Division). We would particularly like tothank the nominated officer for this project, Dr Tom Simpson and Miss Ann Ward (Chair of the SteeringCornmittee) for considerable guidance and helpful comments throughout the duration ofthis project.We would like to express our thanks to all those people who have facilitated the progress of the project, in particularmembers ofthe project steering committee for helpful comments and advice on the draft project reports:Miss A. Ward (Minerals Division, DoE) Dr M. Meharg (Countryside 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 of Rural Affairs)ofBirds)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 ofRural Affairs)(Cumbria County Council) Mr D. Stroud (Joint Nature Conservation(Cumbria County Council)Committee)(English Nature) Mr S.F. Shorthose (Humberside 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 of the Joint Nature Conservation Committee, English Nature, Countryside Council forWales, Scottish Natural Heritage, Countryside and Wildlife Branch of DOE-NI, and local Wildlife Trusts forwillingly providing inforrnation for the project and allowing access to unpublished details of 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 andprovide inforrnative discussion and advice. We particularly thank 1. Blackie, 1. Bromley and M. Robinson (InstituteofHydrology), M. Cox (Gifford & Partners), H.A.P. Ingram (University ofDundee), M.C.F. Proctor (University ofExeter), 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 of Groningen) and Dr Hans Joosten (StateUniversity ofUtrecht) for many valuable insights and comm'ents on the draft project documents.We would also like to thank all those who kindly provided photographs for inclusion in the reporto


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


VIRESTORATlON OF DAMAGED PEATLANDS2. Characteristics ofcut-over raised bogs 312.1 Introduction 312.2 Effects of peat extraction on bog rernnants and refugia 322.2.1 Introduction 322.2.2 Hydrological effects 32Introduction 32Effects ofdrainage upon chemical characteristics 34Effects ofdrainage on bog vegetation 34Effects ofdrainage on bog invertebrates and birds 352.2.3 Habitat fragmentation 36Introduction 36Size ofremnants 36Shape ofremnants 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 ofcut-over bogs 41Water storage characteristics ofresidual peats 42Peat thickness and vertical water loss 422.3.3 The chemical environment ofcut-over bogs 42Mineralisation 43Exposure offen peat or underIying mineral ground 43Runofffrom the surrounding catchment 442.3.4 The physical environment ofcut-over bogs 442.3.5 The vegetation ofcut-over bogs 442.3.6 The fauna ofcut-over bogs 45Invertebrates 45B~ ~PART 11. PRINCIPLES OF RESTORATION3. Aims and general principies for peatland restoration13.1 Options for after-use of darnaged peatlands3.2 Airns of restoration3.2.1 The concept ofrestoration3.2.2 Restoration objectives3.2.3 Choice ofoptions(i) Maintenance or recreation ofwildlife interest not pertaining to bogs(ii) Maintenance or re-establishment ofviable populations oftypical bog species(iii) Maintenance or re-establishment ofa regenerating, self-sustaining bog ecosystem3.2.4 Species-centred versus mire-centred restoration3.2.5 Restoration opportunities in current peat workings3.2.6 Constraints on restoration objectives3.3 Sorne principies of peatland restoration3.3.1 Scope ofrestoration3.3.2 Approaches to restoration515151515152525555565757575758


CONTENTSvii3.4 PrincipIes for restoration of raised bogs 583.4.1 lntroduction 583.4.2 Conditions required for the .establishment ofbog species 603.4.3 Pathways ofbog restoration 603.4.4 Starting conditions 603.4.5 Suitability ofsites for restoration 604. Recolonisation oC peat workings 634.1 Introduction 634.2 RecoIonisation of peat workings by pIant propaguIes 634.2.1 Seed banks 634.2.2 Diaspores and dispersal distances 644.3 Effects ofhydroIogicaI conditions on revegetation 654.3.1 Significance ofwater 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 ofresidual peat 714.5 ExternaI constraints on revegetation 724.5.1 Introduction 724.5.2 Effects ofatmospheric pollution 72Introduction 72Possible implications for bog growth and restoration 724.5.3 Lowering ofregional groundwater levels 724.5.4 Climatic constraints 724.6 RecoIonisation of peat workings by invertebrates 734.7 RecoIonisation of peat workings by birds 745. Rewetting damaged and cut-over peatlands 755.1 Introduction 755.2 Establishment ofsuitabIe hydroIogicaI conditions for raised-bog restoration 755.2.1 PrincipIes ofrewetting damaged and cut-over bogs 755.2.2 Establishment ofan acrotelm characteristic oflittle-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 ofwater level by ditch blocking 78(b) Non-intervention - 'natural' reconformation ofpeat to position ofperched water mound 79(c) Sculpting ofthe peat surface to the position ofthe perched water mound 82


viiiRESTORATION OF DAMAGED PEATLANDS(d) Elevation ofthe water level by containment within wall bunds(e) Elevation ofthe mire water level by increasing water levels in the surrounding area(f) Inundation using parapet bunds(g) Inundation by reduction ofthe level ofthe peat surface to fonn lagoons(h) Provision ofsupplementary water5.4 Rewetting options for extensive peat workings in bog peat5.4.1 IntroductionSituation, topography and rewettingWater levels5.4.2 Block cuttingsIntroductionEffects oftopographyThe problem ofbaulksConclusion5.4.3 MilIed-peat workingsIntroduction(a) Ditch blocking(b) Impoundment ofwater in lagoons(c) Impoundment ofwater in sculpted hollowsConclusion5.4.4 Depth of inundation5.5 Rewetting extensive peat workings in fen peat5.5.1 Introduction5.5.2 Rewetting offlat fen peat surfaces(a) Ditch blocking(b) Irrigation by telluric water via ditches or by surface flooding(c) Impoundment ofwater in lagoons or sculpted hollows5.5.3 Rewetting offen peat basins5.6 Integrated restoration of remnant massifs and commercial peat fields5.6.1 Introduction5.6.2 Independent water management ofmassifs and peat fields(a) Preservation ofthe peat massifby bunding5.6.3 Reduction ofheight ofaH or part ofremnant massif(a) Natural reconfonnation ofthe surface ofthe massif(b) Reduction ofthe height ofthe massifby peat removal5.6.4 Elevation ofthe water table around a remnant massif(a) Elevation ofthe water table in basins(b) Reconstruction ofthe water mound around a remnant massifon flat sites5.7 Maintenance ofremnant massifs during peat-extraction operations5.7.1 Introduction5.7.2 Bunding5.7.3 Non intervention (except ditch blocking)5.7.4 Conclusion6. Restoration options and peat working practices6.1 Introduction6.2 Restoration options for ombrotrophic peat surfaces6.2.1 Climatic regimes and restoration options6.2.2 Assessment ofrestoration options6.3 Restoration options for minerotrophic peat surfaces8384858687888888898989909092929293939696979898999999100100100100101101101101102102102103104104105105106107107107107108119


CONTENTSix6.4 Restorations options for mineral substrata 1206.5 Optimisation of 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 ofvegetation 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 considerations7.3.1 Introduction7.3.2 Land costs7.3.3 Restoration procedures and management(a) Personnel(b) Specialist advice(c) Management operations(d) Monitoring and maintenance7.3.4 Financial assistance7.4 Preliminary collation of information (desk studies)7.4.1 Cartographic details7.4.2 Use ofaerial 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 developmentPlanning 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 ofsite in relation to whole peat body129129129129130131132132134134134134134135135136136137137137137137137137138138139139139139139139


xRESTORATION OF DAMAGED PEATLANDSSurface and sub-surface topography; peat depthsGeology and soils underlying and surrounding the siteAccess for machinery and equipmentLocation ofexisting features7.5.3 Land use7.5.4 Hydrology7.5.5 Substratum characteristics and water quality7.5.6 Survey and assessment of biological interest - flora and fauna7.5.7 Survey ofarchaeological and palaeoecological interest7.5.8 Potential for control of 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 of supplementary water8.3 Buffer zones8.4 Practical implications of 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 ofSphagnum from small vegetative fragments9.2.4 Regeneration ofSphagnum from spores9.2.5 Facilitation ofSphagnum establishment and rafting9.3 Inoculation with vascular plants9.4 Legal aspects of transplantation9.5 Mitigation of adverse chemical effects9.5.1 Phosphorus fertilisation9.5.2 Base- or nutrient-enrichment9.6 Importance of 'bunkerde' to revegetation10. Vegetation management and after-care10.1 Introduction10.2 Scrub control140140140140141141143143145146146146146149149149149149150150152152152155155156157157157157157157158158158159159159159159161161161


CONTENTSxi10.3 Mowing10.4 Grazing10.5 Fire10.6 Management and succession of herbaceous fen vegetation10.7 After-care ofwater 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 of 'success'11.3.1 Hydrology11.3.2 Swelling and growth ofpeat11.3.3 VegetationInoculated plant materialRates ofchange11.3.4 Invertebrates11.3.5 Birds11.4 General comments163163163163164164164164165165166166166167168168168168168169169169169171171References173ApPENDICESAppendix 1Appendix 2Appendix3Appendix 4Appendix 5Appendix 6Appendix 7Glossary of termsLegislation relating to peat extraction and restorationoptionsSynopsis of characteristics of the main plant speciesassociated with lowland raised bogs in Britain.Plant species recorded on raised bog sites in the UKBird species nomenclatureSummary of restoration measures implemented in selectedpeatland sites in lowland Britain and parts ofNW EuropeUseful contact addresses181187194199203204210


XIIRESTORATION OF DAMAGED PEATLANDSList oC Figures1.1 Stratigraphical sections across Cors Caron (Dyfed), Bowness Common / Glasson Moss(Cumbria), Coalburn Moss (Clydesdale) and Flanders Moss West (Stirlingshire).1.2 Diagrammatic profile across a raised bog, ilIustrating sorne ofthe terms used in the texl.1.3 "Classic" topographical development of raised bogo1.4 Hydroseral succession of ombrotrophic bog from various starting conditions.1.5 Distribution ofsoils identified 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 of peat and bog succession.1.7 Water budget ofa raised bog and terms used in hydrological modelling ofthe'groundwater mound'.1.8 Stratigraphical section across Raheenmore Bog (Ireland).1.9 Typical zonation ofplant communities across a raised bogo1.10 (a)Diagram ofthe succession ofspecies forming the peat in a typical"hollow-hummockcycle (regeneration complex). (b) Niche zonation within the micro-topography of a bogo2.1 The concept ofmassifs & depressions.2.2 Potential causes of dehydration of a raised bog massif.2.3 Conceptual ilIustration ofthe potential water drawdown ofthe perched water mound in araised bog as a result ofmarginal damage.5.1 The three main types of 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 ofpeat wastage.5.4 Approaches to rewetting badly-damaged remnant peat massifs based on reflooding.5.5 Revegetation ofre-wetted block-cut peatland.5.6 Terraced cascade re-wetting ofsloping cut-over peat surfaces.5.7 Restoration of peat excavations by inundation.5.8 Rewetting of remnant massifs and peat fields.5.9 Protection of massifs alongside peat extraction by bunding.8.1 Construction ofshallow internal bunds using peal.5699lO121416212431323478798185909597103105152List oC TablesSIS2S3S41.11.21.31.4Summary ofpossible starting conditions on cut-over bogs.Summary ofmain factors affecting restoration options.Practical constraints and possible solutions in the restoration ofcut-over mires.Factors which can be simply recorded, measured or monitored.Sorne distinguishing features of fens and bogs.The current condition ofraised bogs in Britain, as identified by the National PeatlandResource Inventory.Modified version ofthe von Post scale for assessing the degree ofdecomposition ofpeal.Main plant community-types ofombrogenous mires in Britain, as identified 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 of 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 of physiognomic categories of vegetation within cut-over peatlands.Summary ofpossible starting conditions on cut-over bogs.Recolonisation of cut-over surfaces by rooting or rafting.Summary ofthe likely outcomes ofdifferent options of raised bog restoration, from acontrasting range ofstarting conditioris.Potential scope of a feasibility study concerning the restoration ofa cut-over or damagedpeatland site.Primary interested parties in the formulation of a restoration scheme.Useful consultees in the formulation ofa restoration scheme.Approximate ranges ofcosts for selected restoration techniques.Possible sources offinancial or practical assistance for restoration schemes.Standard survey methods applicable to survey of invertebr~teson cut-over peatlands.Suggested plant indicator species for monitoring progress towards a raised bog objective.Vegetational indicators ofpotential problems with respect to revegetation with bog species.Invertebrtlte species associated with little-damaged raised bogs, which may be useful in theassessment of 'success' of restoration initiatives.Invertebrate species associated with partly-damaged raised bogs, which may be useful inthe assessment of 'success' ofrestoration initiatives.222743526166109131132133135136144167167170170List ofBoxes1.11.21.31.41.52.13.13.25.15.25.37.1Hydromorphological types ofbog in Britain: the concept of 'raised bog'.Climate and the occurrence ofraised bogs.Origins and development ofraised bogs.The acrotelm layer ofraised 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 ofre-soaking approaches to rewetting.Approaches to rewetting based on surface inundation.Hydrological modelling.4681315465359788488142


xivRESTORATION OF DAMAGED PEATLANDSList oC PlatesNo/e /ha/ de/ails olmos/ al/he si/es iIlus/ra/ed are given in Appendix 6.1.1 Aerial view ofthe 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 ofthe 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 ofSphagnum found on ombrotrophic bogs.Sorne vascular plant species found on ombrotrophic bogs.Remains ofa 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 ofraised-bog 'remnant'; Holcroft Moss (Cheshire)..Calluna-dominated vegetation on drained raised-bog surface at Moine-Mhor (Argyll).Birch and Rhododendron invasion on raised-bog 'remnant'; Wreaks Moss (Cumbria).Sphagnum-dominated bog vegetation confined to cut-out pools, surrounded 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 of peat stockpiles; Bolton Fell(Cumbria).Peat extracted by the extrusion method; Montiaghs Moss (Antrim).Large-scale extraction of'fuel-peat', leaves trenches and 'islands'; Solway Moss(Cumbria).Peat extraction by the rotavating and ridging method (Somerset Levels).White marl deposit underlying peat, exposed in a drainage channel through cut-over bog;Turraun Bog (Offaly, Ireland)Eriophorum angustifolium growing in an excavated peat pit, surrounded by Moliniadominatedvegetation on drained bog surface; Asíley Moss (Lancashire).Recolonised hand-peat cutting; ~illaun Bog (Ireland).Recolonisation offen 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 ofblock peat cuttings; Risley Moss (Cheshire).Sphagnum cuspida/um colonising forming a raft in a flooded 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 reflooded, marl-based peat workings at Turraun Bog(Ireland).5.1 Getty's Mire, Somerset Levels. Former peat workings mechanically contoured to thepredicted shape ofthe '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 flooded to the level ofthe top ofthe baulks; Fenns Moss (Clywd).5.5 Recolonisation offormer block peat cuttings; Peatlands 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 ofthe peatsurface as a series of depressions and hummocks; Leegmoor (N. Germany).5.9 Tussocks ofMolinia caerulea, killed by flooding; Fochteloerveen (The Netherlands).5.10 Extensive colonisation offormer bare peat surfaces by Sphagnum cuspidatum and Moliniacaerulea, within shallowly-flooded lagoon; Lichtenmoor (N. Germany).5.11 Floating rafts ofvegetation developed in reflooded, bunded, 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 wooden trackway within a raised-bog remnant at Corlea (Co.Longford, Ireland).9.1 Storage ofbunkerde, alongside current peat extraction, for future use in bog restoration.Steinhuder Moor (Lower Saxony, Germany).10.1 Scrub cutting at Roudsea Moss (Cumbria).10.2 Birch trees killed by deep flooding; Neustadter Moor (Germany).10.3 Die-back ofbirch trees attributed to flooding; Thome Waste (S. Yorkshire).707083869191929294969898104151153154160162162162


Surnrnary51 Background and introductionPeatlands are wetland ecosystems in which thesubstratum is composed largely or entirely ofpeat. Peatis an organic soil formed primarily from the remains ofplants that have accumulated in situ. Peat accumulatesin wetland habitats, largely because waterlogging andassociated anoxia retards the decomposition of plantmaterial. Peatlands can be divided 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 consideration is also given torestoration of fen peat workings.In Britain, as in much of north-west Europe, peatlandswere once very extensive and until recently, sorne ofthese areas were largely regarded as unproductivewasteland. In consequence, in Britain as widelyelsewhere, a substantial proportion of 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 of bog that has retained much of its(presumed) ,original character is undoubtedly small:figures collated for the National Peatland ResourceInventory (NPRI) suggest that in Britain the proportionof 'near-natural primary raised bog' which remains isonly about 6 % of the original extent of raised bog ofsorne 70,000 ha (although any SUCh estimated figureshave to be treated with sorne caution, not least becausethe concept and compass of the category called'lowland raised bog' is itselfopen too debate).In recent years there has been a growing recognition ofthe importance of lowland raised bogs for naturalhistory, science and conservation. Important featuresinelude:• visual character ofthe peatland landscape;• peat archive (archaeology, palaeoecology);• biological resource (communities and species of 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 ofthese peatlands through mineral extraction activitiescarried out under valid planning consents. Many of theconsents lacked planning conditions controllingmethods ofworking, restoration and aftercare.This report, prepared for the Department of theEnvironment, provides guidance on the potential forthe restoration of 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 provides backgroundinformation and scientific advice for formulating andimplementing restoration strategies for the after-use ofcurrently worked or abandoned cut-over bogs. It isintended 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 of the abandoned peat fields; and (ji) themaintenance (if needed, restoration) of vegetated peatremnants.A separate report contains the results of a wide-rangingcollation and review of 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 provide background informationand the context and elaborate on the points made here.Two broad caveats underlie all of 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 of a bogdamaged by peat extraction, it may be possible torepair or regenerate a bog by restoring conditionssimilar to those under Which it originally developedand hence to encourage the return of typical raised-bogspecies, both flora and fauna. In sorne instances thismay even offer a 'value-added' approach in terms ofwildlife 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 of decades;


XVIlIRESTORATION 01' DAMAGED PEATLANDSmoreover, given the present 'state of the art' it is notpossible to guarantee that a peat-accumulating systemwill subsequently redevelop. These guidelines andobservations should not be used to provide a justificationfor peat extraction on little-damaged bog sites.(2) Not all of 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 ofsuccess, but tohelp enhance knowledge and understanding ofeffective restoration practices, it is suggested that allattempts at the restoration of damaged peatlands shouldbe regarded as experimental, and the projects carefullyrecorded and monitored. There is still much to learn.The advice given here is based upon currentexperience, knowledge and thought, but the guidelinesmay need to be amended or updated as new techniquesand results from existing studies become available.With respect to the main subject of this report, i.e. bogrestoration, the terminology proposed by R. Eggelsmannand co-workers has been followed in which:rewetting is the re-establishment of surface-wetconditions;renaturation is the redevelopment of anappropriate vegetation;regeneration is the renewed accumulation ofpeal.These concepts are here grouped under the generichead of restoration, but they are by no means discreteand separate: indeed, the redevelopment or regenerationofa 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 considered as twolayered (diplotelmic) systems comprised of 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-dead 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 of water discharge from the bogo1 The catotelm is not, strictly speaking, 'inert'.The catotelm is defined as the zone of permanentsaturation, is largely anaerobic, and usually comprisesthe bulk of the peat of 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 develop by a variety ofpathways. The 'c1assic' developmental sequence showsinitiation of ombrotrophic peat from withinminerotrophic swamp or fen, which has developed overa pool or lake as part of a hydroseral or terrestrialisationprocess; however, raised bogs may also developover once relatively dry land, by paludification.Starting points for raised-bog development includesuch diverse habitats as reedswamp, floating vegetationmats, herbaceous fen, fen carr, woodland andsaltmarsh. The ombrotrophic peat may overlie a layerof fen peat or rest more-or-Iess directly on a mineralsubstratum. In the past, raised bogs have developedspontaneously in many parts of Britain. They arethought to represent climax ecosystems.Raised bogs provide an acidic, waterlogged, lowfertility environment, associated with the developmentofa characteristically species-poor flora and fauna.52.2 The vegetation ofUK raised bogsThe vegetation of ornbrotrophic bogs in Britain israther species-poor and comparatively uniformo Mostplant species 'characteristic' of Iittle-darnaged raisedbogs also occur quite widely in sorne other habitats.However, although the vegetation may be confined to alimited range of species, some combinations of plantspecies are apparently unique to bogs. The Ericatetralix-Sphagnum papillosum raised and blanket mirecommunity (NVC: MI 8) may be regarded as the'natural' core community-type of rnany lowland raisedbogs, and hence its recreation can be seen as the mainfocus ofthe restoration of darnaged raised bogs.The vegetation cover, in particular the abundanc~ ofsome Sphagnum species, is of critical irnportance to thedevelopment of the bogo This is because they providemuch of the physical basis of the bog itself and ofsome of its environmental conditions. In large measurethe vegetation defines the habitat. This is because:• plant growth provides the basis for peat formation,water storage and impeded drainage;• plant growth provides the basis for much of themicrotopography of the site and thus creates small-scalewater gradients;• the growth of Sphagnum species helps to create thestrongly acidic conditions of ombrotrophic peat andwater.


SUMMARYXIXWithin raised bogs, plant species show sorne microhabitat'preferences', particularly associated with theheterogeneous microtopography of the surfaces, whichis induced primarily by plant growth. Certain plantspecies tend to oc.cupy fairly distinct zones with respectto water level, either as part of the small-scale mosaicof a patterned bog surface [see Figure 1.10] or as partof a wider change in water level from the wet centre tothe drier margins of a bogo It is possible to recognise abroad pattern of vegetation zonation across the surfaceof at least sorne little-damaged raised bogs, from thecentral complex ofshallow pools and hummocks to thedrier rand.Examination of sorne of the main characteristics oftypical bog plant species enable the fol1owing general¡Joints to be made:• they are mostly ofgeographic wide distribution;• they are not specific to ombrotrophic bogs;• most are long-lived perennials;• there is little evidence that seeds and spores are generallyimportant in maintaining populations in undisturbedbogs;• seeds of 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 of 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 ofraised bogsInvertebrates forro an important part of the animal lifeof 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 of ahigh proportion of notable and rare insect and spiderspecies both within the UK and on mainland Europe,and a number of species can be identified for whichraised bogs appear to have particular conservationimportance. These include 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 mayoffer a wider range of invertebrate habitats than little-damaged raised bogs, and consequently, may support awider species range than the latter, although the speciesconcerned are not necessarily characteristic of bogs.The extensive, bare surfaces created by modernextraction methods may be far less amenable torecolonisation than the smal1-scale hand peat cuttings.52.4 The birds ofraised bogsOpen areas of little-damaged bogs typically have lowbird density and low species richness, and very fewbird species are considered to be particularlycharacteristic of raised bogs. The lack of 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 of bogs offer a limited foodsupply to birds and sorne of the species which do breedare common and widespread breeding specieselsewhere in Britain. Species composition can bestrongly intluenced by the relative degree of tloodingor desiccation and vegetation-types (e.g. scrub) developedon damaged sites. Both species richness anddensity may be greater on partly-damaged sites, largelyowing to the increased variety ofavailable habitats.Birds of particular conservation value which occur onlowland raised bogs in Britain include " significantpopulations of breeding teal, red grouse, black grouse,dunlin, curlew, redshank, nightjar and twite, andwintering populations of pink-footed geese, Greenlandwhite-fronted geese, greylag geese, hen harrier andmerlin.53 Archaeology, palaeoecology andrestorationPeatlands are important for archaeology andpalaeoecology as they have the potential to providedetailed evidence of post-glacial vegetational history,environmental change and human occupation inspecific areas (both for the site itself and itssurroundings), through preservation within the peatlayers of organic and inorganic artefacts, as well aspollen and plant and animal macrofossil remains. Peatcutting is also considered to be part of the 'industrialheritage' and abandoned areas may have positive valueas a derelict industrial landscape. Archaeologicalaspects should therefore be considered 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 isextruded 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, considerable damage to the surfacevegetation and microtopography stiH occurs. Thetechnique is akin to mole-draining and often leads tosurface-dry conditions.54.3 Starling conditions forrestorationThe starting conditions for restoration that arepresented by cut-over bogs may thus varyconsiderably. Table SI summarises sorne typicalstarting features ofcut-over sites.55 General aims and principies forrestoration55.1 Aims ofrestorationRaised-bog sites that have been damaged by peatextraction or other land-uses have various possibleafter-uses. In the past, these have often includedafforestation, conversion to agriculture, use as refusetips etc. However, changing attitudes and circumstances,coupled with a recognition of the conservationvalue of 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 include arequirement on the peat industry to restore their sites,possibly to enable raised-bog conditions to re-establish.Table 51. Summary of possible starting conditions on cut-over bogs.TopographyTopography may be very variable across an abandoned peat extraction complex, depending on the method and extent of peatextraction. Two situations can be distinguished, at several scales [2.1]:Massifsblocks with an overall convex or water shedding profile.Depressionshollows wilh an overall concave or water holding profile.Nole thal depressions may occur within massifs.Block cutting often produces a regular system of baulks, flals and trenches, but can sometimes result in a largely flat surface.Mil/ing often produces a series of long peat fields, usually as cambered beds.Peat workings are often lower than adjoining refugium areas (which may be uncut remnants or revegetating cuttings).Water conditionsPeat extraction and drainage modify or destroy 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 of 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 of 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 of a little-damaged bog is typically acidic and nutrient-poor. Peat extraction and drainage may lead to changes inthe physical and chemical characteristics of the peat available for recolonisalion [Chapter 2]. For example:• rewetting dried peat may lead to release of nutrients;• rewetting dried peat may lead to further acidificalion;• peat extraction may expose fen peat or mineral ground;• bare, dry peat provides an inhospitable physical environment for vegetation establishment.VegetationThe vegetation of remnant peat surfaces and of abandoned peat workings can be extremely variable, depending upon suchconstraints as degree of damage, depth of extraction, topography, base status, nutrient status, water level (and source) and lengthof time since last worked [Chapter 41. Areas to be restored may thus inelude 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' of raised-bog sites include:• 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 of these various foci. The requirements forthe preservation or, where appropriate, restoration ofthese features are not identical. For example, it may bepossible to preserve sorne of the features of a 'boglandscape', or the archival value of a raised-bog peatdeposit, without necessarily retaining, or redeveloping,al1 of the characteristic biota of 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 redeve10pment of a 'bog 1andscape',whilst possible, is likely to be long-term and outwiththe foreseeable future. A further complication of choicearises in those raised-bog sites which have been badlydamaged but where the replacernent habitat has itselfdeveloped a high conservation value centred on speciesand habitat conditions that are essentially atypical ofraised bogs. There is also a need to consider the currentcondition of a site when determining most appropriateafter-use. It is recommended that the appropriateoptions for specific sites are discussed with natureconservation advisers, in the light of the informationcontained in this report [in particular Chapters 4, 6 and7].The following objectives are currently adopted in theconservation management of sorne raised-bog sites inthe UK:• the maintenance or re-establishment of wildlifeinterest not pertaining to bogsThis may inelude: heath (wet and dry); rough grass;birch scrub and woodland; open water; reedbeds;herbaceous fen; fen meadow; fen woodland.• the maintenance or re-establishment of viablepopulations oftypical bog speciesThis may include bog species-populationsmaintained on badly-damaged bog surfaces orredeveloped within peat workings etc. Such sitesmay support, and be valued for, a range of species(sorne uncommon) other than bog species,including both tlora and fauna.• the maintenance or re-establishment of aregenerating, self-sustaining bog ecosystemThis ineludes the maintenance of the on-goingdevelopment of an existing little-damaged bog; theregeneration of a damaged peat massif; andinitiation of 'new' raised bogs in peat workings. Invegetation terms, such sites have, or, it is hopedwill redevelop, vegetation referable to the MI 8 bogcornmunity over al1 or part oftheir surface.There are thus at least two rather different approachesto the conservation and restoration of damaged raisedbogs. One is essentially species-centred and aims tomaintain or re-establish viable populations of typicalbog (or other) species. The other is mire-centred, tomaintain or recreate a developing raised-bog ecosystem(with associated bog species). These two approachesare not necessarily mutually exclusive.It is possible to maintain or re-establish populations ofmany bog species on damaged bog surfaces (providingthey do not dry excessively). Such artificial situationsmay maintain numbers of 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 of supplementaryspecies on damaged sites with increaseddiversity of habitats (including those produced by pastpeat extraction activities and those atypical ofbogs).In principIe the regeneration of a Sphagnum bog maybe expected to occur spontaneously in a variety ofsituations. However, SOrne starting conditions are moreimmediately suitable for raised-bog redevelopmentthan are others; and where the object of restorationinitiatives is to regenerate an ombrotrophic ecosystemwithin the foreseeable future, it is likely to be desirableto consider active procedures that will optimise andfacilitate such a process, rather than to adopt a laissezfaire approach in which natural processes of miredevelopment are just left to sort themselves out.Where parts of cut-over raised-bog sites haveconsiderable existing conservation interest, there isoften an understandable desire amongst conservationiststo rnaintain or enhance the status qua. By contrast,there may be scope for a wider choice of 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 of alternative 'dryland'habitat). However, even this does not necessari1ypreclude the development of raised bog in the longtermo


SUMMARYxxiii55.2 PrincipIes o(raised-bogrestorationAs different species and restoration objectives mayhave markedly different environmental requirements,the creation of appropriate habitat conditions can onlybe considered in terms of the specified objectives. Thepurpose of rewetting damaged peatlands is not just tomake thern wet, but to províde condítíons appropríatefor the desired renaturation and regeneration objectives.The development ofrestoration strategies needs toconsider the conditions required to realise the specifiedobjectives, whilst recognising, for example, that theconditions needed to re-establish desired types ofvegetation 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 of thedesired objectives. It is particularly appropriate forsites with limited damage. Rebuilding involves theredeveloprnent of the peatland and implies that thedesired endpoint cannot be produced directly butrequires phased construction, with a starting point ofienrather 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 of bogs extensively damagedby commercial peat extraction will usually requirerebuilding rather than repair.The aim of restoring cut-over peatlands to raised bogmay be achieved following four different paths:• direct colonisation of bog peat by plants associated withtypical bog vegetation (M 18);• colonisation of ombrotrophic water by plants and mossesassociated with bog pools followed by successionalinvasion ofother bog species;• colonisation of fen peat (or wet mineral soils) by fenplants followed by successionaI development to bog;• hydroseral colonisation of minerotrophic water to formfen and thence bogoRestoration initiatives must endeavour to createenvironmental conditions which ·are conducive·to thedevelopment of acid mire vegetation and peataccumulation, and re-instatement of an acrotelm withproperties comparable to that of a little-damaged bog,with the intention of leading to the development of aself-sustaining, ombrotrophic system. To halt orreverse hydrological effects of peat cutting anddrainage and their impacts on the flora and fauna, twomain objectives must be realised:• establishment and maintenance of consistently wetsurface conditions, maintained primarily by rainfalJ;• development of a suitable peat-forming vegetation-type,dominated by Sphagnum species.In practice, these may be brought about by thefollowing measures:•••••increase in appropriate retention of nutrient-poorprecipitation input;prevention or reduction of water inputs from othersources;faci litation ofwaterlogging;facilitation of colonisation by bog specics, in particular,Sphagnum spccies;reduction ofwater-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 of 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 of unplanned restoration, this cannotbe commended as a reliable approaeh to realise aspecific restoration goal. The 'empirieal approach' isone in which restoration is substantially based upon anintuitive appraisal of the requirements for habitatmanipulation, rather than upon the data acquisition andprediction, which forms the basis of a 'measuredapproaeh'. 80th of 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 mayprovide the only realist option when data acquisition isinadequate or of limited predictive reliability. To yieldmaximum benefits for restoration, data acquisitionshould be: (a) focused upon answering specifie,defined questions that are critícai to particular aspectsof restoration; (b) sufficiently well resourced to enSUrethat reliable and useable data are eollected; and (e)performed by experieneed practitioners who are awareof the inherent problems and likely limitations of theirstudies. Emphasis must be placed on the need forcollection of relevant and relíable data and for aconsidered appraisal, at the outset of planning arestoration strategy, of 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 of plan will be required to optimiserestoration, particularly where it is desired to restore


xxivRESTORATlON OFOAMAGED PEATLANDSTable 52. Summary of main factors affecting restoration optionsLegal considerationsNational, 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 ofway, grazing rights. public utilities etc.)Practical considerationsTopography (within site and in relation tosurrounding landscape) (includes size andshape of site, and disposition of surface)HydrologyPeat depths and types (or mineralsubstratum)ClimateFlora and faunaArchaeology I PalaeoecologyChemistryAccess by machineryPractical assistanceFinancial oonsiderationsWil/ affect decisions on most appropriate after-use (particularly with respect toplanning conditions and costs)Wil/ affect decisions 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 of retaining water on site, preventing minerotrophicinputs etc. and methods by which these can be achievedIt is important to establish causes ofdryness, degree ofdrainage, water inputs andoutputs. interactions with water in surrounding 'catchment' etc.; affects feasibilityof potential options; provision ofappropriate hydrological conditions determinesrecolonist species and type ofsuccessionHydrological, physical and chemical implicationsAffects feasibility ofpotential options for water retention, and timescales forphasing of workPreservation of existing interest; availability ofrecolonist species (especial/ySphagna); availability orprovision ofappropriate hydrological and chemicalconditions for individual species; possible conflicting conservation demandsPreservation of existing interest; monitoring during extractionBase and nutrient status of substratum (peat or mineral) and irrigating waterdetermines recolonist species, and rates of recolonisation; air pol/ution mayinfluence recolonisation, especial/y by SphagnaMay affect feasibility ofdifferent management operations, particularly in relafion tophasing of workPossibilities may affect management options (includes machinery, survey,monitoring, management etc.)May affect management and monitoring options (possibilities for compensationand grant-aid etc.; costs ofsurveys, feasibility studies, management operations,on-going maintenance etc.)the raised-bog habitat. A plan is required to ensure that,inter alia:• areas of existing natural history interest that will not besubject to further peat extraction are safeguarded;• 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 identified.Formulation of such a restoration plan for a raised-bogsite requires the acquisition of sorne information aboutthe site in question. Information (environmental andbiological) is particularly required (i) to help selectappropriate restoration options; (ii) to identify theconstraints upon the chosen options and to enableinformed decisions to be made on the most appropriateways to achieve specific objectives; and (iii) to providebase-line data for monitoring purposes. Consultationwith various statutory and non-statutory bodies willform an important part of the planning stage. Theseinelude the local mineral planning authority, heritage,conservation and water resources bodies. It is alsoIikely to be necessary to involve specialists in arder,for example, to carry out survey work; interpret theresults; assist in the preparation of an appropriaterestoration scheme with detailed specifications andperhaps occasionally to provide legal advice.


SUMMARYxxvThe variability of starting conditions amongst damagedlowland peatlands means that a universal statement of'information required' cannot be made, although it ispossible to identify some of the main types ofinformation that may be required.Assessments will be based on information derived from(a) a preliminary 'desk study' by collation of existinginformation and (b) from on-site investigations. Thelatter, together with interpretation of the information,may require the expertise of specialists from severaldifferent disciplines. Collection of superfluous informationshould be minimised by careful scoping of thesite assessment programme (an example of the potentialscope ofa feasibility study is given in Table 7.1).56.2 Potentiallegal and land-useconstraints on developmentThe relevant legislation (local, national andintemational) which may affect developnient[Appendix 2] should be investigated and itsimplications for restoration options identified. Themost important areas to be considered concemlegislation relating to planning, conservation and waterresources. Consultations with the local planningauthority, conservation bodies and water resourcesbodies are therefore of particular importance. Searchesshould also be made for possible constraints such ascommon land, rights of turbary, rights of way, riparianrights, mineral rights, shooting rights, grazing rights,location of public utilities such as gas pipes, electricitypylons etc. The implications ofany such constraints forthe project should be assessed.56.3 Financial considerationsUnless funding for restoration work has been agreed inadvance, the feasibility of restoration options maydepend 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 of the field investigations is to build on theinformation gathered in the preliminary desk-study,enabling all the relevant options to be considered in theformulation of an appropriate restoration strategy. Sitesurveys must necessarily gather information on a widerange of inter-related topics (topography, hydrology,peat depths etc.), so it is desirable 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 of thelikely limitations oftheir studies.Site physical characteristicsA broad survey of the topography and physicalcharacteristics of the site should be carried out toobtain information on the following factors, if notalready available in sufficient detail from existingdocumentation:• general size and shape; extent of sitc in rclation to wholcpeat body;• surfacc and subsurfacc topography; pcat depths;• gcology and soils undcrlying and surrounding thc sitc;• acccss for machinery and cquipmcnt;• location of cxisting tracks, pathways, boundaries,buildings and other structures; 10cation of potentialhazards (e.g. rubbish tips).HydrologyThe major problem for the restoration of most damagedbog sites is the lack of sufficient water of appropriatequality at or near the surface of the bog to sustain thegrowth of peat-building Sphagna. lt is essential toidentify the causes of dehydration and the main waterinputs and outputs in different areas of 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 recommended that expert hydrological advice issought on the level of detail required for an adequatehydrological assessment of a site in relation to theproposed restoration objectives. Information whichmay be required could include the following (at leastthose items marked * are likely to be needed):• climatic information*;• dctails ofwatcr courses* (type, distribution, slope, degreeof functioning);• water outputs*;• topographical disposition of peat fields* and remnants*;peat depths* and sub-surface contours;• peat hydraulic conductivity;• vegetation characteristics;• distribution and stability ofopen water*;• potential for water supply;• local and regional context of the site.Substratum characteristics and water qualityThe chemical properties of water and peat will have aprofound influence on the plants that will colonise agiven area of peatland, and on the likely course ofsubsequent succession [Chapters J. 2 & 4]. They mayalso affect the long-term preservation of some archaeo­IogicaI structures. Thus some basic chemical data may


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


SUMMARYxxviiThe essential problem of restoratio~ of bog vegetationon a damaged surface is one of 'kicking' the systemfrom the 'damaged surface' stable state to a 'bogacrotelm-based'stable state. The difficulty of this isthat the conditions required to redevelop an acrotelmwith the properties typical of little-damaged bogsurface are in considerable measure provided by thissort of acrotelm itself. A solution to this problem is totry to construct devices that mímic sorne of theproperties ofthe original acrotelm and which permit itsredevelopment by sustaining the growth of typical bogspecies. Many of the different approaches to bogrestoration essentially represent different ways ofattempting to solve this problem.The re-instatement of a Sphagnum-based vegetation ona damaged ombrotrophic surface is widely regarded asa most desirable aim ofraised-bog restoration [Chapter3]. It requires the establishment and maintenance ofconsistently wet surface conditions. The extent towhich this is possible will be inf1uenced by theprevailing climatic conditions and regulated by themain water-balance terms of each bog, viz. rate ofprecipitation input, rate of 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 depressions(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 of 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 includesorne bog species - .though they are ultimately likely tobe wasting assets.Because of their situation, effective rewetting of 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 depend upon the topography anddisposition of the abandoned surfaces and the c1imaticcontext. The f1at or gently sloping surfaces of modemcommercial peat fields are ofien well suited torewetting over extensive areas. Nonetheless, therewetting ofpeat fields cannot be divorced from that ofpeat massifs, particularly if the aim is to regenerate abog across the whole site, integrating both peat fieldsand the massifs (see below).57.3 Restoration options forminerotrophic peat surfacesThe type of vegetation that develops in abandoned peatworkings in fen peat is primarily a function of waterdepth (and stability), water quality (particularly baserichnessand nutrient-richness) and managementregime (if any). Peat workings within fen peat canprovide a variety of habitats, which are valued forconservation for various reasons and in sorne cases aremanaged to maintain or redevelop these interests:• open water (interest often mainly ornithological andentomological);• reedbeds (interest often mainly ornithological andentomological);• herbaceouslen (various types);• len woodland;• len meadow;• Sphagnum bogoProspects for restoration of minerotrophic surfaces willdepend critically upon the topography of the site, thewater level that can be maintained and the quality ofthe water used to achieve this (Table 6.1c). In SOrnecases revegetation within f100ded peat workings hasproduced sorne of the most important areas of fencurrently extant within the UK. Such hydroseralsituations are also susceptible to Sphagnumestablishment and in sorne locations considerablethicknesses ofSphagnum peat have accumulated (up to1 rn depth 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 of periodic dryness and irrigationwith base-rich water.The formulation of desirable restoration options for fenpeat sites is ofien more difficult than for sites based onbog peat as there is ofien more scope for habitatmanipulation and of renaturation outcome. A primarydecision is whether to focus upon the recreation of bogor fen, though these options are not mutually exclusive,as sorne forms of fen can give rise to bog vegetation.With the fen option, the choice then becomes the typeoffen desired, as this can be inf1uenced by determiningwater sources and water levels. The choice ofobjectives is Iikely to be determined by topography,availability (and quality) of minerotrophic watersources and implications for on-going management andmaintenance as well as by conservational desirability.Procedures adopted for rewetting fen peat will dependstrongly on the surrounding topography of the peatworkings. In general, rewetting can be achieved mostreadily where the wórkings form a c10sed depression(within bog peat, fen peat or mineral soil) or wherethey have been deliberately bunded. In this situation it


xxviiiRESTORATION OF DAMAGED PEATLANDSmay be possible to inundate the depressions. 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 of adjoining land.Bunding may be used to help hold water on the site,both to prevent tlooding of adjoining land and tomaintain a high water level in the fen peats. In sornesituations, it may be necessary to provide a drain tocarry away water from the agricultural land, to helpprevent the bund from drying out, and occasional1y toprovide 'top-up' water to the fen in dry summers.57.4 Restoration options for mineralsubstrataIn sorne sites peat has been extracted to expose largeareas of the underlying mineral substrata. Specificationof restoration options for this situation may be subjectto the same problems as for fen peat with respect tovariation in the character of water sources and sinks. Itis further complicated by the great variability ofphysico-chemical characteristics of the substrata,which, for example, may vary from very acidic gravelsto base-rich clays. Growth of 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 provide the basis for the development ofboginthelongterm.57.5 Integration of the restoration ofremnant massifs andcommercial peat fieldsIn sorne situations the restoration of damaged peatlandscan be approached piecemeal. This approach is likelyto be most satisfactory when it is possible to provideindependent hydrological control of particular landparcels. For example, in the fen peat basins ofindividual holdings in the Somerset Levels it may ofienbe possible to renature each working independently ofthe others. Similarly, sorne sealed depressions withinombrotrophic peat may be rewetted independently oftheir surroundings; indeed, such an approach may bethe only practical possibility in sorne sites where cutoversurfaces have been lefi at widely differing levels.This approach may be very effective in maintainingpopulations of bog species within the landscape (i.e.production of a series of 'bog-gardens') but it is lesssuited to the co-ordinated regeneration of an entiremire [see Chapter 5], for which a more holisticapproach to water management is likely to be desirable.The options for the water management of 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 maintenanceof high water levels in the massif and does not attempt torestore the bog as a single entity. The possibility of futureintegration, as accumulating peat over the peat fieldscoalesces with that on the massif, is not precluded 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 depend upon thesalient characteristics of the water mound associated withthe remnant massif. Approaches which have beensuggested are (i) to reduce the height ofthe massif to thelevel of a sustainable water mound; (ji) to elevate thewater levels (over the peat fields) around the remnantmassif; (iii) grading ofthe 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 ofconservation interests.In many instances, restoration of a raised bog does notdemand the rewetting of adjoining land, even in thosecases where it once formed part ofthe original peatlandarea. However, in sorne instances localised rewettingcould enhance the coherence of the bog or effectiverewetting of a bog may only be possible by sornemanipulation of 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 underlying aquifer would otherwise form theimpermeable base to the water mound. Rewetting ofpeat workings in fen peat may have greaterrepercussions upon the adjoining land as ofien theability to rewet the workings may depend upon watersupply and retention that is determined, directly orindirectly, by adjoining land drainage systems.57.6 Optimisation ofpeat workingpractices and startingcondítíons for restorationIt is not possible to set out universal guidelines ondesirable working practices, as these will partly dependupon site-specific features, incIuding:• conservation objectives;• character ofthe existing biological resource;• character and configuration of the remaining peat deposit(especially topography and peat properties);


SUMMARYXXIX• environmental context (especially c1imate, but alsocharacteristics and use ofthe adjoining landscape);• existing or future planning constraints.However, it is possible to identify sorne of theunderlying principIes and suggest working practiceswhich should facilitate the restoration process, andwhich should be taken into account, particularly ifplanning perrnissions and conditions are under review.General requirements include:• a scientific assessment of the character of the site,possibly by independent scientists, with particular regardto features important in determining desirable andfeasible restoration options, based on factors identified inChapter 7;• a restoration strategy should be devised 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 of operations (in parts or all of the site), peatfields should be configured into an (agreed) conditionthat will optimise restoration (i.e. to maximise use of insitu machinery, operators and infrastructure) (Chapters 5&~. -The following principIes should be taken into consideration,and irnplernented where possible:• Important refugia (which may include Iittle-damagedareas of bog, as well as revegetated cuttings or damagedareas with an important biological resource) should beidentified and steps taken to preserve or enhance theirexisting conservation interesl.• If feasible and necessary a buffer zone (Chapter 8]should be designated around the core part of anyrefugium areas, which should also remain uncul.• Work should start on the restoration of abandoned areasand maintenance of refugia as soon as possible, so thatdehydration 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 depths ofpeal.• Ifthe aim is to regenerate ombrotrophic bog directly, it isrecomrnended that as a general rule a minimum of 50 cmof 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 develop from this, by naturalsuccessional processes, but this may take longer thanwhen ombrotrophic conditions are retained in situ.]• Where possible, 'nursery' pools for the 'farming' ofSphagnum should be initiated, to provide an inoculum forabandoned areas (Chapter 9].• Drainage operations should be assessed, and wherepossible redesigned to minimise impacts on remnants andareas undergoing restoration. In low rainfall areas it maybe desirable to pump drainage water into abandoned peatworkings etc., although this will partly depend on thequality ofthe pumped water (Chapter 5].57.7 Rewetting and revegetationOnce an area has been brought out of production,further operations should start as soon as practicable tofacilitate the creation of optimum conditions forrewetting and reyegetation, including the building ofconstructs, such as bunds where necessary [Chapters 5,8 and 10], though this should be planned to ensure thatrewetting initiatives do not preclude 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 of the rnachineryavailable on site for restoration work. Sorne of thernain constraints to be overcorne and potential solutionsare identified in Table S3.RewettingApproaches considered for minirnising hydrologicalchange within upstanding peat rernnants and forrewetting cut-oyer sites include:• elevation ofthe water level by ditch-blocking;• natural subsidence of peat to the position of the perchedwater mound;• sculpting of the peat surface to the position of theperched water mound;• elevation ofthe water level by containment within bunds;• elevation of the water level by increasing water levels inthe surrounding area;• inundation using bunds;• reduction ofthe level ofthe peat surface to form lagoons;• provision ofsupplementary water.The potential applications and limitations of theseprocedures in different situations are considered 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 rnade of the existing network ofernbankrnents etc., raising levels where necessary,although the permeability of the baulks should first bedetermined to assesstheir efficacy. On milled surfaces,it rnay be necessary to subdivide large peat fields tocreate lagoons to facilitate rewetting and renaturation.Conyersely, on block-cut surfaces, depending on the


xxxRESTORATION 01' DAMAGED PEATLANDSTable 53. Practical constraints and possible solutions in the restoration of cut-over bogsConstraintSloping surfaces and culting fields atdifferent levelsUneven topographyLoss of bog basal area, withsteepened hydrological gradientsWater losses through drainageLack of water storageWidely fluctuating water levelsWater loss through base of bogInput of water of 'undesirable' qualityLack of recolonist bog species,especially SphagnaPresence of 'undesirable' plantspecies (e.g. birch and Molinia)Dry, bare surfacesShallow depth of 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 of'paddy-fields' where necessaryReconform surface to create more level conditions; lower the height ofsome baulksPeripheral bunding; raise water le veIs in claimed areas surrounding site; providesupplementary 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-tightProvide permanent inundation; consider use ofmulch (e.g. bunkerde 1 ) if available.Increase control of water levels and increase water storageInvestigate nature ofsub-peat mineral material and connectivity with regional waterleveIs - remedy ifpossible (a greater depth ofresidual peat may help to reduce theamount ofdownward seepage)Block or re-route sources ifpossibleInoculation from elsewhere on site (or furlher afield); Sphagnum 'farming' andinoculationRemoval of vegetation, followed by raising of water leveIs to keep in check. Mayneed to consider chemical treatmentRaise water leveIs (inundate if necessary); inoculate with plant material; consider useofmulch (e.g. bunkerde) if availableConsider using mineral material for bundingConsider alternative habitats as such or as precursor to bog developmentConsider use of lime or ferliliserPositive featuresBaulks and trackwaysLocalised depressions or trenchesExisting conservation ¡nterestPresence of Sphagnum speciesUse to retain water, ifpossible, (check functioning first), although may be necessaryto reduce height ofbaulks to encourage rewetting; use for access and firebreaksUse to identify where water naturally collects as a basis for developing rewettingstrategy; use for Sphagnum 'farming'Preserve and enhance where possible; use as 'core'Use as sources ofinoculum (where abundant) or as nuclei from which to spreadconfiguration remaining, it may be desirable to flattenbaulks to achieve a more level area for rewetting,(though keeping sorne of them to help retain water). Itshould be possible to use sorne ofthe material from the'redundant' baulks to fill the ditches. However, proceduresinvolving the rnovernent of peat and altering theconfiguration of 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 deliver peak discharges from the bog,otherwise erosion of the regenerating peat surface, ordamage to the dams, bunds or recolonist vegetationmay occur.1 see glossaryAfter-care and vegetation managementCertain practices are used widely in the management ofvegetation of damaged bogs and bog remnants, fromwhich sorne common principies can be identified[Chapters 3, 9 & JO]:• vegetation management is necessary to reduce theinvasion and spread of 'undesirable' 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 made to restore raised bog, except as an interimmeasure;• it may be necessary to consider the use of herbicides tocontrol 'undesirable' species;• it may be necessary to consider encouraging revegetationby 'desirable' species, through inoculation of diasporesor whole plants, in particular, Sphagnum species;• adequate provision for control offire is essential;• ongoing maintenance of bunds and dams may berequired. .


SUMMARYXXXIConsideration should be given to implementingpractical management procedures as soon asproduction ceases, both to reduce the establishment of'undesirable' plant species, especially if it is notpossible to raise water levels within a short time, and tostart encouraging establishment of 'desirable' plantspecies. Where 'abandoned' fields lie within the zoneof 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 ofvegetation may be useful inacting as 'nurse' species for Sphagnum inoculum).Full renaturation and regeneration of rewetted peatfields is Iikely to be slow, partly on account of the'difficult' nature ofthe ombrotrophic environment (andthe intrinsically low relative growth rates of bogplants). As the cut-over areas regenerate into bog theymay be expected to become increasingly selfsustaining.However, sorne degree of maintenance maybe needed in the early stages of rewetting andrenaturation, such as rémoval of scrub from dry siteswithin the peat fields. The condition of the peat bunds,especially the outer ones, will also require periodicinspection and, if needed, sorne maintenance. Theexpected intrinsically-slow renaturation of the peatfields is likely to mean that sorne (intermittent)maintenance may be required for much longer than anafter-care period of 5 years. The restoration schemeshould be designed to minimise on-going managementrequirements\ but also to make it practicable for themto take place, ifneeded.Natural recolonisation of cut-over bogs by plants maytake place quite readily where there are local refugia oftypical bog species. However, where these do not exist,or have a sparse range of species, or where sites areparticularly large, it may be necessary 'to consider themerits of 'inoculating' the damaged sites with selectedspecies either by transplantation of plant material orseeding. Plans for inoculation of rewetted areas mustbe considered carefully with respect to the phasing ofrestoration operations, as the practi'cable options willdepend critically on the planned hydrological regime.Clearly, provision of the optimum water regime, bothin terms of quality and quantity, for the desiredvegetation-type will· be an important basic consideration[see Chapters 4 and 5]. Conversely, the restorationscheme developed should take into account the\ For example, by ensuring that the floors of lagoons can be keptinundated, to minimise opportunities for establishment ofundesirable species; a strongly undulating, or sloping, surface maycreate periodical1y dry areas that are susceptible to birchencroachment elc.availability of plant inoculum. Legislation conceminguprooting of plants and transplantations must be takeninto consideration [Chapter 9].The main feature of the vegetation of an undamagedraised bog is the extent of the Sphagnum cover, which,besides being characteristic, plays various importantróles in the functioning of the bog [Chapter 1]. Thus,one of the most important factors in the restoration of adamaged bog is the question of how to regain theSphagnum cover, particularly in sites which possessfew refugia with conditions suitable for the survival ofSphagnum species. A lack of appropriate, availablepropagules may hinder recolonisation, and it may bedesirable to consider inoculation with plant material.Clearly, it will be necessary to wait for hydrologicalconditions to stabilise following any rewettingmeasures before undertaking any inoculation or transplantationwork. For large-scale restoration, removal ofSphagnum from donor sites is likely to be consideredunsatisfactory, and the possibility of increasing theavailability of propagules by farming Sphagnum couldbe considered. This could be started in abandonedareas well in advance of complete cessation ofextraction to provide an ongoing source of inoculum.It may also be appropriate to consider inoculation withsuitable vascular plants. Where possible, it is recommendedthat 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 avoided. 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 of vegetation incertain situations. ,For example, there is evidence thatthe establishment and spread of Sphagnum withinembryonic bogs can be facilitated by the presence of'nurse species' such as Molinia caerulea, Eriophorumvaginatum and Juncus effusus, or the provision of'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 sides, or detached and Iifted fromthe base ofthe cuttings.SS Recording and monitoringProcedures and progress of monitoring schemes shouldbe monitored, for the following reasons:• . all schemes must be regarded as essentially experimental,and therefore recording is important in increasing theknowledge oftechniques elc;


xxxiiRESTORATION OF DAMAGED PEATLANDS• provision of 'base-tine' data so that progress can beassessed and the restoration programme revised wherenecessary;• provision of 'hard' data so that current and futuremanagers (and other interested parties) know the startingconditions, exactly what has been done and can continueto assess the degree of success, in order to formulateappropriate further management strategies;• provision of information that can be used to assess theapplicabitity and potential of similar schemes at othersites.As recolonisation may be rather slow, monitoring mayneed to be long-term, and projects should be devisedaccordingly.Monitoring procedures need to be set up with c1earlydefinedobjectives and with identified yardsticks bywhich the direction and extent of change can bemeasured. It may be difficult to carry out and interpretin a meaningful way. It is recommended 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 detail ifpossible) will allow identification of selected species orpriority areas (e.g. those identified as refugia), plusspecies of special conservation status for regularmonitoring checks to assess response to managementoperations;• the hydrological and biological response within arepresentative selection of cut-over areas should beregularly monitored;• annual review of results to allow assessment of anychanges needed to the management programme.It may be desirable to involve specialists in detailedmonitoring periodically in order to assess progress indetail, but it is possible to make sorne simple recordsand measurements which will provide usefulinformation and give a good insight into progress[Table S4].Sorne hydrological measurements should be madebefore deciding 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 ofvertical water loss. Similarly,once the lagoons are constructed, a further period of atleast ayear should elapse to ensure that water levelswill stabilise before making decisions on plantingoperations, so that appropriate areas can be targeted,plant material is not wasted and any adjustments can bemade without fear of damage to the vegetation.As each restoration initiative should be regarded as'experimental', it is desirable that the details andoutcome should be disseminated through publicationsor accessible reports.59 Prospects and costsThere are numerous examples of spontaneousrevegetation of (mostly) small-scale peat workings andon sorne damaged mires revegetated peat cuttingsprovide the 'best' examples of 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 of younger workings thathave been kept appropriately wet since abandonmentprevent specification of the lower time threshold. [Itcan, of course, also be argued that recolonisation ofthese workings has been favoured by specialcircumstances, such as their (usually) small size andpossible 'shoeing' ofthe cuttings.]Restoration 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 of them have been in sites where problems ofwater management have been exacerbated by severalunusually dry summers and by vertical loss of waterinto a permeable subsoil. They have also mostly beencarried out as post-extraction procedures, rather than asTable 54. Factors which can be simply recorded, measured or monitoredThese include:• careful recording of management operations undertaken (including time taken and costs);• water level depth and stability (using data from dipwells, WALRAG's and stage boards);• recolonisation of rewetted areas (and others), especially by Sphagnum species;• birch death;• Molinia death;• 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 made on any water control structures (dams, bunds etc.) and remedial action taken as necessary;• records should be made of events beyond the control of site managers (e.g. heavy storms, fires, vandalism etc.) whichmay influence the future interpretation of 'success' of the project.


SUMMARYXXXIIIan integrated programme of extraction and restoration.It is nonetheless evident (a) that a wide range of bogplant species can invade 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 of aquatic Sphagna can rapidlycolonise large areas. Sorne of the rewetting initiativesin NW Germany have shown a massive expansion ofSphagnum cuspidatum over extensive areas. This eventprovides much optimism for regeneration prospects asin both the natural development of bogs and that ofrecolonised peat working's, a wet Sphagnumcuspidatum phase has provided a basis for spontaneoussuccessional develópment of a more diverse vegetationcomposed of 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, provided thattwo conditions are satisfied: (i) that the site isaccessible to potential recolonist species (if it is not,then re-introduction of species will need to beconsidered); and (ii) that the chemical composition ofprecipitation inputs will support the growth ofrecolonist species. [It is possible (but by no meanscertain) that the growth ofsorne bog species, especialIysorne species of Sphagnum, may be considerablyconstrained 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 redevelopa characteristic bog vegetation and that peataccumulation wilI recommence in time. It is difficult tospecify the likely time-scale involved, but known ratesof spread and establishment of bog vegetation suggestthat, depending on the starting conditions, effectiverevegetation may often be possible within the upperthreshold of 70 years known from the spontaneousrevegetation referred to aboye, and perhapsconsiderably more quickly than this, especialIy if it ispossible to discover, by further research, the conditionsneeded to optimise the establishment of the bogbuildingSphagna upon the lawns of Sphagnumcuspidatum.Effective renaturation does, of course, require effectiverewetting. It is important to note that sustainedrewetting of relatively flat, cut-over surfaces maysometimes be achieved more easily and effectivelythan that of residual massifs. These may show atendency to remain 'high and dry', unless providedwith substantial bunds to help retain water. Moreover,the long-term stability of peripheral bunds is notknown. Such considerations are of great importance interms both of the optimal surface configurationrequired at the cessation of peat extraction and of thepossibility of premature termination of peat extraction.The desirability ofcreating comparatively flat, uniformsurfaces for initiation of wide-scale bog redevelopmentmust, of course, be balanced against the need to retainsorne residual massifs on account of 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 of restoration are likely to depend 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 considerablevariation, reflecting specific site circumstances and,probably, the 'one-off' nature of may initiatives. Sorneof the most reliable guides to costing come from NWGermany, where a number of bogs have now beenprepared for restoratioil. These suggest that preparationcosts of cut-over surfaces are in the region ofnoo - 400 ha'¡ when appropriate equipment exists onsite and f800 - 1250 ha'¡ when it has to be brought in.


BackgroundPeat and peat extractionPeatlands are wetland ecosystems in which the substratumis composed largely or entirely of peat. Peat isan organic soil formed mainly from the remains ofplants that have accumulated in si/u. Peat accumulatesin wetland habitats, primarily because waterloggingand associated anoxia retards the decomposition ofplant material.GlobalIy, peatlands are very widespread and extensive,occurring in aH but the drier regions ofthe world, fromthe tropics to the tundra (Gore, 1983a, b; Lugo,Brinson & Brown, 1990). Estimates of the globalpeatland resource vary considerably and none areprobably very accurate. Values of over 40 millionhectares of the land area are sometimes suggested(Bather & Miller, 1991).The waterlogged conditions required for peat accumulationare provided by two broad circumstances. Thefirst is in situations where more-or-less permanentsaturation is provided by telIuric water (i.e. waterderived from the ground and which has had sornecontact with mineral substrata, such as those thatsurround or underly the peatland). Amongst otherfactors, this may be because of a high regionalgroundwater table, groundwater discharge or impededdrainage of various water sources (such as landdrainageor river floodwater). But in alI such cases, thewetness of the wetland is a product, at least in part, ofwater that has had sorne residence within, or contactwith, mineral soils and substrata. Peatlands thatdevelop under the influence of telIuric water arereferred to as minerotrophic peatlands, to which thetermfen is often applied as a synonym.In sorne c1imatic regions peat is also able to accumulatebecause relatively high and consistent precipitation,coupled to comparatively low rates of evapotranspiration,permit the maintenance of permanently wetconditions perched aboye the level of the mineralground and groundwater table. Such conditions lead tothe formation of a peat deposit 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 oftenapplied as a synonym. In many instances they havedeve10ped from fen.In Britain, as in much of north-west Europe, bothminerotrophic and ombrotrophic peatlands were oncevery extensive. The total area of fen in Britain, past orpresent, has not been quantified, but was undoubted1yonce great. The largest fen complex (The Fenland ofEast Anglia) was once a huge wetland basin, coveringan area of more than 1200 km 2 (a total which inc1udessorne 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 of over 2500 ha. On the oppositeside of the North Sea, in The Netherlands and LowerSaxony, much greater lowland bogs once occurred.The biggest had an estimated area in excess of1000 km 2 (Barkman, 1992) (i.e. about 1Y2 times thearea ofthe island ofAnglesey).Although sorne peatlands have long and intricatehistory of interaction with human societies (Coles,1990), given their once-huge area it is scarcelysurprising that over the last few centuries much of thefocus of human activity in peatlands has been to drainand c1aim them for a more remunerative use. Sorneminerotrophic peatlands have been particularly amenableto agricultural conversion, their derivative soilsoften being both base-rich and nutrient-rich. The peatsof the Fenland basin of 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 andenrich the bog peat. Sorne have involved the applicationof lime and fertiliser, sometimes using 'nightsoil'(sewage) as a source of nutrients; others haveentailed physical removal ofthe peat. At Thome Waste(S. Yorks.), the primary stimulus to drainage and peatremoval in the nineteenth century seems to have been adesire to lower the altitude of the bog surface so that itcould be 'warped' - that is, covered with silt by inundationwith estuarine water at high tides (Smart,Wheeler & Willis, 1986). In the Forth vaHey ofCentralScotland, CadeH (1913) reports how large areas of peatwere stripped to expose the underlying carse clays foragriculture. The unwanted peat was jettisoned into theriver to such an extent that fish stocks were damaged.Such profligacy with the peat resource suggests that itwas not at aH in short supply, as peat is likely to havebeen of sorne value to the inhabitants of the ForthvaHey as a fue!.


xxxviRESTüRATlüN ür DAMAGED PEATLANDSPeat has a number of properties that make it a valuedresource and it has found a very wide range of 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 of longstanding. Records indicate that various peatlands havebeen dug for fuel since Medieval times and, in sornecases, probably long before. Most of the accessiblelowland peat deposits, and various upland ones, showsigns of former domestic peat cutting, especiallyaround their margins. The effects of these 'domestic'activities should not be underestimated. In the earlynineteenth century, peat was removed from up to 90%of the surface of sorne fens in the Norfolk Broadland(Giller & Wheeler, 1986; J. Parmenter, unpublisheddata), mainly to provide 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 of removal of 1m depth of peatfrom an area of 1 ha every 50 years (Wheeler & Shaw,1995). At Thome Waste, eighteenth century peatextraction was considerable and led to the agriculturalconversion of a sizeable portion of the south-west partof 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 of Britain, and there is a smallamount ofcommercial fuel peat production. Elsewherethe fortunes of the peat industry may well have flaggedhad it not been for the widespread adoption of peat bythe horticultural industry as a base for growing media.Peat has long been an important ingredient of varioussoil-based composts, such as the John Innes compostsdeveloped in the 1930s, but it was not until the 1960sthat the potential benefits ofcomposts based largely, orentirely, on peat were recognised and promoted,revitalising peat extraction.The properties of peat are largely a product of the plantspecies that produced it and the conáitions under whichit accumulated. Both fen peats ('sedge peat') and bogpeats ('moss peat') are harvested in Britain but theSphagnum-rich moss peats are of particular value tohorticulture, because of their structure, waterholdingcapacity, low fertility, sterility and consistent character.Most moss peats are extracted from lowland bogs,primarily from sites which contain thick deposits ofsuitable peat, which are in comparatively dry regions(to facilitate drying of the material) and which arerelatively close to the main markets. Most of these sitesare sometirnes referred to as 'lowland raised bogs'.In Britain as widely elsewhere, a substantial proportionof 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 of 'primarynear-natural' raised-bog vegetation cover whichremains is only about 5 - 6 % of the original extent ofraised bog ofsorne 70,000 ha.AlI of these estimated figures have to be treated withsorne caution, not least because the concept andcompass of the category called 'Iowland raised bog' isitself open to debate. Nonetheless, it is clear that inEngland, Wales, southem and central Scotland the areaof lowland bog that has retained much of its(presumed) undamaged character is undoubtedly small.The 'peat debate'In recent years there has been a growing recognition ofthe importance of lowland bogs for natural history,science and conservation. Features which are perceivedto be important include:• visual character ofthe peatland landscape;• peat archive (archaeology, palaeoecology);• biological resource.The importance of lowland bogs as a biologicalresource is most obviously expressed in terms of theirpopulations of typical 'bog species'. However, theyalso have importance in supporting populations ofspecies of wider habitat-range in landscapes frornwhich other semi-natural habitats have largelydisappeared. Sorne of these species may persist in partsof bogs that have been partly darnaged. Damaged sitesmay also support populations of sorne uncornmonspecies which are not really typical of lowland bogs butwhich have established upon them in response tochanges in habitat conditions, such as those induced bydrainage and peat extraction.The recognition of the irnportance of sorne lowlandbogs for wildlife etc. has led to sorne concem withregard to their continued exploitation. As, today, peatextraction is the principal form of on-going utilisation,there has been sorne suggestion that the operations ofthe peat industry should be curtailed or reduced.The response of the British Government to the debateon peat in the House of 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 sorneof these peatlands through mineral extraction activitiescarried out under valid planning permissions. However,it was also recognised.that many of those permissionswere granted in the early years after the passing of the


BACKGROUNDxxxviifirst Town and Country Planning Act in 1947. This wasbefore the nature conservation importance of peat areashad been fuIly appreciated. Many of the permissionslacked planning conditions controIling methods ofworking, restoration and aftercare. The Governmentconcluded that there was a need for a full assessment ofall the relevant issues which had been raised.Scope of the reportThis report is the outcome of a project commissionedby the Department of the Environment (MineralsDivision) in 1992. The main aims ofthis were to assessthe potential for and Iimitations of restoring workedoutand damaged lowland peat bogs in the UK and toprovide the basis for guidance and options forappropriate working practices and methods to restorethese bogs, the main focus being on natureconservation requirements.The study has proceeded through two phases:(i) A coIlation and review of 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 forconsideration by a Steering Group of the project and arevised version of this is available from theEnvironmental Consultancy, University ofSheffield.(ii) The information and experience collated for theinitial working document has been utilised to preparethis present document, which provides backgroundinformation and scientific advice on the practice ofrestoration ofcut-over lowland peatlands. It is intendedfor 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 ofcurrently worked or abandoned sites.This report is concerned with the restoration ofpeatlands that have been damaged by peat extraction,with particular regard to lowland bogs. It gives a widerangingreview of much of the available informationand experience relating to the science and art ofrestoration of peatlands subject to peat extraction,based on practical experience and currentunderstanding of salient ecological processes whichoperate within peatlands; it identifies sorne of thepotential opportunities provided by restorationinitiatives, and associated difficulties; it examinesvarious approaches to restoration that may be used andconsiders 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 of lowland raisedbogs with conservation interest, makes it important thatefforts are made to active/y preserve extant areas toprevent further degradation and, where possible, torestore damaged areas and attempt to recreate thehabitat conditions suitable for the development of thecharacteristic flora and fauna ofraised bogs.Cut-over peatlands can be broadly divided into twostructural components: the peat cutting fields and uncutbog remnants. The 'remnants' sometimes retainconsiderable biological interest, even when adjacent toon-going peat extraction. This report thus addressestwo rather different, but related, main issues:(i) restoration ofthe abandoned peat fields; and(ii) the maintenance (and, if needed, restoration) ofvegetated peat remnants, both during and after peatextraction ofadjoining areas.This document is intended to be used for theformulation of future planning policy with regard topeat workings and restoration, but it is not itself apolicy document. Similarly, it is intended for use as aguide to best practices in the restoration of worked outor damaged peatlands, but is not intended to provide aprescriptive 'management handbook'.StructureThe material presented in this document falls fairlyreadily into three main parts. The first part considersvarious aspects of peatland ecology relevant torestoration and with particular reference to sorneeffects of peat extraction upon the characteristics ofpeatland sites. The second part builds on this to outlinesorne of the objectives of peatland restoration andexamines relevant principIes and information to assesspossible approaches to restoration and sorne of theconstraints upon them. The final part is concemedmore with various practical aspects of restoration, suchas identifying the sort of information that may berequired to undertake a restoration programme or sorneof the possible methods of facilitating the process.However, the overall focus of this report is not toprovide detailed technical guidance. Nor is it toprescribe universal restoration formulas for lowlandpeatlands. This is not least because the permutations ofpossible restoration objectives and site-specificconditions in which restoration takes place prevent anysimple recitation of a 'recipe' for restoration. Rather,an attempt has been made to identify the salient issuesinvolved in peatland restoration initiatives and providean overall factual and conceptual basis which it ishoped will enable informed decisio.ns to be made andstrategies developed that are applicable to the peculiarcircumstances ofindividual peatland sites.


xxxviiiRESTORATION OF OAMAGED PEATLANDSCitationsThis volume is. a much condensed version of theoriginal working document [see aboye]. Although itcontains numerous references to the sources ofinforrnation upon which it is based, it is not practicableto inelude all relevant citations, nor the details of otherpieces ofevidence (field observations, discussions etc.)which have contributed to various comments andconclusions. Comprehensive citations and other detailscan be found in the working document.Scope for restorationOne important component of this review was anevaluation of the potential for the restoration ofworked-out 01' damaged bogs to regenerate, maintain 01'increase their nature conservation value; and to provideguidance on the practicality of such procedures. This isbecause peat extraction does not 01 necessity destroy,01' irreversibly change, the salient environmentalconditions and circumstances that perrnit the growthand reproduction of many typical bog species and theforrnation of bog peat. In principie, the effect of peatextraction is to remove sorne of the accumulated peatand to cut the surface of the bog back to an earlierstage in its development so that, depending upon thecondition and conforrnation of the 'new' surfaces, itmay be possible to encourage the regeneration of 'new'raised bogs within the worked-out ramparts ofthe 'old'ones. That potential exists for the redevelopment ofbog vegetation is illustrated by the spontaneousrecolonisation of sorne abandoned peat workings andby sorne experimental attempts to regenerate bogvegetation. Nonetheless, many current commercialoperations are on a much larger scale than those of 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 withincidental peat contents, such as the pollen grains etc.thatpreserve a palaeoecological record. The palaeoecologicalrecord cannot be restored and whilstrecolonisation by plants and animals typical of bogsmay be possible in the long-terrn, it will not onlyrequire the redevelopment ofconditions appropriate fortheir growth but may also depend upon the survival ofthese species in a refuge adjoining, 01' near to, the peatworkings whilst extraction is taking place.Two broad caveats underly aH of 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 of a bogdamaged by peat extraction, it may be possible torepair 01' regenerate a bog by restoring conditionssimilar to those under which it originaHy developedand hence to encourage the retum of typical raised-bogspecies, both flora and fauna. In sorne instances thismay even offer a 'value-added' approach in terrns ofwildlife 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 of decades;moreover, given the present 'state of the art' it is notpossible to guarantee that a peat-accumulating systemwill subsequently redevelop. It is therefore suggestedthat these guidelines and observations should not beused to provide a justification for peat extraction onlittle-damaged bog sites.(ii) Not aH ofthe 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 ofsuccess, but tohelp enhance knowledge and understanding ofeffective restoration practices, it is suggested that allattempts at the restoration of damaged peatlands shouldbe regarded as experimental, and the projects carefullyrecorded and monitored. There is still much to leam.The .advice given here is based upon currentexperience, knowledge and thought, but the guidelinesmay need to be amended 01' updated as new techniquesand results from existing studies become available.TerminologyA deliberate attempt has been made to reduce thenumber of 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 aredefined in the text and a glossary (Appendix 1) is alsoprovided. With respect to the main subject of thisreport, i.e. bog restoration, the terrninology proposedby R. Eggelsmann and co-workers has been followed,in which:rewettingrenaturationregenerationis the re-establishment ofsurface-wetconditions;is the redevelopment ofanappropriate vegetation;is the renewed accumulation ofpeat.These concepts are here grouped under the generichead of restoration. However, note that they are by nomeans discrete and separate: indeed, the redevelopment01' regeneration ofa 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 of Lowland Peatlandsused for Peat Extraction


Chapter 1Lowland peatlands1.1 Peatlands: fens and bogsDifferent types of peatland can be recognised based onvarious characteristics (Gore, 1983a). One of the mostwidely-used distinguishing features is the nature of thewater supply. Von Post & Granlund (1926) subdividedpeatIands into three main types - ombrogenous,topogenous and soligenous examples - reflecting thedifferent primary causes of surface wetness and peataccumulation. This e1assification is stilI widely 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 of the topographyof 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 inputsof telluric water (i.e. water derived from the groundand which has had sorne contact with mineral substrata,such as those that surround or underIy the peatIand)and they are ofien referred to as minerotrophic ('rockfed')peatlands (or fens). By contrast, ombrogenous('rain-made') peatIands (or bogs) are exelusivelyombrotrophic ('rain-fed'), with the supply of water totheir surface being derived directIy and exelusivelyfrom precipitation. Various broad differences can beobserved [Table 1.1] but, nonetheless, certain types offen can be very similar to bogs in many of theircharacteristics and it is difficuIt to provide a simple,universal specification of how the two types can, inpractice, be consistentIy distinguished (Wheeler, 1993).Whilst (as in this account) ecologists ofien use theword 'bog' to refer to ombrotrophic peatlands and'fen' to mean minerotrophic examples, such usage isby no means universal. Sorne wetlands that are ofiencalIed 'bogs' are actuaIly fens in that they areminerotrophic in character. For example, most of theSphagnum 'bogs' of the New Forest (Hampshire) arestrictIy-speaking 'poor fens', as they receive substantialinputs of 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 ofa peatland site.The term 'mire' has received a variety of usage (e.g.Ratcliffe, 1964; Gore, 1983a,b). It is ofien used as asynonym for peatland (Gore, 1983a), but sorneworkers also inelude sorne mineral-based wet landwithin the compass of 'mire'.In Britain, peat extraction currentIy takes place both infens and bogs, but commercial extraction ofbog peat ismuch more widespread than is that of 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 of fens and bogsWater sourceNutrient statusCharacter ofsubstratumPeat typesPeatpHSpecies diversity ofvegetationFenPrecipitation plus telluric water (minerotrophic)Nutrient-poor to nutrient·rich (may be supplementedby enrichment of water supply from agriculture etc.)Usually peat but may have varying mineral content;some mineral soilsTypically various mixtures of 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 dependent on nutrient supply, pHand management)809Exclusively from precipitation (ombrotrophic)Nutrient-poor (nitrogen may besupplemented by atmospherically-derivedenrichment)PeatTypically Sphagnum mosses with somesedges, herbs and woody (ericaceous)speciesTypically < 4.5Typ'ically low (unless damaged)


2RESTORATION OF DAMAGED PEATLANDS1.2 Origin and development ofpeatlandsThe origin and development of peatlands, both asindividual sites and as part of the broader landscape, isofien complex and is beyond the scope of 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 of open waterand by the waterIogging ofonce-dry land.The process by which water becomes wetland is ofienreferred to as terrestria/isation or hydrosera/succession (Weber, 1908; Tansley, 1939). It occursaround lakes and pools and can lead to the completereplacement of once open water by peatland. Thedetails of terrestrialisation processes can be complex(Walker, 1970), but they usually proceed by one oftwomain routes - rooting or rafting. Rooting (or lit/oral)successions occur when water bodies graduallyaccumulate deposits of silts, muds and peats. Theshallowing water becomes subject to centripetalinvasion by plants of swamp and fen, rooting on theaccumulating sediments. By contrast, in the rafiingprocess, vegetation grows across the surface of openwater to form a floating mat, composed of peat andplants. In its early stages, this rafi of precociouspeatland is ofien thin, unstable and quaking and welldeservesthe name of schwingmoor ('floating mire')which is sometimes given to it. But later, it maybecome so thick and consolidated that the former existenceof a floating rafi can only be deduced by peatstratigraphical studies. Rafting successions are particularIycharacteristic of small, sheltered and ofien deepwater bodies, and have occurred quite frequentIy inkettle-holes and similar basins.The processes associated with terrestrialisation havehad a pervasive influence upon the conceptual developmentof paludology, to the extent that the term'hydrosere' is sometimes used loosely (and incorrectly)for all forms of developmental change in wetIands.However, many peatlands have not developed by theterrestrialisation ofopen water but by the swamping, orpa/udification, of once relatively-dry land (Cajander,1913). It is ofien not clear, just on superficial inspection,which mechanism has been instrumental in thedevelopment of a particular. peatland and, in consequence,the past occurrence of the two processes inBritain is not really known. Nonetheless, there can belittle doubt that, in terms of the total area of 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 of many lowland rivers(such as The Fenland of East Anglia) have largelyformed by paludification. So have the huge areas ofbog peat that blanket many upland landscapes. Suchcontrasting situations as these point to a variety ofcauses of paludification, inc1uding climatic change,land-sea level change and deforestation.The initial type of peatland that develops byterrestrialisation of open water is usually a form of fen,but in suitable c1imatic regions [1.31, ombrogenouspeat may subsequently develop within and upon this asimpeded drainage of precipitation permits the gradualaccumulation of layers of ombrotrophic peat aboye thelevel of mineral soil water influence. Paludification ofdry land also ofien leads, first ofall, to the formation ofminerotrophic mire, which again may sometimes besubject to progressive ombrotrophication. However, insorne circumstances paludification can resuIt in a moreor-lessdirect development of ombrotrophic peat,without a significant intervening minerotrophic phase.Ombrogenous bogs are thought to be c1imax ecosystems,which have developed spontaneously from avariety of starting points and which are believed to bestable, at least when undamaged.1.3 Types of fens and bogsMinerotrophic peatlands occur in a very wide varietyof situations, wherever the water table is sufficientlyand consistently high to sustain peat accumulation. Thedistribution and occurrence of fens is largely determinedby an interaction between landscape topographyand local or regional, hydrology. Likewise, the grossmorphology of a fen is ofien largely a reflection of thefeatures of the landscape in which it occurs. Deepaccumulations of fen peat are most characteristic oftopogenous sites, e.g. ground hollows, basins and riverflood-plains. Various classifications of 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 oftopographical situations to minerotrophic examples butboth their geographical distribution and the range oftopographical situations in which they can form isstrongly constrained by climate. This is because theirdevelopment requires a sufficiently high rate ofprecipitation input (ofien coupled with low rates ofevapotranspiration) to permit peat to accumulate aboyethe level of the mineral ground or the influence oftelluric 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 development have yet to be established,but examples occur from the tropics to the


CHAPTER 1: LOWLANO PEATLANOS 3Plate 1.1 Aerial view of the west bog, Cors Caron (Dyfed). The drier margins of the raised bog are picked out by thelighter colour of the vegetation, with the River Teifi forming the 'Iagg' on one side of the bogo [Photo: J. Davis]boreal regions. In temperate Eurasia, most ombrotrophicmires occur between the latitudes 50-70° N(proctor, 1995).By their nature, ombrogenous mires form as a peatdeposit raised aboye the level of the regional watertable, the underlying minerotrophic peat and mineralsoil. The shape and dimensions of bog-peat depositsvary very considerably, depending primarily upon theirage, the underlying landforms and the climatic regimein which they have developed. In the drier regions ofBritain, bog formation has been restricted to flattishsurfaces or very gentle slopes, whereas in the wetter,cooler regions of the north and west, it has also beenable to occur upon quite steeply sloping terrain. Thisdifference has provided the basis for the recognition oftwo, rather ill-defined, main categories of 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 of broad, flat valleys, the heads of estuaries orshallow basins [Plate 1.1]. In their most distinctivedevelopment they form shallow domes of ombrogenouspeat delimited usually by mineral ground, fenor watercourses. They sometimes form large complexesin which tracts of bog are separated by watercoursesor fen. In Britain, sites that are usually called raisedbogs typically occur in regions with an annualprecipitation range of c. 800-1200 mm a- Iand with140-180 wet days a-) (Rodwell, 1991), though the fullrange is wider than this [BOx 1.2]. [See al so 1.5]Blanket bogs: These are ombrotrophic peatlands that'blanket' large areas of 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 of c. 1200 mm a- 1 and morethan 160 wet days a- I(Ratcliffe, 1977). In much ofEngland and Wales they are restricted to the higheraltitudes (above c. 400m) but in westem and northemparts of Scotland and Ireland they descend to near sealevel. The capacity of blanket bogs to form on slopesmeans that they ofien form much larger tracts ofcontinuous ombrogenous peat than is the case withraised bogs. They are most usually delimited by atransition to mineral soil (ofien a peaty podsol). andsometimes form very large complexes in which areasof 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 of these bog'types' have not been critically or rigorously defined and theterms have been applied loosely to sites, sometimes withoutexamination of their actual features.'Classic' raised bog in Britain, as described by Tansley (1939),reflected the observations of Weber (1908). ft occupied adiscrete lowland site; it had developed by hydroseral successionfrom open water (open water ~ swamp ~ fen ~ bog);and it formed a shallow dome of 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' model, forexample, in mode of origin, gross morphology or altitude.In the 'c1assic' raised bog, ombrogenous peat, developed upona flat surface of fen, formed a dome independent of theunderlying base. Such 'independent doming' is sometimesregarded as part of the character of a raised bog, butexamination of stratigraphical sections reveals that thecharacteristics of domes of ombrogenous peat in sites that arenormally considered to be raised bogs can show muchvariability. The degree of 'doming' appears to be a product ofage, topographical situation, basal area and c1imate. It is ofienmost evident in small bogs; larger examples ofien do notappear strongly domed, but may form an extensive plateau ofpeat with steep edges (Ratcliffe, 1964). The surface of the bogpeat may sometimes be strongly related to the underlyingtopography, as when the summit of the dome reflects anunderlying mineral ridge. Such sites may have developed bythe coalescence of 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 of distinction as many of the sitesthat are normally called 'raised bogs' in the British Isles and onthe European mainland have developed by expansion acrossridges of mineral ground (for example, most of the Lancashiremosses (C.E. Wells, unpublished data).The range of hydromorphology of those British sites that areofien 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 'independent' domeand a flat base, having originated by autogenic successionfrom preceding phases of fen and open water. The stratigraphyof Bowness Common-Glasson Moss points to a sitewhere peat initially developed, hydroserally, in depressions,but grew out of these to coalesce across substantial ridges.Flanders Moss West seems to have developed largely bypaludification. Its section illustrates the manner in which the'doming' of some British raised bogs reflects the contours ofthe underlying mineral ground. The section of Coalburn Mosspoints to a gently sloping site without a c1ear dome; moreover,undulations in its surface show some parallel with theunderlying relief. Such systems have strong hydromorphologicalaffinities with some examples of blanket bog, and theactual point of distinction is far from clear - a confusionexacerbated by the occurrence within some blanket boglandscapes of mires with strong affinities to many 'Iowlandraised bogs' (see below).Raised bogs may be surrounded by a minerotrophic lagg,which is sometimes considered to form par! of the concept ofraised bogo The actual character of the lagg of many Britishbogs is difficult to assess, as it has frequently been destroyed,but a well-developed, or complete lagg, may not have been afeature of 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 of minerotrophicfen or mineral soil. Distinctive, moat-like laggs areofien most evident in basins where the lateral expansion of thebog has been constrained topographically. In other cases, aswhere a dome of ombrogenous peat has extended beyond theformer limits of a basin, the lagg, if present, may largely be aproduct of. t~e growth of the bogo Elsewhere, minerotrophicmires adJolnlng or surrounding a raised bog may predate thebog and be substantially independent of il. In yet other sitesthe 'Iagg , has effectively been imposed upon the bog, aswhere water courses and regular f100ding has preventedfurther lateral expansion of ombrotrophic peat (Ratcliffe, 1964).Such considerations suggest that it may be best to excludethe lagg from any general concept of raised bog and to restrictthis specifically to the deposit of ombrogenous peal.It ismore dimcult to identify a 'classic' concept of blanket bog- It 15 ofien Informally considered to be ombrogenous peatlandwith a more upland and north-western distribution than raisedbog, which blankets large tracts of land, conformed by thetopography and restricted only by the steeper slopes and otherobstructions. There is a tendency to regard all ombrogenouspeatlands within 'blanket bog regions' as blanket bog, irrespectiveof their actual character, and even to consider theirgreat extent, across a wide variety of relief, as a diagnosticfeature. However, location is not a hydromorphological attributeand size alone seems a specious basis for a distinction ofbog types - especially as, elsewhere in Europe, lowland'raised bogs' once covered areas of comparable magnitude tosome tracts of blanket bog [1.4]. The key distinguishingfeature of blanket bog is the occurrence of ombrogenous peaton hillslopes and it is far from clear that the ombrogenouspeatlands of the basins, flats and gentle slopes of 'blanket bogregions' are necessarily fundamentally different - in terms oftheir origin, gross form and stratigraphy - from the 'raisedbogs' of drier c1imates. Indeed, various stratigraphical sectionssuggest that some units of bog embedded within a 'blanketbog landscape' have greater similarity with 'raised bogs'elsewhere than they do with the blanket peats on adjoiningslopes (e.g. Department of Agriculture and Fisheries forScotland, 1962-8). If such units are included within a broadconcept of 'blanket bog', they expand this to encompass muchof the hydromorphological range of 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 of hill bogand topogenous bog used by the Scottish Peat Survey. Onthis basis, the 'blanket peatlands' of oceanic regions can beseen as a mosaic of hill bog, topogenous bog and varioustypes of fen, whilst 'Iowland raised bogs' of drier regions arereferable to topogenous bogoThe variability of ombrogenous mires in Britain undoubtedlymakes it difficult to formulate a clear and coherent concept of'raised bog'. We suggest the following tentative, workingdefinition of 'raised bog' in the UK: "Ombrogenous mires inwhich much of the vegetation is typically referable to, orclosely allied with, or derivative from (e.g. as a result ofdamage), Erica tetralix-Sphagnum papillosum mire (Rodwell,1991); they may exhibit a dome (or domes) of peat independentof the underlying subsoil contours, but this is not alwaysthe case; some (usually older) examples contain deep(sometimes > 5m) bog peat, which is frequently little-humifiedin the upper layers." Mires thus identified 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 depressions and ridges, over whichthe bog has developed); in some instances they havedeveloped by coalescence of adjoining mires (sometimesoriginating in separate basins). Such sites may be surroundedby mineral ground, fen or an ombrotrophic 'hill peal'. Using thisdefinition, most sites of 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.MudeII 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 deposits 11I1 Sphagnum peal HH ~=======~ um;naled sandy clay • Silty clay (I.warp) • Oay mud (u.warp)o Wood fragments Sphagnum peal H5-10 ~ Boulderday U Coarse detritus 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 profile across a raised bog, illustrating some of the terms used in the text.blanket bog specifically to refer to the ombrogenouselements of this.In Britain, most commercial peat extraction concernslowland raised bogs and these are the focus of thisaccount.1.4 Sorne features of raised bogsOn casual inspection, little-damaged raised bogsfrequently appear to be rather featureless, uniformtracts of waterlogged ground, sometimes with a windsweptdesolation that may be perceived variously asdismal or delightful. They vary very considerable intheir size. In Britain, embryonic 'raised bogs' (e.g.areas of ombrogenous peat within fens) may cover justa few square metres, whilst the largest raised bogs arein excess of 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 of 1000 km 2(Barkman, 1992). The depth of peat in raised bogs isvery variable and depends particularly upon the age ofthe deposito Thicknesses of bog peat reported fromBritain typically range between about 1 and 5 m.The overall topography of little-damaged raised bogsvaries considerably. Sorne (usually rather small)examples have a quite strongly domed appearance inwhich the profile of the bog peat deposit approximatesto a half-ellipse. In others, the peat deposit 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 of the bogmargins with the adjoining mineral ground is markedby a moat-like lagg, normally supporting fenvegetation. [A diagrammatic profile across a raised bogis shown in Figure 1.2]. However, the naturalmorphology of many raised bogs, especially the naturalstate of the margins, is not really known, as peatextraction and agricultural conversion has altered thetopography of most sites. Commercial peat extractionusually alters the configuration of the entire bog whilstdomestic extraction, or agricultural improvement,Box 1.2 e/imate and the occurrence of raised bogsThe formation of a deposit of ombrotrophic peat, and to some extent its dimensions, is dependent upon the c1imatic regime inwhich it occurs, especially the ratio of precipitation to evaporation [see Box 1.5], but the precise range of c1imatic circumstances inwhich bog formation can occur is not well understood, partly because some water balance terms have received but Iimited study.Water supply to bogs is frequently specified just in terms of precipitation input, but this has to be balanced against potentiallosses by evapotranspiration. (The amount of evapotranspiration is influenced by such factors as solar radiatiqn, air and surfacetemperatures, wind speed and relative humidity. Vegetation-type and mulching effect of the moss or Iitter layer also affect it.)Moreover, the annual mean values that are usually provided for these variables may not be as significant to the development andmaintenance of bogs as are seasonal values, though the importance of these latter has been little-quantified. Factors such as thefrequency of rainfall (proportion of rain-days, i.e. days with 1 mm or more of precipitation), number of days with sunshine, relativehumidities, temperature, exposure etc. may be of considerable importance in maintaining some ombrotrophic systems. In regionswith smaller rates of evapotranspiration, raised bogs can form with lower precipitation input. Various notional figures have beensuggested as a minimum precipitation thresholds for the development of raised bogs (e.g. 460 mm, S Sweden; 600-700 mm, NGermany). In the UK, peatlands that are usually called raised bogs occupy a wide range of 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 of restoration of damaged sites and the nature of therestoration procedures that can be used.


CHAPTER 1: LOWLAND PEATLA D 7Plate 1.2 Distinctive microtopographical patterning of 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 of presumed features such as therand and lagg is ofien not known. In some cases, bysharpening the edges, marginal damage may haveaccentuated the domed appearance of peat deposit.Direct and indirect drainage may also have causedsome changes in the topography of many sites,including little-damaged examples, but the nature andextent of this can scarcely even be guessed.In Britain, as in other regions of 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 of the European mainland, whereconifer species can be important components of at leastthe landward zones of bogs. lt is possible that, even inBritain, trees may once have been natural componentsof bog vegetation, at least towards the margins, andperhaps more widely in extended dry periods (elCasparie, 1972), and that the role of grazing andbuming in preventing natural scrub encroachment hasbeen underestimated (H. 1ngram, pers. eomm.).The vegetation of little-damaged bogs forms a miresurface with a characteristic appearance, based upon itsmain constituents ofsub-shrubs, 'sedge-like' plants andbog mosses (Sphagnum species) [see PIates 1.4 and1.5]. The sub-shrubs are mostly members of 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 of theCyperaceae) inc1ude the cotton grasses Eriophorumangustifolium and E. vaginatum. Sphagna are ofien keycomponents of the vegetation, in terms of their coverand their contribution to the surface processes and peatformation of the bog [1.7; 1.8; 1.9]. The vegetation oflittle-damaged raised bogs and blanket bogs has agenerally similar overall appearance, but there aresome broad differences between them in terms of theirspecies composition (Rodwell, 1991).Some parts of the surface of 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-tloodedhollows with aquatic species of Sphagnum, but larger,deeper and more permanent areas of open water alsooccur in some bogs. These may range greatly in size,from a few metres to several tens of metres across.Larger examples are variously known as 'bog lakes','moor eyes', 'wells' and 'dubh lochans', the [atterretlecting the appearance of 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 of research, the causes of surface pattern ing arenot at all well understood, neither for the 'hummockhollow'pattem nor the more permanent pools.The surface of a little-damaged raised bog is typicallywaterlogged, despite its elevation aboye the adjoiningland. The highest, more central, parts of the bog areofien the wettest and typically show the mostpronounced development of surface patterning andpool systems, whereas the rand is better drained. Thewet condition are created (in mo t cases) by anaccumulation of rainfall [1.7] and the chemicalcharacteristics of the bog water reflect the compositionof the rainfall, modified by processes within the peatand by the growth of plants. The water of raised bogscan be described simply as being 'acidic and nutrientpoor' [1.9.4].


8RESTORATION 01' DAMAGED PEATLANDS1.5 Occurrence of raised bogsRaised bogs occur widely in temperate and borealregions of Eurasia and North America. They are (orwere) important features throughout much of northernEurope, being particularly widespread and extensive inBritain and Ireland, the Netherlands and north westGermany, southem Sweden and Finland and in theBaltic States. Examples also occur, somewhat separatedfrom the main range, in the foothills and valleys ofthe Alps. There is a tendency for raised bogs in differentregions to show sorne differences in gross morphology,particularly with respect to the concentricity oftheir domes and areal extent (Moore & Bellamy, 1974).In Britain, although many examples have beendamaged or destroyed, lowland raised bogs still have awide distribution. They are especially widespread inthe cooler, wetter regions of the north and west (northwestEngland and southern and central Scotland), butexamples also occur (or once occurred) in a number ofsouthern and eastern localities, including sites in S.Yorkshire, Lincolnshire, Cambridgeshire, Somersetand Sussex. It is possible that raised bogs were onceeven more widespread in these drier regions than iscurrently recognised, as in sorne situations agriculturalconversion and ancient peat-cutting may have removedmost traces of former ombrotrophic peat. Figure 1.5shows the distribution of peat soils that are regarded bythe National Peatland Resource Inventory (Lindsay elal, in prep) as being associated with raised bogs inEngland, Scotland and Wales.Raised bogs are particularly characteristic of lowlandregions of Britain, where they occur in basins, alongflood-plains, at the heads of estuaries elc. However,examples have been described also from more uplandsituations, such as Tarn Moss, Malham (W. Yorks.)and Dun Moss (Perths.) which are both at about 350 maltitude.Raised bogs have developed both by terrestrialisationand paludification processes and sometimes by acombination of the two mechanisms. Although they aremainly initiated in depressions or on flat surfaces,continued upward accumulation of bog peat haspermitted sorne examples to spread onto adjoining,once-dry, slopes and to coalesce across ridges ofmineral ground [Box 1.3].Box 1.3 Origins and development o( raised bogsRaised bogs may originate and develop by a variety ofpathways. The 'c1assic' developmental sequence (Weber,1908) [Figure 1.3] shows initiation of ombrotrophic peat fromwithin minerotrophic swamp or fen, which has developed overa pool or lake as part of a hydroseral or lerreslrialisalionprocess. However, it has long been recognised that raisedbogs have also developed by the swamping of ground thatwas once relatively dry, either more-or-Iess direcUy or, moreusual/y, through an intervening (sometimes short-Iived) phaseof fen (Cajander, 1913). This process is known aspaludification. Thus starting points for raised bog developmentinclude such diverse habitats as reedswamp, f10atingvegetation mats, herbaceous fen, fen carr, woodland andsaltmarsh [Figure 1.4). Common to al/ of these developmentsis the progressive upward growth of peat aboye the level ofinfluence of groundwater, leading to a surface irrigated almostentirely by precipitation inputs. The character of this is, in largemeasure, independent of its starting 'conditions. The timetaken for the development of 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 of raised bog have developed initial/y in abasin, often as a late phase of hydroseral succession, buthave subsequently expanded over adjoining 'dry' land. Thisprocess can lead to the fusion of adjoining raised bogs toproduce a larger unil. The very extensive raised bogs of 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' of ombrotrophic peat out of the original basin ontoadjoining mineral ground produces, at least initial/y, a thinhumified peat-type that, both in character and situation, isreminiscent of some types of blanket bog peal. This has beenIitUe documented in Britain but is probably quite widespread.Examples are thought to occur at Wedholme Flow and WaltonMoss (Cumbria).In some mires the development of bog peat has been socomplete as to cover most traces of former fen. However,more usual/y the apparent present-day dominance of somepeaUand sites by bog reflects the drainage and agriculturalconversion of once-adjoining fen. This may be the case, forexample, in situations where some, or al/, of the bog peat hasbeen left unclaimed on account of the greater difficulties ofconverting it into productive agricultural land. Deep peatexcavation sometimes exposes underlying fen peat andprovides the possibility for the re-establishment of fenvegetation.The initiation of ombrotrophic peat implies impeded drainageof precipitation inputs. This may be produced in various ways.Where the bog peat has developed from fen and swamp, thenthe low-permeability bottom of the bog is frxed either by thefen water table itself, or by the surface of low-permeability fenand wood peats. Where bogs have developed bypaludifrcation, the basis for the establishment of permanenUywet conditions may be provided by a variety of 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 of a high groundwater table within the porousmedium (as in zones of groundwater discharge) or because ofthe development of low permeability pans of 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 of 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 ofHer MIJUty'J Slitionary Offic:.. Ce) erOW" Copyn&ht.Figure 1.5 Distribution of soils identified by the National Peatland Resource Inventory as associated with raise!bogs in England, Scotland and Wales, by 10 km square. [Diagram provided by Scottish Natural Heritage].


CHAPTER 1: LOWLAND PEATLANDS111.6 Current condition of 8ritishraised bogsScottish Natural Heritage are preparing an inventory ofthe extent and condition of raised bogs in Great Britain(Lindsay el al.; in prep.), on behalf ofthe 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 of raised bogs and the 'bes1'land cover classes identified for each site.The category of 'closed-canopy woodland' includesboth forestry plantations and sites that have becomespontaneously wooded, although the majority iscommercial plantation. Thus, wooded bogs, togetherwith the agriculture,and urban categories, account forsome 48% of 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 considered to be areaseffectively 'los1' from the raised-bog resource, then theresidue represents some 36,000 ha of raised-bog sitesin variable condition. Only a small proportion of this isregarded as being more-or-Iess 'natural' (littledamaged).The biological condition of the remainder isnot specified, but it cannot be assumed that it has noconservation value, even in terms of 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 provide a richrepository of bog species. For example, WedholmeFlow, which retains some of the finest examples oflittle-damaged Sphagnum-rich raised-bog vegetation inEngland, is categorised under its major land-use classof 'secondary - revegetating'. Likewise, it should benoted also that the area of bog designated as'secondary - active commercial peat extraction'contains some large expanses of vegetated (sometimesrevegetated) bog peat, as well as active peat fields.There can be little doubt that the total area of 'goodqualityraised bog' remaining in Britain is small, norabout the identity of some of the main causes ofdamage. However, the loss of 'quality' in bogs may notjust be a product ofdirect damage of the type identifiedin Table 1.2. In various lowland mires, once-diverseSphagnum communities have been replaced by lawnsdominated by one species, Sphagnum recurvum (Tallis,1973). The explanation of this is not known: pastsulphur pollution, enrichment with atmospheric nitrogensources, especially perhaps ammonia, or someother form ofenrichment from agricultural sources, areall candidate hypotheses. Such considerations make itdifficult to be confident about the full measure ofimpact and significance of the more direct forms ofdamage identified 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 destruction.Table 1.2 The major land cover classes* on raised bogs in Britain, as identified by the National Peatland ResourceInventory (Lindsay et al, in prep). Source: Department of the Environment (1994).England Scotland WalesCondilion class Number Area Number Area Number Areaof bogs (ha) of bogs (ha) of bogs (ha)Primary - near-nalural 1 8 49 2673 5 2694Primary - degraded (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 of lhe dominanI land cover c1ass on each site. Thus, for example, ~he figures foraclive commercial peal cutting include more than just the area eilher permitted for, or aclually affecled by peal exlracllon (see lexl).


12RESTORATION 01' DAMAGEI) PEATLANDS//Increased waterretention I waterloggingEstablishment of /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 ofdecompositlonratesFigure 1.6Main mechanisms leading to accumulatíon of peat and bog succession.1.7 Hydrology and morphologyof raised bogs1.7.1 IntroductionIn any wetland ecosystem, hydrological processes helpdetermine the character of various environmentalfeatures, such as water chemlstry, nutrlent avallabílltyand degree of soil aeratión. These in turo influence theidentity of the flora and fauna of the mire. lnombrotrophic peatlands hydrological processes andvegetation are linked through a positive feed-backmechanism whereby the accumulation of the deadplant remains as peat also helps to determine sorne ofthe hydrological processes [see Figure 1.6].1.7.2 The diplotelmic mireHydrologically, raised bogs can be considered as twolayered (diplotelmic) systems comprised of anuppermost 'active layer' (or acrotelm) and a lower socaBed•inert layer' 1 (or catote/m) [Figure 1.2). Thecatotelm is defined as the zone of 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 of the living vegetation covertogether with underlying, recentIy-dead 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 levelof the pennanent water table is elevated and the boggrows upwards. Water moves quite readily through theupper layers of the aerote/m, which both contains andhelps to regulate water·level fluetuations caused byvariation in water inputs and outputs. lt forros the maioconduit of water discharge from the bogo The aerotelmhas high perrneability to water near to the surface, butbecomes more impenneable with depth as the peatbecomes more consolldated and deeomposed(humified). Water movement and fluctuations meanthat conditions in the acrotelm remain largely aerobicand it is here that microbial activity is strongest.The aerotelm of a little·damaged bog can be regardedas an integrated combination of plants (especiallySphagnum species), peat and water. Plant growthcontributes to the formation of a structure which hassorne capacity for hydrologícal self-regulation andwhich helps to maintain conditions suitable for thecontinued growth and survival of the plants. Suchfeedbacks help to rnaintain the growth and character ofthe bog surface [Figure 1.6], and the acrotelm is criticalto the nonnaJ deveJopment and functioning ofa 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 of 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 of permanenl saluralion. Perhaps lhe moslremarkable fealure of lhe acrolelm of a growing raised bog isthal il provides a struclure which can aceommodaleconsiderable fluctuation of water level whilst sustaining lheeonlinued growth (or al leasl survival) of the bog planls lhalullimately conlribule lo lhe aeeumulaling peat mass.The acrolelm layer of a Iittle-damaged bog may be readilymodified or destroyed by various operalions. Peat exlraclionoften 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 ofthe cutling, thus providing direet re-inslatement of the surfaeelayer.) Other processes, such as drainage, dehydralion,repeated and deep burning, can also much modify itsproperties. The primary objective of resloration of damagedbog surfaces must be to reereate an acrolelm with propertiessimilar to those of the original. The primary problem of suchiniliatives is that some of the properties thal are provided 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' of much bog restoralion is lherefore to contrive tomimic on the exposed peat surface some of lhe. functionalproperties of the original acrotelm unlil a 'new' acrotelm hasdeveloped.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 of 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 of periodic lack ofprecipilalion inpul coupled with on-going evapotranspiralion.Hence lhe surface of lhe zone of perrnanent saturation willsink, leading once more lo a diplolelmie slruclure. This newsurfaee layer will serve lo feed lhe calolelm wilh rechargewater, thus providing one of lhe funclions of the originalacrotelm, bul il lacks some of lhe olher characlerislies of 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 of permanent saturalion (i.e. lhe uppersurface of the calolelm) [see Box 1.5] has fallen to a lowerlevel in the peat mass. In lhis situation the peal below the newlevel of permanent saturation can still be regarded as alegilimale 'calotelm', but the original catolelm peat aboye ildoes nol possess all lhe funclional characlerislics of lheoriginal acrolelm. Such consideralions suggesl lhat il isimportanl lo dislinguish belween an aerolelm defined jusI asthe upper layer lacking permanenl saluration and an acrolelmas a slruclure possessing lhe properties characlerislic of alitlle-damaged bog surface. However, such a lerminologicaldislinetion has not yet been made, 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 of the bog (the catote/m) usuallycomprises the bulk ofthe 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 ofien strongly-humified. It has a much lower permeabilitythan the acrotelm and correspondingly muchslower rates of water movement within it. Bydefinition, the catotelm is permanently saturated withwater. It provides a water-saturated, anaerobic base tothe acrotelm and the impeded drainage therebyproduced gives the hydrological basis to developmentand growth of the raised bogo [This is additional to theimpeded drainage in the underlying substratum orminerotrophic peat which permitted the initiation of anombrotrophic nucleus.] Although most microbialactivity occurs within the acrotelm, there is also sorneactivity ofanaerobic microbes within the catotelm.1.7.3 The water balance ofa I'aisedbogIn an ombrotrophic peatland, the only source of waterto the surface is from precipitation (rainfall, snow, fogetc.). Sorne of this is retumed to the atmospherethrough surface evaporation and plant transpiration(together termed evapotranspiration), while theremainder gradually seeps laterally towards the edgesof the bog, mainly through the surface layers(acrote/m) or vertically to become stored within thelower layers (catote/m) [see Figure 1.7]. Vertical lossofwater downwards through the base ofthe bog via thecatotelm is generally assumed to be negligible, althoughthis may not always be the case [see Chapter 2].Although a raised bog develops because of an overallprecipitation surplus, during sorne parts of 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 of a mire can be represented as: P - E - U - G - t,W =Owhere P =precipitation; E =evapotranspiration; U =flux density with which water enters the catotelm;G =leakage through the base of the mire (generally very small); t,W =increase in storage.For a raised mire of approximately circular plan, the maximum height of the 'groundwater mound' (Zm)can be estimated from the equation:UIK=2Z m 2 IL 2where K =hydraulic conductivity of the peat; L =radius of the mire.Figure 1.7 Water budget of a raised bog and terms used in hydrological modelling of the 'groundwater mound'(after Ingram, 1987) 11.7.4 The shape and size ofraisedbogsThe formation of a dome of ombrotrophic peat and, tosorne extent, its ultimate shape and height, is dependentupon the climatic regime in which the peatland occursand most notably on the ratio of precipitation toevaporation [see Box 1.5]. A clear understanding ofthehydrodynamics of raised-bog systems has emergedonly in the last twenty years, with the recognition thatthe waterlogged conditions which permit ombrotrophicpeat to accumulate aboye the level of the regionalwater table (or impermeable substratum) are producedby impeded drainage of rainwater through the peatmass (Ingram, 1982). This has lead to the formulationof models to predict the size and shape of raised bogs,based on standard groundwater hydrology and soilphysics [Box 1.5].A major limitation of aH models which attempt toexplain the shape and size of raised bogs just in termsof hydrodynamics is the likelihood that the dimensionsand profile are actually determined by several interactinginf1uences. These include the constraints of thetopography of the landscape in which the bog occurs,the degree of slope upon which it is developed, the ageand mode of development of the bog (i.e. by spreadingfrom a single nucleus or by multiple nucleation) andthe rate of peat decay. Clymo (1991) has pointed outthat the calculated 'hydrologicallimit' of a bog may bevery much greater than its measured height on accountof ongoing peat decomposition. Disparities will begreatest in bogs of large basal area and thehydrological limit may only be reached in rather smallsites. A consequence of this is that, within a givenregion, strongly-domed bogs may be primarily afeature ofsmall sites whereas bigger bogs may be moref1at-topped. Thus, in Britain, the two main 'types' ofraised bog which sorne workers have identified,plateau raised bog and concentric domed bog, maymore ref1ect the basal area of the peat deposit thanfundamental differences.1.8 Peat profiles and types ofpeatIn very broad terms, the stratigraphy of a Iittledamagedraised bog can be summarised as:living plants + loose acrotelm peatombrotrophic catotelm peatminerotrophic peat 2The acrotelm is usually sorne 10 - 40 cm deep, but theother layers can show much variation in thickness,depending on the age, situation and development ofthebogoThe ombrotrophic catotelm peat (which, in most cases,1 Reproduced from Ingram (1987) by permission of the RoyalSociety ofEdinburgh and H.A.P. Ingram.2 This may be extremely thin in sorne examples that havedeveloped by paludification.


CJlAPTER 1: LOWLA D PEATLA DS15is the focus of interest of the peat industry) ofien showssubstantial variation in character, between sites andwithin sites and both laterally and vertically [see Figure1.8]. The character, and stratigraphy, of bog peat isdetermined by the vegetation that produced it, theconditions in which it formed (which affect lhe rate ofaccumulation) and post-depositional changes. Thelower peat layers of bogs are often darker, morehumified and more solid (greater bulk density) than theupper layers. This is due in part to lhe effecls ofcompression and decomposition coupled, but may alsoreflect differences in the composition of lhe peatformingvegetation and the circumstances of accumulation.In sorne peatlands, the catotelm peat is quitesharply divided 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 often a sharp boundary between the lower'black peal' (decomposition degree usually H6 to H8or H9) and the overlying 'white peal' (usually H2 toH5). [' H' values refer to the von-Post scale ofdecomposition (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 often used as loose, illdefinedcategories of variable compass and it cannot beassumed lhat the black peat found at the base of sorneUK bogs is necessarily equivalent with the 'true' blackpeat of continental bogs. For example, sorne Britishbogs (mainly rather young examples) consist almostentirely of 'white peat' (senslI Weber, 1908), butnonetheless the lower peats are usually more humifiedand compacted lhan are the upper ones and they areoften 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 considerable circumspection. They are goodexamples of terms that receive quite widespread usewithout agreement upon their exact meaning andcompass.Box 1.5 The 'Groundwater' Mound hypothesisIn an important contribution to understanding the hydrology,development and shape of raised bogs, Ingram (1982) pointedout: (a) that water and peat accumulates to form a raised bogon account of impeded drainage of rainwater; (b) that thisgives rise to a characteristic near-hemi-elliptical mound ofwater perched aboye its surroundings and supported by thegrowing mass of vegetation and peat that has developedbecause of ils presence; and (c) that the surface of this mounddetermines the surface of the catotelm (the zone of permanentsaturation) and hence the shape and dimensions of the bog(because the unsaturated zone is thin and is moulded aroundthe catotelm). This suggestion, and ils implications, havecome to be known as the 'Groundwater Mound hypothesis'.The concepts and title of the 'Groundwater mound hypothesis'are based on standard groundwater hydrology and soilphysics. They recognise that the surface of the zone ofpermanent saturalion of a raised bog is analogous to thegroundwater table between ditches in a drained field (that ¡s,highest midway between the ditches and declining towardsthem). Thus this hypothesis is not specific to peat soils or toombrogenous bogs - ¡ndeed, its importance is particularly inits recognition that the behaviour of the water table in bogscan be understood and described in terms of 'normal' soilhydrology and physics, with regard to the impeded drainage ofrainfall - and not, as some previous workers had supposed, interms of capillary rise of 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 derived from meteoric sources andis thus not what hydrologists most usually understand bygroundwater, ;.e. water derived from telluric sources. To helpavoid confusion, in this report reference is made to a'groundwater' mound or a 'perched water mound'.'Groundwater' Mound theory indicates thal the profile anddimensions of the catotelm are a function of (i) the shape andsize of the basal plan of the bog; (ii) lhe net recharge to thecatotelm; and (iii) the overall permeability of the accumulatingcatotelm peat [see Figure 1.7]. The relationship thus infers thattaller groundwater mounds are associated with higher rates ofwater input or slower seepage and with greater basal area(Bragg, 1989). Support for the model has been derived from aquile close correspondence between observed and predictedprofiles of some Scotlish bog sites (Dun Moss and EllergowerMoss).The 'Groundwater' Mound hypothesis undoubtedly provides avery useful conceptual basis for understanding thedevelopment and shape of raised bogs. It also helps todemonstrate some of the hydrological repercussions ofdamage to bogs. For example, an important consequence ofthe model is that operations which serve to reduce the basalarea of a bog (such as extensive drainage and conversion foragriculture or peat extraction around its margins) may lead to aconcomitant reduction in the height of the water mound in theremnant of bog and hence a drying-out of some, or all, of itssurface.The 'simple' 'Groundwater' Mound model does, however, havesome limitations. It is a static rather than a dynamic model(Schouwenaars, 1995); it assumes a single value of hydraulicconductivity for the catotelm, whereas actual conductivitiesmay show very considerable spalial variation (Kneale, 1987); itassumes a flal base and is most readily solved for peatlandsof relatively simple plan. Some of these limitations (e.g.difficulties of obtaining a meaningful estimate of catotelmpermeability) are common to all models; others may beresolved by more sophisticated developmenls (e.g. of finiteelement models).Some further practical limitalions of 'groundwater' moundmodels 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 developed over zones of groundwaterdischarge. A model, accurately but confusingly, known as the'groundwater' model (Glaser, 1987; Glaser, Janssens &Siegel, 1990) has recently been developed to describe thistype of 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 of Bord na Mona.]H values indicate the humification degree of 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 of peat insuch attributes as bulk density, porosity and waterstorage capacity. This can affect the use of peat as ahorticultural medium and ils suitability as a substratumfor restoration [2.3l. Peat-based composts are ofienmade by blending different peat types from differinglocations in a bogoWeakly-humified light peats are particularly valuablefor horticulture because of their loose structure andhigh porosity. They are generally less desirable thandarker peats as a fue!.Strongly-humified dark peats have been much-prizedas fuel peats but have been generally of less value tothe horticultural industry. Nonetheless, they are widelyused blended with light peats in sorne peat-basedcomposts and can a1so be used by themselves. Theirimportance to horticulture may be expected to increaseas reserves of the upper, lighter peats become depleted.


CIIAPTER 1: LOWLA D PEATLA D 17Table 1.3 Modified version of the von Post Scale for assessing the degree of decomposition of peat (from Surton& Hodgson, 1987). [Reproduced by permission of the Soil Survey and Land Research Centre]Degree of Nature of liquid Proportion of peat Nature of plant residues Descriptiondecomposition expressed on extruded betweensqueezingfingersH1 Clear, colourless None Plant structure unaltered; fibrous, UndecomposedelasticH2 Almost clear, yellow- None Plant structure distinct; almost Almostbrown unaltered undecomposedH3 Slightly turbid, brown None Plant structure distinct; most Very weaklyremains easily identifiable decomposedH4 Strongly turbid, brown None Plant structure distinct; most Weakly decomposedremains identifiableH5 Strongly turbid, Very little Plant structure clear but Moderatelycontains a little peat in becoming indistinct; most decomposedsuspensionremains difficult to identifyH6 Muddy, much peat in One-third Plant structure indistinct but Well decomposedsuspensionclearer in the squeezed residuethan in the undisturbed peat;most remains unidentifiableH7 Strongly muddy One-half Plant structure indistinct but Stronglyrecognisable; few remains decomposedidentifiableHa Thick mud, Iittle free Two thirds Plant structure very indistinct; Very stronglywater only resistant remains such as decomposedroot fibres and wood identifiableH9 No free water Nearlyall Plant structure almost Almost completelyunrecognisable; practically no decomposedidentifiable remainsH10 No free water AII Plant structure unrecognisable; Completelycompletely amorphousdecomposed1.9 The vegetation of Britishraised bogs1.9.1 Plant species and vegetationtypesThe vegetation of ombrotrophic mires is of greatimportance, not just in its own right but because itprovides the physical basis of the mire itself and helpsto define some of its characteristics and conditions.This is because:• plant growth provides the basis for peat formation,water storage and impeded drainage;• plant growth provides the basis for much of themicrotopography of the site and creates smallscalewater gradients;• the growth of Sphagnum species helps to createand regulate some characteristics of the bogsurface environment.Although a range of vascular plants are found in bogs,some of the most characteristic and important plantspecies of bog vegetation are the bog mosses of thegenus Sphagnum [Plates 1.4 and I.S]. Some ten speciesare common components of lowland bogs in Britain.They grow in pools, lawns and hummocks andcontribute to the formation of these structures. Sphagnapossess neither roots nor specialised conductive tissuesfor internal water transporto They do, however havesome capacity for external transport of water, bymovement between the stems, branches and leaves.The leaves of Sphagnum contain two types of ceIls:narrow, sinuous photosynthetic cells and large waterfilledhya/ine ceIls. These latter cells allow even deadremains of Sphagnum to store a great deal of water andSphagnul11 plants are reported to contain up to 40 timestheir dry weight as water (Romanov, 1968). Sphagnaare of great importance to the development of manybogs. They are ofien the major peat-producing species,they help create the characteristically-low pHenvironment of bogs and they can store large volumesof water. They contribute to regulation of the waterbalance of a bog's surface, through the storage ofwater, a 'mulching' effect during dry periods and acapacity for 'bleaching' when drought-stressed (whichhelps to reflect solar radiation).The vegetation of ombrotrophic bogs is typically ratherspecies-poor and comparatively uniform, probablyreflecting the specialised nature of the habitat. Manybog species have a wide global distribution and some(for example Sphagnum mage/lanicum) occur in bothsouthem and northem hem ispheres. Over 130 plantspecies have been recorded from UK bogs (Wheeler,1993), but only sorne SO of these are particularly characteristicof little-damaged raised-bog sites [Appendix4]. Most of these species also occur, sorne widely, in a


18RESTORATION OF DAMAGED PEATLANDSphagnum capillifolium tSphagnum magellanicum tSphagnum cuspidatum tSphagnum papillosum tSphagnum fuscumSphagnum recurvum tPlate 1.4 Sorne characteristic species of 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 of 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 of the others oeeur in poor fen as well asin bogs. When growing in the ombrotrophie habitatsome of 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 of dalllageor atmospherie pollution.Although bog yegetation eontains a limited range ofplant speeies, eertain speeies eombinations appear to beunique to bogs [Table lA]. [n a little-damaged raisedbog, small pools are typieally oeeupied by yegetationof the SphagnulII cuspidalulll-S. recurvulll bog poolTable 1.4 The main plant eommunity-types of ombrogenous mires in Britain, as identified by the National VegetationClassification (Rodwell, 1991). The principal community-types of little-damaged raised bog are shown in bold type.For further details of community types of 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-Rhytidiadetphus 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 splendens 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 inelude: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 of the rest of 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 ofthese (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 ofthe bogo The other (the Empetrum nigrum-Cladoniasub-community, M18b) represents vegetation with agreater prominence of ericoid plants and usuallyoccupies rather drier conditions, such as may occurfurther from the centre ofthe bogo Near the edge ofthebog, the drier rand may sometimes also support anErica tetralix-S. papillosum (M 18) community, butofien has examples of 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 surfaceof at least sorne little-damaged raised bogs, from thecentral complex of shallow pools and hummocks to thedrier rand and thence to a minerotrophic lagg [Figure1.9]. In many sites, the natural character of a presumedlagg is not known, as marginal areas have ofien beendamaged or removed by drainage, agricultural conversionor peat cutting. Very ofien, 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 of its natural character. lt is ofienassumed that the rand is naturally drier than much ofthe bog and that it is naturally treeless but, given thecurrent propensity for tree invasion of slightly-driedsurfaces in little-damaged bogs, it would be of interestto know why trees were naturally absent from a drierrand, if indeed they were.It can also be difficult to specify the presumed 'natural'condition of the main expanse of little-damaged bogs.This is partly because even little-damaged sites haveofien been subject to sorne disturbance (including, insorne cases, deposition of atmospheric contaminants)but it is also because the vegetation of even anundisturbed bog is not completely stable. Peat stratigraphicalevidence points to both abrupt and gradualchanges in the past vegetation composition, with ashifiing tendency for dominance of bog surfaces by'hummock species' versus 'hollow species', probablymainly in relation to changing conditions of surfacewetness, such as may sometimes reflect climatic shifis(Aaby, 1976; Barber, 1981). Dry phases may show anabundance of ericoid species with Sphagna suppressedand, sometimes, even localised tree invasion (Casparie,1972).The causes for sorne major changes in the compositionof 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 of bog vegetation - andthe desired objective of bog restoration initiatives.However, the E. tetralix-S. papillosum community isofien considered to be the 'natural' core community-Figure 1.9 Typical zonation of plant commu.nit~es across a .raised ?og ~after Rodwell, 1991). [see Table 1.4 foridentity of communities] [Reproduced by permlsslon of Cambridge Unlverslty Press.]


22RESTORATION OF DAMAGED PEATLANDStype of many lowland raised bogs, and its recreationforms a focus ofthe restoration of damaged raised bogs[see Chapter 3].The vegetation of 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 ofbogplant speciesSorne plant species of bogs are long-lived perennials(e.g. plants of Eriophorum vaginatum may live formore than 100 years) and, for these, recruitment ofnewindividuals may be of limited importance to speciessurvival in undisturbed bogs. However, other species(e.g. Drosera spp.) are short-Iived and have a greaterdependence upon seed production to maintain theirpopulations.Diaspore production and dissemination is important forall bog species in the context of restoration ofdamagedbogs because the ability of plant species to recolonisefresh peat surfaces, or to re-establish on 'old' ones,depends largely upon their reproductive capacity andthe dispersal and survival of their propagules. Thedispersal agents of the seeds of sorne bog species arenot well known. The seeds of many species are small« 4 mm length) and Iight, leading to a presumptionthat wind dispersal may be of particular importanceand that the seeds may be able to travel over wide areasfrom one isolated raised bog to another (Moore, 1990).However, sorne studies suggest rather limiteddispersability of certain species (Poschlod, 1995).Seeds of sorne bog species can be dispersed by wateror trampling, but the general significance of 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 decades, but not in perpetuity), but there isconsiderable variation in this capacity (Poschlod, 1988,1989, 1995) (Appendix 3). Considerations of 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 of greaterimportance to the rewetting of uncut bog surfaces.Most wetland plants have sorne mechanism forvegetative expansion, which can sometimes lead to thedevelopment of large clonal patches of particularindividuals. This may be important for the maintenanceof populations in situ but is Iikely to provide ratherslow rates of recolonisation on abandoned, bare peatsurfaces.Wetland plants generally have a good capacity toregenerate from fragments but the actual significanceof this for spontaneous recolonisation of cut-over peatsurfaces by bog species is not known. It does, however,facilitate the propagation and planting of bog species,should this be seen as desirable. In particular,Sphagnum species can be readily propagated fromTable 1.5 Informal physiognomic-habitat categories of raised-bog vegetation in Britain. [NVC - see Table 1.4]'Bog-Sphagnum' vegetatíonAccommodates vegetation in which Sphagnum species typical of bogs are prominent, often dominant, components. It includes 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 of the surface of littledamagedraised bogs.'Para-bog-Sphagnum' vegetatíonRefers to vegetation with broad similarities to 'bog-Sphagnum' vegetation, but which differs either in not containing all of thespecies typical of 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 often sparse or represented mainly by taxacharacteristic of the drier microsites within bogs (e.g. S. capillito/ium), but in some (richer) examples it is possible to find most ofthe characteristic species of 'bog-Sphagnum' vegetation scattered sparsely. Various additional species, particularly taxa associatedwith drier conditions may also occur. This category includes some examples of NVC communities M15, M20, M25a. Suchvegetation may be indicative of partial damage to a bog surface (e.g. burning or drainage) but it may possibly also be a naturalconstituent of some little-damaged bogs, as on the drier slopes of a rand or as part of a 'still-stand' condition.'Dry bog' vegetatíonIncludes a range of 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. Whereidentifiable, the vegetation-types of this eategory inelude:wet heath (some examples referable to M15)dry heath (e.g. H9)Molinia grassland (richer examples =M25; others are near-monocultures of Molinia)bracken-dominated vegetationbirch scrub ((some examples referable to W4)'Dry bog' vegetation-types are almost always assoeiated with some form of damage to raised-bog sites, most typically drainage.


CIIArTER 1: LOWLAND PEATLANDS23small fragments. The significance of these factors forthe revegetation of cut-over bogs is discussed further inChapter 4.1.9.3 Characteristics ofbog plantspeciesExamination of sorne of the main characteristics oftypical bog plant species enable the followinggeneralisations to be made:• mostly ofgeographic wide distribution;• not specific to ombrolrophic bogs;• most are long-lived perennials;• seeds and spores may have IiUle importance inmaintaining populations of sorne species in undisturbedbogs;• seeds of most species are light and may be rcadilydispersed;• typically have slow relative growth rales;• apparenlly efficient at scavenging nutrients from dilulesolutions;• often efficient internal conservation of nulrienls;• ombrotrophic conditions scem generally sub-optimal forgrowth.The main characteristics of sorne of the typical speciesfound on raised bogs in Britain are given in Appendix3.1.9.4 Habitat conditions andvegetation ofraised bogsThe environment of raised bogs is not well-suited tothe growth of many plant species. The low pH valuesand limited availability of nutrients makes theombrotrophic habitat 'difficult' even for the growth ofspecies tolerant of 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 ofienoccupy rather distinct positions with respect to waterlevel, either as part of the small-scale microtopographicalmosaic of a patterned bog surface (e.g.Ratcliffe & Walker, 1958; see Figure 1.10) or as part ofa wider change in water level from the wet centre to thedrier margins of a bogo Species of the genus Sphagnumofien show c1ear and well-documented distributionpattems with respect to water levels (Ratcliffe &Walker, 1958; Vitt, Crum & Snider, 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 of 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;Pedersen, 1975; Clymo & Hayward, 1982; Hayward &Clymo, 1983; Luken, 1985)pH and base-richnessThe ombrotrophic waters of 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 of hydrogen ions (pH values are ofienbelow 4) is partly a product of acidification induced bythe growth of species of Sphagnllm (Clymo, 1963;Clymo & Hayward, 1982; Andrus, 1986), whilst thesmall concentrations of 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 orders of magnitude has been reported (Bellamy& Rieley, 1967; Karlin & Bliss, 1984; Giller &Wheeler, 1988).The ionic composition of bog water shows quite stronggeographical variation, reflecting variation in soluteconcentrations in rainfall. There is a gradient ofchemical conditions in bogs across both Britain and theEuropean mainland (Bellamy, 1967; Proctor, 1992). InBritish bogs, concentrations of several ions, especiallysodium, are greater than in more continental examples,reflecting maritime influence. [Sorne ranges ofchemical concentrations are given in Table 2.1].Plants typical of 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 of 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 recorded from sites with water pH values of c. 6.5(Andrus, 1986; Lindholm & Vasander, 1990; Shaw &Wheeler, 1991). Several plant species that arecharacteristic constituents of bog vegetation in Britainare confined to fens in more continental parts of 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 of the succession of species forming the peat in a typical "hollow-hummock cycle(regeneration complex) (Tansley, 1939) [Reproduced by permission of Cambridge University Press].Round-Ieavedsundew(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 of such sitesapproach that of weakly minerotrophic fens (Shaw &Wheeler, 199 1; Proctor, 1992). However, it is far fromcIear that this is a sufficient explanation (Malmer,1986).The response of typical bog species to very low pHenvironments « 3.0) has been rather little studied, butthere is evidence that growth of sorne species isimpaired at such levels (Austin & Wieder, 1987;Richards, Wheeler & WiIIis, 1995; Money, 1994).Sphagnum colonisation ofrich fens in Britain is usuaIlypioneered by a smaIl range of species (e.g. S.squarrosum, S. fimbriatum, S. palustre and S. recurvum;Shaw & Wheeler, 1991) which are particularlytolerant of 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 regarded as being'unproductive' and infertile ecosystems. Estimates ofvegetation production rates are hampered by thedifficuIties of obtaining meaningful measures ofSphagnum productivity (Clymo, 1970), but estimatesof above-ground net production of ombrotrophicvegetation are typicaIly in the range of 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 of fen (Wheeler & Shaw,1991).Low availability of nitrogen or phosphorus is likely tobe a major constraint upon primary production in bogs.Fertilisatiori of bog peats usuaIly increases theproduction rates of vascular plants and may evenenhance the growth of Sphagnum, at least in the shortterm(Tamm, 1954; Reinikainen, Vasander & 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 deposition from atmospheric sources(Aerts et al., 1992). The low availability of 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' redistributionof 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 of Sphagnum species in water may also beconstrained by availability of carbon (as CO2) (Baker& Boatman, 1985; Baker & Macklon, 1987). This mayhelp to explain the poor growth of aquatic species (e.g.Sphagnum cuspidatum) that is sometimes observed indeep water (Boatman, 1983; Paffen & Roelofs, 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 of 'acid rain' [i.e.sulphur dioxide and derivatives, especiaIly bisulphite;nitrogen oxides (N0x) and derivatives,. especiaIlynitrate; and ammonia]. There is very little direct informationon deposition ofcontaminants into British bogs,but interpolated maps provide estimates of emissionsand possible rates ofdeposition (UKRGAR, 1990).Various experiments have demonstrated thatSphagnum species are differentiaIly sensitive to S02and derivatives (HSO)-), but at concentrationsconsiderably greater than current ambient values(Ferguson, Lee & BeIl, 1978; Ferguson & Lee, 1980).Total S02 emissions in the UK have decreased by sorne40% from national peak values at around 1970(Gilham, Leech & Eggleston, 1992) and, whilst highconcentrations of S02 may have led to thedisappearance of 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 of atmospheric sources of nitrogen(NOx and ammonia) to the growth of bog species is notwt:I1 understood. There is a quite widespread suspicionthat deposition of nitrogen may be responsible for theloss of sorne Sphagnum species from bogs and anexpansion of Molinia caerulea and perhaps even ofbirch, but critical evidence for this is lacking. Ndeposition can act as a fertiliser for vascular plants andunder certain circumstances is thought to encourage thegrowth of 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 of dry deposition of ammoniaupon bog plants, though UKRGAR (1990) suggest that"over much of the country ammonia dry deposition isbelieved to dominate total nitrogen deposition."1.10 The invertebrates of raisedbogslnvertebrates form an important part of the animal lifeof 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 identification of them allwould require the time and expertise of manyindividual specialists. The information reviewed for thepresent reports was thus mainly derived from a largebody of mostly fragmentary evidence and ad hocrecords as most studies have concentrated onparticular invertebrate groups and have collectivelybeen conducted with a wide range of aims. In general,invertebrate studies of raised bogs appear to have beenstrongly biased towards insects and arachnids (spidersand harvestmen).Invertebrate species found on bogs may be herbivores,camivores or detritivores, but in general there are fewbog 'specialists', perhaps reflecting the waterlogged,oxygen-deficient, acidic environment with 'poorquality'food sources. However, several invertebratesurveys to date have suggested that raised-bog sitessupport populations of a high proportion of notable andrare insect and spider species both within the UK andon mainland Europe. Lowland raised bogs in the UKappear to have particular conservation importance for anumber of 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 ofdata is ofien hampered by lack of detailed habitatinformation). Many species also show markeddifferences in their degree of specificity to raised bogsin different parts of their geographical range. TheBritish Isles are on the edge of 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 largestOrder of insects within the UK with more than 6,000known species. However, most of the more familiarstinging species (the aculeate wasps, bees and ants) arelargely associated with dry habitats, and those that maybe caught within raised-bog sites include many that areeither transient or nest or forage outside of the boghabitat (von der Heide, 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 often 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 of theHymenoptera species associated with peat bogs, a highproportion are of conservation interest. For example,Kirby (1992) suggests that "[t]here are relatively fewHeteroptera associated specifically with bogs, but alarge proportion of them are local or rare". Thisprobably largely reflects the scarcity ofthe bog habitat.Herbivorous insects are ofien oligophagous (occasionallymonophagous) 1 and may be limited in theirdistribution by the availability of suitable foodplants.Thus, the great majority of species with conservationinterest are likely to occur in habitats which include thegreatest diversities of potential foodplant species. withlimited distributions. The limited herbivorous msectfauna of raised bogs may therefore reflect the floristicpoverty of raised bogs.Bogs that have been subjected to hand-cutting orsimilar peat-removal regimes and which have sincerevegetated may offer a wider range of invertebratehabitats than little-damaged raised bogs andconsequently, may support a wider range of species.Many taxa seem to have either a preference orrequirement for the range of 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 speciesregarded as having great conservation interest inlowland raised bogs, it is the mix of microhabitatspresent in areas that have been subjected to traditionalhand-cutting over a period of time that seems to beimportant in their continued survivaI. In sorne sites,hand cuttings may also offer wet refugia for sornespecies when much of the remainder of the site surface1 Oligophagous: restricted to a small number of food plants;monophagous: restricted to one species or variety offood plan!.


CHAPTER 1: LOWLAND PEATLANDS27has become damaged and dry. However, an increase inhabitat and species diversity due to disturbance is notconsidered by the conservation agencies to provide anincrease in conservational 'value' over the naturalnessof an undamaged bogo The extensive, bare surfacescreated by modem extraction methods may be far lessamenable to recolonisation than the small-scale handpeat cuttings.There have been few studies of the behavioural orphysiological selection processes that lead to peatlandspecies being found in a particular habitat, but thehabitat requirements of many invertebrate species willbe govemed by both the requirements of the adult andthe juvenile stages (larva, pupa, etc.). These may berather different, necessitating the presence of two ormore different and perhaps even spatially separatedfeatures. Natural Sphagnum hummocks and hollowsserve in part to provide this sort of microtopographicalheterogeneity. However, in general, high water tables,ensuring that Sphagnum remains saturated, appear tobe essential for the continued existence of many'desirable' species in raised-bog sites, even thoughmany of them [see Table 1.6] seem to require an'interface' situation between Sphagnum and/or barepeat and drier zones.Dragonflies are ofien 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 ofdifferent sizes. In general, dragonflies benefit fromsome protection from the wind and are favoured bysites with peat walls, adjacent scrub or at the edges ofraised bogs where woodland may act as a windbreak(R.G. Kemp,pers. comm).Most species of carabid beetle display a considerabledegree of latitude 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 considered to have particular conservation importance inthe UK.Species Order RDB 1 NotesstatusHeliophanus dampfi Aranae RDB Associated with peat in Europe, and in the UK known only fromCors Fochno (Dyfed) and Flanders 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 caraboides Coleoptera RDB2 Occurs in a range of 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 beenrecorded from a number of 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 definitions.


28RESTORATlON OF DAMAGED PEATLANDShabitat type, such as lowland raised bogs, at leastthroughout aH oftheir range.Many invertebrate species, including dragonflies,benefit from areas of open water and would bedisadvantaged by loss of 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 of critical importance: (i) the maintenanceof high water tables and (ii) the presence ofa moderatediversity of habitat types with elements of bare peat,open water of various sizes, Sphagnum hummocks,sorne grass, sedge ami/or heather c1umps and sornerather drier banks.1.11 The birds of raised bogsRaised bogs in Britain have been modified andfragmented to such an extent that an assessment of the'typical' omithological resource of '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 considered to becharacteristic ofthe habitat.There is a paucity of detailed site-specific omithologicaldata from raised bogs in Britain. Available dataindicate low bird density and low species richness onopen areas of Iittle-damaged bogs. The lack of treesand shrubs make them largely unsuitable for passerinesthat require perching posts and nesting sites aboyeground leve!. The vascular plants of bogs offer aIimited food supply to birds and sorne of the specieswhich do breed are common and widespread breedingspecies elsewhere in Britain.The naturaHy low density and species richness of birdpopulations on raised bogs does not imply lack ofconservation interest. Birds of particular conservationvalue (see Batten el al, 1990) which occur on lowlandraised bogs in Britain include significant populations ofbreeding teal 1 , red grouse, black grouse, dunlin,curlew, redshank, nightjar and twite, and winteringpopulations of pink-footed geese, Greenland whitefrontedgeese, greylag geese, hen harrier and merlin.The number of bird species breeding on the opensurface of an unmodified raised bog is small andbreeding densities are generally low. Meadow pipit andskylark are the two most characteristic species of raised1 Latin names of 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 ofother 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 golden plover and dunlin,seem to have declined 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 oncewidely 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 declineof these breeding species of little-damaged lowlandbogs has received Iittle attention. It is c1early arelatively recent phenomenon which may possibly beattributed to habitat fragmentation and lowering ofwater levels.Sorne of the more extensive raised bogs are importantas wintering sites for grazing wildfowl species. Ofthese, the Greenland race of white-fronted geese hasreceived much attention. A significant proportion ofthe world population of this distinctive race winter inthe British Isles (Batten el al., 1990), historicallyretuming each year to certain lowland bogs. AlthoughtraditionaHy associated with these bogs many of the'Greenland white-fronts' have abandoned raised-bogwintering sites in Britain and Ireland in favour ofaltemative habitats (Pollard & Walters-Davies, 1968;Ruttledge & Ogilvie, 1979; Fox & Stroud, 1986;Madden, 1987; Foss, 1991; Warren el al., 1992). Thereasons for this behavioural change may includeincreased disturbance and habitat loss, together withestablishment ofwildfowl refuges in, other areas.Modification of raised bogs has introduced a newmosaic of habitats which has increased the diversity ofthe bird species occurring on the former open areas,although many of the additional species are thosewhich naturally occupy the bog margins. The responseof bird communities to peat cutting and associatedchanges is complex because ofthe diverse nature ofthechanges that can be induced by these activities.Depending on the degree of damage, such changes mayhave a more marked effect on spatial distributions andrelative abundances of species rather than increasingspecies diversity in a particular site. Many specieswhich occur on 'intact' bogs also occur on modifiedsites, provided that sufficiently large areas of their'preferred' habitat remain. However, if treesextensively invade damaged bog surfaces, such speciesare eventually replaced by woodland birds.


CHAPTER 1: LOWLANO PEATLANOS29Species richne s and bird density generally increaseswith the development of scrub or occurrence of fen.Although the early stages of 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 degree of flooding, desiccation and scrubc1earance on damaged sites. Bog restoration initiativeswhich involve impoundment of surface water maysuffer from the effects of pioneer bird colonists, suchas wintering gulls, for example through guanotrophicationand physical damage.1.12 Non-avian vertebrates ofraised bogsNon-avian vertebrates (mammals, amphibians reptiles)usually form a relatively minor part of the conservationinterest of raised-bog sites but records from raised-bogsites have included such species as otter, mountainhare, deer and adder. Bogs may also constituteimportant feeding areas for bats, especially aroundmarginal habitats.1.13 Archaeology, palaeoecologyand restorationPeatlands are important for archaeology andpalaeoecology. They preserve remains of many of theplants that onCe formed their living surface and ofsorne of the animals (especially Coleoptera) thatinhabited this. The pollen rain, produced from thebog's surface and from the surrounding landscape, isofien preserved exceptionally well. The e, and otherfeatures, provide a valuable palaeoecological archive.This can be used, for example, to reconstruct, thecharacter of past post-glacial environments, climaticchange and flooding episodes, vegetational history,human occupation and management history.Some peatlands (especially fens) have been a focus ofpast human activity and a rich range of artefacts maybe preserved in the peal. Peat excavation has ofienhelped to reveal sorne artefacts, for example the headof 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 destroyed others. The peatlands of theSomerset Levels have provided particularly greatarchaeological interest (e.g. Coles & Coles, 1986;Plata ~.6 Remains of 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 (funded byEnglish Heritage and the Universities of Cambridge andExeter). [Photo: Somerset Levels Project].Somerset Levels Papers, 1-15, (1975-1989), asexemplified by the Sweet Track [Plate 1.7]. Bycontrast, sorne of the raised-bog sites investigated bythe North-West Wetland Survey have, as yet, yieldedfew artefacts (Middleton, 1990-1992).Peatland restoration schemes may need to consider therequirements for preservation of 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 of raised-bog restoration is toregenerate a new raised bog, at the very least this willrequire effective rewetting of the peatland. The followingfactors merit consideration [see also Chapter 7]:• the removal or disturbance of peat will also remove thehistorie and industrial landscape, the immediate palaeoenvironmentalrecord and any artefacts.• survey of the landscape and of archaeological featurescould form part of fteld investigations prior to initiationofa restoration schcme [Chapter 7].• raised water levels can lead to erosion where they adjoinupstanding blocks of peat, thus destroying both thepalaeo-environmental record and surviving structures. Itmay be necessary, both to minimise erosion and toencourage revegetation, to construct breakwaters in largeareas of open water.• the potential for damage to in situ artefacts, sites and thepalaeo-environmenta1 record by the roots or rhizornes ofsuch species as Phragmites should be considered in boththe deliberate encouragement and potential forcolonisation b such species (although such species areunlikely to prov'de much of a problem in ombrotrophicsystems).• in sorne cases, it will be desirable to preserve peatdeposits and archaeological structures in situ. Schernesdesigned speciftcally for nature conservation should alsoconsider the in situ conservation of archaeologicaldeposits.Peat extraction is also part of the 'industrial heritage'of Britain and abandoned, cut-over bogs forro a'derelict industrial landscape'. Even drainage schemesand methods used can have historical interest. If suchtopics and artefacts are perceived as legitimate areas ofinterest, 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 of human intervention in peatland ecosystems,and, perhaps in the future, constructs associated withrestoration may be valued as much as artefacts of'conservation archaeology' as for their ecologicaleffects.


Chapter 2Characteristics of cut-over raised bogs2.1 IntroductionPeat extraction directly removes both the peat and theliving surface from those areas of bog where it occurs.lt may also affect adjoining areas of uncut peat,particularly through indirect drainage. Thus it is importantto consider not only the direct effects of peatextraction, and their implications for restoration, butalso its inf1uence (or that of other reclamationmeasures) on bog remnants. The various techniques ofpeat ex raction used may inf1uence restoration options,as the conditions remaining when the sites areabandoned differ. Approaches to the rewetting of sitescut-over by different methods and the preservation ofbog remnants are considered in Chapter 5.Where any substantial peat extraction has taken place itis likely to have much modified the topography of theoriginal bog and the resulting conformation will be animportant determinant of rewetting approaches. Twobroad, but not exact, topographical situations can berecognised, depending on whether the area in questiontends to shed or hold water. These situations will bereferred to respectively as massifs and depressions[Figure 2.1].A massifcan include:• tbe entire mire, in relation to the topography of thesurrounding landscape;• a remnant ofthe original ombrotrophic dome;• a surface that has been cut-over but which is proudofsurrounding cut-over areas;At each particular scale the structure tends to have anoverall convex or water shedding profile.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 profile.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 adepression relative to the surrounding land. Similarly, apeat cutting or field may form a depression within amire remnant which is itself a 'massif as the generalsurface lies aboye the level ofthe surrounding land.M ------.PeatDMOMineral substratumMassif(water-shedding area)Depression(water-col/ecting area)Figure 2.1The concept of massifs & depressions [see text].


32REsrORATION OF DAMAGED PEATLANDS2.2 Effects of peat extraction onbog remnants and refugia2.2.1 IntroductionSorne sites affected by peat extraction retainundisturbed areas of vegetation that support typical bogspecies. In others, recolonised, formerly-disturbedareas may provide refugia. In botb cases, they maysustain an important biological resource and tbeirprotection may be important both in terms ofan overallprogramme of mire conservation and as a means ofconserving plants and animals adjacenrto areas of ongoingpeat extraction as sources of recolonist species[see Chapter 4]. The preservation of undisturbed areasshould be an important part of a restoration strategyoManagement and maintenance of such refugia need tobe carried out alongside ongoing peat extraction andnot left until extraction has ceased [Chapter 6].In gross terms, marginal damage, including peatextraction, can be considered to have two major effectson bog remnants:a) hydrologicaI - disruption of the hydrological integrity ofthe 'groundwater' mound; increase in the hydraulicgradient between the remnant and its surroundings;b) fragmentation of habitat.These effects are considered belowoon such factors as the nature of the underlying mineralsubstratum].• increase in evapotranspirative losses through the growthof 'undesirable' 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 of these factors, altbough the first two areperhaps the most common causes of dehydration. Thefactors leading to dehydration are perhaps tbe greatestthreat to the ecohydrology of mires because bylowering tbe water table and accelerating the rate ofDirect dramageReduction in basal area2.2.2 Hydrological effectsIntroductionThe surface of bog massifs can be dry for variousreasons, ofwhich drainage is one oftbe most direct andobvious. However, even without direct drainage of themassif, water conditions may be considerablyinfluenced by otber factors, for example, extraction ofsurrounding peat, since one of tbe features of tbe'groundwater mound' concept is that the height of thewater mound may be considerably in.f1uenced by itseffective basal area [Chapter 1].Surface drying may thus be promoted by variousagents, depending on the situation [see Figure 2.2].These include:• direct drainage ofthe peat body;• indirect drainage through loss of basal area of the peatbody, by agricultural conversion or peat extraction;• indirect drainage through lowering of adjacent watercourses, or regional groundwater tables (this wil1 dependon the permeability ofthe underlying mineral ground);• reduced water storage capacity ofthe dehydrating peat orpeat layers remaining after extraction;• reduction in depth of peat may be associated withdecreased resistance to vertical seepage through thebottom of the bogo [The importance of this wil1 dependLowering o(adjacent water courses orregional groundwater tablas (?)Growth o( 'undesirable' speciesDecreased reslstanca to vertIcal seepagePeat :~.:~. Mineral substratumFigure 2.2 Potential causes of dehydration of a raisedbog massif (see text).


CH PTER 2: CHARACTERISTICOF CUT-OVER BOGS33decomposition of the peat, changes in the physicalproperties of the peat, and the hydrology, morphologyand ecology of a mire are likely to take place, some ofwhich may be irreversible. Although any assessment ofthe effects of drainage on the physical properties ofpeat have to qualified by reference to peat types, thefollowing responses are sorne of those which have beensuggested as typicaJ following drainage of peatland(see e.g. Clausen & Brooks, 1980):¡!lcrease ;!l:decrease ;n:subsidence;bulk density;amplitude ofwater fluctuation;active porosity;water content;water storage coefficient;permeability.Thus, for example, drainage results in primaryconsolidation followed by shrinkage, secondarycompression and flllally wastage of the upper layers ofthe bog (Hobbs 1986), and can lead to considerablereduction in the height of the peat surface. Observationsat the Holme Post (Hutchinson, 1980) providegraphic evidence of the effects of drainage andagriculture in the progressive lowering of 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 of130 years, tbe surface has fallen by nearly 4 m. In theearly stages of drainage of a virgin bog, the peatshrinkage could be as much as 0.2 m per year.,although the rate of peat loss may decrease with time.Ivanov (1981) suggests that an average rate of collapseafier drying over a period of 40-50 years varies widelyfrom 1-2 to 8 cm per year, and cites the formula givenby Maslov (1970) for calculating rates of peatshrinkage. .Many, perhaps most, British bogs have been affectedby drainage to some degree. This can range fromextensive drainage in preparation for peat extraction,which was subsequently abandoned (e.g. RoudseaMoss, Cumbria) to the digging of one or moreboundary drains across the bog, marking ownership(e.g. Wedholme Flow, Cumbria), and to the grosseffects of adjacent peat extraction and conversion foragricult}lTe. In most cases it is difficult to separate theeffec~ of peat extraction upon adjacent bog remnantsfrom other causes of damage such as drainage, as bogshave ofien been subject to various forms of damage.However, it seems likely that effects are ofiensynergistic. For example, lowering of the surroundingground surface ofien produces a sharp boundary [Plate2.1], and will increase the hydraulic gradient betweenthis and the uncut surface, thereby increasing theefficiency of any drains. As the basal area is reduced asa result of peat extraction, a new perched water moundis formed within the peat remnant. The shape andposition ofthe new water mound will be determined bysite-specific conditions. In sorne examples it may nolonger reach the surface of the bog, which iscorrespondingly dry [Figure 2.3]; in others, where thedrop of water level has not been great, or where theamount of marginal damage is small in proportion tothe residual area of bog (or possibly where a change inthe permeability of the peat has lead to a reduction inwater runoft) the water level may still reach the surfaceof the bog peat, at least in the more central areas.lnterpreting the impact of drainage on bog systems iscomplicated by their 'diploteLmic' or two-Iayeredstructure and its role in maintaining the hydrologicalstability of the bog; in undisturbed bogs the acroteLmbuffers the catoteLm from sorne extemal influences[1.7]. Where drains are cut into a well-developedSphagnum-rich acroteLm, the hydrological andecological impact of drainage may be expected to bewidespread on the bog surface because of the hightransmissivity of the acrotelm (lngram & Bragg, 1984;van der Schaaf el al, 1992). The plant species(particu1arly Sphagnum mosses) that are particularIycharacteristic of little-damaged acrotelms may beespecially susceptible to any induced periods ofdehydration and there may be an interaction betweenchanges in the character of 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 of the potential waterdrawdown of the perched water mound in a raised bogas a result of marginal damage.hydrological [unctioning of the bog as a result ofdrainage. For example, drainage may lead to a bogsurface from which former hollows and pools havebeen lost, thus affecting factors such as water storageand run-off (Ivanov, 1981) (see below) and reduce thecapacity of the acrotelm to consistently 'feed' thecatotelm with water and maintain a relatively stablewater regime. The small hydraulic conductivity of thecatotelm means that the effect of an individual drainageditch upon the water table in the catotelm may beconfined to a few metres either side of the drainageditch. This is recognised in the preparation andmaintenance of bogs for peat extraction, where ditchspacings of c. 10-20 m are needed to provide effectivedrainage of the upper layers of peal. Shrinkage as aresult of loss of water from these layers usually meansthat drains have to be deepened each year, and it maytake up lo ten years for a newly drained bog to be in asuitable condition for extraction to commence.Effects of drainage upon chemicalcharacteristicsBesides causing physical loss, drying of peat is likelyto induce biochemical oxidation, mineralisation andrelease of hydrogen ions and nutrients. Even on littledamagedbogs, seasonally low water levels maysubstantially increase acidity, and subsequent rewettingcan lead to the release of various ions on the risingwater table (e.g. Braekke, 198 J). rn damaged sites,with frequent or protracted dry episodes, theseprocesses may be accentuated. It is likely that theoxidation of reduced sulphur compounds during dryperiod may be an important mechanism of(temporary) acidification. In sorne circumstances,concentrations of 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 of Sphagnum andsorne other typical bog species. Mineralisation of thedrying peat mayal o contribute to nutrient release andsuch effects may be exacerbated by water table instabilityand recurrent dry periods. Certainly, increasedconcentrations of various solutes have been measuredin water draining cut-over bogs compared with littledamagedbogs (e.g. Clausen & Brooks, J983a, b).However, the permanence of these effects, or theirsignificance to revegetation prospects is not known.E ects of drainage on bog vegetationAs a result of the c10se relationship between waterlevels and the distribution of plant species on bogs, it isc1ear that drainage will affect the vegetation, as well asthe peat of raised bogs. The definition o[ bog communitiesis likely to become 'blurred' under the impact ofdrainage, leading to impoverished types. The magnitudeof the effect will depend on the degree of 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 of the hollows, anincrease in species such as Calluna and Molinia and,possibly, invasion of woody species, particularlybirches (e.g. Eigner & Schmatzler, 1980; Bolte,Flügger & Cordes, 1985; Montag, 1989) [Plates 2.2,2.3,2.4]. A large sustained reduction of water levels isIikely to lead to an eventual los of bog speciestogether with loss of the original acrotetm and aerationof lhe upper catotelm peat, leading to cessation of peatdeposition and bog growth.In many sites damage (from whatever source) hascaused significant drying-out of the uncut surfaces suchthat the only remaining bog flora survives in the wetterconditions of abandoned workings. In other cases, bogremnants have survived alongside peat extraction,Plate 2.2 Molinia-dominated surface of raised-bog'remnant'; Holcroft 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 de pite removal of adjacent peat. Examplesinelude Wedholme Flow (Cumbria), where l11uch of theuncut dome appears to retain high water levels withtypical bog vegetation, despite continued adjacent peatextraction. However, the long-term effects of this arenot known.The effects of 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 of bog surfaces are usualIyregarded as undesirable: the taxa that replace typica[bog species have less intrinsic con ervation 'value'.Plate 2.4 Birch and Rhododendron invasion on raisedbog'remnant'; Wreaks Moss (Cumbria). [see also Plate10.1]Plate 2.5 Sphagnum-dominated bog vegetationconfined to cut-out pools, surrounded by Cal/unadominateddry bog surface; Bankhead Moss (Fife).Effects of drainage on bog ¡nvertebrates andbirdsThe changes in the hydrology and vegetation of a bogoutlined above will affect the bog fauna through changesin habitat and concomitant changes in vegetationstructure and food sources ele. (for example, loss ofopen 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 ofSphagnum remain saturated appear to be essential forthe continued existence of sorne 'desirable' invertebratespecies in raised-bog sites, though sorne of themmay also require an 'interface' between Sphagnum andbare peat or drier zones. For example, drying appearsto have had deleterious effects on populations of theRDB 2 category muscid fly, Phaonia jaroschewskii (=crinipes), at Thorne Waste (Skidmore, 199 [). The rarebeetle Bembidion humeraLe may also be favoured bythe maintenance of 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 of mire-associated bugs, forexample, Micran/ha marginaLis and PachybrachiusLuridlls (Kirby, 1992a). Many dragonfly species benefitfrom the maintenance of areas of open water (e.g.Sphagnum pools of various sizes) and may be expectedto suffer if these disappear, either through drainage orby them becoming choked with vegetation. tudies ofthe effects of raising water tables in bogs that hadpreviously been partially drained have generally shownwhat have been interpreted as favourable responses ofinvertebrate 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 of birch scrub as a result of dryingprovides a mosaic of different habitats which mayfavour various non-mire invertebrate species, some ofwhich may be uncommon, for example, the bog bushcricket, Metrioptera braehyptera (Shirt, 1987), theclouded buff moth, Diaerisia sannio and the cranefly,Pi/aria meridiana. It usually leads also to an increasein the number of breeding bird species compared withthose typical of open bogo For example, the drierconditions in combination with the provision of songposts, in the form of birch scrub, undoubtedly favourthe spread of such species as tree pipit, whinchat andstonechat on certain sites. Light scrub, characterised byscattered pioneer birch and Scots pine, can favour thecolonisation of bogs by nightjar. Nightjars usually nestat the base of 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 of '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 development of denser scrub encourages anessentially woodland bird community to develop(RSPB, 1983; Fuller, 1982).2.2.3 Habitat fragmentationIntroductionUtilisation of bogs for agriculture and forestry has leadto a large loss of 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 of peatworkings. Changes in the size and shape of the remnantbogs may have various repercussions. As well aspossible effects upon the hydrologic stability of theremnants, it may also affect their capacity to sustaincommunities or independent populations of particularspecies (in which case it may be impossible to maintainthem).Size of remnantsThere is considerable interest amongst conservationistsin the relative merits of several small, versus singlelarge reserves in the conservation of biodiversity ofthreatened habitats. May (1975) pointed out that, as arough rule, a ten fold decrease in area would lead to ahalving of the equilibrium number of species presentand concluded that several small areas would supportless species than a large area of equivalent size.However the general conclusion of most of the studiesconceming the single large or several small(S.L.O.S.S.) debate was that several smaller reservescontain more species than a single large reserve ofequivalent total area. However, the advantage ofconserving a number of small sites rather than a singlelarge reserve will also depend on such factors as theoverlap of species present in the small sites (Higgs,1981), the stability of the sites, and geographicaldistribution and requirements of the species.The importance of critical minimal areas forconservation of plant communities has not been widelystudied, mainly because area usually accounts for onlya small amount of the variation in species richness indifferent sites and ultimately sites and species mayneed to be considered individually for conservationpurposes. However, typical bog vegetation occurs insome tiny sites « 2 ha), when habitat conditions areappropriate.For animal populations the importance of the size ofthe site relates to such factors as habitat specificity andterritoriality, together with reliability and availability offood source. Fragmentation of 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 define critical minimum areas forprotection of 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-of-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 of bare orsparsely vegetated ground for a viable population. Forsome species (for example, the dragonfliesSomatoehlora alpestris and S. aretiea) only extremelysmall pools are needed for larval survival (Stemberg,1982), though for the maintenance of viablepopulations a number of 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 dependspartly on the distribution and density of its food supply.Thus, predators might be expected to be more abundantin areas where there is an abundance oftheir prey.


CIIAPTER 2: CIIARAeTERISTICS 01' CUT-OVER DOGS37In the case of dragonflies, which are amongst thelargest insects inhabiting raised bogs, sorne measuresof male territory size suggest that the minimum size ofrefugium 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 of 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 of habitat for maintenance of aviable population than smaller ones. Hence, for the vastmajority of insects and arachnids inhabiting lowlandraised bogs, nearly all of which are significantlysmaller than dragonflies, the minimum effective areafor a refugium is likely to be far smaller.It should be noted that maintenance of minimum areasfor conservation of any particular species presupposesthat conditions within such refugia can be maintainedin the same condition as they would have had when thearea was surrounded by larger areas of bogo Further, itremains an unresolved problem to know whetherefforts aimed at maintaining populations of any givensingle species would also ensure survival of thecommunity of invertebrates as a whole.BirdsThere have been very few studies relating to the spatialrequirements of birds occurring on raised bogs. InSweden, Bostrom and Nilsson (1983) observed thatbreeding-bird species richness increased strongly withbog area and that the density bf most waders washigher on larger (>50 ha) than smaller bogs. Theseauthors considered that, from a conservation point ofview, 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 determine theminimum areas of refugium for those species. It mustalso be recognised that the requirements of certainspecies may also inelude adjacent (o~ nearby) habitats,thus further complicating the application of the refugiaconcept to birds on bog habitats.Examination of notification documentation for Sites ofSpecial Scientific Interest containing raised bog 1 , hasfound records of six taxa which have only beenrecorded from sites greater than 100 ha. These ineludefive very rare breeding species on raised bogs (merlin,hen harrier, Montagu's harrier, dunlin, golden plover)and one wintering subspecies (Greenland white-frontedI Many of these inelude habitat other than raised bogo or derivedhabitats, which represents a significant limitation ofthe 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-headed gull, short-eared owl,grasshopper warbler and reed bunting, and winteringmerlin and hen harrier seem to be associated with sitesof between 50-) 00 ha in Britain. Black grouse andtwite have only rarely bred on raised bogs of this size.Birds also found on smal\er raised-bog sites in Britain«50 ha) include breeding mallard, red grouse, curlew,snipe, redshank, nightjar, cuckoo, meadow pipit,whinchat and skylark, plus wintering short-eared owl.Shape of remnantsThe shape of a habitat remnant has been considered tobe important in the minimisation of 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 riskof invasion by uncharacteristic species and input ofagro-chemicals etc. which may lead to eutrophication,mineral-enrichment etc. The effect of shape may beobscured by other unidentified sources of variation.Although shape itself is probably not of major concemin the general preservation of nature reserves, forraised-bog remnants the importance of shape is morelikely to relate to the preservation of a favourable waterbalance, than preservation of species per se - a bogremnant of 'simple' plan shape is likely to be easier torestore hydrologically than one with a complex marginoThe provision of buffer zones to reduce edge effects isperceived to be one practical solution to the protectionof particularly susceptible sites [8.3].2.3 Peat extraction methods andhabitat conditions2.3.1 Peat extraction and residualtopographyThe surface configuration of the cut-over areasremaining after peat extraction has stopped dependslargely on the method and duration of the peatextraction and the extent of drainage, both throughdirect alterations in topography and indirect effectssuch as slumping of the peat.There are three main methods of 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 of theseoperations: drainage; removal of surface vegetation;drying ofthe excavated peat on the surface to achieve asuitable moisture content (typically c. 50%); provision


38RESTORAnON OF DAMAGED PEATLANDSof trackways for acce s, passage of vehicles, trains etc.Main baulks are often left at intervals for passage ofmachinery, 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 oftransporting equipment and materials acros a site, andalso acting as bunds l to retain water in the peatworkings 2 .The main extraction techniques are described below, inrelation to the conditions remaining on the site whenthe extraction ceases.Block cuttingBlocks of peat are cut out from a vertical face andstacked on baulks alongside to dry. Drying of the peatis thus more dependent on winter c1imatic conditionsthan is the case for milled peat production.Block cutting can create a range of surfacetopographies, dependent upon the exact proceduresused. The method often produces a regular system ofbaulks, 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, of, for example, a few Sphagnum species.The character of the surface is important in consideringrestoration options. It may often be possible to useexisting baulks and tramways to increase waterretention; in other cases, as where there are numerousnarrow ridges, it may be desirable to level the surfacesand fill in sorne of the trenches by bulldozing thebaulks into them.Traditional hand cuttingWhen carried out on a small scale, the results of peatcutting by hand can be a fairly haphazard disposition ofthe surface topography [Plate 2.6]. However,'organised' (± commercial) hand cutting could be asextensive as machine block-cutting, sometimes leavinglarge areas denuded of peat and vegetation and with asimilar regular topography ofbaulks 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 of the term damhas been restricted to refer to structures built to block linear watercourses [see Chapter 8].2 The efficacy of the baulks as bunds will depend on their size,intactness and degree ofdehydration ofthe 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 of the rnain 'advantages' of hand cutting (forsubsequent restoration) is that the surface vegetationwas sometimes thrown back into the trenches, and mayprovide inoculurn for revegetation. The slow speed ofextraction also allows the bog species (plants andinvertebrates) in the trenches to become establishedbetween successive cuts. This 'shoeing' is probably ofgreat importance in determining the course and time ofrecolonisation [Chapter 4]. Revegetation of such areasdepends critically on the hydrological regime that hasbeen maintained after the cessation of operations.Where the cuttings have been kept sufficiently wet,they have often developed sorne 'good' examples oL.bog vegetation.Machine block-cuttingMachine block cutting is essentially a rnechanisedversion of the traditional hand cutting method, but canbe carried out on a larger scale with greater speed andeach cut is usually deeper [Plate 2.7]. The ground isusually prepared by drainage (both open drains and slitor mole drains), rernoval of trees and scrub andlevelling of the surface. The 'topsoil' is removed fromthe area to be cut, and either spread alongside orpushed into the trenches. Cuts are typically e. 50' apart,3' deepi x 2'4" wide (c. 15 x 1 x 0.7 rn). The peat is cutinto blocks, and stacked alongside 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 ruderal, non-wetland species.The presence of 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 of baulks and thefloor of cuttings.Milling (or rotavation)Milled peat production involves scraping or vacuumingoff a thin layer ofpeat (15-50 mm) from the surface ofbare peat fields. The surface of the moss is firstprepared for peat extraction by drainage at e. 15-20 mintervals and stripping off the surface vegetation with ascrew leveller sorne 5-10 years before extraction canbegin 2 . This reduces the water content of the peat andincreases the load-bearing capacity to facilitate harvestby machinery. The vegetation may be removed, or ispushed into the middle of the extraction fields andcornpressed by peat-extraction machinery. It graduallyrots and can be further worked to provide a camber tothe bed to irnprove the surface drainage. In bogscontaining a high proportion of highly humified peats,surface runoff to drainage ditches may account for arelatively high proportion of 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 deepdrains, a system of under-drainage by mole drains maybe installed [Plate 2.8]. Drainage reduces the waterI The effective depth of each cut is usually less than 3' as there issorne wastage.2 The time taken will depend on the permeability of 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 of the peat. In general, the harvestingcycle takes about three days, but this depends 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 of drainage, but alsofrom the repeated passage of 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 of 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 development of restoration strategies. Forexample, large areas must be worked simultaneously tobe economic (e.g. for efficient use of personnel andequipment when climatic conditions are suitable forharvesting) such that an integrated, phased program ofextraction followed by restoration may be difficult toachieve [6.5].Extrusion ('Sausage') peat productionThis technique is mostly used for production of fuelpeat, and is used on both raised and blanket bogs. It isused both on a small scale, for example by crofters inScotland and lreland, and commercially. The rotatingblade of 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 depth of peat that can beworked, although when this is reached, it would bepossible to continue extraction by surface milling.As for all methods, the peat deposit must be drainedprior to extraction. The fields are also cambered toincrease surface run-off and avoid puddles etc.Intensive drainage is not always considered necessaryas increased energy would be needed to extrude 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 of peat stockpiles; 80lton Fell (Cumbria).[See also cover photograph of 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 tofacilitate collection of the peat 'sausages' by machinerather than by hand. In this case, the residual surface issimilar to that left by milling. However, the method ofextraction 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, considerabledamage to the plants and microtopography still occurs,mainly through cutting of the roots and fibrous 1ayer,compaction due to the passage of machinery andpersonnel and deposition of peat on the surface(Bayfield el al., 1991; Meharg, Montgomery &McFerran, 1992; I Miller, pers. comm.). Bayfield el al.(1991) consider in detail the impacts of extrusioncutting on the vegetation of and runoff from blanketpeats.Other production methodsPeat may be won by methods other than thosedescribed aboye. For example, fuel peat is sometimesextracted from deep trenches, whereby the soft peat isextruded onto a conveyor belt and then cut into blocksbefore being laid on the ground to dry. This leavesdeep, wet trenches and may sometimes create 'islands'of peat [Plate 2. 11], both of which may provide asuitable habitat for recolonisation, particularly ifsurface vegetation were to be returned directly,although further examination of such sites is required.In Somerset, smaJl-scale peat extraction is often carriedout by rotavating the peat and forming into ridges todry [Plate 2.12] before removal to stockpiles.Plate 2.11 Large-scale extraction of '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 bagsPeatlands have to be drained for efficient peatextraction. The degree to which sites are draineddepends upon individual site characteristics and thepeat extraction technique used. Drainage is primarilyneeded for permitting access by machinery but it is alsoa prerequisite for some drying of the peat, espeeiaJly insurfaee milled sites. However, it is not the aim ofdrainage to remove as much water as possible, as toomuch drainage would allow the lower layers of peat tooxidise and waste. The drains are therefore deepened asneeessary, usually annu By.Few data are available on the hydrology of raised bogsduring peat extraetion, but it is evident, for example,that whilst removal of vegetation may reduce waterlosses by evapotranspiration, the dense network ofdrains (whieh may be linked to a pumping system)ensures that the rate of water loss through runoff willbe higher than that of undrained bogs. In cut-over bogsit must be aeeepted that drainage wiU cause alterationsto some of the eharaeteristies of the original bog, forexample, changes to sorne of the hydrophysiealattributes, such as water storage eapacity and peatpermeability, sorne ofwhieh may be irreversible [2.2].The water level that develops, spontaneously or byengineering, within an abandoned extraetion complex


42RESTORATlON OF DAMAGEO PEATLANOSis of crucial importance to the subsequent revegetation.In large measure, it will be a product of the topographyof the abandoned peat workings (see aboye), c1imateand functioning ofthe drainage system. The water tableof cut-over bogs is ofien characterised by a greaterdegree of fluctuation than that found in intact systems(Meade, 1992; Money, 1994, 1995). This may partly bea reflection of the existence of drains, but also becausethe exposed peat surface lacks the hydro-regulatoryproperties of an intact bog surface [1.7]. Hence, cutoversurfaces may be very wet, or flooded during thewinter, but dry and dusty during the summer.Water storage characteristics of residual peatsThe lower peats that are lefi following peat extractionmay differ in various properties from the peats aboyethem, either in consequence of changes induced bydrainage (Hobbs, 1986) or because of their intrinsiccharacter [1.8]. This may influence their suitability forrestoration. It is widely considered that variation incapacity for water storage may be important in thisrespecl. Even deep catotelm peat may have high totalporosity (Reynolds el al., 1992), but the ratio ofmacropores (> 50 ¡.tm) to micropores is thought to beof more importance to water storage capacity(Schouwenaars, 1982; Blankenburg & Kuntze, 1986);the structure of strongly-humified peat gives it a higherratio ofsmall 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 of 'free' water (the loose Sphagnum peat ofa typical bog acrotelm can contain sorne 85% of 'free'water compared with only sorne 8% in stronglyhumifiedpeat (Streefkerk & Casparie, 1989)). Thisleads to higher water table fluctuations, as for the sameamount of 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 of the acrotelm and the catotelmpeats, trends are less readily apparent within thecatotelm peal. Porosity and bulk density t:!1ay vary bothwithin and between peat types and the broad categoriesof '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 ofienregarded as being independent of the behaviour ofgroundwater in the fen peat or subsoil aquifers belowit. Indeed, 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 underlying 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 ofthe 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 of 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 of 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 typicallyof low fertility and supports low rates of primaryproduction. The chemical characteristics of raised-bogwaters vary temporally and spatially. Typical valuesare summarised in Table 2.1. A major control on thepattern of variation is rainfall quantity and quality,itself controlled by factors such as proximity to the seaand degree of atmospheric pollution. Coastal raisedbogs are generally richer in solutes (see for example,Boatman el al., 1975; Sparling, 1967) and the chemicalenvironment may approach that of weaklyminerotrophic fens (Wheeler, 1988; Shaw & Wheeler,1991 ).There has been ¡ittle detailed work on the effect of peatextraction on the chemical environment of raised bogs,but there is sorne empirical evidence to point to sornedegree of chemical enrichment (e.g. Clausen & Brooks,1980). This may be as a result of:J. chemical changes caused by drainage (e.g. acidificationand mineralisation + nutrient release from the aeratedpeat layers);ii. exposure of the underlying fen peat or mineral sub-soil;iii. nutrient runofffrom the surrounding catchment. .Few chemical data exist for peat extraction complexesin the UK, but a number of samples have been takenfrom parts of Thome Waste (Smart, Wheeler & Willis,1989; Money, 1994) and from Danes Moss, Cheshire(Meade, 1992). In general the concentration of 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 of poor fenrather than ombrotrophic bog (Tallis, 1973) (Table2.1). It is not always evident why such chem icaldifferences occur: for example, the high concentrationsof NH 4 recorded from the milling fields at ThorneWaste, in comparison with vegetated cuttings, may bebecause it is released in consequence of peat operationsor because it is derived from other sources (e.g.atmospheric inputs) but lack of vegetation cover meansthat it is not assimilated by plants. At theseconcentrations of NH 4 some degree of toxicity toSphagnum magellanicum (Rudolph & Voight, 1986)and S. cuspidalum (Press el al, 1986) may occur,though evidence of the response of Sphagnllln speciesto N enrichment is inconsistent.MineralisationMineralisation of drying peat [2.2] may contribute torelease of solutes and increase availability of pIantnutrients (Gorham, 1956; Braekke, 1981). It has beensuggested that in block-cut sites mineralisation maylead to some movement of 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 evidence to besubstantiated. The amount of 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 of Sphagnum and othervascular plants. For example, extremely low pH values« 3.0) may be detrimental to the growth of some bogspecies, including some species of Sphagnlll11 (Austin& Wieder, 1987; Richards el al. 1995; Money, 1,994).Very high concentrations of nitrogen may be damagingto some SphagnulII species (Press el al., 1986;Twenhoven, 1992), though evidence for this is notc1ear-cut (Rudolf & Voight, 1986; Baker & Boatman,1990; Aerts el al., 1992), nor is the likely effects ofvery high concentrations of sot (Ferguson el al.,1978; Ferguson & Lee, 1982-3; Austin & Wieder,1987; Rochefort, Vitt & Bayley, 1990). The significanceof 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, modest enrichment of someelements (e.g. phosphorus) may enhance the growth ofsome bog species including some Sphagna (Baker &Boatman, 1992; Money, 1994, 1995).Exposure of fen peat or underlying mineralgroundThe domes of ombrotrophic peat which form raisedbog have often developed over fen peat, which usuallyhas greater base-richness than the former. This isreadily shown in chemical profiles. For example,samples from Striber's Moss (Roudsea Mosses,Cumbria; Gorham, 1949) showed the trend ofincreasing pH (and conductivity) with depth, 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 of fen rather than bog vegetation (White,1930; Poschlod, 1989, 1992). Even where fen peat isnot directly exposed, a shallow layer of residual peatmay be penetrated by some fen plants rooting in theunderlying mineral ground. As well as modifying thetloristic composition of 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 detected].Natural bog waters(UK & Ireland)*Danes Moss,(Cheshire)vegetated block-cuttings(Meade, 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 fromdeeper layers.Exposure of underlying mineral material may also leadto base-enrichment, but this effect will much depend onthe chemical characteristics of the sub-soil. In sornesites (e.g. parts of Thome and Hatfield Moors),underIying sands and gravels are themselves of low pHand base status (pH 3 - 4) (B.D. Wheeler, unpublisheddata). There have also been reports of low pH valuesassociated with sorne basal clays.Where the exposed substrata are very base rich (forexample, exposure of marl at Turraun Bog, Ireland)[Plate 2.13], rich-fen vegetation is likely to redevelop.Most typical raised-bog species do not occur in suchsituations and redevelopment of raised bog will dependon a slow build-up of 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 of poor-fen plantspecies.Runoff from the surrounding catchmentIn areas where peat has been extracted to below thelevel of the regional ground water table or to a positionwhere the surface may receive run-off from thesurrounding catchment, there is a possibility thatgroundwater may be able to run onto sorne or all ofthesite, and cause nutrient or base enrichment (Pigott &Pigott, 1959; Meade, 1992). The potential for a generalingress of groundwater will depend on the topographyof the site. It may be particularly likely to occur in sitesin basins; where areas of fen, which buffered the raisedbog against ingress of groundwater have beendestroyed; or where ditches draining adjoining landhave been deliberately introduced into the bogoExamples of the latter inelude Dane Moss (Cheshire),Plate 2.13 White marl deposit underlying 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 development of an appropriaterestoration strategy, as it may severely limit thepotential options for after-use, if remedial action is notfeasible.2.3.4 The physical environment ofcutoverbogsPeat 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 considerable temperaturetluctuations (Tallis & Yalden, 1983; Heikurainen& Sepplilli, 1963; Salonen, 1992) and thus provide aninhospitable environment for establishment of plantpropagules and animal colonists. [see also 4.4.2]2.3.5 The vegetation ofcut-over bogsThe vegetation of remnant peat surfaees and ofabandoned peat workings can be extremely variable,depending upon sueh constraints as degree of damage,depth of extraction, topography, base status, nutrientstatus, water level (and souree) and length oftime sincelast worked. Money (1994) has surveyed the vegetationof peat cuttings in a range of British bogs - all of thevegetation-types recorded from uncut bog surfaeeshave also been reeorded 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 of the speeies characteristie of raisedbogvegetation on uncut surfaces have also beenrecorded 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 providethe 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 of specieson uncut surfaces of British raised bogs and theiroccurrenee within peat cuttings. TIle rarer bog speciesare rare also in peat cuttings or have not been recordedat all from them. Some species (e.g. Sphagnumimbricatum and S. fuscum) whieh have not beenrecorded 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 concluded that peat cuttings are notintrinsically unsuitable for the growth of most, or all, oftypical bog species (including rare specie ). However,many of the cuttings that support a rich variety oftypical 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 ofpropagules.The main factors influencing the natural, spontaneousrevegetation of cut-over bogs are discussed further inChapter 4.Plate 2.14 Eriophorum angustifo/ium growing inexcavated peat pit, surrounded by Molinia-dominatedvegetation on drained bog surface; Astley Moss(Lancashire). [see also Plate 2.5]2.3.6 The fauna ofcut-over bogsPeat extraction creates disturbance and destroys theimmediate habitat for animals, removing importantstructural features as well as food sources so that thecapacity of much of the bog fauna to survive peatoperations will depend upon the availability ofproximate little-disturbed habitats, or of 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, ofienoffer a wider range of habitats for birds andinvertebrates than do undamaged raised bogs and maysupport a wider range of 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' of such sites over thenaturalness of an undamaged bog, particularly wheregeneralist species replace specialists. However, sorneof 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,surrounded by Calluna-dominated vegetation on drycut-over bog surface; Killaun 80g (Ireland).Invertebratesome abandoned peat workings are rich in invertebratespecies. A number of 'conservationally-desirable' taxaseem to have either a preference or requirement for therange of 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 beprovided locally (Kirby, 1992a). An example of suchan insect is the caddisfly Hagenella c/a[hra[a (Wallace,199 1). For many species that are cited as being of greatconservation interest in 10wland raised bogs, it is themix of microhabitats present in areas that haverevegetated over a period of 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 of cut-over bogs is extremely variable, depending upon such constraints as depth of extraction,topography, nutrient status, water level and age (i.e. length of time since last worked). In sorne examples, cuttingshave recolonised to produce clearly identifiable examples of specific NVC community-types [see Table 1.4] (whichin sorne cases may be absent from the rest of the site), although these may not have developed the full associatedtypical microtopographical structure of hummocks and hollows. In other cases, the vegetation may be an atypicalspecies mix, either because of sorne extraneous influence (e.g. nutrient input), extreme environmentalheterogeneity within the cuttings or the vagaries of the recolonisation process. In the lalter case it is possible thatthe vegetation may develop towards a recognisable NVC community-type in time.(1) 'Bag-Sphagnum' vegetatían: Sphagnum-based vegetalion sueh as is eharaeteristie of liltle-damaged raisedbogs in lhe UK (M18) and bog pool communilies (M2, M3) occur wilhin peat workings, lhough they vary in thedegree 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 of Aehnaeree (Argyll), Thorne & Crowle Moors (S.Yorks. lUnes.). In sorne sites, such communities are better developed in peat cuttings than on the 'intact' peal.(ii) 'Para-bog-Sphagnum' vegetatíon: Many peat workings support examples of this vegetation category, whichincludes surfaces that may support a wide varjety of typieal bog species, though no!' in the same proportions, orwith the same vegetation strueture, as is charaeteristie of 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), Peatlands Park (Armagh) and Thorne & Crowle Moors.(iii) 'Dry bog' vegetation: Orier peat workings support a range of vegetation types with few, if any bog species.They include the physiognomic eategories of wet heath, dry heath, Molinia grassland, birch scrub, bracken etc.Some examples are impoverished versions of M15, M19, M25 and W4 communíties, but many are not c1earlyreferable to any NVC vegelation-type. There are numerous examples of these vegetalion-lypes, including AstleyMoss (Lancashire), Cors Caron, Oanes Moss, Fenns & Whixall Moss (Shropshire I Clwyd), Glasson Moss, HolcroftMoss (Cheshire) [Plate 2.2], Moss Moran (Ounfermline), Peatlands 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 sornedegree of enrichment (e.g. Thorne Waste: Smart et al., 1986). However, where underlying fen peat has beenexposed by extraction, or where there is substantial ingress of minerotrophic water, true fen vegetation may occur.A large range of fen vegetation-types have been recorded from cut-over bogs, the variety reflecting differences inwater quality (base status and nutrient status), depth and vegetation management. Examples include a number ofmires at whieh little, if any, raised bog now remains 1 ; sites whieh are more obviously raised-bog sites includeBrackagh Bog (Armagh), Cors Caron, Cors Fochno, Tarn Moss (Malham) and the Somerset Levels.Fen community-types recorded from cut-over bogs include: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 underserubPteridium aquilinum-Rubus fruticosus agg. underserubCommon physiognomic orhabitat descriptorspoor 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 woodlandunderserubunderserub, 50me (perhaps most) of 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, of the ombrotrophie peat has beenstripped away, presumably by domestie eutting (e.g. Cliburn Moss (Cumbria), Heart Moss (Kirkcudbrightshire). Examples fromelsewhere inelude Woodwalton Fen (Cambridgeshire) and Wartle Moss (Aberdeenshire).


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 provide 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,evidence for this proposition is rnostly absent.Nonetheless, the large size of 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 of this report, not least becausecornprehensive data do not exist. [This is partlybecause rnany fen and raised-bog sites have notreceived detailed 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 ofien notvisually evident.]BirdsThe response of bird cornrnunities to peat extractionand associated changes is cornplex because of thediverse nature of the changes that can be induced bysuch activities. Many species which occur on intactbogs also occur on rnodified sites, provided that sufficientlylarge areas of 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 of wildfowl, wadersand birds of prey have been attributed to the effects ofthe expansion of intensive peat extraction (Lirnbert,Mitchell & Rhodes, 1986).Disturbance, lack of food sources and nest sites islikely to severely lirnit the use of cut-over areas bybirds. However, as bare areas revegetate, the birdspecies which recolonise will depend on such factors asthe distribution and arnount of open water and the typeofvegetation which develops, and the site's geographicallocation. Thus, for exarnple, an increase in openwater habitat is likely to attract waders, wildfowl andgu[[s. However, as open water becomes occluded byvegetation, such species rnay be eventually displaced.Sorne species of conservation irnportance rnay have'unnatural' spatial distributions on damaged bogs, forexarnple, species naturally occurring in scrub 01' fenaround the rnargins of little-darnaged bogs rnay extendinto the central areas of darnaged examples where thereis an increase in these habitats [see also 2.2.2].Restoration objectives need not be in contlict with theconservation of these species provided sufficient effortis put into ensuring the availability of sufficientsuitable habitat in the appropriate sector of the bogo Forexarnple, Thome Waste is estirnated to hold alrnost 2%of the British breeding nightjar population (Roworth,1992), but it has been suggested that those currentlynesting towards the centre of the bog rnay beaccornrnodated on the bog rnargins through properrnanagernent of over-dense 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 of songposts, in the form of birch scrub, undoubtedly favourthe spread ofthese species on certain sites. An increasein open scrub habitat rnay benefit species such asnightjar [2.2.2].A wide range of bird species are potential recolonistsof peat cuttings in fen peat, and rnay inelude suchspecies as sedge warbler, reed warbler, water rail,rnoorhen and coot. They are likely to be determinedparticularly by the character and area of the vegetationand depth of water. Extensive reedbeds occur in sornefen peat cuttings and rnay support such species asbittern, bearded tit and rnarsh harrier as well as variouswildfowl. The avifauna associated with other types offen vegetation and habitats has not been systernaticallystudied, but a range ofwetland birds rnay be supported:Fuller (1982) provides sorne surnrnary inforrnation. Fencarr rnostly supports woodland birds, rather thanwetland specialists, but rnay nonetheless provide a veryrich bird resource. The perceived desirability ofpopulations of, say, nightingales within a raised-bogsite is likely to depend upon particular views of theairns and objectives (and practical possibilities) ofconservation and restoration at particular sites [Chapter3]. Sorne former raised-bog sites on the SornersetLevels have already developed into nationallyirnportantwetlands for birds.


PART 11PrincipIes of Restoration


Chapter 3Aims and general principies tor peatlandrestoration3.1 Options for after-use ofdamaged peatlandsPeatland sites that have been damaged by peatextraction- or other operations have various possibleafter-uses. In the past, these have often ineludedafforestation, conversion to agriculture, use as refusetips etc. and there has sometimes been a presumptionthat similar use might be made of some currentworkings, once they had been abandoned. However,changing attitudes and circumstances, coupled with arecognition of the conservational value of 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 of this reportoLowland peatlands are perceived to be important forvarious features additional to their potential forexploitation. These inelude their value as a 'peatlandlandscape', for their archaeological and palaeoecologicalarchive and for wildlife. The requirements for thepreservation or, where appropriate, restoration of thesefeatures are not identical. For example, it may bepossible to preserve sorne of the features of a 'boglandscape' or the archival value of a raised-bog peatdeposit without necessarily retaining, or redeveloping,aH of the characteristic biota of 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 redevelopment 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 of wildlife interestin damaged peatland sites. No attempt is made tospecify conservation policy by recommendingparticular objectives - rather, some possible objectivesand options are identified and discussed.3.2 Aims of restoration3.2.1 The concept ofrestoratiolJThe word 'restoration' has a broad compass (Wheeler,1995), but is nonetheless often misused, sometimesbecause of a failure to recognise that it mus! refer to aspecific object or objective. In a1l of its nuances ofmeaning, restoration implies an attempt to retum anobject to something like its 'former condition'.However, peatland ecosystems often undergoconsiderable changes as they develop and a damagedsite may have had several distinct 'forroer conditions'.Semantica1ly, it would be legitimate to try to restore asite to any of 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 of 'restoration' have ledsome workers to search for other terros to refer a nonspecificrecreation of 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 Restoration objectivesFoci of 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 of these foci. For example, it is possible tomaintain or recreate typical bog plant communities


52 RESTORATION OF DAMAGED PEATLANDSTable 3.1 Occurrence of physiognomic categories of vegetation within cut-over peatlands. (For identity ofphysiognomic 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 widespread 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 ofienrelate to the maintenance or enhancement of existing'interest' ofpeatlands, restoration initiatives can have abroader scope as, ofien, badly-damaged sites may havevery limited existing interest and various restorationpossibilities can be explored.Restoration objectives (for nature conservation) areusually a combined product of the perceiveddesirability of a particular option, its cost andpossibility. The first two of these considerations areessentially determined by choice and budget; only thelatter provides an absolute constraint.An assessment of the conservational 'desirability' ofthese objectives may need to take into account:• the intrinsic interest and importance for natureconservation of the habilat-type and associated biota,locally, regionally and nationally;• the scarcity of the habitat-type and biota, locally,regionally and nationally• local objectives for nature conservation;• national (and international) objectives for natureconservation.Freedom of choice of restoration options is sometimesconstrained by existing conservation interest. This maybe the case, for example, where raised-bog sites havebeen badly damaged but have developed a replacementhabitat with high conservation value centred on speciesand habitat conditions that are atypical of raised bogs.In this circumstance, restoration of ombrotrophicconditions may not be universally welcomed. In sorneformer raised-bog sites 'restoration' consists ofpreventing spontaneous redevelopment of bog, in orderto retain prized fen habitats (Beltman, van der Broek &Bloemen, 1995).Damaged raised bogs can support a variety ofvegetation-types and habitats, depending upon specificconditions [Table 3.1]. An informal assessment of theintrinsic 'interest' and scarcity of these is given in Box3.1. A number of these may be seen as an acceptable,or desirable, focus for conservation, restoration orrenaturation.3.2.3 Choice ofoptionsIn 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 ofthese.(i) Maintenance or recreation of wildlifeinterest not pertaining to bogsA number of former raised-bog sites in Britain arecurrently prized and conserved partly or completely forhabitats and species that are not typical of raised bogs.This category of 'interest' is rather broad.One category of replacement habitat that is conservedon a number of former raised-bog sites is fen (ofienwith open water habitat). This has usually developedeither because past peat extraction has exposedunderlying fen peat or mineral soil, or because theombrotrophic surface has been lowered sufficiently toallow ingress of 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 of bog species. whilst cuttings contain fenspecies. Such sites may have very considerable 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 identity and characteristics afphysiagnamic categaries, see Table 1.5 and Bax 2.1J'Bog-Sphagnum' vegetation.Bog-Sphagnum vegetation is particularly characteristic ofIittle-damaged bogs; it is uncommon and is often cited asthe preferred, or ultimate, vegetation goal of restorationinitiatives in raised bogs, in terms of the species it supportsand beca use of its (inferred) association with regenerating,self-sustaining mires.'Para-bog-Sphagnum' vegetation.This broad category represents vegetation that may containa wide range of bog species. In richer examples it may bepossible to find most of the characteristic species of bog­Sphagnum vegetation, though perhaps scattered over largeareas and often with various additional species, particularlytaxa associated with drier conditions. Such vegetation maybe a natural component of some bog sites, but it tends to beregarded as not being 'true' bog vegetation and in manyinstances may represent a derivative of 'bog-Sphagnum'vegetation associated with some form of damage.Nonetheless, it may provide a substantial reservoir of bogspecies. It is often 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 of bogspecies, including some Sphagna. Drier examples arereferable to various types of dry heath. May support someuncommon bird and invertebrate species and is regarded asan important component of some damaged bog sites (e.g.Thorne and Hatfield Moors). Widespread in some parts ofthe UK but uncommon in many lowland agricultural districts.In some areas, dry raised bogs provide important heathlandsites. Some examples are susceptible to invasion by birchand, in dry situations, bracken.Molinia grasslandExamples on bog peat range considerably in character fromricher examples that support a small range of typical bogspecies to those that are very species-poor and coarse.Robust Molinia is often effective in suppressing associates,even in quite wet conditions. Usually regarded as'undesirable' by conservationists. May be susceptible toinvasion by birch. Widespread outwith peat/ands. Exampleson fen peat may be much more species-rich.BrackenTypically species-poor vegetation, confined to dry sites inbogs. Widespread in other habitats. Potential associatesare suppressed by the strongly-dominant fern. May invadeand replace drier examples of heathland and Moliniagrassland. Generally regarded as 'undesirable' byconservationists.Birch scrubBirch can colonise over a wide range of wetness conditionsand is a potential invasive species of some bog, heath andMolinia stands. Its ground vegetation is strongly determinedby the character of the vegetation colonised by the birch.Early stages of birch encroachment may have little impactupon the characler of the biota, but the development ofclosed-canopy scrub is usually associated with aconsiderable change in the character of the groundvegetation and fauna. For this reason birch encroachment isusually regarded as 'undesirable', 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 of increased humidityand shade. Birch scrub may support a quite rich avifauna,comprised mainly of woodland species.Open waterLarge expanses of deep open water within bog peatgenerally have a sparse vegetation. Shallower examplescan develop dense mats of aquatic Sphagna which may bea precursor to the redevelopment of regenerating bogvegetation. Open water in peat workings within fen peat cansupport a rich assemblage of 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, of complex food-chain interactions.When present, some aquatic plants are thought toform the basis of fen-raft development. Open water is alsosusceptible to hydroseral colonisation (by swamp species)from the margins.ReedbedsBeds of Phragmites australis and Typha spp. occur widelyas recolonist species of shallow-water peat pits, often, butnot exclusively, in sites irrigated with nutrient-rich water.They often 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.] Widely distributed, but extensive (>20 ha)examples are infrequent. Drier examples are oftensusceptible to scrub encroachment.Fen vegetationA wide range of types of non-reed fen vegetation candevelop 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 of fen vegetation is inverselyproportional to the nutrient-richness of the irrigating water;examples developed under the influence of nutrient-poorbut base-rich water are often particularly scarce and valuedby conservationists. Base-richness and water level alsoinf1uences vegetation composition. Many types of open fenvegetation require management to maintain speciesdiversity and to retard scrub colonisation, which often leadsto 1055 of some uncommon species typical of open fen.Invasion by Sphagna can also occur, in some cases as partof the process by which fen develops into bogoFen meadowsVarious types of fen meadow vegetation can occur on fenpeat surfaces, ranging from examples dominated by rushes(Juncus spp.) and sedges (Carex spp.) to fen grasslandcommunities. Some of these communities may be speciesrichand have considerable biological value.Fen woodlandMuch conservation management of fens attempts toprevent extensive development of scrub and carroNonetheless, fen woodland is often rich in plant species,though many taxa of open situations are absent from denseshade. It may also support a rich avifauna, most typicallycomprised of woodland species. Various types of 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 deliberately managed as fen (reedbeds)for their omíthologieaJ interest (e.g. LeightonMoss - Plate 3.2). ome examples are likely to developspontaneously into bog, but this will be at the expenseof mueh or all of the fen habitat and speeies and suehan event may be regarded as undesirable by sorneeonservationists.Also ineluded in this eategory are conservation siteswhieh support replaeement habitats of relatively lowconservation interest assessed nationally, but whichmay be important locally as wildlife habitats or aslandseape features. Examples of this inelude wetlandsites within worked-out peat-extraction sites [Plate 3.3]and dry raised bogs that have developed into birchwoods' some are managed as nature reserves, othershave trees protected by Tree Preservation Orders.(ii) Maintenance or re-establishment of viablepopulations of typical bog speciesThe objeet of eonservation and restoration managementof many raised-bog sites is to maintain or re-establishviable population of typical bog species. [n manyinstances, the objeetive is to re-establish Sphagnumrichvegetation (comparable to the MI8 communitytypeof the National Vegetation Classification) oversorne or all of the site. In other cases it i consideredthat it may only be feasible to retªin or recreatecommunities typical of damaged bog surfaces (whichmay nonetheless support a very wide range of typicalbog species).In a number of peat extraetion sites, typical bog speciesare supplemented by sorne species of other (drier)habitats, usually in sorne forro of habitat mosaie. Sorneof these species are themselves uncommon and form animportant part of the perceived conservationimportance of the mire. lt is recognised that at sornesites (e.g. Danes Moss, Cheshire) management thatfavours the development of bog may be detrimental tosome non-bog bird specie .In sorne peat extraction complexes, the reestablishmentof typical bog vegetation (especiallyM18) may represent a 'value-added' approach, in thatthe vegetation present prior to current peat extractionwas not 'good-quality' bog vegetation.(iii) Maintenance or re-establishment of aregenerating, self-sustaining bogecosystemThe object of conservatíon and restoratíon managementof a number of raised-bog sites is to restore them to aregenerating, self-sustaining ecosystem with theappearance and composition of 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 of their surface alongwith an appropriate topographical conformation (e.g.Cors Caron, Wedholme Flow) but it may also be seenas a desirable restoration objective for sites that havebeen much-darnaged by peat extraction. Such anobjective is obviously well suited to the maintenance,or increase, ofpopulations of typical bog species, but itmay be detrimental to non-bog species that form partofthe existing wildlife resource ofsorne sites.Regeneration of a 'new' raised-bog system does not ofnecessity have to occupy the entire former area of 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-establishmentof a 'regenerating bog' may represent a 'valueadded'approach,' in that the mire had beenconsiderab}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 of naturalhistory interest on damaged raised bogs. They are not,of necessity, mutually exclusive. One is essentiallyspecies-centred and aims to maintain or re-establishviable populations of typical bog (or other) species.The other approach is mire-centred, and aims tomaintain or recreate a developing raised-bog ecosystem.The species-centred approach does not demand aregenerating mire. It is possible to maintain or reestablishpopulations of many bog species on damagedbog surfaces or in peat pits. Is sorne, but not all, casesplant species may form a vegetation similar to that oflittle-damaged bogs. Such artificial situations maymaintain numbers of typical bog species as effectivelyas on a little-darnaged or regenerating bogo Biodiversitymay even be increased relative to a Iittledarnaged bog by the growth of 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 of contrastinghabitats accounts for the high biological interest ofsorne cut-over raised-bog sites, especially when theinterface between adjoining habitats supportsspecialised organisms.Restoration initiatives which attempt to restore thewhole site as a single, regenerating mire are less Iikelyto result in a close juxtaposition of contrasting habitatsand may produce sites with lower biodiversities than isthe case with a species-centred approach, but the biotawill be comprised mainly oftypical bog species.The choice between species-centred and mire-centredconservation and restoration initiatives is likely to beinfluenced by a variety of considerations, not leastpracticability and costoAttempts to regenerate the entire mire as a growingentity are arguably more 'natural' than is themaintenance of artificial habitat mosaics. Indeed,sometimes the latter strategy is effectively a form of'bog gardening' with an ongoing requirement forperiodic 'weeding' (e.g. birch clearance etc.) andsometimes even 'watering' (e.g. supplementaryirrigation). A practical consequence of this is that themaintenance of artificial bog habitat mosaics willusually have a recurrent management cost whereas thiswill be less true of a naturaJly regenerating bogoHowever, the initial outlay of attempts to regenerate anentire mire may be considerably greater th3n thatrequired just for the protection of existing interest,though this will depend strongly upon the startingpoint.In sorne cases, it may be possible to provide suitablehabitats for atypical bog species of great conservationvalue around the periphery of 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 of 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 of topography or cost, to rewet the areasufficiently well for bog regeneration without furtherremoval of 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 of 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 Restoration opportunities incurrentpeatworkingsIn general, where parts of cut-over raised-bog siteshave considerable existing conservation interest, be itan 'original' bog surface on a remnant massif, or bogspecies that have recolonised abandoned peat pits, orareas of fen which have developed in minerotrophicworkings, there is ofien an understandable desireamongst conservationists to maintain the status quo, orto enhance it By contrast, there may be more scope foran open choice of 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 isconsidered desirable 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 ofgroundwater, 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 of environmentalmanipulation, the only real choice is in the typeof minerotrophic wetland that is to be recreated (or, orcourse, sorne form ofaltemative 'dryland' habitat).Where fen peat remains covered by bog peat, direct reestablishmentof raised bog is more feasible, but evenhere it would, ofcourse, also be possible to deliberatelyexpose the minerotrophic deposits to recreate fen overall or part of the site. For whilst there is sometimes atendency to regard the exposure of 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 developed from fen itwould be a more 'natural', and possibly more stable,way ofregenerating 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 offers a wide range of opportunitiesfor the creative restoration of mires. Whilst alaissez¡aire approach may be undesirable, equally withsorne 36,000 ha of damaged raised bog potentiallyavailable for restoration [1.6], there is scope for avariety of objectives to be realised. However, there is areal need to develop objective ground-rules to helpdecide restoration and renaturation options, prioritiesand areas in situations, such as denuded peatlandswhere there may be much scope for choice.As one of the main objectives of bog restoration is tocreate a Sphagnum-based bog vegetation and a regeneratingbog, and as this is likely to be considerablymore difficult than the redevelopment of sorne otherspontaneous vegetation-types (e.g. birch scrub), thiswill provide the main focus of much of this reportoHowever, sorne attention is also given to the optionsfor the creation of certain types of fen vegetation. Thecircumstances likely to lead to the development ofsorne other types of habitat with natural history valueare summarised in Chapter 6.3.2.6 Constraints on restorationobjectivesThe realisation of particular restoration options isdetermined by considerations of feasibility andpracticability. Sorne potential constraints include:• unfavourable starting conditions (see below);• lack ofresources;• legal constraints (for example, obligation to maintaindrains in or around site);• obligations to neíghbouring land-owners (for example,need to avoid waterlogging ofadjoining land);• conflicting conservation aims:these may be induced, for example, by the presence ofarare species, which is not typical of the bog habitat.Opinions vary on the merits of conserving atypical,rare species versus regeneration of 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 of other special interests, without abandoningan objective of bog restoration.A summary of the main factors affecting restorationoptions is given in Table S2 [Summary].3.3 Sorne principies of peatlandrestoration3.3.1 Scope ofrestorationThe term 'restoration' can be used to apply to variousobjects. Sorne workers use it loosely to refer just toprocess of reinstatement of habitat conditions thoughtto be appropriate to the objectives. Thus rewetting of apeatland is sometimes referred to as 'restoration'. It is,of course, semantically legitimate to claim to have'restored' former water levels to a drying-out sitewithout taking into account the wider repercussions ofthis process. However, comprehensive site restorationimplies not only reinstatement of former environments,but also redevelopment of a biota similar to a formercondition and, where applicable, re-establishment ofthe '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 of appropriate environmentalconditions and (ii) subsequent colonisation by targetspecies. Kuntze & Eggelsmann (198 1) subdividedrestoration, 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 of appropriate water levels is usuaIlythe primary task in the restoration of peatIandsdamaged by commercial peat extraction.'Renaturation' refers to recolonisation of the peatIandby plant and animal species and the fonnation ofcharacteristic communities. 'Regeneration' refers to bere-establishment of sorne ecosystem processes, such aspeat accumulation. This phase is fundamental torestoration strategies which aim at whole mireregeneration, but is of 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 of appropriate habitat conditions can onlybe considered in tenns of the specified objectives. Thepurpose of rewetting damaged peatIands is not just tomake them wet, but to provide conditions appropriatefor the desired renaturation and regeneration objectives.The development ofrestoration strategies needs toconsider the conditions required to realise the specifiedobjectives, whilst recognising, for example, that theconditions needed to re-establish desired types ofvegetation 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 of thedesired objectives. It is particularIy appropriate forsites with Iimited damage. Rebuilding involves theredeveloprnent of the peatIand and implies that thedesired endpoint cannot be produced directly butrequires phased reconstruction, with a starting pointofien 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 of bogsextensively damaged by commercial peat extractionwiII usuaIly require rebuilding rather than repair.3.4 Principies for restoration ofraised bogs3.4.1 IntroductionIn principie at least, the restoration of damaged raisedbogs may be easier than that of sorne other habitats.This is because, whilst peat e'xtraction considerablydamages 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, developed spontaneouslyfrom a variety of starting-points, including fenand wet mineral soil. This suggests that reneweddevelopment ofraised-bog ecosystems may be possiblein a quite wide range of circumstances. Indeed, givenappropriate conditions, it may be difficult to prevent'ombrotrophication' from taking place.There are two major requirements for raised-bogrestoration: (i) availability of an adequate supply ofprecipitation of appropriate quality and its sufficientretention at the bog's surface to provide effeotiverewetting; (ii) availability of 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 of drainage systems, because the surfaceconformation tends to shed water and because the capacity ofthe natural bog surface for hydrological self-regulation hasbeen lost (see below);(ii) deep 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 of exposure of fen peats by excavation,ingress of groundwater or other contamination); bogvegetation may not be able to develop directly in suchsituations, though it may be able to develop indirectly bylonger-term successional processes;(v) atmospherie pollutants may be detrimental to the growthofsorne bog plants;(vi) recolonist species may not be available c10se to the bogbecause of destruction oftheir refugia.


CHAPTER 3: AIMS AND GENERAL PRINCIPLES59Box 3.2 Hydrochemical constraints on bog restorationIndividual cut-over raised-bog sites vary considerably in theirconditions and characteristics. Although certain features (suchas the presence of a layer of ombrotrophic peat) may facilitatesome restoration options, and hence determine 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 developedspontaneously, they are Iikely to be able to redevelop from arange of starting conditions on sites where they onceoccurred, though undoubtedly this process will takeconsiderably longer from some ~tarting points than others.Ultimately, there are two main constraints on the potential ofsites to redevelop into raised bogs: (i) availability and reteritionof an adequate supply of meteoric water of appropriate quality;and (ii) availabi/ity of recolonist species. The first of these maybe influenced by conditions external to the raised bog and,because of this, be particularly intractable.The input of sufficient meteoric recharge water to bog surfacesis a prerequisite for bog development and climatic conditionsprovide a primary regulation of bog restoration options[Chapter 1], though the exact nature of climatic constraintsupon ombrotrophic peat development and the range of climaticconditions under which this may occur is not known withprecision: suggested threshold values of annual precipitationrecharge required for bog development have been derivedmainly by correlations based on the known distribution of bogsand the seasonal distribution of precipitation is almost certainlyimportant in determining the growth of bogs [see Chapter 1],though its effect has not been well quantified. Workers in NWEurope (Kuntze & Eggelsmann, 1982; Streefkerk & Casparie,1989) consider that the current precipitation : evaporationbalance is suitable for raised-bog development in much of thisregion, though it is difficult to predict effects of future climaticpatterns. In some sites, groundwater discharge may also havesome importance to the overall water balance of the bog eventhough the surfaces are fed exclusively by precipitation[Chapter 1]. The interaction of this with other components ofthe water balance in relation to threshold precipitation valuesis not well known.The suitability of me~eoric water for raised-bog redevelopment,in parts of NW Europe at least, is open to question. It ispossible that atmospheric contamination of rainwater ('acidrain') plus dry deposition of atmospheric N may constrain thepossibilities for bog growth, especially with regard to thegrowth of certain Sphagnum species. As discussed elsewhere[4.5] the significance of this problem is not really known, butmay be serious.The retention of water within bog sites may be determinedboth by conditions within the mire and by those outside it.Retention problems internal to the mire can often 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 of surplus. ExternaI influences upon thewater balance may be less tractable, such as those created byregional changes in hydrology. A lowering of groundwaterlevels is seen as a considerable constraint upon bogrestoration in parts of NW Germany and The Netherlandswhere bogs have developed over permeable substrata inwhich a high groundwater level has effectively provided thebase of the perched water mound. The extent to which this isan important component in the water balance of British bogs isnot known, but it is almost certainly a feature of some sites. Itcannot be divorced from other conditions within the peatland.Thus, the 'problem' of ditches which cut through to the mineralsubstrata is only Iikely to affect substantially the hydrologicalintegrity of the mire where the mineral ground acts as a watersink; otherwise such ditches can be readily dammed, as anyother drain. Similarly, it may be of greater importance in peatcutting sites where only a thin layer of residual bog peat isavailable to constrain downwards seepage of water(Schouwenaars, 1993).The retention of water within specific parts of bog sites isconstrained by the same considerations mentioned aboye, butmay be determined additionally by the surface topographycreated by peat extraction (Joosten, 1992). This may demandadditional attention, if it is intended to rewet all, or most, of thesite.In many cut-over sites, water retention problems are stronglyexacerbated by the lack of adequate water storage within thepeal. Peat extraction usually removes the upper fibrous layersof moss and peat and exposes the lower, more humified peatlayers. The latter, more highly decomposed peat, typically hasa much lower water storage capacity than the former (theoriginal acrotelm [1.8, 2.3]). Moreover, the plant species thatoften readily colonise such surfaces (e.g. Molinia caerulea)may induce high rates of 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 stagesof renaturation, the Sphagnum layer, if present at all, is notthick enough to regulate evapotranspiration losses effectively.Strategies aimed at regenerating bog vegetation may need tofind 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 demands some substantialhydrological control of a disturbed or regenerating mire beforeattention focuses on revegetation.The impact of minerotrophic surface conditions (created byexposure of underlying fen peat or mineral sail, or by ingressof telluric water) upon restoration prospects depends 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 often support a mixture of 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 of bogo It is possible that bog willeventually develop spontaneously from fen in such conditions,but it is likely to take longer than in poor fen. This is, however,partly dependent 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 development of semif10atingrafts of vegetation.


60REsrORATION OF DAM¡\GED PEATLANDSIt may be noted that sorne of 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 often 'external' constraints are less easilyremedied than are 'interna!' ones.3.4.2 Conditions required for theestablishment ofbog speciesThe main focus of raised-bog restoration initiatives isto pravide conditions suitable for colonisation andgrowth of species typical of little-damaged bogs,especially species of 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 of telluric water to the growingsurface.The establishment of Sphagnum-based vegetation is ofgreat importance to raised-bog restoration, because (i)development of a 'bog-Sphagnum' vegetation is aften aprime focus of restoration initiatives; (ii) it contributesto the regulation of surface wetness and to re-developmentof a characteristic bog acrotelm; and (iii) growthof Sphagnum may help regulate the chemical environmentof the developing mire by acidification (especiallyimportant to the development of ombrotrophicnuclei within minerotrophic conditions).The exact conditions required for effective establishmentof 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 wide variety of situations,though a common feature of these is generally a highand fairly stable water level. This may be provided:• by high and frequent precipitation input (sorne c1imatespermit Sphagnum growth in a range of situations,including sloping ground);• by a mat of vegetation semi-floating within (shallow)water;• by a stable water table, at or just below the surface of 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 of 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 of quarries, railway ballastetc.) when conditions are appropriate. Establishment ofa Sphagnum cover in such situations does not meanthat bog will neeessarily develop in these sites, but itdoes suggest that ombrotrophic vegetation can beregenerated from a range ofpossible starting points.Note that in sorne instances a stable, slightly subsurfaceminerotrophie water table in fen peat or mineral soilscan provide 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 of high precipitation input.3.4.3 Pathwaysof bog restorationReflecting the range of circumstances from whichraised bogs can naturally originate, restoration ofdamaged raised bogs can follow four main pathways.1. direct colonisation of bog peat by plants associated witht)'pical bog vegetation (MI8);20 colonisation of ombrotrophic water by p\ants anó mossesassociated with bog pools followed by successionalinvasion of other bog species;30 colonisation of fen peat (or wet mineral soils) by fenplants followed by successional development to bog;40 colonisation of minerotrophic water to form fen andthence bogoThe first of these pathways can be considered to be aformofrepair. The other three are forros ofrebuilding.Of these, pathways (3) and (4) may represent themechanism by which the bog naturally developed,whilst pathway (2) is more artificial in these sense thatbogs are not normally initiated in ombrotrophic water(though they may subsequently develop ombrotrophicflooding surfaces or bog lakes).3.4.4 Starting conditionsIn bog restoration initiatives, the pathway, speed andextent to which conditions suitable for the growth oftypical bog species can be realised depends strongly onthe starting conditions at each site (Table 3.2). Bogrestorers need to assess the conditions and problemsspecific to each site and, from these, determine themost appropriate restoration possibilities andprocedures. In sorne cases it may be desirable, ifpossible, to modify sorne starting conditions tofacilitate the restoration process. The principies andmethods by which this can be achieved form the maiofocus ofthe remainder ofthis reporto3.4.5 Suitability ofsites for restorationVarious workers have pointed out that cut-overpeatlands may vary considerably io their potential forrestoration, depending 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 of groundwater abstractionbeneath a bog) may prevent effective rewetting,or make it very cost1y, and it may then be appropriateto consider 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 of 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 dealof manipulation. There are numerous examples of suchsites in which 'renaturation' has produced little morethan thickets ofbirch and swathes ofbracken.Table 3.2 Summary of possible starting conditions on cut-over bogs.TopographyTopography may be very variable across an abandoned peal exlraclion complex, depending on lhe melhod and exlenl of pealexlraclion. Two situalions can be dislinguished, al several scales [2.1]:MassifsDepressionsblocks wilh an overall convex or water shedding profile.hollows wilh an overall concave or water holding profile.Note that depressions may occur within massifs.Block cutting ofien produces a regular system of baulks, f1ats and trenches, but can sometimes result in a largely nal surface.Miffing ofien produces a series of long peat fields, usually as cambered beds.Peat workings are ofien lower than adjoining refugium areas (which may be uncul remnants or revegetating cutlin!)s).Water conditionsPeal extraction and drainage modify or destroy 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 of 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 of 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 of a little-damaged bog is typically acidic and nulrient poor. Peal extraction and drainage may lead to changes inthe physical and chemical characterislics of the peat available for recolonisation [Chapter 2]. For example:• rewetting dried peat may lead to release of nulrients;• rewetting dried peat may lead to further acidification;• peat extraction may expose fen peat or mineral ground;• bare, dry peal provides an inhospilable physical environmenl for vegetation eslablishment.VegetationThe vegetation of remnant peat surfaces and of abandoned peat workings can be extremely variable, depending upon suchconslraints as degree of damage, depth of exlraction, lopography, base slalus, nulrient status, water level (and source) andlength of time since last worked [Chapter 4]. Areas lo be restored may lhus inelude 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 of peat workings4.1 IntroductionThe most obvious feature of peat extraction is that itremoves the living vegetation from a bog to leave abare and ofien dry surface. Although natural,spontaneous colonisation by vegetation of sorne sortwill undoubtedly occur on such surfaces withoutfurther intervention, the aim of most restorationschemes will be to try to optimise conditions toencourage colonisation and establishment by speciesapptopriate to a specific restoration objective.The revegetation of cut-over bogs is considered heregiving attention to factors that may constrain orinfluence the renaturation processes. The techniquesavailable to facilitate recolonisation of vegetation areconsidered in Chapter 9.Studies on the natural revegetation of cut-over siteshave indicated that the vegetation of such areas can bebroadly categorised into four groups [2.3.5; 3.2]:• bog-Sphagnum vegetation;• para-bog-Sphagnum vegetation;• vegetation typical of'dry' bogs;• vegetation typical offens.In sorne instances, natural colonisation of abandonedhand-cut, or commercial block-cut, areas has includedmany more bog species than spontaneous colonisationof a recently-abandoned, unmodified milled surface.This is due to factors such as topography, water levels,possible 'shoeing' I and availability of propagules andage (time since last cut). There is Iittle evidence tosuggest that vegetation typical of undamaged raisedbog, with a cover of actively growing Sphagnum. willspontaneously retum to extensive milled surfacewithout sorne degree of intervention.Water regime appears to be the primary factor affectingrecolonisation by wetland plants, but both physical andchemical conditions of 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 made to impound water).Spontaneous recolonisation ofien results in vegetationI Return ofvegetation to the cuttingssimilar to that in the dry areas of block-cut sites, ofienwith few, if any bog species (e.g. E. vaginatum,Molinia) accompanied by a range of 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 of the characteristic fen plant species andmany distinctive fen vegetation-types occur widely inrevegetated workings. Moreover, abandoned peatcuttings provide the main reservoir for sorne speciesand vegetation-types, especially in England. This isbecause such peat cuttings help to provide a wet fenand hydroseral environment in circumstances whichwould otherwise be comparatively dry and solid.Several of 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 of cut-overpeatlands can be identified as:• availability of recolonist species;• physical and hydrochemical conditions, including type ofpeat;• water regime.These factors must be taken into account in consideringthe potential for revegetation of cut-over areas, andwhat, if any, measures should be taken in order tofacilitate the recolonisation by typical bog (or fen)species.4.2 Recolonisation of peatworkings by plantpropagules4.2.1 Seed banksRather little examination has been made of thecharacter of 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 of viable seedshave been recovered from the uppermost peat of 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 of 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 of peat canretain a viable bank of various bog species (Poschlod,1995), though this depends 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 of uncutremnants may retain viable seed, which may respond torewetting initiatives. 'New' diaspore banks may alsodevelop in abandoned, revegetating peat cuttings, butvery often they are comprised of the seeds of various'weed' species, atypical of bogs, which have beenderived either from sources external to the bog or bythe spontaneous recolonisation of the abandoned cutoversurfaces. In many such cases the species concernedwill be unable to regenerate in a rewetted area, butthey may provide a reservoir for a few species, such asJuncus effusus and Molinia caerulea, which may beconsidered 'undesirable', at least in large quantities.4.2.2 Diaspores and dispersa/distancesThe lack of a seed bank in the peat of newlyabandonedcut-over surfaces means that spontaneousrevegetation is dependent upon the dispersal of 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 of dispersion formost bog species - indeed, in sorne cases the dispersalagent is not conclusively known. It is likely that mostrapid colonisation would be selective towards specieswith wind-dispersed diaspores. Diaspores of variousbog species have been recorded 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 indeed isthe ability of Sphagnum to establish onto bare peatfrom genninating spores. However, wind dispersal ofSphagnum is not necessarily restricted to its spores.Vegetation fragments of various bryophytes can bewind-dispersed to peat surfaces upon which they canregenerate (Poschlod, 1995).There is at least sorne evidence of the rapid colonisationof the wet floor of an abandoned sandstonequarry by bog species, including Sphagna, apparentlycolonised from a source sorne 14 km distant (Andreas& Host, 1983). However, the limits of dispersabilityare not realIy known and recolonisation of isolatedmires may possibly be constrained by this. Recolonisationrates will probably depend upon the proximityof the worked-out areas to a source of propagules,though input ofcolonists from refugia may also dependon the character ofthe intervening habitat, for example,the presence of woodland or scrub around a remnantmay reduce the influx of propagules of species usualIydispersed by wind. The importance of 'corridors' forwildlife conservation has received recent attention, butthe significance ofthese to bog plant species is unclear.It is important that, where possible, reservoirs ofpopulations of bog species are maintained close to peatextraction sites as the presence 'on site' of typical bogspecies is likely to considerably enhance the rate and'quality' of natural recolonisation of bare surfaces orfloating rafts and increase the speed of development ofthe more 'desirable' communities. Even where there isno uncut refugium for bog species, the survival ofSphagna in drainage ditches has been shown to be ofvalue as a source for the spread of Sphagnum onto cutoversurfaces and the subsequent fonnation of floatingrafts. In sites lacking refugia, it may be necessary to reintroducespecies (see below).The availability ofappropriate propagules is, ofcourse,no guarantee of revegetation by these species withinabandoned peat workings as the conditions providedmay 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 of 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 desired ones. Anecdotalevidence from various workers has suggested that therate and extent of birch colonisation of bogs is relatedto the proximity of mature trees 1 , but that colonisationand establishment of 'undesirable' species is reducedwhere water levels are sufficientIy high. However, theevidence suggests that it would be desirable to controlpopulations of 'weed' species both within and aroundrevegetating mires to reduce the potential invasion ofsuch 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 of the block peat cuttingsand relation to water level: baulks dominated by Molinia caerulea, the base of cuttings by Eliophorumangustifolium, and the trenches mainly open water. Sphagnum species (S. squarrosum, S. fimbliatum, S. palustre,S. recurvum) were recorded in the base of the cuttings and trenches. (See also Plates 2.14 and 2.15]4.3 Effects of hydrologicalconditions on revegetation4.3.1 Significance of water levelThe importance of water level to the vegetationcomposition and structure of 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 ofthe main factors affecting the recoloni atíon of cutoverbogs by different plant species. Individual wetlandplant species may occupy rather dístinct zones withrespect to water level [1.9], although the actual waterlevel 'preferences' of mo t bog and fen plant species,(including bryophytes) have yet to be established withprecision. Thus, for example, sorne species areespecially tolerant of (and may 'prefer') quite deepwater conditions (e.g. Typha species); others seemtolerant of only shallow inundation (e.g. many forbs l );yet others may help form, or a least grow upon.tloating rafts of vegetation. Sphagnum specíes showtrends in mícrotopographical distribution with respectto water level [see Figure 1.1 O]. The depth of water(above or below the surface) in abandoned cut-oversurfaces may therefore be expected to have animportant gross control upon the composition ofrecolonist vegetation [Plate 4.1], although any simpleprediction of likely developments of vegetation ingiven water level conditions is hampered by effects ofthe mechanism of recolonisation [4.3.2], and may beintluenced by the chemical conditions [44]. Optimaldepths of inundation are discussed in Chapter 5.The tability of the water table is also c1early importantin influencing which species may recolonise pealworkings. A strongly fluctuating water table may beinconducive to the colonisation of many typical bogspecies (and most importantly to Sphagna) and favourthe growth of less desirable 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 ofshaJlow lagoons, thereby helping to increase waterstorage, reduce water level fluctuations and to promotethe establishment of wetland species, particularlytloating Sphagnum rafts [see Chapters 5 & 9].I Forbs are non-graminoid herbs


Table 4.1 Vegetation recolonisation of cut-over surfaces by rooting (plants establish by attachment to the "solid" substratum) or rafting (growth of plants and vegetation, floatingin or on (sometimes shallow) water).Requirements:Water leveIsSurfaceconfigurationRootingSub-surface I shallow f100dingNo specific configuration required, other thanfor general retention of water; pools or pitsshould have gradually sloping sides.RaftingDeep and persistent inundation (optimum depth is probably c. 50 cm, unless supplementary f1otation mechanism available).Steep-sided pools I pits; may be necessary to create sub-divisions of large peat fields using baulks to reduce potential fordamage to developing raft by wind or wave action.VegetationOccurrence of plants with sufficient buoyancy to f10at (either on the surface, or at least within the photic zone).Examples of 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. demissa, Cirsium ¡Facilitation ofrecolonisationAdvantagesDisadvantages¡ spp., C. dissectum. ¡Inoculation with seed or rooted plant materialand 'seeding' with Sphagnum fragments.Does not require inundation.Existing 'desirable' vegetation (if present) isnot destroyed.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 of '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 debris or an artificial material to accelerate recolonisation and reduce wind andwave action. Loose peat debris ± existing vegetation may detach from the bottom and f1oat.Inundation of the surface allows substantial water storage and may help to retard or even prevent establishment of speciessuch as birch, Molinia and Cal/una. Such species may also be killed by inundation.Vertical mobility of the raft allows the developing 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' of vegetation before cuttings have filled with peat,thereby allowing precocious invasion of species that will not grow in deep water environments.Rafts may create conditions and support the vegetation that are known precursors of the natural development of raised. bogs,e.g. lawn and hummock-forming Sphagna, even in base-rich conditions.Peat cuttings in fen peat have provided conditions for the development of conservationally-desirable plant communities.Requires adequate control of water levels to ensure permanent inundation and to prevent "grounding" of the raft before thearea is self-sustaining; may require subdivision of large peat fields into smaller areas to avoid excessive damage to a fragiledeveloping raft of vegetation by wind and wave action.Existing 'desirable' vegetation (if present) potentially destroyed (although in some circumstances may become detached fromthe bottom and f1oat, thus accelerating revegetation).


C1IAPTER 4: RECOLONISATlON OF PEAT WORKINGS67One potential problem in the creation of large floodedlagoons is the possible attraction of certain birds(particularly gulIs and wildfowl), which may lead tonutrient enrichment through inputs of faeces, possiblygiving rise to the establishment of atypical vegetation,such as a dominance of the rush JUI7CUS ejfusus.However, the extent of the problem and the preciseconditions which may encourage such birds have yet tobe established, and there is at least sorne evidence thatbog vegetation can establish over 1. ejfusus at the sitesof former gulI colonies (Baaijens, 1984, cit. Joosten &Bakker, 1987).lt is often suggested that an additional advantage ofvery wet conditions in recolonising peat workings isthat they help to suppress undesirable species such asbirch or Molinia. Whilst in gross terms this is probablycorrect, both of these species can often 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 of 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 sidesof 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, depending 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 deeper flooding, topromote rafting. In sorne sites the possibility for evencrude control of the water levels may not exist, but inthose situations where it does, it becomes important toassess the merits of the two colonisation pathways.Salient features of rooting and rafting are summarisedin Table 4.1.RootingThe identity of species colonising peat surfacesdepends upon the depth and behaviour of the watertable (coupled with the chemical conditions) [4.3.1;4.4]. If the water table is substantialIy below thesurface of the peat for alI or part of the year, this wilIselect against species largely dependent uponpermanently, consistently high water tables (such assorne SphagnulJ1 species) in favour of 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 of much flooding, in favour of emergentspecies (e.g. Eriophorum angustifolium). When thewater exceeds a certain depth the water wilI becometoo deep for most species to survive rooted to the peat,and colonisation wilI depend on species able to floatand form rafts (see below). It is difficult to specify amean critical water depth because:a) it varies between species;b) it differs for lhe new colonisalion of planls compared tothe persislence of established plants. In general, manywelland plants are able to survive, rooted, in considerablydeeper water lhan that in which they would be able loestablish (from seed).Where pools of water are too deep to pennit theinvasion of any given particular species by rooting,unless rafting takes place its establishment is deferreduntil shalIower conditions prevai!. This may occurbecause of the gradual accumulation of organic mudsand peats within the pool, as part of autogenic 2terrestrialisation of the water (hydroseral infilling); byinputs of alIochthonous 3 sediments (e.g. wind-blownpeat); or through a sustained lowering of the waterleve!.RaftingThe term 'rafting' is used here to refer to the growth ofplants and vegetation, floating in or on (sometimesshalIow) water. By definition it requires some degreeof at least seasonal inundatíon. The identity of speciesforming the rafts wilIlargely depend upon the chemicalconditions; raft-forming species include Menyanthestrifoliata, Phragmites australis, Typha spp.,Eriophorum angustifolium and aquatic Sphagnumspecies). Individual plants may be free-floating or theymay be attached to the margins of the pools, fromwhence they have expanded across the water. WhenwelI developed, rafting may short-circuit the usualterrestrialisation process by producing a skin of vegetationat the water surface in deep cuttings before theyhave filIed with peal. It therefore permits the earlyinvasion of plant species that will not grow in very wetconditions. The term 'rafting' also includes the growthof loose mats ofSphagnum etc. within the water [PI ate4.2]. These may or may not ultimately form a surfacefloating raft, depending on topographical and water1 Strictly speaking the term 'attachment' is more correct, asbryophyte species do not have roots.2 autogenic = 'self-made'3 allochthonous =externally derived


68 RE TüRATlü üF DAMAGED PEATLANDPlate 4.2 Sphagnum cuspidatum forming a raft in a fiooded lagoon within worked-out peat cutlings; AmsterdamscheVeld (Bargerveen, The Netherlands).e ndition , and in shallowly-flooded sitegrounded for at least part of the year.they may beWhere a raft of vegetation forms, it is usually initiallyfragile; decomposing portion 111 a detach and fall tothe floor of the pool and ontribute to upwardaccumulation of organic material. But rafts u uallyincrease in thickne , both b an increa e In livingplant material and by entrapment of mud and peal. Ins doing the raft will gradually tabilise and ultimatelywill be able to upport trees (see below).The occurrence of a rafting c loni ation pr ce doesnol mean thal colonisafon of the water b dy isindependent of its depth. For example, ome f them re aquatic Sphagna (e.g. S. cllspidatllln) gro wellin fairly shallow open water bul less well in deepondition, p ibty becau e of limiled uppty ofdi olved carbon ource e.g. Baker & Boatman, 1990;Paffen & R elofs, 1991; .loo t n, 1992; Mon y, 1994).11 eems likely that lhe 'oplimum' inundation regimefor lhe promotion of aquatic Sphagna will usually be atrade-off betw en a need to avoid deep inundatíon tomaximise phagnum growth and a need to tore asmuch exce water as is needed to avoid desiccationd Iring dr period.. Depths grealer lhan .50 cm s emgenerally un uitable for good growth of aqualicphagna in bog water (e.g. Money, 1994) thoughexception also occur, ~ r e ample, S. auriclllatllnl isknown to grow in a lake at depthZielone, Poland (pers. obs.).up to 10m at.le ioroAlthough rafting recolonisation may result in an initialeradication of 'undesirable' 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'grounded' the urface may remain slightly proud ofthe water and may be suitable for e tablishment ofeedling birche elc. The degree to which this is aproblem may vary between ites. It i not diflicult tofind 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 beconcluded thal noaling raft of phagnllln will remainfree from woody cover, but this may, of course, be partf a natural I c s ional progres ion loward raisedbogo The problem is exacerbated when Ihe raft is onlydeveloped in hallow water, a 'grounding of the peatraft may lead t urface-dry conditions.Re torallon strategies aimed at Lhe production of raftsof vegetation seem to be particularly effectiveapproache lo the rewetting and revegetation of peatworking in both bog and fen peat in that (i) theyrequire inundalion of the mire surface (i.e. they permit


CCHAPTER 4: RE OLONl ATIO OF PEAT WORKING,69substantial water storage); (ii) they allow thedeveloping 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 ofthe raft prevents its inundation. However, the potentialimportance of rafting hould not just be seen in termsof the production of small-scale ombrotrophic tloatingrafts, important as the ma be, but also as afundamental strategy for regenerating an acrotelm-liketructure ayer large areas of derelict raised bogs. Insuch ituation the development of floating rafts maybe the onl effective way of 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 & Yalden, 1983) [Plate 4.4].Such physical instability of the substratum is perhapsbest reduced by the development of 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 of vegetation canalso help to buffer against fluctuations in water contentand temperature of the surface peat, for example byreducing the drying effect of the wind, and providing amore favourable microclimate for the establishment ofphagnum 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 development of a naturalcover is to be preferred.4.4 Physical and chemicalinfluences on revegetation4.4.1 IntroductionDifferent plant pecie are adapted to grow underdifferent environmental conditions. The conditionsprevailing at a given site largely determine whichavailable pecies are able to coloni e and establish. Themajor environmental influences upon the compositionof mire vegetation are: water supply (rainfall amountand frequency, water depth and flow); base status;nutrient status and (in a few cases) saJinity. There mayal o be physical constraints on revegetation,particllJarly of bare peat surfaces. The effects of sorneof these variables are identified below. In addition toenvironmental variables, vegetation managementpractices have a critical role in controlling andmaintaining the character of many herbaceollsvegetation-types, particularly in fens - these areconsidered 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 provide an inhospitableenvironment for establishment of 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 of seedlings of bog plants, but may also leadto crust formation and cracking of 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 of methods, asthese have not been widely tested.4.4.3 Chemical factorsIn Britain, an important control on the attern ofspatialand temporal variation in plant species distribution inombrotrophic mires is rainfall quantity and quality,itself controlled by factors sucb as proximity to the seaand degree of atrno pheric poHution (Proctor, 1995).Two further major influences up n the peciecomposition of mire vegetarion are tbe ba e andnutrient status of the substratum.Plate 4.5 Polygonum amphibium and Typha latifoliacolonising peat cuttings in fen peat; Somerset Levels.Plate 4.6 Polygonum amphibium colonising reflooded,marl-based peat workings at Turraun 80g (Ireland).(See also Plate 2.13]Base statusBase status exerts a primary influence upon thecomposition of fen and bog vegetation. The base statusof the water in peat workings is determined primarilyby the characteristics of the peat (and underlying subtrata)and the quality of any irrigating water inputs.These influences will substantially constrain thecharacter of the invading vegetation, though otherinfluence may modify ome of their effects fore ample whilst fen plant species are the typicalrecolonists of peat cuttings with base-rich water [PIates4.4 and 4.5], the development of a semi-floating raft ofvegetatian may facilitate the establishment ofSphagnum-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 of most ions isgenerally higher in the water and peat frorn peatworkings than from less disturbed situations and sometimesprovide chemical conditions more like those ofpOOl' fens than ombrotrophic bogs [2.3.3]. There is alsoevidence to uggest that in ome circum tances,chemical change resulting from drainage of the peatand seasonal fluctuations in water levels can lead toincreases in acidity (pH


CHAPTER 4: RECOLONISAnON OF PEAT WORKINGS71development into ombrotrophic bogo By contrast, if thepeat is f1ooded, there is potential for development of aseral, f10ating fen vegetation which may provide atemplate for more rapid redevelopment of bogvegetation.It is possible that where only a small thickness of peatremains at the base of peat workings there may besorne chemical inf1uence from the underlying mineralground. The effect of this will depend upon itscharacter - Sphagnum can recolonise base-poor sandsand gravels quite readily and sorne excellentSphagnum-based communities have developedhydroserally in small pits within glacial sands (e.g.Delamere Forest, Cheshire).Nutrient statusThe ombrotrophic bog environment is typicallynutrient poor and infertile. However, disturbance of thepeat through peat extraction operations or dehydrationcan lead to mineralisation of the drying peat andnutrient release [2.2.2; 2.3.3]. There is little evidencethat this is inimical to revegetation prospects bySphagnum species, but data are sparse. In many sites itis not obvious whether augmented N concentrationsderive from disturbance of 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 of underlying fen peat or clayscan, in principie, also expose a substratum that is morenutrient-rich than was the overlying ombrotrophic peat.The quality of irrigating water inputs from sourcesother than precipitation should be carefully assessed,and ifnecessary, polluted water diverted away from thesite.A wide range of fen communities have been recordedfrom recolonised peat workings, developed either onsolid peat or hydroserally. As a general rule, thosewhich are particularly welcomed by conservationistsfor their intrinsic value are those which have developedin conditions of low fertility; such vegetation-types areofien species-rich, frequently contain variousuncommon plant species and are themselves rare:Nutrient-enrichment of abandoned fen peat workings,particularly by nitrogen or phosphorus, is typicallyassociated with the development of a vigorous, coarseand species-poor vegetation that has limited botanicalvalue, although it may still provide an importanthabitat for other groups such as birds or invertebrates.4.4.4 Peat-typeThe nature of the peat surface presented for recolonisationmay depend on the type of peat exposed [1.8;2.3]. Weakly-humified peat is thought to provide 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;Roderfeld, 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 of thefunctional attributes of the original bog acrotelm.However, it has also been suggested that sorne littlehumifiedpeat is too deficient in nutrients to sustaingood regrowth of sorne bog species (J. Blankenburg,pers. comm.), and there is little clear evidence tosuggest that the weakly-humified peat is necessari/ymore desirable for encouraging revegetation of cutoversurfaces than is strongly-humified peat as this isalso related to the nature of the rewetting strategy[Chapter 5]. Evidence from The Netherlands (e.g.Joosten, 1992) suggests that weakly-humified peatthrown back into peat cuttings as a type of bunkerde[9.5] may facilitate the formation of a f10ating rafi onwhich Sphagnum and other species could colonise.Exposure of fen peat will undoubtedly inf1uence thecomposition of the recolonist species, as the chemicalenvironment is likely to be more conducive to theestablishment of fen rather than bog vegetation (seeaboye).4.4.5 Depth o(residual peatIn broad terms, the effect of residual peat depth uponthe prospects for rewetting and subsequent revegetationis likely to be important in two main ways:• the intrinsic characteristics of the peat-type that isexposed at a particular depth;• the effect of the thickness of the residual peat layer as abuffer against underlying conditions and vertical waterloss by seepage.The intrinsic characteristics of the peat are related to,and partly determined by, its position in the peat profile[1.8]. The chemical composition may be of 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 depth 01' residual peatthat is needed to minimise, to an acceptable level,downward seepage losses into the underlying mineralsubstrata in appropriate sites is likely to dependstrongly on the permeability 01' the peat. Studies arehampered by difficulties of making an accurateestimate of vertical seepage. Schouwenaars,Amerongen & Boortink (1992) provide evidence thatrates of downward loss are inversely related to residualpeat depth. A 'critical depth' against seepage has notbeen established, but Blankenburg & Kuntze (1987)suggest that at least 50 cm of a low permeability,


72RESTORATION OF DAMAGED PEATLANDSstrongly-humified peat is needed to keep downwardseepage losses below what they considered to be anacceptable rate of 60 mm a-l. Similarly, Schouwenaars(1993) suggests that at least 50 cm of stronglyhumifiedpeat (H ~ 7) is mostly sufficient to guaranteelimited water losses, whereas for less stronglyhumifiedpeat (H 5-7) a minimum thickness of I mmay be required, unless the water pressure in theunderlying aquifer lies aboye the base ofthe 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 of this water balance term in thosesites where this is a possibility; experience elsewheresuggests that it may have profound repercussions forthe success ofrestoration initiatives.A minimum depth of ombrotrophic peat may beneeded to help prevent enrichment from underlyingbase-rich substrata (fen peats or mineral ground), eitherdirectly or through plant roots being able to tap anyunderlying enriched conditions. Again a critical depthhas not been established, but various considerationspoint to a depth of 50 cm as a desirable minimum, aview shared by various workers (e.g. Eggelsmann,1980).Note also that the depth of residual peat consideredmust take into account the depth beneath the f100r ofdrainage channels and the disposition of the peat fieldsin relation to the underlying topography of the mineralsub-soil [see also Chapter 6].4.5 External constraints onrevegetation4.5.1 IntroductionEarlier sections of this chapter have considered therelationship between sorne internal conditions of cutoversites to their revegetation prospects, for example,lack of recolonist species and hydrological andchemical factors. However, there are also sorneexternal processes which may inf1uence thecharacteristics of the site which it may not be possibleto manipulate directly.4.5.2 Effects ofatmospheric 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 ofSphagnum (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 of the'chemical balance' of the mire water, such asenrichment with nutrients that would normally begrowth-lirniting.Possible implications tor bog growth andrestorationThe assessrnent of the effects of atmospheric pollutantsand implications for growth of bog species is hamperedby lack of data and the difficulty of relating plantresponse to specific concentrations of different pollutants.However, it seems likely that in present circumstancesthe deposition of nitrogen oxides and ammoniarnay have more significant effects on growth of bogspecies than sulphu'r dioxide. Atmospheric pollutionhas probably inf1uenced the composition of thevegetation of 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 detrimental effects of nitrogenouscontaminants upon lowland bogs are not known, but itis possible that these may differ for the maintenance ofexisting bog vegetation compared to the recreation ofbog comrnunities on cut-over sites, not least becausethe latter may be subject to additional sources ofenrichment in consequence of disturbance,rnineralisation etc. [2.3.3]. Further work is required toprovide critically definitive evidence in order toestablish whether current levels of atmosphericpollution are disadvantageous to the prospects forregeneration ofraised bogs.4.5.3 Lowering ofregionalgroundwater levelsA decrease in regional groundwater tables mayinf1uence the water balance of sorne sites [2.3.2],although it rnay be possible to mitigate these effects byretaining a sufficient depth of 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 of 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 of rainfall,temperature, humidity and evapotranspiration may allaffect the water balance of the mires and the potentialfor regeneration of 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 of apeatland vegetation are Iikely to be different from thosenecessary for its establishment. For example, a c10sedcarpet of Sphagna is able to preserve moisture byforming a 'mulch' over the surface, and 'bleaching' ofthe Sphagna on dehydration helps to ref1ect incidentradiation, thereby helping to reduce the loss of waterfrom the peat surface / acrotelm (Schouwenaars, 1990).However, until a c10sed carpet is achieved, theindividual plants are more likely to be susceptible todesiccation during periods of low rainfall andhumidity.4.6 Recolonisation of peatworkings by invertebratesVery little is known of the colonising abilities ofraised-bog invertebrates, but it is Iikely that dispersalwill be limited in flightless species or those havingreduced wings (as in the case of sorne beetles andbugs). However, the carabid beetle, Agonum ericeti isknown to be f1ightless in the UK and indeed over muchof its range (Thiele, 1977: 291; Lindroth, 1985) but itis nevertheless widely distributed in suitableoligotrophic mires. In sorne species mobility may beeffected by methods other than flight, though it mayalso ref1ect in part, a greater contiguity of raised-bogareas in the past.The importance to dispersal ofthe habitat-type betweenthe refugium and areas to be colonised depends greatIyon the mode of dispersal of 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 of dragonflies,for example, are markedly migratory in their behaviour(though sorne notable raised-bog species are more-orlesssedentary). At the other extreme, many flightlessspecies such as sorne beetles and bugs, may be unlikelyto enter areas of unsuitable habitat (i.e. areas that aretoo shady, dry, friable, alkaline, etc.); Thiele (1977:214) intimated that substratum type was probably animportant determinant of movement in carabid beetles.Nevertheless, studies have shown that a surprisinglylarge number of invertebrate species are capable. ofcolonising even remote islands ofsuitable habitat givensufficient time.Rates of recolonisation of cut-over areas are likely tobe strongly inf1uenced by the character of thevegetation developed within the workings, and also bythe proximity of refugia for 'desirable' invertebratespecies - nothing is known about the potential toinoculate regenerating areas with appropriateinvertebrates in the absence of nearby refugia.Nevertheless, studies by Heaver & Eversham (1991) ofextraction sites at Thorne Waste which had beenworked up to the 1970's but which were since largelyundisturbed and wet, show that colonisation of at leastsorne species can occur fairly rapidly (including in thiscase sorne 27 scarce or rare taxa). Such successfulrecolonisation was probably dependent on thepersistence of the recolonising species in nearbyrefugia, but provides at least sorne evidence thatconservationally-worthwhile, more or less balancedinvertebrate communities can reassemble within c. 50­70 years given the presence of adjacent refugia,perhaps even less, although the communities that existat this time are undoubtedly still transitional. However,rates of recolonisation will c1early also depend on theavailability and proximity of potential recolonistspeciesThere have been very few studies of the behavioural orphysiological selection processes that restrict peatlandinsect species to particular types of 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 ofspecific food sources (plants, animals or detritus),vegetation height and structure are also likely to beimportant determining factors, as are the amount anddistribution of open water and hydrological regime(e.g. Key, 1991). For example, an increase in provisionof open water habitat by management such as ditchblocking or creation of pits or scrapes, ofien 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 of raised bogswhere woodland may act as a windbreak (R.G. Kemp,pers. comm.). It should be remembered that the habitatrequirements of a species will be govemed by both therequirements ofthe adult and also, the larva, pupa, etc.,and that these may be rather different, necessitating thepresence of two or more different and perhaps evenspatially separated features.


74RESTORATION OF DAMAGED PEATLANDS4.7 Recolonisation of peatworkings by birdsAlthough most birds show strong site fidelity fornesting, roosting etc, ringing recoveries c1early showthat many species do not remain in the same area (oreven the same continent!) throughout the year. In viewof such natural mobility it might be assumed that birdswould readily abandon a site following adverse habitatchange, or high levels of 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 of their geographicalrange, the chances of recolonisation of the sitefollowing restoration measures would be considerablyreduced.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 of 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 ofextensive cut surfaces in the longer termoDisturbance, lack of food sources and nest sites islikely to severely limit the use of expansive areas ofnewly cut-over bog by birds. As these areas becomerevegetated birds may readily colonise, although reestablishmentof a community which is characteristicof little-damaged raised bog is unlikely in the shorttermo The species which colonise will largely dependon the distribution and amount of open water and thetype of vegetation which develops (as well as the site'sgeographical location), being influenced by suchfactors as suitability and availability of food sources,nesting sites, roosting sites, vegetation structure etc..For example, increased provision of open water hasbeen shown to attract breeding waders and duck(including teal) which may be attributed to increasedfood availability (e.g. aquatic invertebrates, includingOdonata, Hemiptera, Coleoptera and Diptera) (Fox,1986a). The development of birch scrub attractsspecies typical of woodland: willow warbler being themost characteristic species of pioneer birch woodland,with a number of other passerine species also beingrepresented. Where fen vegetation develops in oId peatworkings, additional species such as sedge warbler,reed warbler, water rail, moorhen and coot can beattracted to breed. Conversely, loss of suitable habitatas a result of rewetting may reduce the numbers ofsuch species as nightjar and skylark.


Chapter 5Rewetting damaged and cut-over peatlands5.1 IntroductionIn any project aimed at restoring or recreating wetlandecosystems, long-term success depends upon theprovision of a hydrological regime appropriate for theestablishment and maintenance of the target wetlandbiota. It is not possible to give a simple, or universal,prescriptive solution to the problems of rewetting peatextraction complexes as this will depend critically uponsuch site-specific factors as topography, dispositionand character of the peat fields, peat type and climateas well as the objective of restoration. However, it ispossible to identify sorne general principies, problemsand solutions, based upon attempts at restoration [seespecific references and Appendix 6J, and to discemsorne broad categories of context in which bogrestoration is likely to occur. In this chapter, the principies,potential and limitations of various rewettingprocedures are discussed. The adoption of 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 of a typical,Sphagnum-rich, bog vegetation, but sorne altemativesare considered briefly.5.2 Establishment of suitablehydrological conditions forraised-bog restoration5.2.1 Principies of rewetting damagedand cut-over bogsThe exact character of water management in bogrestoration and conservation may depend 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 of its former species). It will alsodepend upon the topography ofthe area (e.g. whether amassif. or a depression [2.1 J) but in all such situationsthe primary problem of rewetting is that of retainingsufficient meteoric water so that the peat surfaceremains consistently wet year-round. A characteristicfeature of little-damaged bogs is that saturatedconditions are maintained close to the surface for muchof the year, i.e. they have a cOllsistently high watertable. Although bog plants have sorne capacity totolerate occasional dry periods (depending on theirduration and magnitude), successful bog regenerationalso requires permanently wet conditions. Low waterlevels are not only unsuitable for the growth of manybog plant species but may also promote further oxidativedecomposition of the peal. On an ombrotrophicpeat surface, precipitation is the sole source of recharge,and hydrological management must seek to retainas high a proportion of this as is possible l to illitiatemire regeneration or to maintaill existing surfaces.Both the 'base-line' water level in raised bogs (Le. thelimit of permanent saturation) and the magnitude offluctuations aboye this, are regulated by similar(though not identical) processes. The limit ofpermanent saturation is provided by the position of the'groundwater' mound surface in relation to the miresurface and is a reflection of the variables thatdetermine 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 of permanent saturation. Theyare essentially a reflection of the consistency ofprecipitation recharge, the capacity for water storage inthe upper layers (which is a function of the storagecapacity of the peat, fraction of open water etc.), thevegetation, climate and the regulation of water lossesthrough run-off and evapotranspiration. In disturbedmires, drainage and peat extraction may reduce waterstorage capacity at or near the peat surface (Joosten,1992) relative to that of intact mires (Galvin, 1976;Eggelsmann, 1981, 1988a); removal of the acrotelm 2also removes sorne natural capacity for hydrologicalself-regulation; and recolonisation by plant speciessuch as Molinia or Betula may increase rates of1 while allowing for discharge of periodic water excess.2 The term 'acrotelm' refers to the surface layer ofa peatland that isaboye the limit of permanent saturation. In this broad sense, cutoyerbogs also haye an acrotelm, but one which lacks some of thedistinctiye features of the acrotelm layers of 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 develop which may create channels ofpreferential water flow and help to drain the surface. Incombination, these processes ofien result in damagedbog surfaces having a much greater amplitude of 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 of the system is in considerable mea~uremaintained by the functional characteristics of 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 ofdrought. When the originiil acrotelm of a raised boghas been destroyed (as by peat extraction), its capacityfor water storage and run-off regulation is reduced andan altemative 'stable state', may develop, but onewhich is essentially characterised by relative instabilityof various environmental variables, especially waterleve!. This condition is supported by various feed-backmechanisms, including the growth on a summer-drypeat surface of various deep-rooted plant species withhigh rates of evapotranspirative water loss. Theimportance that loss of the original bog acrotelm hílS torenaturation of damaged sites is partly determined bythe frequency and volume of recharge as well as by thewater storage characteristics of the 'new' acrotelm (i.e.the unsaturated zone formed by the upper layers of theremaining peat). However, in many situations the netresult is that whilst in wet (winter) conditions thesurface may become saturated, or even flooded, in dry(summer) periods it dries considerably. In suchsituations, the water level fluctuations may be ofsufficient magnitude to prevent recolonisation of thepeat surface by bog (especially Sphagnum) species andhence to prevent redevelopment of an acrotelm whichhas the functional characteristics of 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 ofrestoration of bog vegetation on a damaged ombrotrophicsurface is that of 'kicking' the system from the'damaged surface' stable state to a 'bog-acrotelmbased'stable state. The difficulty of this is that theconditions required to redevelop an acrotelm with theproperties typical ofa little-damaged bog surface are inconsiderable measure provided by this sort of acrotelmitself. A solution to this problem is to try to constructdevices that mimic sorne of the properties of theoriginal acrotelm and which permit its redevelopmentby sustaining the growth of typical bog species. Manyof the different approaches to bog restorationessentially represent different ways of attempting tosolve this problem.5.2.3 Approaches to rewettingThe main aims ofwater management for the restorationof raised bog can be summarised:• identify causes of dry conditions;• increase retention of nutrient-poor precipitation input;• eleyate level of 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 of attempting to elevate the level ofpermanent saturation within the peat or of reducing theamplitude of water level fluctuations near the surface,usually by increasing water storage (or both).Rewetting procedures depend upon whether the aim is(i) to rewet a remnant of upstanding peat (or to retainits wetness); or (ii) to provide appropriately wetconditions in extensive cut-over surfaces. Theseparation of these two situations - massifs anddepressions [2.1] - is sometimes rather arbitrary butthey provide a simple conceptual basis on which toconsider different approaches to peatland restorationand help in the formulation of generalised restorationstrategies applicable to more than one site and fordifferent scales within an individual site.'Rewetting' of mires implies the creation of surfacewetconditions, but there is scope for variation in thedegree of wetness which may be desired 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 of the peat(usually sub-surface) for much ofthe year.Water level is above the surface of the peatfor at least part of the year. The degree offlooding can vary typically between shallow« c. 20 cm) and deep « 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 ofthese situations, the retention of water is ultimatelydependent upon the maintenance of a water tableperched aboye that in the surrounding depressions.'Groundwater' mound concepts [Box 1.5] are thusappropriate for considering various conceptual optionsfor the rewetting of bog massifs.Various strategies for rewetting bog massifs areidentified below, based upon approaches that haveeither been used or proposed. Sorne cannot be regardedas well tried and tested and, where appropriate, theirIimitations are identified. The choice, and effectiveness,of any of these options is likely to be inf1uencedstrongly by:• the causes and extent ofdehydration I darnage;• the nature ofthe peat;• the nature ofthe c1irnate;• the exact topography ofthe site.The choice of option wiII also be determined bywhether the aim of rewetting is to mainlain an existingbog vegetation or to renalure a badly-damaged peatsurface [Chapter 6].The surfaces of 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 ofa site;• site has been drained;• excess vertical seepage occurs frorn the catotelrn into theunderlying aquifer..Various feedback mechanisms' may exacerbate theseeffects:• developrnent of vegetation with greater rates ofevapotranspiration than typical for a little-darnaged bogsurface;• deveJopment of fractures and fissures wilhin lhe pealconsequent upon drying;• loss of sorne ofthe attributes ofthe original acrotelrn.The concept of the basal area of a peatland being toosmall to maintain the perched water mound c10se to thepeat surface derives from the 'groundwater' moundtheory, in whichthe height and shape of the watermound that defines the upper Iimit of the catotelm isrelated to the basal area and plan of the mire. This isillustrated in Figure 2.3. However, it is not axiomaticthat a reduction of basal area will necessarily lead to areduction of the height of the water mound overall ormuch of the bogo This is because in sorne bogs,especially large ones, the actual height of 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 decomposition in the catotelmprevents the hydrological maximum being reached(Clymo, 1984)). Thus in large bogs it may be possibleto make a considerable reduction of the total areawithout lowering the height of the water mound overmuch of 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 of drains upon a bog surface will dependupon their disposition, depth 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 of water by vertical seepage downwards from thepeat into an underlying 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 of the bottom of the peat, has sincebeen reduced consequent upon groundwater abstractionele. This is considered to be an important source ofwater 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 of this for restoration in relation toresidual depths ofpeat 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 of thereduced perched water mound, one main object ofrewetting is to bring it back to an 'appropriate' positionwith respect to the peat surface over all or part of 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 of approaches for rewetting bog massifshave been identified [see Box 5.1]. The salient features,Iimitations and appropriateness of these approaches fordifferent situations are considered below. Note thatthese approaches are not mutually exclusive. It is ofienpossible, and may be necessary, to combine differenttechniques to achieve optimum rewetting of massifs,due to the heterogeneous nature of many peatextraction complexes. AII of the approaches assumethat drainage ditches are blocked. For one, this is theonly requirement. Three main types of bund have beenidentified - 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 ofthe water level by ditch blockingNon-intervention - natural subsidence ofpeat to the position ofthe perched water moundSculpting of the peat surface to the position of the perched water moundElevation of the water level by containment within wall bundsElevation of water level by increasing water le veIs in the surrounding areaProcedures based mainly on inundalion:(f) Inundation using parapet bunds(g)Inundation by reduction of the level o, the peat surface to form lagoonsOlher proeedures(h)Provision of supplementary water5.3.2 Methods(a) Elevation of water level by ditch blockingFundamental to aH rewetting options of peat massifs isblockage of any ditches that drain them [Figure 5.2 (i)],and this is the main focus of 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 depend onthe factors contributing to their dryness (including thehydraulic conductivity of the peat and underlyingsubstrata) (see, for example, Schouwenaars, 1995). Insorne cases where superficial ditches provide more-orlessthe only reason for dehydration, ditch-blockingalone may be sufficient to provide effective rewettingof the mire surface, or, particularly, to maintain theexisting interest of a little-damaged mire surface.Indeed, in sorne little-damaged sites spontaneousSurface bundsWall..bundocclusion of(small) ditches has occurred.Limitations• The prime limitation is that in sorne sites periodicsurface dryness may be a consequence of factorsother than drains. Where dryness has been inducedby an overall shift in the height of the water moundconsequent upon a reduction ofthe basal area ofthemire, 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 deep andextensive, slumping and wastage may have causedconsiderable change in the topography of parts ofthe massif. In this situation the topographicalposition of such ditches may mean that even whenfull of water they have little effect upon impedingdrainage from sorne higher parts of the bogo InParapet bund..weakly-humified peatstrongly-humified peatopen waterbundFigure 5.1 The three main types of bund which have been identified as being used in bog restoration projects.Surface bunds restrict lateral run-off through the upper horizons of weakly-humified peat; parapet bunds extendaboye the level of the adjoining peat massif, to form a long, low surface dam against which water may beimpounded; 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, of its periphery.


CHAPTER 5: PRINCIPLE OF REWEITl G 79sorne circumstances a stepped cascade of dams maybe used to circumvent this difficulty.• In damaged massifs without an acrotelm characteristicof a little-damaged bog, ditch-blocking maynot be adequate to ensure a water table that issufficiently stable close to the peat surfac~ to permitthe extensive establishment of Sphagnum species.This is mainly because evapotranspirative waterloss, coupled with dry episodes lead to a reduction[~OCklng •••In,(ii)Use of wall bunds around margins~ ~- ._--~;Resoaked peatWallbund,J.(iii) Raise water level in surroundings of bog(a) Water level al surface o,surrounding land.~ Unsaturated~ peat(b) Water level ffooding surrounding landlofwater leve!. The extent to which this limitation isimportant depends upon the topography of themassif and its climatic situation. It is especiallyimportant on surfaces with limited water storageand in regions that experience periodic andsustained droughts.Possíble applicatíon• Blocking of 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 of 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 ofBritain.Potentíal for vegetatíon restoratíonIn appropriate conditions, ditch blocking has beenshown to help maintain existing bog vegetation, and toimprove lhe condition of somewhat degradedvegetation (e.g. Roudsea Moss, Cumbria). We know ofno examples where ditch-blocking alone has led to thewidespread regeneration of 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 of abadly-damaged massif surface may sometimes createcondjfons suitable for sorne individual bog species. Inthe cooler and wetter parts of Britain, these mayinelude sorne species of Sphagnum. In other situations,it is more likely to produce wet heath or, whereparticularly ineffective, a 'dry bog' community.(b) Non-intervention - 'natural' reconformationof peat to position of perched water moundPerhaps the simplest approach suggested for therewetting of bog massifs where the peat surface iselevated above the position of the water mound over allor part of the site is one of non-intervention, i.e. topermit natural processes of water drawdown, wastageand subsidence to OCCllr. Its underlying presllmption isthat upstanding peat blocks will, by oxidation,slumping e/c., eventually reconform to the position ofthe 'new' groundwater mound within the massif. Insuch a process, increased humification of 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, evidence for the efficacy of 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 PEATLANDSof 'accommodation' of the effects of marginal damageon otherwise little-damaged bogs (e.g. WedholmeFlow, Cumbria; Clara Bog, Ireland). Its potential valueprobably depends very strongly upon the startingconditions, in particular the prevailing c1imate. Twoextreme starting conditions are considered below.A: Site with badly-damaged surface with water moundwell below surfaceThis situation is typical of a number of dry remnantmassifs, where the surface is fairly dry over much ofthe expanse, supporting heath, Molinia, bracken, birchetc. and perhaps a few bog species that are relativelytolerant of 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 indecades and possibly centuries, depending on theheight difference between the peat surface and theposition of the surface of the perched watermound);• during this period part, or all, ofthe surface may berather dry and incapable of 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 of theircharacteristic fauna and flora, and sometimesinduce considerable loss of hydrological integrityof the peat by fissuring;• the presumption that the wasting peat surface willequilibrate at sorne stage at the zone of permanentsaturation is questionable [see Figure 5.3]. In adiplotelmic mire an important role of the acrotelmis to supply water to the catotelm and hencemaintain the zone of permanent saturation. Bycontrast, when a badly-damaged peat surface haswasted (Iet it be assumed) to the position of theperched water mound, other than in climaticregions where there is a near-constant input ofmeteoric water, the position of the water moundwill continue to sink periodically below the peatsurface in response to periods of dryness. Hence asthe peat surface subsides, the zone of permanentsaturation will also sink beneath it. Such periods ofsurface dryness may not only constrain the reestablishmentof bog species; they may also permitongoing wastage. It is then possible that theeventual consequence of a 'natural wastage'scenario will be the loss of the entire ombrotrophicpeat deposit. This process is likely to beexacerbated if the subsiding surface is rather dryand supports a vegetation with high rates of evapotranspiration(e.g. dominance of 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 of bog (especially peatforming,Sphagnum-based) vegetation except,perhaps, in c1imatically-favoured localities.B: Site with well-developed bog vegetation subject tominor marginal water drawdownThis situation is representative of a site which hassuffered sorne marginal damage (for example, by peatextraction) and water drawdown, but where a welldevelopedbog vegetation exists over much of thesurface and where the water-mound remains near thesurface over much of the mire. In this situation theeffect of marginal damage may have Iimited impactupon the rest of the mire, or processes of small-scalereconsolidation and slumping may permit rapidreconformation ofthe affected part ofthe surface to thesurface of the new position of the perched watermound. The main limitations of non-intervention maythen just be:• drying of the margins of the massif will occur, theamount being determined by the degree of waterdrawdown;• the edges may gradually conform to the edge of thewater mound by slumping, oxidation etc.; theymay, however, not rewet, and may continue tooxidise.Possible applicationThere is little evidence to suggest that naturalreconformation of the peat surface of a badly-damagedbog massif to the perched water mound will occur orwill produce suitable rewetting of 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 of 'good' quality bog vegetation whenthe mire is subject to an extensive reduction in theheight ofthe perched water mound.Situations where a non-interventionist approach to'rewetting' may be acceptable are likely to be oneswhere the effects ofdrying will be small or where otherrewetting strategies are not feasible, for example:• in a mire site which supports 'good' quality bogvegetation over much of its area and where only themarginal areas are dry, if it is considered that driermargins are acceptable, and no lowering of 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 of the bog have been removed (throu!~h peatextraction or conversion to agriculture). The water moundsinks to a position determined by the new dimensions of themassif, so that permanently saturated conditions are nowwell sub-surface. A new zone of peat that is not permanentlysaturated becomes established in the upper part of theformer catotelm./ / / / / / / / / // / / / / / / / / / / // / / / / / / / / / / / /~CPeat oxidation and decomposition occurs in the periodicallydry upper part of the former catotelm. Coupled with othercauses of subsidence (slumping, deflation etc.), theunsaturated surface of the mire gradually wastes towardsthe zone of permanent saturation./ / / / / // / / / / / / // / /l/ / / / / / // / / / / / / /•II•F./ / / / /oContinued wastage in oxic conditions brings the surface ofthe mire increasingly into closer conformation with thesurface of the new water mound. However:E During periodic dry periods, lack of precipitation inputcoupled with evapotranspiration causes the water table tosink below the surface. Thus the zone of 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 decomposition.The sequence of events C-E is repeated and the watermounds gets yet smaller, followed by a further loss ofsurface peal. This process may continue until theombrotrophic peat largely disappears (though it may ofienbe very slow). It could be arrested or retarded (a) by theestablishment of permanently saturated conditions on thesurface (by inundation ?); and (b) by the associateddevelopment of a peat-forming bog vegetation.Figure 5.3 Suggested scenario for the likely changes in badly-damaged peat remnants subject to naturalprocesses of peat wastage. It is relevant to suggestions for rewetting of peat massifs by just allowing wastage totake place and to proposals to remove upper peat down to the predicted position of 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 of the bog remnant; where the bogremnant is large and peripheral damage has beensustained gradually, or where the water drawdownat the edge of the massif affects only a narrowmarginal zone (e.g. because the height differencebetween the surface of the massif and adjoiningareas is small or because the peat is of lowpermeability);• in situations where redevelopment of a Sphagnumrichbog vegetation is not desired or is unlikely tobe feasible for other reasons;• where the surface configuration (e.g. hollows orblock pea! cuttings) of the massif permits theretention of locally wet conditions despite sornedegree ofdrying ofmore elevated parts;• where 'good quality' bog vegetation towards thecentre of the massif is already separated from themargins by a zone of 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.FurlherconsíderationsAs isolated peat massifs left to reconform by wastagemay be rather dry, over sorne or all of their surface,and are perhaps colonised by large stands of birch andbracken, they may be vulnerable to incendiary ev~nts.Severe fires, which ignite the dry peat, may sometlmesaccelerate the restoration process by causingconsiderable loss of peat mass. At Thome Waste,severe fires are thought to have caused a loss of sorne30-40 cm of pea! on sorne dry baulks (R. Meade, pers.comm.) and to have made them more conformable withthe adjoining wet cuttings. Such 'combustion levelling'may, for several reasons, not be seen as a desirablemanagement tool, but there can be no doubt of 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 of existingSphagnum-rich bog vegetation. However, where badlydamagedbog surfaces have been left to waste, theredeveloping vegetation is, in the short term at least,usually Molinia, bracken, birch scrub or heathland.Sorne of the more drought-tolerant bog species (e.g.Eriophorum vaginatum) may recolonise suchsituations. It is possible, particularly in the wetterregions of the UK, that a wider range of bog speciesmay ultimately establish on 'wasting bogs', but wehave no evidence to support this.(c) Sculpting of the peat surface to the positionof the perched water moundA more interventionist version of the 'natural wastage'approach is provided by the interesting suggestion ofBragg (1989) that peat could be removed to form aprofile which, derived from 'groundwater' moundequations, would conform to the predicted position ofthe 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 of this approach are thesame as for the 'natural wastage' approach, especiallythat the zone of permanent saturation is likely to sinkbeneath the position of the sculpted surface during dryperiods [Figure 5.3]; in addition:• it may be difficult to predict the ultimate position ofthe perched water mound;• it may be difficult (and costly) to sculpt the peatmound with the exactitude 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 projectundertaken by the Somerset Trust for NatureConservation is currently in progress, in which asmall area of peat (Getty's Mire) was contoured tothe predicted shape of the 'groundwater' mound[Plate 5.1]. Water level measurements have shownthat the water table was convex in the winter,folIowing quite well the shape of the mound, butbecame concave during the summer. This corroboratessorne ofthe limitations identified aboye.• Sculpturing of the peat surface in the way proposedmay provide suitable conditions for the establishmentof sorne bog species in sorne situations, but itis difficult to see what practical benefits thisapproach confers in comparison with sorne of theother, technically more simple, approachesdiscussed below.Potentíal for vegetatíon restoratíonAs this approach has been little tried, few factualcomments on its efficacy can be made. It seems likelythat it would be possible for sorne 'ofthe more droughttolerantbog species to establish on sorne surfaces andin appropriate c1imatic regimes, even that sorneSphagnum species could colonise. However, we haveno supporting evidence for this.


CHAPTER 5: PRINCIPLES üF REWETIING83(d) Elevation of the water level by containmentwithin wall bundsAn alternative, more elaborate approach to reducingthe peat surface to the position of 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!, of its periphery[Figure 5.2 (ii)]. This can be achieved using a wal!bund, made of low-permeability peat or, if this isunavailable, of inert materials such as plastic (or both)[8.2]. In effect, this raises the impermeable base of thebog and elevates the position of the perched watermound. In the simple form described 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 of abog, particularly if it is done weH [7.3].• As this approach involves elevation of the watermound aboye its natural position, it is potentiallyunstable. The bunds have to be substantial, wellmade and maintained to retain the water; weakbunds may be susceptible to collapse (for example,through a build-up of pre sure behind the bund). Itis possible that, in the long term, bunds maydisintegrate through oxidative decomposition. Asyet there is little direct evidence for this, but sorneaHowance for on-going maintenance of at least themarginal bund may need to be made. Provisionmust also be made for the control of water levels toal!ow discharge of excess water during periods ofhigh 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 of 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 considerable thickness of weakly-humified peat(e.g. Meerstalblok and Engbertsdijksvenen, TheNetherlands). The relatively high permeability of thistype of peat means that such massifs are particularlyprone to water loss at the cut margins. In suchsituations waH bunds need not extend to the bottom ofthe peat deposit; it may be sllfficient just to insert aplug of 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 ofbadlydamagedmassifs, 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 aconsiderable height differential between the top ofthe wal! bund and the level of the adjoining ground,but very tall bunds are likely to be unstable and,where the height difference is great (>2 m) a seriesof stepped bunds would be desirable (or the surfacefrom which peat is being removed should be gradedup 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 of 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 of 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 of, existing bogvegetation (e.g. Meerstalblok, The Netherlands). Itsefficacy as a starting point for renaturation of a badlydamagedmassif surface is less cIear; it seems likelythat fluctuations of the water table may be inimical tothe establishment of a Sphagnum-based vegetation, indrier regions at leasl.(e) Elevation of the mire water level byincreasing water levels in the surroundingareaA further possible method for elevating the surface ofthe 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 adeeply sub-surface water mound in a peat massif hasresulted [rom a reduction of the basal area of the mire,sorne hydrological control of the surrounding land,particularly that which once formed part of 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 of the drainage of the surrounding peatworkings or cIaimed land will be sufficient to soelevate the water mound within the remnant massif asto rewet its surface adequately. The nature andmagnitude ofany such effects will depend primarily onthe topography and relative heights (hydraulic head), aswell as the amount of recharge to the catotelm andhydraulic conductivity of the peal. However, if it ispossible to increase the water level on the landsurrounding the remnant sufficiently (i.e. by floodingit) this could provide 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 ofadjoining agricultural land.• It may often be difficult to elevate the water tableover the adjoining land sufficiently to re-soak themassif. This largely depends 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 of thesurrounding water table would probably require acomplex series of 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 ofthe massifmightdamp water level fluctuations, though thesignificance of this would partly depend upon theconfiguration ofadjoining inundated areas.Possible application• This approach could possibly be used to help rewetbog massifs in small basins.• It could be used as part of a co-ordinated strategyfor the restoration of a remnant massif andsurrounding peat workings. [This is discussedfurther below.]• This approach could also be used if it was thoughtdesirable that agricultural land once cIaimed fromthe bog should be retumed to a form ofwetIand.Box 5.2 Efficacy of re-soaking approaches to rewettingRe-soaking approaches (i.e. approaches aimed at elevating lhe surface of lhe perched waler mound c10se lo lhe peal surface)have achieved variable success in bog resloralion. depending 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' development of bog vegetation and an acrolelm characlerislic of little-damaged raised bog);lhey are reported as being appropriale for siles which are damaged bul which retain a thick horizon of fresh, weakly-humifiedpeat, which can slore water well and, in appropriale condilions, even swell in response lo lhis, thus taking on some of theproperties of 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 provide an adequale 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 of dryness (as is lhe case wilh some dilch blocking procedures); or lhal lhey do nol provide 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 of minimising the effecls off1uclualing water levels may be by inundalion slralegies. These are nol Iikely lo be provided jusI by a 'groundwaler' mound profilewhich, al besl, is Iikely lo be al lhe surface for only part of 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 of much existing conservation value and torenature adjoining peat workings etc.• There is tittle evidence to suggest that a retum ofthe entire former area of 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 of thepeat surface may be considerably lower than thepredicted hydrological maximum, i.e. the watermound can be sustained at this level with a bogbasal area considerably less than that of the originalm¡re; and (b) the construction of any lagoons thatmay be necessary to elevate the water level acrossthe adjoining land may be a less stable approachthan is the construction of wall or parapet bundsaround massifs. Nonetheless, sorne control ofdrainage in the surrounding land (as in'hydrological buffer zones' [8.3]) may well in sornecircumstances ameliorate sorne difficulties ofrewetting the peatland.• This approach may be useful as part of an overallrestoration strategy in situations where Ioss of waterthrough downward seepage is thought to be aproblem.Patential far vegetatian restaratianElevation of water tables over peat workings around aremnant massif has been used with considerablesuccess at the Bargerveen reserve in The Netherlandsand is discussed more fully below.(f) Inundatian using parapet bundsThe use of parapet bunds for rewetting [Figure 5.4 (i)]represents a development of the bunding approachdiscussed aboye [5.3.2(d)]. Both approaches, in effect,raise the impermeable ba e of the bog and elevate theposition of the perched water mound. The difference isthat with parapet bunds the bunds extend aboye thelevel of the adjoining peat massif, to form a long, lowsurface dam against which water may be impounded,and it is possible to accumulate water on the top of thepeat massif. The extent to which this is possible willdepend upon the topography ofthe massif. If it is domedthen the effect will be to produce a moat of water; ifflatter, it may be possible to inundate larger areas.Limitatians• The limitations of this approach are similar to thatdiscussed under 'wall bunding' [5.3.2(d)]. However,because this approach provides for somesurface inundation, it effectively increases waterstorage in the vicinity of 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 amplitude of water-Ievel flux andprovide an environment more conducive to theestablishment of typical bog species on degradedbog surfaces.• One of the main problems with the use of thisapproach is that on sloping massifs it may not bepossible to rewet more than a small proportion ofthe surface. In strongly domed bogs it may benecessary to have a series of concentric bunds ifmore widespread 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 of the failure ofother, more simple, procedures to produce thedesired goals. For example, parapet bunding hasbeen constructed in part of the Engbertsdijksveen[Plate 5.2], in recognition of the failure of ditchblocking to rewet the mire remnant. In other sites(e.g. Meerstalblok), previous wall bunding has beenextended upwards to form a parapet to permitflooding of parts of the mire surface.


86RE TORATION 01' DAMAGEO PEATLAOSwidely used lo maintain wet conditions within peatmassifs, as in sorne mires old peat workings withinupstanding bJocks of peat provide wet conditions withregenerating bog vegetation. This approach mayprovide a more stable olution to rewetting than doeseJevation of the water level using wall bunds, in that itis Jess dependent upon bunding for ils success, and alsobecause it involv s reducin the height of much of thepeat surface to a position where the lagoons will holdwater. lt also ofien leads to larger fl oded 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 ofien bedesirable to subdivide the main lagoon into a series ofsmaller compartments.Plate 5.2 'Parapet' bund, causing flooding at themargin of an upstanding peat remnant; Engbertsdijksveen(The Netherlands).• This is an expensive restoration procedure, but isone that may be more suited to the renaturation ofbadly-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 ofthe elevated massifs at Thome Waste which arecurrently difficult to keep wet. In view of its likelycost, it is particularly appropriate to apply thisapproach to areas which already have a known andimportant biological interest.• Where the vegetation of the massif is already of'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 of, existing bogvegetation. It has also been used with sorne uccess torewe degraded bog surfaces, though as these initiativesa -e mostly recent, it is difficult to judge their long-termpotential for renaturation.(9) Inundation by reduction of the level of thepeat suñace to form la900n5An alternative restoration option attempts to resolve therewetting problem not by elevating the water level butby decreasing the elevation of the peat surface to forma lagoon [Figure 5.4 (ii)]. It differs from the approachof sculpting the peat surface to the water mound[5.3.2(c)] in that it aims to produce a series of hollowsthat can store water. The inundated areas may beconfigured to act as growth lagoons for direct plantcolonisation 01' as feeder tanks to help soak adjoiningbaulks of 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 detrimental 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 of bog species) thana mire-centred one (regeneration of 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 determined by the hydrodynamics of themassif. Moreover, ongoing wastage of the driersurroundings may mean that this is not sustainablein the very long termoPossíble applicatíonsoThis type of renaturalion has occurred, inadvertently,al many rai ed-bog sites, where hollows andlagoons currently provide some of the mainreservoirs for bog specie and Sphagnum-richvegetation e.g. Thorne Moor , S. Yorks.). [SeeChapter 2].• It is particularly well suited lo renaturation ofbadly-damaged bogs in drier regions as it canreadily provide the flooded conditions appropriatefor the development of semi-floating rafts ofSphagnum.• It is likely to be an effective rewetting strategy forpeat massifs comprised largely of stronglyhumifiedpeal.• It is particularly appropriate for surfaces that havelimited existing biological interest.• If con tructed as part of an agreed commercial peatextraction process it would be considerably 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 canprovide the main repository of typical bog species insorne massifs and that they have potential to developinto examples of Sphagnum-rich vegetation comparableto M18 communities.Further considerationsThe value of excavation of pits to optimise water levelconditions in mires has long been recognised byconservationists; shalIow scrapes 01' deeper excavationshave been dug for various purposes. The evident valueof topographical depressions is seen in a number ofmires that are otherwise rather dry, where peat cuttings,01' other holIows provide the only reservoir of bogspecies. Even where extensive ditch blocking 01'bunding operations are being considered to raise waterlevels, smalI scale cuttings may help to provide atemporary habitat for Sphagna, to act as foei fromwhere the Sphagnum can expand across the surfaceonce an adequate water regime has been reinstated 1Clearly the scale of any peat excavation operations wiIIalso depend on other management being consideredand the desired end-point, and, of course, the conditionofthe existing vegetation (ifany).Removal of a layer of surface peat on sorne drainedsites prior to rewetting may have other potentialbenefits. It may remove dry mineralised surface layersof peat, which may be enriched (Eigner & Schmatzler,1980; Jortay & Schumacker, 1989), though it is farfrom clear if this is an important consideration. It canalso remove short-term seedbanks of potentiallyun~esirable species such as Molinia 'and, of course,physicalIy removes any unwanted speeies as well.This restoration approach, deliberate 01' spontaneous,can be very effective at creating a series of 'boggardens' within damaged massifs. These may support alarge reservoir oftypical bog species, but this approachis more' obviously 'artificial' than are sorne otherrewetting strategies. The perceived suitability of thisapproach thus depends strongly upon the objectivesformulated for restoration. One of its features is thatparts of the massif surface are not rewetted and areparticularly' susceptible to ongoing oxidation andwastage, which may threaten the long-term stability ofthe 'bog garden'. Of course, this constraint applies toalI rewetting approaches where part of the surface isaerobic for much of the year and does not support peatproducingplants.(h) Provision of supplementary waterAn alternative approach to the problems of waterretention is to directly irrigate peat massifs (01' indeedpeat workings) with water. This is generally onlyappropriate for smalI peat remnants because of thelarge volume of water and resources that are required.This approach has also been little tried (examplesinelude Dosenmoor, Germany (Müller, 1980); ShapwickHeath, Somerset; Thorne Waste, S. Yorkshire).Clearly, the original causes of dehydration and currentwater losses also need to be carefully investigated (andremedied as far as possible) in order to assess thefeasibility of providing supplementary water through apumping scheme.Possíble applicatíonsFor most situations, the use of elaborate pumpingschemes should be avoided as they are non-sustainable.However, pumping may be considered in certaincircumstances, for example:• to 'kick-start' the system - i.e. to provide an initialinput of 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 of drought.Clearly, ifthis approach is considered, then to maintainan ombrotrophic vegetation it is important that onlyombrotrophic water should be introduced, as theconsequence of introducing minerotrophic water is topromote the development of 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 of the large volume ofwater and resources that are required.• Unless provision has been made to store largevolumes of meteoric water, in many cases the onlysupplementary water available is likely to beminerotrophic.• Oxygenation and movement of the water maystimulate decomposition of 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 of the approaches to rewetting described here are basedupon resoaking of the peat rather than inundation. Resoakingstrategies may help to elevate the level of permanentsaturation within a massif, but the water table may still showconsiderable f1uctuation and may not provide the consistentlywet peat surface that is required for renaturation. Restorationbased upon surface inundation thus provides a reweltingapproach, which, on the basis of field evidence, can provide avery satisfactory basis for the development of 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, of well-deveJoped Sphagnum vegetation (M 18a) inabandoned, f100ded peat cultings coupled with an absence ofsuch vegetation on adjoining uncut surfaces. Such cutlingsinitially develop loose rafts composed of the more 'aquatic'Sphagnum species, but species such as S. capillifolium, S.magellanicum and S. papillosum can subsequently establish.The value of some surface inundation is primarily (a) that itincreases the water storage at the surface of the bog; (b) thatany decrease 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 provides a good medium foreolonisation by some Sphagnum speeies and (d) it iseondueive to the development of floating rafts of vegetation,whieh can remain wet even with considerable water-Ievelf1uetuatións. This approaeh does, however, have its ownlimitations, in particular that optimal inundation eonditions foreffeetive reeolonisation are not known with eertainty. They aredetermined inter afia by sueh eonsiderations as: (i) optimalwater eonditions for growth of some Sphagnum speeies; (ii)meehanisms of rafting; (iii) problems of wave damage; (iv)problems of 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 wooden trackway (The Sweet Track, seePlate 1.7). As the only water supply available wasminerotrophic, this has unfortunately lead to thedevelopment of fen woodland on the Sphagnum peat.At Thome Waste, water has been pumped from drainsin the area of active peat workings into sorneabandoned cuttings. As this has only been carried outrecently, it is too early to comment on the success ofthis approach, although there is preliminary evidencethat flooding has retarded the previously-vigorousgrowth ofsorne birches.5.4 Rewetting options forextensive peat workings inbog peat5.4.1 IntroductionPeat workings most ofien represent topographicaldepressions with respect to any adjoining peat massifand rewetting may ofien be easier to achieve than on amassif. This is because problems of 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 alsoprovide the opportunity of conforming the peat surfaceto maximise its potential for water storage. Ideally,agreement on final desired conformations would bereached by negotiation between conservationists andthe peat industry.The two main problems of rewetting peat extractioncomplexes are related: (i) providing adequate waterstorage; and (ii) preventing lateral (and possiblyvertical) water loss. The solutions to these problemswill depend upon (a) the topography and disposition ofthe peat fields; (b) the nature of the remaining peatexposed; and (c) the climatic contextoSituation, topography and rewettingApproaches suitable for rewetting abandoned peatworkings depend very much upon their situation andcharacter. Workings can occur as large complexesclearly distinct from remnant massifs, but also asdepressions within massifs. In sorne cases, such aswhere there are small peat cuttings within a dome ofraised peat, or where only a limited amount of peat hasbeen removed, so as to leave a damaged but stillupstanding dome, the problems of maintaining apositive water balance and the options for rewettingmay be much the same as those for the mire massifs, asdiscussed above l . Indeed, in sorne cases former peatextraction has inadvertently produced a conditionsimilar to that suggested as an option for rewetting ofsorne raised-bog remnants [Figure 5.4].In other cases extraction of peat has progressed so faras to remove most traces of the original peat dome andto leave a sometimes complex arrangement of peatfields, ditches and baulks largely unrelated to theformer topography of the mire. In this situation therewetting strategy need take little direct account of theformer disposition of the peatland as the solutionbecomes essentially one of engineering. This mayinclude artificial manipulation of the water table andconstruction of lagoons etc.1 Note, however, that this will ín sorne considerable rneasuredepend upon the character ofthe residual peal.


CHAPTER 5: PRINCIPLES OF REWETII G89Even in sites that have been largely cut-over, theconsiderations advanced for the rewetting ofupstanding 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 of rewetting ofa massif.The approach adopted to rewetting peat workings islikely to be determined primarily by the topography ofthe residual peat, or of the underlying mineralsubstrata. The surface topography of 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 wide-scale rewetting by simpleprocedures. The peat fields may also sometimes bequite steeply sloping, which not only causes problemsof water retention, but may also induce sorne measureofsurface gullying and erosionoWater levelsThe critical question of 'desirable' 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 of what is desirable may becomesubsumed by the practicalities of what is possible(depending on the rewetting strategy), in abandonedpeat fields there may be a much greater opportunity tospecify desired 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 of waterprovision within the peat needs to be compensated bysorne other supplementation mechanism, especiallyretention of surface water (i.e. inundation). In thiscircumstance, the rewetting of peat extractioncomplexes becomes a question of how water can beimpounded (which is largely a function of topography)and to what appropriate depth.Areas of open water can function (i) as growth lagoons(i.e. to provide an aqueous matrix for pioneer bogvegetation); or as (ii) feeder tanks (to rewet adjoiningblocks of solid peat by water seepage). Experience hasshown the importance of the former approach in thedevelopment of floating rafts of vegetation [4.3], andthe use of open water as a growth lagoon is thereforeconsidered as being of primary importance. This is notnecessarily incompatible with their use asfeeder tanks,depending on the water balance.oWhere peat has been removed c10se to the base of themire, the lowered surface may be increasinglysusceptible to inputs of minerotrophic water from thesurrounding landscape. Unless it is thought desirable torecreate fen vegetation (or such water is base-poor),such supplementary water is undesirable and it isnecessary to ensure that a sufficiently impermeablestrip of peat remains around the mire as a buffer zone,to prevent ingress of groundwater [8.3]. For this samereason, deliberate pumping of groundwater into theworkings to help maintain a high water level would besimilarly undesirable [5.3.2(h)]. Removal of peat c10seto the base of the mire is also likely to increase rates ofvertical seepage downwards, in situations where thisprocess can occur (e.g. Schouwenaars, 1993).5.4.2 Block cuttingsIntroductionExtraction of peat using the block-cutting method oftenproduces a regular system of baulks, flats andtrenches l [2.3.1]. The disposition of 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'bunded', in whole or in part, by baulks which confersorne hydraulic integrity upon the cutting. Blockcuttings are also often quite small and this, with itsassociated high edge:area ratio, may provide bothprotection from wind and wave action in inundatedsites and facilitate colonisation by plants and animals.Many re-flooded block cuttings have beenspontaneously colonised by Sphagnum-based bogvegetation (sometimes referable to M 18) and in sornesites sustain a rich biological resource. The c10sejuxtaposition of wet cuttings with contrasting habitats(e.g. heathland on separating baulks), and the interfacebetween them, may contribute to the high biodiversityand natural history interest of such sites. However, itnot axiomatic that block-cutting sites are richrepositories of bog species, nor that they are alwaysreadily rewetted.It is sometimes suggested that block cuttings are moreamenable to recolonisation than, say, milling fieldsbecause of plants and animals that have survived upon(or have recolonised) the intervening baulks of peat (orwithin the trenches). This is very likely to be correctwith comparatively small-scale peat operations, but it isnot a universal feature of block-cutting procedures. Insorne block-cutting complexes, the environment andvegetation of the baulks has been so modified (e.g. bydamage and dehydration) 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 osof has been of such short duration a to 'sterilise' thesurface of the baulks as effectively as any millingoperations.Ditch-blocking is likely to be a prerequisite for therewetting of block-cut sites, and in some situati ns itmay also be necessary to reduce rates of vertical waterloss into the subsoil by completely filling the drainageditches. The presence and functioning of tile or moledrains across the peat fields should also be a sessed,and drains blocked as necessary. However, the effectivenessof ditch-blocking alone for rewetting willlargely depend on the topography of the site. [See also5.4.3]Effects of 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 (Meade,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 of 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 of theperched water mound in the massif as a whole, andrewetting of the cuttings will be dependent uponrewetting strategies for the massif (see aboye). Cuttingssituated within weakly humified peat may beparticularly influenced by the behaviour of the watertable in a surrounding peat mas if and in circumstanceswhere the perched water is low they may beparticularly susceptible to dehydration, despite anygreater storage properties of such peal. However, manyabandoned commercial cuttings are within quitestrongly-humified peal.Some block-cutting sites possess a very uneventopography, with various states of revegetation [seeFigure 5.5]. Where cuttings have been made 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 of strongly-humified peat within a cuttingcomplex. In this situation it may be difficult to devise arewetting strategy that provides optimal water levelconditions for a large number of cuttings, at leastwithout a large amount of earthworks. Here, it may benecessary to consider an integrated approach usingditch blocking and parapet bunding (possibly in additionto and extending existing baulks) together withsome removal ofpeat to produce a more level field.The problem of baulksAlthough the network of 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 of wet,revegetated cuttings separated by strips of heath or,Floating raftFigure 5.5 Revegetation of re-wetled block-cut peatland. In this configuration of cutting surfáce, the shallow poolsperiodically dry out and support only vegetation with purple moor-grass and cotton grass. The deeper pools showsimilar water level flux but have deve10ped a floating raft of Sphagnum which accommodates this change. Theuneven topography permits good revegetation of some individual cuttings, but is less well-suited to re-wetting of 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, development of scrub, or even vigorousEriophorum vaginatum, on the baulks may eventuallyshade l11uch of 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 of Eriophorum vaginatum onthe f100r of the cuttings shades growth of Sphagna inthe ditches. Baulks are ddminated by Molinia caerulea.Plate 5.4 Block peat cuttings f100ded to the level of thetop of 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 of the baulks [Plate5.4], so that they can be more effective as feeder tanks.However, there is little current evidence 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 wide range of bog species will establish. Thisis not least because water tables tend to drop during thesummer months, though the magnitude of this willpartly depend upon the climate. One suggested solutionmay be to promote irrigation of the baulks by a networkof grips extending from the cuttings, but we havenot seen this employed in practice. This would alsodepend on maintaining water levels so that the gripsdid not act as drains in periods of low water supply.An additional consideration with regard to raising thewater level in the cuttings is the height di fferencebetween the base of the cutting and the surface of theadjoining baulk, when this is great (> 50 cm). Theresultant deep water in the cuttings may not be optilllalfor growth of even aquatic Sphagnul11 species r5.4.I;5.4.4].AItemative approaches to the problem of too Illanybaulks are to reduce their height, total area orfrequency (especially where the cuttings comprise alarge number of thin, parallel baulks), as carried out atPeatlands Park (Arrnagh) [Plate 5.5]. Such operationsall require the removal of 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, carefulconsideration should be given to the most desirableratio of baulk to cuttings in terms of achievingrewetting objectives and to the height of the baulks.Increases in the ratio of 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 of the baulk, and the water balance l11ayshow greater losses than gains (Beets, 1992).If it is impractical to reduce the height or area ofbaulks, and where high water tables in the adjoiningcuttings do not adequately rewet their surface, considerationmay be given to inundation of the baulks byelevated water levels across part or all of the cuttingcomplex. The feasibility of this will depend largely on


92RE TORATION OF DAMAGED PEATLADSPlate 5.5 Recolonisation of former block peat cuttings;Peatlands Park (Armagh). Lowering baulk heights andraising water levels resulted in extensive colonisationby Sphagnum cuspidafum. The area is normallyf100ded in winter.the topographical situation of 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 concluded that, in ertain circumstances,block-cut urfaces may provide a good template forrevegetation, but that this i not an invariable property.Also, even where ucces fui revegetation has occurredwithin block-cutting, he developing pockets of m 'revegetation may not readily spread from the cuttings tocoalesce across baulks. Approaches to the restorationof block-cutting complexes may therefore need to bephased to consider (i) the water rnanagement andrevegetation f individual cuttings (i.e. the nucleationof bog regrowth and ii) the wider issue of watermanagement and revegetation of the entire peat-cuttingcomplex. It shou Id be noted that once ubstantial partsof 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 of surfacemilling [2.3]. In this, a succession of thin layers of peatare shaved from the surface of cambered beds duringeach harvesting season. The fields are usually large,and are typically drained by a serie of deep 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 depth of 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 ofthe most difficult peat surfaces to restore, apparently onaccount of their extensive area and featureless, andsometimes sloping, topography. Where they haveexposed strongly-humified peat they may beinconducive to adequate water storage and retention.Water retention is particularly problematic on slopingfields, which normally suffer rapid runoff and,sometimes, erosiono Nonetheless, there is little reasonto suppose that milled fields are necessarily moredifficult to rewet than would be block cuttings made ona similar scale. This is because milling fields canthemselves be sculpted to provide a topographyanalogous to block cuttings, or can be bunded to retainwater. Both of these activities require investment ofresources into surface preparation for restoration.There are currently few examples of long-termrestoration projects on milled surfaces, but it is likelythat restoration will only be possible if successfulattempts are made to retain precipitation, to preventerosion and to accelerate vegetation colonisation bymanipulating the surface relief (Pfadenhauer, 1989).(a) Ditch blockingBlocking of drainage ditches is essential to preventwater loss from milled peat fields. As for blockcuttings,in sorne situations it may also be necessary toreduce rates of vertical water loss into the subsoil bycompletely filling the drain'age ditches and to take intoaccount the effects of any mole or tile drains across (hepeat fields.Limítatíons• The effectiveness of ditch blocking in rewettingmilled surfaces will depend largely upon thetopography of the site. Where the milled fields aresloping, ditch blocking is unlikely to retain water ator near the surface of 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 of the year.• Even on flat sites, ditch b[ocking alone is unlikelyto produce a water regime conducive to the reestablishmentof a full complement of bog species.This is because there is ofien considerable flux ofthe water tableo In dry periods, the water tabletypically sinks sorne considerable 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 provide much surfaceinundation. [t thus offers little potential forincreasing storage of surplus precipitation water,nor provides conditions for establishment of bogspecies other than those which are most tolerant ofperiodic dryness.Possíble applicatíans• Ditch-blocking is likely to be a prerequisite for therewetting of all milled surfaces.• [n most cases ditch-blocking is unlikely to besufficient for regeneration of a bog vegetation onmilled peat fields. An exception to this is wheremilled fields are surrounded 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 of bog vegetation, except perhaps verylocally in shallow depressions. Usual observeddevelopments 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 theredevelopment ofSphagnum-rich bog vegetation.(b) Impaundment of water in lagoon5One approach to rewetting milled peat surfaces is tocreate a series of lagoons which impound meteoricwater [Plate 5.7]. These not only prevent, or reduce,lateral water run-off but also serve to store water. Thishelps to prevent the occurrence of low sub-surfacewater levels during prolonged dry periods and alsoprovides an appropriate growing medium for pioneer,aquatic species ofSphagnum. Such lagoons provide thesame sort of habitat as do the cuttings of block-cutpeatlands. They can be created either by leaving baulksof peat in si/u during extraction (unless these havebecome too dry to be effective) or by building walls ofpeat 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 of water, subject to considerable wind andwave action e/c.On sloping surfaces problems of rapid runoffexacerbate lack of 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 of water inconstructed lagoons; Gardrum Moss (Falkirk). [Photo: C. Turner]cascade [Figure 5.6] (see Nick, 1993). These reduceerosion on slopes to a minimum, hold precipitationwater on to the area and regulate discharge of surpluswater, ideally to retain sufficient water to be favourablefor Sphagnul17 growth. Lagoon cascades 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 ofthe site.The dimensions and disposition of the lagoons willdepend on the fall in height across the surface of thearea to be rewetted, but areas of 1-10 ha have beensuggested. The size may also depend on the dispositionof the proposed lagoons in relation to the surroundingland, as in sOllle situations, the creation of such Jagoonsmay come under the provisions of the Reservoirs Act,if permanently tlooded [Appendix 2]. The naturaldisposition and accumulation of water across thesurface should be studied and the information utilisedin any design 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 of lagoons is more expensive thanditch blocking.•••Construction requires an adequate availability of arelatively impermeable construction material(ideally 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 bottomof a bog may be suitable. In this case it isimportant to ensure that a sufficient thickness ofpeat remains to supply material for wall buildingas well as to limit any downward seepage, withoutpenetrating to underlymg fen peat 01' mineral soilin those sites where this would disadvantage thedesired renaturation.Lagoon walls may require some maintenance forlong-term stability. In practice this Illay be ofconsequence only for the outer peripheral walls a ,ideally, renaturation should be well advanced bythe time that internal walls deteriorate. Nonetheless,it is always possible that heavy stonnscould cause premature dalllage to internal walls.On flat surfaces at least, the lagoons are likely toprovide a rather uniform water depth 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 cascade re-wetting of 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 of agreater variety of species, but these may weJlinelude birches and Molinia on the drier places.• Areas of 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 provideconsiderable opportunity to influence the characterof the recolonist vegetationwater levels.Potential for vegetation restorationby manipulation ofThis 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 of extensive carpets ofSphagnum clIspidatum, ofien with species such asMolinia caerulea and Juncus effusus [Appendix 6]. Insome cases, these latter seem to encourage growth ofSphagnum species [9.2]. Peat stratigraphical studieshave shown that in numerous rai ed bogs thedevelopment ofa bog-building vegetation (with speciessuch as Sphagnum magellanicum, S. papillosum) hasarisen from a et phase of Sphagnum cuspidatum.Thus, whilst most examples of 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 developmental pathway(as has occurred in some older, block-cut sites). Giventhe isolation of 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 reestablishmentof some Sphagnum species, or othelwiseinnuence the development of the vegetation.(e) Impoundment of water in sculpted hollowsAnother approach to the rewetting of extensive milledftelds would be to scrape large, shallow hollows in thepeat, to produce a scalloped surface which stores waterin the depressions. [n principie, this is similar to theconstruction of lagoons, but relies upon the excavationof peat rather ti an the construction of 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 deep enoughto store much water (to c. 50 cm depth) thisapproach would require substantial excavation andmovement of peat.• In ites which have retained only a thin layer ofombrotrophic peat, substantial excavation may beimpractical, or is likely to ex pose underlying fenpeat or mineral soiJ. The effect this would haveupon revegetation will depend upon the exactcharacter of these materials.• The sloping sides of the scallops provide asubstantial hydrological gradient from flooded tofairly dry. Whilst this may well increase the rangeof specie that can quickly establish on the peatsurface, it is also likely to provide considerableopportunity for the ma ive establishment of'undesirable' species such as Molinia and birch inthe drier areas.ConelusionIn some sites, milling ha produced natural hollows andbasins within the peat, which may provide a focus forwater storage but these may be small. In others, anentire milling lield may form a very large basinbounded by walls of 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 ofthe surface, as a series of depressions and hummocks(Eggelsmann, 1987, 1988b - see also Nick, 1993;J-Iealhwaite & Gottlich, 1993), may help o increasestorage [Plate 5.8]; and subdivision of the field bybaulks may help to reduce damage to developingvegetation by wind turbulence and wave action (thoughthe evidence that this is necessarily desirable isinconsistent). A further benefit of small-scale topographicalmanipula ion is that the heterogeneity mayassist recolonisation and establishment of variousspecies. Unfortunately, sorne of these latter mayinclude birches and Molinia on the drier spots and insome instances such approaches to rewetting take onmore the appearance of the cambered beds used byforesters to plant conifers in waterlogged soils than thatof an exercise in mire restoration!The optimal strategy for rewetting and restoring milledsurfaces will partly depend upon particular sitecircumstances. [n general the approach adopted inNorth Germany (e.g. Leegmoor) has much tocommend it, with the construction of paddy-field likelagoons (1-10 ha may be an appr priate size), thoughpossibly with a slightly greater degree of inundation(see below). Thi appears to be the only effectivestrategy where the milling fields are sloping - design ofthe restoration of the mire will be strongly dependentPossible applications• [n principIe this approach could be used in many ofthe same situations as lagoon . The choice betweenthe two methods is Iikely to rest mainly upon depthof residual peat, engineering convenience, slope ofthe site and on whether it is desired to regeneratebog across most of the milling field surface or justwithin excavated hollows.• We know of no site where this approach has beenused on more than a very limited scale (viz. byexcavation of surface scrapes) (e.g. SomersetLevels).Plate 5.8 An attempt to increase microtopographicalvariation by small-scale sculpting of the peat surface asa series of depressions 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 devise configurationsthat can benefit, if neces ary from 'gradient feeding' orsome other form of water supplementation. Where thesurface is flat and confined, few earthworks may benecessary, but even here sorne degree of compartmentalisationmay be de irable. If there is next-to-notopographical variation within the lagoon thu created,some minor topographical manipulation of the peatsurface could be countenanced but it is not evident thatthis offers much material advantage. As an alternativeto formal lagoons, excavation of shallow depressionsscraped 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 of peat approximating to thepredicted position of the 'groundwater' mound (Bragg,1989). However, there appear to be inherent practicalproblems with this approach, and it cannot berecommended until there is further evidence that it mayprove to be an appropriate strategy [5.3.2(c)].5.4.4 Depth of inundationAs within peat extraction complexes there isconsiderable opportunity to determine and manipulatethe maximum height of the water table by engineering,it is necessary to identify an appropriate water level.Various considerations 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 provide an adequate basis forrevegetation of uch sites, except where somesupplementary water (such as is provided by gradientfeeding) is available to help maintain water level inthe cut-over peats. By contrast, sorne degree of urfaceinundation increa es water storage, provides a suitablegrowth medium for pioneer species of Sphagnum andpermits the development of tloating mats of 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 of 'undesirable'plant species, such a Molinia caerulea [Plate 5.9] andbirch [see Plates 10.2 and 10.3].The depth of water impounded within lagoons ele. maynot always be easily regulated - the depth will reflectwater availability, topographical or constructionalfeasibility rather than ecological desirability. However,choice of an 'ideal' water depth is influenced byseveral considerations:• In a block-cut peatland, deep filling of the (bunded)cuttings may be desired, to help rewet the adjoininguncut peal. The feasibility and suitability of thiswill depend upon the height difference between thetop of the uncut peat and the bottom of Ihe cutting.• In any cut-over peatland, the depth of winter(a) Not flooded(b) Floodedwater level fluxFigure 5.7 Restoration of peat excavations by inundation. In (a) the maximum water level only reache to aboutthe level of the cutting surface. Thus in dry periods the declining water level leaves the cutting sUrface relativelydry. Fluctuations in water level of this sort are mainly conducive to the growth of a small number of species such ascotton grass and purple IT'0or grass. In (b) the cutting surface is relatively lower, so that for most of 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 deep water may preclude grawth of 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 determined by water lossduring the ummer - i.e. it needs to provideufficient storage to prevent water levels going toofar below the urface for long period during thesummer. Depths of winter inundation of 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 wateldepths that are continuously supra-surface, but nottoo deep (50 cm summer depth seems to be anoptimal maximum value, unless there i someadditional aid to tlotation).• Sorne of the 'bes' examples oC revegetation seenwas as floating rafts on deep (c. I m depth) water(e.g. Meerstalblok and Haaksbergeveen, TheNetherland ; Wieninger Filz, . Germany), but themechal1lsm of raft formation in such circumstancesis not always well estabJished.The approach of hallow-water flooding used in somenorth-German peatlands (e.g. Leegmoor - Plate 5.10)has been very successful in permitting the colonisationof extensive bare peat surfaces b Sphagnum speciesand may provide an appropriate way forward. It stillremain subject to considerable water level fluctuation,though it may be expected that this effect will diminishas a thicker mat ofSphagnum accumulates.In situations where it is readily possible to have deeperwater 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 ofombrotrophic vegetation in shallow tlooded conditions;and then (b) to impose deeper inundation upon this.There is some evide ce that the established vegetationmay lin to fonn a tloating raft when flooded.Attention should also be given to inoculation ofrewetted areas with plant material (includingSphagnllm pecies), the use of artificial aids to raftingand the po sibility of 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 of Molinia caerulea, killed byflooding; Fochteloerveen (The Netherlands).Plate 5.10 Extensive colonisation of former bare peatsurfaces by Sphagnum cuspidatum and Moliniacaerulea, within shallowly-flooded lagoon; Lichtenmoor(N. Germany).5.5.1 IntroductionIn Britain commercial extraction of fen peat (bothwithin and without former raised-bog sites) is practisednow only in the Somerset Levels. However, extractionof fen peat once occurred much more widely, andformer excavation of bog peat has led to the exposureof underlying fen deposits in numerous mire sites.The topography of fen peat workings shows internalva iation (retlecting excavation techniques) andvariation with respect to the urrounding landscape,reflecting events both in th mire and the widerlandscape. Some deposit form massifs slightlyelevated aboye the surrounding land cape, much aswith bog peat massif. This configuration may arisebecause of drainage and shrinkage of the surroundingland. In other sites, the exposed peat surface may bemore-or-less level with the urrounding land, or peatremovaJ may have produced depressions below thegeneral ground leve!. When abandoned, thesesometimes readily tlood with telluric water.In broad terms the rewetting of fen peat surfaces issubject to many of the same constraints as those of bogpeat surfaces of comparable topography, and similarrewetting strategie may be appropriate. llowever, anadditional consideration is possible inputs of telluric


CHAPTER 5: PRINCIPLES OF REWETTING99water. The fact that fen peat has formed indicates thatat one time this horizon of the developing mire hadbeen irrigated by telluric water. This may have originatedfrom various sources (springs, river inundationetc.) which today are not always readily identifiable(and may no longer exist), on account of natural orman-made changes to the hydrology of the mire'scatchment (e.g. embankment of rivers, construction ofdrains etc.). In consequence, possible telluric presentdaywater sources (and waterquality) available torewet fen peat workings may bear little relationship tothose under which the fen peat was laid down.Because there are various possible sources of telluricwater input into cut-over fen peat (and sometimes thepossibility of no obvious source at all) it iscorrespondingly difficult to make generalisations aboutwater management options applicable to many fen peatworkings.The restoration significance ofany telluric water inputsto the rewetting of cut-over fen surfaces depends uponthe desired objective of restoration. On the one hand,such inputs may sometimes be instrumental in helpingto rewet the site; on the other, they promote theredevelopment of fen vegetation. If this is not seen tobe a desirable development (i.e. if the restorationobjective is bog), it may sometimes be possible to buildperipheral bunds or dams both to impound meteoricwater and to exclude telluric inputs. In this situation,revegetation wiII still re-commence upon minerotrophicpeat, but an absence of further telluric waterinputs should help to shorten the fen phase. Thesuccess ofthis approach will depend considerably uponthe topography of the deposit, the character of telluricinputs (if any), and the quality of precipitationrecharge. Where the fen peat surface has only just beenexposed, and where the peat deposit stands proud ofthe surrounding land, precipitation can be the majorsource of water input, and rewetting considerations arethen much the same as with bog peal. However, wherepits have been dug into the fen peat, so that the peatsurface is below that of the surrounding landscape, it iscorrespondingly more difficuIt to excIude telluricinputs. And whatever the topographical situation it maybe difficult to exclude telluric inputs when these arederived from upwelling groundwater springs.The outcome of rewetting strategies on fen peatdepends both upon the character of 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-development ofa fen vegetation which may haveonly a long-term potential to re-develop 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-developmentof bog vegetation (e.g. van Wirdum, 1995).5.5.2 Rewetting off/at fen peatsurfacesThe following broad strategies can be adopted, eitherindividually or in combination:(a) Ditch blockingThe potential value of ditch-bJocking depends upon thetopography of the site. Where the peat surface iselevated with respect to sorne or aH of the surroundingwater table, ditch blocking will help retain water on thesite and will usually be a prerequisite of restorationinitiatives. It may principally retain meteoric waterinputs, though retention of minerotrophic water mayalso occur in sorne situations.If adopted as the sole approach to rewetting, ditchblocking is liable to be subject to the same limitationsidentified aboye for bog peal. The main differences are(a) that it may be easier to maintain a permanently highwater table, depending on the relationship of the peatworkings with the surrounding landscape and watertable and (b) that, even if periodically low water tablesoccur, the vegetation that re-develops (sorne form offen or fen meadow (if grazed or mown) or fen carr (ifunmanaged)) is more likely have higher conservationvalue than would the vegetation developed on bog peatin a similar situation. (This is because low-productivityvegetation on moist, base-rich peat is itself uncommonand ofien species rich.)In sorne topographical situations, ditch-blocking maybe needed, not to retain water on the site, but to preventthe ingress of minerotrophic water, should this beregarded as undesirable.(b) Irrigation by telluric water vía ditches or bysurface floodingMinerotrophic water from sources internal or externalto the peat deposit can be distributed around the cutoversurface by ditches, either with or without moregeneral surface flooding at times of water surplus.External water sources may incIude adjoining riversand drains, but where the peat deposit is aboye thelevel of the adjoining land, external water may have tobe pumped into the mire. The cffects of theseprocedures depends upon the topography of the site;slight depressions may accumulate water whilstmounds may remain largely dry. Fen sites dependingon river-flooding or ditch irrigation can showconsiderable seasonal water flux. Much ofthe peat maybe waterlogged during the winter months, but duringthe summer there will be a tendency 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 of fen vegetation upon the peatsurface, but its character depends primarily upon thedegree and permanence of soil saturation, the chemicalcomposition of the peat and the irrigating water andtype of vegetation management (if any). The mostlikely development is of a form of fen vegetationtypical of 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-development ofbog, not least because of the incidence of low summerwater tables. It is most appropriate for situations wheremaintenance, or recreation of fen vegetation is arestoration objective, or as a specific, short-termmeasure.(e) Impoundment of water in lagoons orsculpted hollowsA fen peat surface can be engineered to producelagoons or sculpted hollows that retain water (asdescribed 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 described in section 5.4, with theadditional constraint that it may be necessary to takesteps to exclude minerotrophic water when appropriate.However, proximity to minerotrophic water sourcescan also mean that a more stable water table is morereadily maintained. Where lagoons are designed toproduce surfaces inundated with minerotrophic water,likely developrnents are as in 5.5.3.Note that sorne types of fen peat may be a less suitable(Iess cohesive and more permeable) constructionalmaterial than sorne bog peats.5.5.3 Rewetting offen 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 depressions. Sorne former (now revegetated)peat excavations in fen peat have been large (> I6 ha).Such peat cuttings are very widespread in fens. Sornecurrent excavations in the Somerset Levels formcomparable basins.The water budget of cuttings in fen peat may be morecomplex than that of comparable examples in bog peatand water management options again will depend 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 provide an important supply ofminerotrophic water. In sorne cases it may be necessaryto install devices that can regulate the water level to apredetermined maximum.Where such hollows are rewetted with rninerotrophicwater, fen vegetation can redevelop rapidly, itscharacter being determined largely by water depth andtluctuation, base-richness, nutrient-richness andmanagement regime (if any). Spontaneous rewetting ofpeat-cut basins within fen peat has occurred in a largenumber of mire sites in the UK (sorne of thern formerbog sites). When they are retlooded, hydroseralrecolonisation can occur, ofien producing tloating matsof fen vegetation. These rafis, when irrigated by waterof suitable quality (nutrient poor but relatively baserich)can provide a suitable basis for spontaneoussuccession to bog, as well as having rnuch intrinsicvalue (sorne prime examples of fen vegetation inBritain occur in recolonised peat cuttings).In sorne instances it rnay be possible to excludeminerotrophic 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 desired to recreate a nutrientpoorwetland.5.6 Integrated restoration ofremnant massifs andcommercial peat fields5.6.1 IntroductionIn sorne commercial peat workings, peat extraetion hasoceurred across almost all of the surface, leaving anexpanse of peat fields with no remnant massifs..Inother sites the peat fields are interspersed withupstanding remnant massifs, of various dimensions.Remnant massifs may varyeonsiderably in theireharaeteristics. Small remnants are ofien dry and mayhave rather Iittle biological interest. Other exarnples,particularly larger ones, may retain a wealth of typiealbog organisms, either as a surviving part of the original


CHAPTER 5: PIUNCIPLES OF REWETTING101bog surface (e.g. Wedholme Flow, Cumbria), or asspecies that have recolonised older peat workings uponthe massif (e.g. Thorne Waste, S. Yorkshire). Theretention of the species complement of such sites isimportant both in its own right and because it providesa proximate source of recolonist species for theoperational peat workings [Chapter 2]. The peatstratigraphy and archive of the massifs may a\so beconsidered 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 identified aboye [5.3.2(b)] withrespeet to the possible rewetting of individualmassifs by 'natural wastage', of eourse, apply alsoin eomposite peatland sites, viz. that there is littlereason to suppose that the surfaee of damagedmassifs will neeessarily rewet satisfaetorily just inresponse to wastage. It is possible that the massifwould eompletely, if gradually, waste away to theposition of the water level maintained in the peatfields.• The feasibility of this approaeh for rewetting of themassif depends upon the topography of the site andthe possibility of impounding water over the peatfields to a depth suffieient to saturate a signifieantproportion ofthe massif (see below).Possible applicationsThis approaeh to integrated restoration may sometimesbe determined by laek of 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 of the water level withín thesurroundíng peat fields (usually ínundation)elevates the positíon of 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 of the margins (and probably loss ofvegetatíon 'quality' at the períphery) either beeausethe total area of the 'good quality' vegetation islarge or beeause the amount of peripheral damageís predieted to be small;• where the climatie regime is suitable (i.e. eool andeonsistently wet) for the direet establishment ofSphagnum on damaged or wasting bog surfaces;• Where the massif is already badly-damaged so thatthere is likely to be little loss of biologieal interestupon wastage, whatever the outeome.(b) Reduction of the height of 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 of themassifto a level at which it can be adequately rewettedintegral with water management of the adjoining peatfields.Limitations• Peat removal would remove the peat archive. [Thismay also eventually oeeur by proeesses of naturalwastage].• Peat removal would remove any biologieal valueassoeiated with the remnant. The extent to whichthis represents a eonstraint depends upon (a) thenature of the biologieal resource of the remnantmassif; and (b) the likely long-term stability of thisresource in the absenee of other water managementmeasures.• Peat removal may destroy the reservoir of speeiesfor reeolonisation of adjoining peat fields. [It ispossible that this could to sorne extent be mitigatedby transfer of the massif surfaee directly to the peatfields, provided that the latter had been rewettedinto an appropriate condition to reeeive it.]Possible applicationsAn exeeption to the aboye situations may be providedwhen the vegetation etc. is demonstrably not stable andwhere 'interest' is likely to be lost anyway. In thissituation a 'reseue' operation (i.e. transfer of sorne orall of the remnant surface to adjoining peat fields in asuitable receptor condition) eould be eontemplated.Peat removal from remnant massifs eould beeonsidered when:• the massif has Iimited value as a reservoir for bogspecies or archaeology;• the massif is unlikely to become effectivelyrewetted by other proeedures, beeause of problemsof'diffieult' topography or lack ofresourees;• when the height difference between the surfaee ofthe 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 of wastage etc.Ideally the potential for the rewetting of massifs shouldbe considered with respeet to the cessation of peatextraetion: there may be little to be gained if prematureeurtailment of peat extraetion results in a bogtopography that is particular\y diffieult to rewet.5.6.4 Elevation of the water table'around a remnant massif(a) Elevation of the water table in basinsAn altemative approaeh to an integrated restoration ofremnant 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 tofill with water, confined by the basin topography[Figure 5.8(a)]. However, this approach is inappropriatefor many commercial peat workings, which areofien on rather flat, unconfined sites. In this situationthe alternative approach, if possible, is to elevate the¡--I (a) Peal workings confined in basinFloodedpeal field(b) Peal workings unconfined(i) Inundation of peal fields(ii) Reconslruclion of water moundFlal peal fieldSlepped peat fielḏ- ­ , -water mound around the residual massif by appropriatebunding. Note that in either case consideration must begiven to the depth to which the peat fields will flood,both in terms of their potential for revegetation andconsiderations of safety.(b) Reconstruction of the water mound arounda remnant massif on flat sitesOn flat surfaces, elevation of the water table on thepeat fields relative to the massif surface is moredifficult than in a basin and will inevitably entail theconstruction of bunds to impound water. In situationswhere the height difference between the surfaces of themassif and the peat fields is small, the construction ofsimple lagoons across the peal fields may be sufficientto maintain high water levels in the massif. However,when the difference is greater, this approach may beinadequate to maintain the surface of 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 of this approach isillustrated in Figure 5.8 (b,ii). It differs from simpleinundation of the peat fields in that lagoons ofincreasing eJevation are used to build the water moundin a series of steps. On level surfaces this may beachieved by a series of bunds of varying height; onpeat surfaces which rise up to the massif, there will beless need for tall bunds and associated deep lagoons.Limitations• This approach involves considerable bunding andmay be expensive, though the magnitude of theoperation will depend upon the height differencebetween the surface of the massif and the peatfields.• Where the surface of the peat fields is more-or-Iesslevel, bunds near the massif will be tall and theassociated lagoons will be deep. Considerationmust be given both to the stability of lhe bunds andto the prospects for revegetation of deep lagoons.• Where the surface of the peat fields rises up to themassif, shorter bunds will be needed, but the slopemay require bunds at frequent intervals.Figure 5.8fieldsRe-soaked peal Mineral subslratumSaturaled peal Open walerUnsoaked peal BundRewetling of remnant massifs and peatPossible application• This approach could be used for the integratedrestoralion of 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 ofcreating 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 considerable successin the restoration of 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 tlooded to help maintainthe water balance of the area. [This stems partly [rom adesire to prevent the po sible development of oxidisingconditions beneath the peat mass as a result of loweringgroundwater table .]5.7 Maintenance of remnantmassifs during peatextractionoperations5.7.1 IntroductionIn sltes where peat extraction is taking place adja entto peat massi[s that sustain important populatio lS ofbog species, it may be desirable to protect these fromexcessive water loss, occurring in consequence of theextraction operations. Factors associated with peatextraction which may contribute to water loss include'(a) direct drainage of the adjoining massif (either as adeliberate policy to drain t e massif, or as a consequenceof ditches dug acro s the ma si[ to evacuatewater from the operational peat workings); (b)reduction of basal area of the massif; and (c) increasein hydraulic gradient between the urfaces of themassif and the peat fields The requirement to minimiseany water drawdown and loss in the massif induced byongoing peat removal will depend largely on theimportan e of 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 of 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 of 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 ofien 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 of vegetation (including Sphagnum euspidatum, S reeurvum, Enophorum angustifo/ium.Eriea tetra/Ix) developed in reflooded, bunded block-peat cuttings; .Meerstalblok (The Netherlands).


CHAPTER 5:. PRINCIPLES OF REWETTING(055.7.2 BundingPeat massifs can be protected from water loss by theconstruction of an impermeable bund around all or partof their periphery. Bunds can be constructed from lowpermeability peat or from an artificial, inert lowpermeabilitymaterial. Various arrangements of bundscan be used, as discussed in previous sections. Therequired character of the bunds wiJl depend upon theheight difference between the massif surface and thepeat field surface and also upon the character of thepeat. When the deeper peat is of sufficiently lowpermeability, relatively shallow bunds may be used tocontain water in the upper, more transmissive peatsrather than needing complete wa/l bunds down theentire depth ofthe massifedge [Figure 5.9].Limitations• Bunding is comparatively expensive.• Where the height difference between the surface ofthe massif and the cut-over peat is large, bunds willneed to be particular well constructed andmaintained. Altematively a series of stepped bundsmay be required [as in Figure 5.8].PossibJe applications• Bunding can be used in a large number of situationsto protect a remnant peat massif from excessivewater loss [5.3]..• In many situations it may be desirable to configurethe peat excavation so that there is a series of stepsup to the base ofthe 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 of bunding is apolicy of non-intervention, other than the blocking ofany ditches that drain the remnant massif. Thisapproach has the advantage of 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 of damage associatedwith water loss [5.3.2(b)].Limitations• In many situations non-intervention may lead tosustained and increasing damage of the bog habitatsupported on the remnant massif.• The extent to which damage will occur will dependupon the character of the massif biota and theextent to which water loss is induced by adjacentpeat extraction. This latter will be determined interalia by the hydraulic gradient, the transmissivity of(a)(c)(b)(d)weakly-humified peat § strongly-humified peatIbundFigure 5.9 Protection of massifs alongside peat extraction by bunding. When the exposed massif is eomposed ofpermeable peat, a wall bund the height of the edge of the massif may be needed to retain water (a), although itsheight can be redueed to some extent by removing less peat immediately alongside the massif (b). When thepermeable peat is underlain by a low permeability peat, the wall bund need only proteet the edge of the permeablepeat (e). In some cases, it may be possible to maintain the surfaee-wet eonditions over mueh of the.massif just bythe use of surfaee bunds to prevent exeessive water loss through the aerotelm (d).


TABLE 6.1 Summary of the Iikely outcomes of different options of raised bog restoration, from a contrasting range ofstarting conditions.The starting conditions (represented in the table by headings in bold type and with a single number identifier (e.g. 1)) have beenchosen as representative starting conditions that have been observed in a number of damaged sites. It should be recognisedthat variants of these may occur and that some sites will present a range of starting conditions - i.e. the options are not mutuallyexclusive.For each type of starting condition, various management options have been presented (designated by a double numberidentifier (e.g. 1.1 )). These are not comprehensive but represent the main options that seem likely to be applicable. Variouspermutations of them can be made, for example to cover various different starting conditions present on one site. Because ofthis, 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 made to retain water on the mire, i.e. that as a base-line minimum outfallsand ditches will be adequately blocked. Thus the 'no bunding' option assumes that ditch blocking, but nothing else, will takeplace.Assessment of the probable effects on water tables, vegetation, revegetation and implications for conservation andmanagement are based on practical experiences of restoration together with current knowledge of 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 of the different options for working practices and subsequent possibilities for restoration need to be carefullyconsidered, as do the potential impacts of peat extraction on the uncut or abandoned areas and the viability of such areas in theabsence of positive management. In some cases, restoration of such areas may represent a 'value-added' 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 Restoration 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 implicationsManagementconsiderationsPeat 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 of heathland, Molinia interest retained, at least in centre.¡ wet; subsidence may grassland or birch scrub near margins Edges may become heathy and¡ occur to reconform unless surface reconformation occurs susceptible to birch encroachment.shape of the mire rapidly. They may provide 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,¡ of 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 of heathland, Molinia ¡ to a greater degree than 1.1. Edges of ¡¡ remnant. ¡ 1.1; subsidence may ¡ effect upon acrote/m ¡ grassland or birch scrub near margins ¡ remnant (outside bunds) may become ¡¡ ¡ occur to reconform ¡ conditions because ¡ unless surface reconformation occurs ¡ heathy and susceptible to birch ¡i i the shape of the mire i of 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 of many components of Much original conservation interestall of 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 dependson objectives for non-bog habitats.Peat may be subject to ongoingoxidative decomposition.Mo/inia grassland, bracken etc. ¡•••••••••••; ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••~•••••••••••••••••••••••••••••••••••••••••• ,4 •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••2.2 ¡ Surface bunding ¡ Drying across most or ¡ Surface bunding ¡ Ultimate loss of many components of ¡ Most original conservation interest lost. ¡ Vegetation management depends¡ of acrotelm / ¡ all of 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 ¡ of the water table. ¡ Eriophorum vaginatum). Replacement ¡ Birch encroachment a problem across ¡ oxidative decomposition............I.. ..l..~~~~~~ .1 1.;r~;;I~;;~.~~~;.~~.;.~~!~: ..~~::~:~ .J..~.~~~~~.. ~~~~ ..1. .2.3 ¡ Wall bunding ¡ Retention of high ¡ Marginal bunds ¡ Retention of 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 of mire. Bunds needim",'oo !m"re i~j~~?gi~~:y 1 !~:~~:i~,~~N,:~~~:~~:~,""'O" ~g~~~:~~~~~:~~~~~¡ ¡ ¡ domed. ¡ ¡ domed.


3 Peat remnant with dehydrated and damaged surface (little or no Sphagnum cover remaining)3.1 No bunding Drying across most orall of site, especiallynear margins. Possiblylocalised wet areas(e.g. in blocked drains)Bog species reduced or lost3.4Parapet bundingaround remnantmarginsRetention of high watertable over some ormuch of site, with localinundation.Success ofrewetting maydepend on originaldegree ofdehydration /damage to peat andon dimensions ofremnant.(depending on climate and severity ofdamage). Prospects for unaidedrecovery depend on climate andnature and severity of damage. Inmany situations redevelopment ofM18-type vegetation is unlikely, butmay be possible to retain a number of¡ species in wetter regions. Elsewhere,¡ replacement by wet heath, dry heath,¡ Molinia grassland, bracken, birch etc.Possible redevelopment of M18-typebog vegetation on rewetted surfaceand, particularly, in shallow-f1oodedareas, even in drier climates.Replacement habitats may persist onhigher areas..Original character of mire surface lostand unlikely to redevelop readily. Insome regions, a number of 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 of redevelopmentof 'good quality' (M 18) vegetation overat least part of remnant. May requireinoculation of vegetation. Birchencroachment a potential problem indrier places.Vegetation management dependson condition of surface andobjectives for a 'damaged bog' or'non-bog' habitat. Peat likely to besubject to ongoing oxidativedecomposition.•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• •..•••••••••••••••••••••....••••.••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 of high water ¡ Success of ¡ Possible redevelopment of 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 of and some potential for increase bog aboye general level of mire. Bunds¡ margins ¡ much of site. ¡ depend on original ¡ remnant, but unlikely in any areas with ¡ conservation interest over all or part of ¡ need to be well made if heightdegree of protracted dry periods. Replacement remnant. May require inoculation of difference is great and may requiredehydration / habitats may persist. vegetation. Birch encroachment a long-term maintenance. Series ofdamage to peat and potential problem. concentric bunds may be requiredon dimensions ofif strongly domed. Removal ofremnantexisting vegetation (e.g. birch)Iikely to be a problem.Remnant left as isolated remnantaboye generallevel of mire. Bundsneed to be well made if heightdifference is great and may requirelong-term maintenance. Series ofconcentric bunds may be requiredif strongly domed. Removal ofexisting vegetation (e.g. birch)Iikely to be a problem.contd-


.:::.!::::: drybracken,Table 6.1 b Restoration 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 implicationsManagementconsiderations4 Cut-oyer peat massif with original suñace lost, exposure of deeper, more humified peats etc. Suñace relatiyely f1at.4.1 No bunding ¡ Surface shows strong Fluctuations in ¡ Liltle recolonisation by bog species Lil ~velopment of original Massif left as dry remnant aboye¡ fluctuations in wetness. 'wetness' created by ¡ except, perhaps, a few drought ce :ion interest of bogo generallevel of mire. Vegetationl May be very wet during lack of sufficient ¡ tolerant taxa (e.g. Eriophorum Replacement habitat may or may not management depends 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 decomposition"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 of bogo ! generallevel of mire. Vegetation! margins ! (4.3) surface may still ¡ wallloss as residual ¡ tolerant taxa (e.g. Eriophorum ¡ Replacement habitat may or may not ! management depends on¡ ¡ show strong fluctualions ¡ peat is Iikely to be of ¡ 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 decomposition"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 of ¡ exposed edge of ¡ bog vegetation on rewetted surface ¡ conservation ¡nterest over aU or part of ¡ aboye generallevel of cut-over! massif. Still strong j massif nol required if ¡ of massif. May require inoculation j massif. ¡ mire. Periodic maintenance of! fluctuations in water level ! in situ dark peat has j ofvegetation.! j parapet may be needed, but as¡ but surface water storage ¡ low permeability. ¡ ¡ ¡ most of impermeability is ai.~=~~~~~~~LLJJ;;1~e~:~;f~;:';~~:~~~4.4 ¡ Peat removal ¡ Creates conditions of 4.3 j Bunding around ¡ Potential for recreation of typical ¡ Potential for regeneration of bog j Massif (or parts of it) no longer! j by excavation of peat ! exposed edge of ¡ bog vegetation on rewetted surface j conservation interest over all or part of ¡ substantially elevated aboye¡ i from all or part of massif. 1 E:~~~~o~:~~f~r~~sif I~; :~:~:ii~n~y require ¡noculation . massif. . generallevel of 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 of bog Mosaic of wet and dry habitats and Not uniform bogo Usuallyj tend to remain wet; permeability, wet ! vegetation within peat cuttings. their interface gives range of considerable birch development onj intervening baulks show conditions can be j Baulks develop a drier vegetation conservation interest, including ridges (= cambered beds of! strong fluctuations in maintained even in ! (wet heath, dry heath, Molinia, elements of bogo foresters). Potential for bog¡ water level and tend to hollows close to 1::::::::::. birch etc.}. expansion out of cultings ontoduring summer. margins of massif. baulks uncertain. Massif may beleft as isolated remnant aboyegenerallevel of cut-over mire. Drypeat Iíkely to be subject to ongoing. . . . ¡ . oxidative decompositíon......................................................................................................................................................................................................................................................................................................................................................................................


"'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 of bog vegelalion ¡ Potenlial for regeneralion of bog ¡ Massif left as isolaled remnant¡ j upon lhe baulks over all ¡ exposed edge of ¡ wilhin peal cultings. Also bog j conservalion inleresl over all or part of ¡ above general level of cut-over¡ ¡ or some of lhe massif as j massif nol required if ¡ regeneralion on f100ded or wet ¡ massif. ¡ mire. Periodic mainlenance of: : well as in lhe peal ¡ in situ dark peat has ¡ conditions of baulks. May require ¡ ¡ parapet may be needed, bul as¡ ¡ cuttings. ¡ low permeabilily. ¡ inoculalion of vegetalion. ¡ ¡ mosl of impermeabilily is a producl¡ ¡ ¡ ¡ j ¡ of 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 of bog Mosaic of wel and dry habilals and¡ hollows wel; inlervening ¡ unlikely lo be vegelation wilhin peal cuttings. lheir inlerface gives range ofNol uniform bogo Usuallyconsiderable birch developmenl¡ baulks show slrong ¡ mainlained in hollows Baulks develop a drier vegelalion conservalion inleresl, including ¡ on ridges (= cambered beds of¡ f1uclualions in waler j close to margins of (wet healh, dry heath, Molinia, elements of bogo : foreslers). Polenlial for bog¡ level and lend lo dry '.::::::::::. massif. bracken, birch etc.). ¡ expansion oul of cuttings onlo!::::::.'::. during summer. ¡ baulks uncertain. Massif may be¡ left as isolaled remnanl abovej general level of 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 of bog ¡ Mosaic of wel and dry habilals and ¡ Nol uniform bogo Birch¡ around massif j extended upwards inlo ¡ nol be needed lo ¡ vegelalion wilhin peal cullings. ¡ lheir inlerface gives range of ¡ encroachmenl on baulks likely lo¡ margins ¡ a parapel (6.3) surface ¡ prevenl waler loss ¡ Baulks develop a drier vegelalion ¡ conservalion inleresl, including ¡ be a problem. Polenlial for bog¡ ¡ of baulks may slill show j lhrough lower peals of ¡ (wet healh, dry healh, Molinia, ¡ elemenls of bogo ¡ expansion oul of 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 of bog vegelalion ¡ Polenlial for regeneralion of bog j Massif left as isolaled remnanl¡ ! flooding upon lhe ! exposed edge of : within peat cullings. Also bog ¡ conservation interesl over all or part of ! above generallevel of cut-over¡ ¡ baulks over all or some ¡ massif nol required ¡ regeneralion on f100ded or wet j massif. ¡ mire. Periodic mainlenance of¡ j of lhe massif as well as ¡ where in situ dark ¡ conditions of baulks. May require ¡ ¡ parapel may be needed, bul as¡ ¡ in the peal cuttings. ¡ peal has low ¡ inoculalion of vegelalion. ¡ ¡ most of impermeabilily is a¡ ¡ ¡ permeabilily. ¡ j ¡ producl of 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 implicationsconsiderations7 Milled surface of ombrotrophic peat: surface sloping7.1 No bunding i Surface does not retaini w.¡".Surface run-off + lack ! Development of vegetation with few.! of storage means that ! if any bog species - heath. Molinia,! surface is dry except ! bracken. birch scrub.¡ during wet parts of ¡year. ¡Little redevelopment of originalconservation interest of bogoReplacement habitat may or may nothave conservation value. Birchencroachment a problem across entiresite.Vegetation management dependson conservational objectives fornon-bog habitats. Likely to beongoing oxidative decompositionof 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-off. Still wide 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 of enriched¡ ¡ level but surface ¡ require inoculation of vegetation. \ \ water. Birch encroachment of drier¡ ¡ water storage (and. in ¡ ¡ ¡ areas may need to be checked.¡ ¡ some situations. ¡ ¡ ¡ Likely to be ongoing oxidative¡ ¡ 'cascade feeding') ¡ j ¡ decomposition of areas that are¡ ¡ reduces effects of ¡ j j not reweUed. Marginal bunds mayj ¡ summer droughts. ¡ j ¡ require periodic maintenance.8 Milled surface of ombrotrophic peat: surface ± flat8.1 No bunding j Surface shows strong ¡ Fluctuations in ¡ Little redevelopment of bog Little redevelopment of original¡ f1uctuations in wetness. j 'wetness' created by j vegetation excepto perhaps. for a conservation interest of bogoj May be very wet during j lack of 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 dependson conservation objective for nonboghabitats. Likely to be ongoingoxidative decomposition ofresidual peat...........; L l..~~~.~~.~~.~~~..~~~.~~~~~~.~.~~~.I~.?~.~~~~: , ; .8.2 ¡ Bunded lagoons ¡ Water retained in j Creates surface j Development of bog vegetation ! Potential for redevelopment of 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-off. Still wide 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 of ¡ areas. ! to prevent ingress of enriched: j ¡ level but surface ! vegetation.! ¡ water. Birch encroachment withinj j ! water storage ¡ j ¡ lagoons unless well inundated.j j j reduces effects of j j j Likely to be ongoing oxidative! ¡ ! summer droughts. ¡ ¡ : decomposition of areas that are! j j not reweUed. Marginal bunds may¡ ¡ j ¡ ¡ ¡ require periodic maintenance.


9 Milled surface of ombrotrophic peal: surface scalloped or forming depressions9.1 No bunding Water retained in Creates surface Development of bog vegetation Potential for redevelopment of 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-off. Still strong heath/Molinia in less wet upper some other species a problem on drier of enriched water. Birchf1uctuations in water areas. May require inocl,Jlation of areas. May be extensive, depending on encroachment within lagoonslevel but surface vegetation. surface configuration. unless well inundated. Likely to bewater storageongoing oxidative decompositionreduces effects ofof areas that are not rewetted.summer droughts.10 Shallow peat deposits upon permeable substrata with lowered groundwater tables10.1 No bunding Effect of lowered If residual peat is too Development of heath, grassland Little redevelopment of original bog Vegetation management dependsgroundwater tables upon thin rewetting of and scrub. No redevelopment of 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 dependent upon impossible. No form ofconservation value. Birch encroachment oxidative decomposition ofdepth of residual peal. remedial action isa problem across entire site.residual peal.50 cm of strongly- known. [Even withhumified ('black') bog sufficient peat depth,peat seems theany ditches c10se to ormínimum needed 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 of landscape hydrology to re-elevate water levelsi i generally.contd-(JI


.j:::::.: quitestatusTable 6.1c Restoration 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 implicationsManagementconsiderations11 Flat surface of fen peat11.1 No action : Wetness of surface will Fluctuations in Development of wet grassland Developing vegetation can include : Without management only a ranki depend upon site 'wetness' created by vegetation, or some form of rough fen species-rich pastures or hay : species-poor herbaceous or wet! topography and the lack of sufficient water or fen carr, depending upon water meadows when managed, and these i woodland vegetation will develop.¡ intrinsic properties of storage in residual peat levels and management may have considerable conservation ¡ Likely to be ongoing oxidativei the local hydrological . coupled with absence value (e.g. Molinia-Cirsium fen ! decomposition of residual peal.i environmenl. May be of 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 develop.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":·;·of 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 development of wetter fen :: : source. Can be used to : are likely to be similar : then provide a suitable basis for ¡ communities, at least locally :¡ ¡ retain meteoric water; ¡ to 11.1 , unless underl- ¡ various types of fen and possibly ¡ ¡: : to exclude 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 : :¡ : of both water supplies j When used to retaín : minerotrophic water, in which case : :: : i telluric water, high : wider development of 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 depends upon ¡ In dry episodes there ¡ Ditch-irrigated sites can maintain fen ¡ Ditch irrigated systems can develop ¡ Some form of management isor periodic topographyand ¡ will be a tendency for ¡ vegetation (but not usually wet-fen ¡ fen vegetation of considerable ¡ Iikely to be required (summer¡ f100ding ¡ availability of 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 of telluric water, ¡ Flooding will be ¡ flooding usually support dry, coarse ¡ Eupatorium fen, Molinia--Cirsium ¡ vegetation and to prevent¡ ¡ parts of fen can be kept ¡ episodic and may lead ¡ fen vegetation or fen grassland. ¡ dissectum fen meadow). Sites just ¡ successional development of¡ ¡ permanently wet to periodic dryness ¡ Quality of water is also important, ¡ irrigated by episodic f100ding may scrub and woodland. May be¡ ¡ ¡ across much of the site ¡ especially in f100ding episodes: input ¡ support low-quality vegetation (e.g. ¡ some ongoing oxidative¡ ¡ ¡ ¡ of high nutrient loadings typically lead ¡ Phragmites-Urtica or Phragmites- ¡ decomposition of peat,¡ ¡ ¡ to impoverished vegetation. Flooding ¡ Eupatorium fen if unmanaged; wet depending 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 provide a ¡ winter f100ding episodes. ¡¡ ¡ ¡ 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 dependent on ! Sphagnum invasion into ! inundated. Dry areas may be! i water storage reduces ! known. i depth, base-richness and nutrient ! terrestrialising lagoons ! subject to ongoing oxidative¡ ¡ effects of summer ¡ ¡ richness of water (see 12, below). ¡ ¡ decomposition of peat.i !droughts.!! ! !: hollows : surface f1ooding. ¡ help impound telluric : characteristic of low-fertility : some management and (perhaps) : ingress of enriched water. Scrub12 Cuttings within fen peat¡ Wetness of cuttings will¡ depend their topography¡ and the intrinsic¡ properties of the local12.1 No intervention(except blockoutfalls)Intrinsically morestable water table than11.1 because cuttingsFen community that develops willdepend upon water sources andlevels.May generate conservation interest.Difficult to speculate on the largenumber of possible communities thatWithout management, vegetationwill develop into a form of fenwoodland. Herbaceous fenhelp to retain watercould develop 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 development of species- ¡ Fen communities may include: Carex ¡ Without management, vegetation¡ nutrient-poor ¡ water level ¡ manipulated by inflow ¡ rich fen vegetation. ¡ rostrata-Potentilla, Phragmites- ¡ will develop into a form of 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 of fen woodland. ¡ conservation value..............•.......= ..:: :::~ ~- -.~~ ~ : -.: ~ ~=;..;.--.~..; ;.-;-.-;;-;;;-;-.; - - ,~.""=~••••F- ~~~~.-..--.--.--.- ...- ~~........ ..~_ _._._•••••••._••_ !~.--!_~!!.! •••••••••••__12.3 ! Soaking with Water near or just above ! Water level : Potential for development of a coarse ! Fen communities may include: ! Without management, vegetation! nutrient-rich water level ! manipulated by inflow ! fen vegetation. ! Phragmites- Eupatorium fen, ¡ will develop into a form of 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" beof great interest. Such situations.¡ . !! ! ! may be best managed for birds.............._ : .: :. :. .:. .contd-..l


p"m",Table 6.1c (continued) [Restoration options for fen peat surfaces (in peat cuttings)]-ocStarting conditionsManagementProbable effectson water tablesOther hydrologicalconsiderationsProbable effects onvegetationand revegetationConservational assessmentConservation Imanagement implications12.4 Shallow f100dingwith nutrientpoor water(precipitation +groundwater)Water level >0 SOcm ! Water level manipulated Formation of deep-water emergent Potential communities include 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 ofien greater onmassifs (which are typically water-shedding areas) thanthey are in depressions (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 of 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 of the whole complex is notfeasible, in which case the remnants may be lefi tosupport sorne replacement habitat, which may includesorne bog species, though they are ultimately likely tobe wasting assets.Because of their situation, peat fields may ultimatelyprovide a more satisfactory basis for bog restoration(especially 'whole-mire' regeneration) than sorne uncutmassifs. This is because they may provide a lesstopographically-varied surface; because, when close tothe mineral ground, they may be intrinsically morestable, both in terms of water regime and peat wastage;and because their effective rewetting [Table 6.1 b] maybe technically less difficult than rewetting of massifs.Nonetheless, in many cases sorne technical interventionwill be required to produce structures that impoundwater against lateral flow and increase storage,although this will depend upon the topography anddisposition of the abandoned surfaces. The flat orgently sloping surfaces of modem commercial peatfields may be quite well suited to rewetting overextensive areas.Nonetheless, rewetting of peat fields cannot bedivorced from that of peat massifs. This is partlybecause cut-over surfaces are themselves sometimeslocated on a massif well-elevated aboye thesurrounding land, in which case considerationspertinent to the rewetting of massifs become equallyapplicable to the peat fields (this is a lesserconsideration when peat has been removed nearer tothe base of the deposit). It is also because an obviouseffect of peat removal is to accentuate the heightdifference between the peat field surface and thesurface of adjoining peat massifs. In this situation itmay still be possible to maintain an independently highwater table in the massif, but is Iikely to be moreexpensive and difficult to do so (depending upon thecharacteristics of the massit). An additional considerationis that of linking the regeneration of the peatfield surfaces to the maintenance of 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, of course, produce an inclined surface which,depending on its slope, may be much more difficult torewet than a flat one.] Where the massifs are badlydamaged, of 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 considerableconservation value there may be little choice but toengineer independent water management strategies forthe massifs and the peat workings.6.3 Restoration options forminerotrophic peat surfacesConsiderably less attention has been directed towardsthe deliberate restoration of raised-bog sites where peatextraction has exposed underlying fen peat. Indeed, thefull occurrence of this circumstance is not even wellknown. This is because, whilst in sorne sites it isobvious that peat cutting of ombrotrophic peat hasuncovered fen peat (e.g. Brackagh Bog, Armagh), inothers bog peat has been removed so comprehensivelythat there is little evidence for the former existence ofbog (e.g. Woodwalton Fen, Cambridgeshire).However, increasing evidence suggests that a numberof sites that are now regarded


120Rt:STORATlON OF DAMAGED PEATLANDSworkings ir1 fen peat is primarily a function of waterdepth (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 often most feasible when it isassociated with sorne ecoJ1omic retum. Grazing orsummer mowing is possible in sorne circumstances andcan produce conservationaJly-desirable communities,as with some of the fen meadows of the SomersetLevels. Such objectives, when coupled with summerdryconditions, are usually incompatible with theredevelopment of bog, although in certain círcumstanees,mowing may enhance the initial developmenttowards bogoThe formulation of desirable restoration options for fenpeat sites is often 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 decision iswhether to focus on the recreation of bog or fen,though these options are not mutually exclusive,especially as some forms of fen can give rise to bogvegetation. If the fen option is selected, the choice thenbecomes the type of fen desired. This can sometimesbe determined by choice of water sources and levels.For examp\e, fen cuttings can be f\ooded 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 excludedand preeipitation inputs are adequate to retlood thecuttings, then a vegetation of more botanica\ interestmay develop, together with a greater likelihood of thesuccessional development of bogo The choice ofobjectives is thus likely to be determined bytopography, availability (and quality) of minerotrophiewater sourees and implications for on-goingmanagement and maintenance as weIl as byeonservational desirability.In general, regeneration of bog within fens occurs mostreadily as a hydroseral development from fenvegetation in peat workings tlooded with nutrient-poor(but not necessarily base-poor) water\ . In appropriatecircumstances Sphagnum can grow rapidly and thicknessesof c. 1 m depth of 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 development 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 of the 'i>ucce'i>'i>ion 'i\~e them'i>e~'1e'i>often of great interest to conservationists, thisspontaneous process of 'ombrotrophication' may notbe universally welcomed.It is obvious that if cut-over surfaces in fen peat are toredevelop fen vegetation (and perhaps ultimately bog)they require water input, but because of the likely (aJ1dusually unknown) complexities of the hydrology ofindividual minerotrophic systems and, with tllecontribution and quality of 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 toidentify broadly the likely effects of the irrigatiJ1gwater in terms of its quality (nutrient poor versUSnutrient rich) on restoration [Table 6.1 e]. In this table,the assumption has been made that tlle residual fen peatis intrinsicany not very fertik ihis assumption may beinapplicable to some sites. Restoration 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 depend strot1..g,lyon the surrounding topography ofthe peat workings. Ingeneral, rewetting can be achieved most readily wherethe workings forro a closed depression (within bogpeat, fen peat or mineral soil) or where they have beendeliberately bunded. In this situation it may be possibleto inundate the depressions. 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) waterloggingof adjoining land. Bunding may be used tohelp hold water on the site, both to prevent flooding ofadjoining land and to maintain a high water level in thefen peats.6.4 Restoration options tormineral substrataIn some sites peat has been extracted to expose largeareas of the underlying mineral substrata. Specificationof restoration options for this may be subject 1.0 thesame problems as for fen peat with respect to variationin the character of water sources. It is further eomplicatedby the great variability of physico-chemicalcharacteristics of the substrata. For example, the pHrange of 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 of the substrataconsiderably determine restoration options and have


CHAPTER 6: RESTORATION OPTIONS AND PEAT-\VORKING PRACTICES 121obvious ramifications with respect to desirable watersources etc. Growth of Sphagna and other bog speciesmay be just as good (if not better) on acid graveIs as itis on ombrotrophic peats. Clays are perhaps the mostwidespread underlying substratum type and are afien(but not always) relatively base rich. Where theyrepresent sorne form of estuarine deposit they may alsobe brackish.Rather little is known about the recolonisation ofrewetted mineral substrata in the peatland context, butthe outcomes of 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 of peatworkingpractices andstarting conditions forrestoration6.5.1 IntroductionIt is not possible to set out universal guidelines ondesirable working practices to optimise startingconditions for restoration following extraction, as thesewill partly depend upon site-specific features:• conservation objectives;• character ofthe existing biological resource;• character and configuration of the remaining peat deposit(especially topography and peat properties);• environmental context ofthe sites (especially climate, butalso characteristics and use ofthe adjoining landscape).Here, sorne of the underlying principies are identifiedand 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 of the character of the site, possiblyby independent environmental scientists (Akkermann,1983), with particular regard to features importantin determining desirable and feasible restoration oplions,based on factors identified in Chapler 7; 1• a resloration slratcgy should be devised 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 of operations (in parts or all of the site), peatfields should be configured into an (agreed) conditionthat will optimise restoration (i.e. to maximise use of insi/u machinery, operators and infrastructure) (Chaplers 5& 8].6.5.3 Working practices fo,.restoration during peatextraction operationsOnce restoration options have been defined 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 tofacilitate the realisation of the objectives. ThefolIowing principIes should be taken into consideration,and implemented where possible:• Importan! refugja (whkJ¡ may include little-damagedareas of bog, as well as revegeü¡tcd cuttings or damagedareas with an important biological resource) should beidentified and sleps taken to preserve or enhance theirexisting conservation interesl. Such areas should not besubject to further peat extraction, unless as part of anagreed rolling programme of peat extraction andrestoration.• If feasible and necessary, a buffer zone should bedesignated around the core part of any refugium areas,which should also remain uncul. (This requirement willpartly depend 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 thatdehydration 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 desired would be too smal!. In this case, residualI These rnay inelude sorne assessrnent of: existing biologicalresource; characteristics of the residual peat deposit (peattopography, type, depth, permeability, storage coeflicient anuposition of water table); downward water loss inlo mineral grounu;character ofminerotrophic 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 depths of peal. [This would help to reducethe hydraulic gradient from the remnant across thecuttings, and may help to reduce drying-out. It will alsomake the design of a 'cascade paddy-field' system oflagoons more feasible. Note, however, lhal this fealurewill depend upon the existing topography and agreedrestoration strategy for the site.]• If the aim is to recreate ombrolrophic bog directly, it isreeommended that as a general rule a minimumof 50 cmof ombrotrophic peat be left in situ. Sufficient peatshould also be left to allow for constructs to impoundwater (bunds or a scalloped surface). [This suggestedresidual depth may vary aeeording to the nature of thepeat and the underlying substratum and its topographyand restoration objeetives. In sites subject to downwardsseepage of water into the mineral substratum, a greaterdepth (> 1m) may be needed to seal to base ofthe bog, inothers, a depth of 50 cm (or less) may be adequate[4.4.5]. The differenee between a minimum depth of 50em and an average depth of 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 depth of peat to be left in situ is an averag.e of 50em.]• Where possible, 'nursery' pools for the 'farming' ofSphagnum should be initiated, to provide an inoculum forabandoned areas [9.2].• Orainage operalions should be assessed, and wherepossible redesigned to minimise impacts on remnants andareas undergoing restoration. In low rainfall arcas it maybe desirable to pump drainage water into abandoned peatworkings etc., although this will partly depend on thequality ofthe pumped water [Chapter 5].6.5.4 Operations followingabandonmentOnce an area has been brought out of production,further operations should start as soon as practicable tofacilitate rewetting and revegetation. This should beplanned to ensure that rewetting initiatives do notpreclude 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 of the machinery available on sile forrestoration work. More specific background and detailsare given elsewhere in this volume [in particularChapters 5, 8, 9 & 10], but the main factors to beconsidered are outlined below.Water managementAH ditches and outfa\ls should be blocked wherepossible to increase retention of 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 provide undesirable mineralenrichment.Topographical manipulationAttention should be given to the creation of optimumconditions for rewetting and revegetation, including thebuilding of constructs, such as bunds. Where possible,use should be made of the existing network ofembankments etc., raising levels where necessary,although the permeability of the baulks should first bedetermined to assess their efficacy. [The movement ofpeat and alteration of the configuration of abandonedpeat cuttings should be carried out as part of an agreedrestoration plan, usually in consultation with thestatutory conservation and archaeological bodies.]Milled surfacesIt may be necessary to subdivide large peat fields tocreate lagoons to facilitate rewetting and renaturation.Block-cut surfacesDepending on the configuration remaining, it may bedesirable to flatten SOme of the baulks to achieve amore level area for rewetting, while utilising sornebaulks to retain water. It should be possible to usesome ofthe material from the 'redundant' baulks to fillthe ditches. .Control of vegetation invasionVegetation management should start as soon asproduction ceases in order to reduce the establishmentof 'undesirable' species, especially if it is not possibleto raise water levels within a short time [Chapter 101.Where 'abandoned' fields lie within the zone ofongoing 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 of rewetted peatfields is likely to be slow, partly on account of theimpoverished nature of the ombrotrophic environmentand the intrinsically low relative growth rates of 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 developmentto a more diverse bog surface is likely to take longer,possibly several decades [6.6]. There is seope forexploring possible means of artificial acceleration ofcolonisation by other bog species [Chapter 9]. As thecut-over areas regenerate into bog they may beexpected to become increasingly self-sustaining.However, some degree of maintenance may be neededin the early stages of rewetting and renaturation, suchas removal of scrub from dry sites within the peatfields (though the extent of this problem will dependpartly on the success of the rewetting procedures). Thecondition of the peat bunds, especia11y the outer ones,will also require periodic inspection and, if needed,sorne rnaintenance. The expected intrinsically-slowrenaturation of the peat fields is likely to mean thatsorne (intennittent) maintenance rnay be required formuch longer than an after-care period of 5 years. Therestoration scherne should be designed to minimise ongoingmanagernent requirements 1 but also to make itpracticable for thern to take place, ifneeded.6.6 Prospects for restorationAn assessment of the prospects of restoration oflowland bogs damaged by peat extraction must besubject to the usual caveats of the precise objectives ofrestoration and the specific conditions of individualsites. Assessment of the desirability and the perceivedsuccess of restoration options also needs to take intoaccount the condition of the sites prior to current peatextraction: sorne, but not all, sites were considerablydarnaged before current peat extraction operations (as aconsequence of drainage, repeated burning, partialagricultural conversion or an earlier phase of peatextraction). In such cases successful restoration rnayserve to enhance the conservation value ofthe site.6.6.1 Remnant peat massifsMany of the 'best' remaining raised bogs in Britainhave been subject to some degree of marginal damageand reduction in area, either through peat extraction orconversion for agricuhure. The fact that they sti11provide a 'good quality' bog habitat points to thecapacity of the systerns to accomrnodate, naturally,sorne degree of marginal damage. The 'cost' of thiscapacity is usua11y some dryíng around the margins ofthe sites and the degree to which this is regarded as1 For example, by ensuring that the floors of lagoons can be keptinundated, to minimise opportunities for establishment ofundesirable speeies; a strongly undulating, or sloping, surface maycreate periodically dry arcas that are susceptible to birchencroaehment elc.acceptable will largely depend upon the proportion ofmarginal damage relative to th~ area of Ettle-damagedbog and upon the consequential effects of the damage.In large sites, with just a small amount of marginalwater draw-down, some loss ofarea may be acceptabIe(although long-term effects may be unknown). Greaterproblems arise where only a small peat remnant is leftundamaged or where, perhaps because of a large heightdifference between the peat fields (etc.) and theremnant surface, marginal water drawdown affectsmost of the bogo Here the damage is likely to result in aloss or reduction of typical bog species over rnuch ora11 of the massif, unless constructive measures aretaken to prevent this. These may inelude theconstruction of bunds around sorne or a11 of theperiphery of 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 'undesirable' colonists such as birch. In thissituatíon attempts to enhance the quality of thevegetation and habitat by further elevation of the waterlevel (where possible) may also meet with sornesuccess, depending upon specific circumstances(though such procedures may not integrate we11 withattempts at restoration of adjoining cut-over surfaces).However, where a massif surface is badly darnaged (sothat it has lost many or mos! of 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 of largemassifs or sites located in particularly cool and wetregions. Elsewhere it rnay be more practical to pennitthe massif to develop into a replacement habitat ofsome more general wildlife interest.6.6.2 Cut-over ombrotrophic surfacesIt is evident from exarnination ofold peat cuttings that,where they have been kept (ofien fortuitously) in asuitably wet eondition, recolonisation by typical bogspecies has occurred, to the extent that in sorneinstances the appearance and composition of thevegetation is little different to that found on some littledamagedbogs, including sorne development of ahummock-hollow patterning. Such examples aretypically sorne 50-150 years old. Although sorne suchexamples are quite \arge (severa\ hectares) they are2 This will partly depend upon the reason why the massif isdamaged and dry.


124RESTORAnON OF DAMAGED PEATLANDSusually on a much smaller scale than currentcommercial operations; moreover, the conditions oftheir restoration may have been rather different to thatof sorne present operations (e.g. close juxtaposition tosources of recolonist species), though in manyinstances critical information is lacking.Restoration initiatives on large commercial cut-oversites are still in their infancy; moreover sorne of themhave been in sites where problems of watermanagement have been exacerbated by severalunusually dry summers and by vertical loss of waterdown into a permeable mineral substratum. Nonetheless,it is evident (a) that a wide range of bog plantspecies can invade such surfaces (where there is aproximate inoculum source); and (b) that it is possibleto rewet the peat fields to the extent that (c) carpets ofaquatic Sphagna can rapidly colonise extensive areas.This latter event permits considerable optimism forregeneration prospects as it is evident (from studies onthe natural development of bogs and of recolonisedpeat workings) that a wet Sphagnum cuspidatum phasehas provided a basis for spontaneous successionaldevelopment of a more diverse vegetation composed ofmore 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,provided that three conditions are satisfied:(i) that the site is accessible to potential recolonistspecies (if it is not, then re-introduction of specieswilI need to be considered) [Chapter 9];(ii) that the chemical composition of precipitationinputs will support the growth of 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 redevelop acharacteristic bog vegetation and that peat accumulationwilI recommence in time. Indeed, the long-termstability of bog development on flat peat-cuttingsurfaces may well be greater than that on upstandingbog remnants.6.6.3 Cut-over minerotrophic surfacesProspects for restoration of minerotrophic surfaces wilIdepend criticalIy upon the topography of the site, thewater level that can be maintained and the quality ofthe water used to achieve this. Fen vegetation ofconservation value has spontaneously redeveloped onextensive cut-over fen peat surfaces, includingexamples that are flat and not flooded (e.g.Woodwalton Fen, Cambridgeshire (Poore, 1956» andexamples in large, flooded cuttings (e.g. Catfield &Irstead Fens, Norfolk (uiller & Wheeler, 1986». Inboth cases revegetation has occurred over large areas(tens of hectares), but the nature of the vegetation thathas redeveloped in each is rather different. Sorneexamples of revegetation within flooded peat workingshas produced sorne of the prime areas of lowland fenwithin the UK. Such hydroseral situations are alsosusceptible to Sphagnum establishment and in sornelocations considerable thicknesses of Sphagnum peathave accumulated (up to 1m depth in c. 100-150years). By contrast, Sphagnum re-establishment onsol id fen surfaces is generally more limited, probablyon account of periodic dryness and irrigation withbase-rich water.For the most part, the particular conditions that wereoperative at the start of the spontaneous revegetation ofcut-over fen peats are, not known. This makesgeneralisation from historical observations to presentdayworkings difficult, other than to recognise theimportance of wet, shallowly-inundated, conditions tothe prospects of re-establishment of specific types offen and the development of 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 limitationsof availability of suitable recolonist species; (ii)deposition of atmospheric contaminants; and (iii) thestability oftelIuric water supply to the fen peat.6.7 Holistic approaches toraised-bog restorationIn sorne situations the restoration of damaged peatlandscan be approached piecemeal. This approach is likelyto be most satisfactory when it is possible to provideindependent hydrological control of particular landparcels. For example, in the fen peat basins ofindividual holdings in the Somerset Levels it may ofienbe possible to rewet and renature each peat workingindependently of the others. Similarly, sorne sealeddepressions within ombrotrophic peat may be rewettedindependently of their surroundings; indeed, as notedaboye [6.2] such an approach may be the only practicalpossibility in sorne sites where cut-over surfaces havebeen lefi at widely differing levels. Such an approachmay be very effective in maintaining populations ofbog species within the landscape (i.e. production of aseries of 'bog gardens') but it is less suited to the coordinatedregeneration ofa single mire [5.6].These observations notwithstanding, habitat continuityis ofien particularly important in the restoration ofmires because of their dependence upon a suitablewater source (and sink). Whilst lack of such continuitymay not prevent effective rewetting it may materialIy


CIIAPTER 6: RESTORATION OPTIONS AND I'EAT-WORKING I'RACTICES 125increase the complexity (and cost) of watermanagement. This problem is sometimes most evidentin attempts to restore fen ecosystems, where sorneseparate peat cuttings may have become isolated fromappropriate sources of minerotrophic water (inputs ofriver 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 of several individual rewettingschemes. In addition, rewetting of bogs in low rainfallregions may only be possible by sorne redistribution ofwater across the entire site (e.g. by a form of 'gradientfeeding' [5.4]). Unless continued pumping iscountenanced, this approach requires inputs from partsof the surrounding mire and hence an integrated watermanagement plan.An integrated approach to site restoration may a)soprovide a rational basis for decisions 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 considered. 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 of a raised bog need notdemand the rewettingof adjoining land, even in thosecases where it once formed part of the original peatlandarea. However, in sorne instances localised rewettingmay be useful, for example, to enhance the coherenceof the mire (e.g. at Wreaks and White Mosses(Duddon, Cumbria) where two massifs of peat are nowseparated by a narrow strip of agricultural land) 01' aspart of a co-ordinated strategy for the restoration of aremnantmassif and surrounding peat workings 01'drained land [5.6].In sorne cases, effective rewetting of a bog may onlybe possible by sorne manipulation of 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' anunderlying aquifer would otherwise form the'impermeable' base to the perched water mound.Rewetting of peat workings in fen peat may havegreater repercussions upon the adjoining land as ofienthe ability to rewet the workings may depend uponwater supply and retention that is determined, directly01' indirectly, by adjoining land drainage systems.Such considerations suggest that the restoration 01'recreation of wetlands as substantial landscape featureswould benefit from the development of a co-ordinatedpolicy of land management. This would requireintegration of the activities and interests of the peatindustry and the conservation bodies and also, inspecific situations, of the Internal Drainage Boards, theWater Authorities, the National River Authorities andagriculturalists. Integration of restoration activities intoan overall plan (and the available options) will alsodepend upon the timing of peat extraction· in specificareas, particularly in those localities where there areseveral operators (e.g. Somerset Levels). In suchsituations the development of a holistic scheme formire restoration would be enhanced if it was possiblefor the co-ordinating body to develop a proactivestrategy for peat extraction rather than to just beresponsive to individual applications.It may also be noted that decisions concerning thedesirability of the various wetland habitat-types thatcould form the most appropriate focus for wetlandrestoration schemes in different parts of the UK couldbenefit from the formulation of a 'national wetlandstrategy'. Amongst other things, this could helpidentify objective ground-rules for assessing prioritiesin wetland habitat recreation, based on such considerationsas the perceived 'value' of particular habitattypes,their national and regional scarcity and thefeasibility and appropriateness of their recreation inspecific locations. Such an approach would help toprovide a rationale for wetland restoration optionsbased on assessed ecological and conservational meritand would thus reduce the chance of options beingchosen on a purely ad hoc basis 01' in response to theoverweening influence of a particular interest group.


PART 111Practical Aspects of Restoration


Chapter 7Planning a restoration strategy7.1 IntroductionThe occurrence of spontaneous and 'desirable' revegetationof some abandoned peat workings shows that insorne instances a measure of bog 'restoration' can beachieved wíthout intervention or planning. However,the existence of large areas of 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 develop a strategy in order to optimise. restoration procedures to achieve specific objectives.This is required to ensure that:• areas of existing natural history interest that will not besubject to further peat extraction are safeguarded;• 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 identified.Formulation of a restoration plan for a cut·over bogsite requires the acquisition of sorne information aboutthe site in question (e.g. Turchenek, Tedder &Kranowski, 1993; Famous, el al. 1995; Ward, Hirons& Self, 1995). Information (environmental andbiological) is required particularly: (i) to help selectappropriate restoration options; (ji) to identify theconstraints upon the chosen options and to enableinformed decisions to be made on the most appropriateways to achieve specific objectives; and (jii) to providebase-line data for monitoring purposes.Consultation with various statutory and non-statutorybodies will form an important part of the planningphase of restoration. These inelude the local mineralplanning authority, heritage, conservation and waterresources bodies. It may also be necessary to engagespecialists in order, for example, to carry out surveywork; interpret the results; assist in the preparation ofan appropríate restoration scheme with detailedspecifications; and to provide legal advice.The variability of starting conditions amongst damagedlowland peatlands means that a universal statement of'data required' for formulating a restoration plancannot be made. However, it is possible to identifysome of the main types of information that may beneeded, the objectives of restoration and the way inwhích restoration may be planned, although specificrequirements are Iikely to vary between sites,depending 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 of 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 of unplanned restoration, this cannotbe commended 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 of therequirements for habitat manipu\ation, rather than upondata acquisition and prediction. This approach has bothmerits and limitations:• some successful restoration initiatives have proceeded inthis way;• ignorance of actual site conditions may mean that thisapproach involves a good deal of '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 dependent upon the personnel involved;some individuals have a c1ear intuitive appraisal ofcontrols on particular conditions within peat\ands withwhich they are familiar; others do not;• this approach is often not readily communicable, nor arereasons for failure or success always easily identified;


130RESTORATION OF DAMAGED PEATLANDS• it is particularly suitable for repair of 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 of extensivelydamaged sites, where larger-scale and innovative habitatmanipulation may be needed;• even in extensivcly damaged sites this approach mayhave sorne contribution to makc; for example, peatworkers often have a good insight into the drains thathave most control of the water balance of the bog, or ofarcas where water naturally accumulates; theidentificatíon of wet conditions to nucleate restorationmay be more easily and accurately assessed byexamining the natural accumulation of 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 devise a well-researched, wellthought-out restoration plan. This is ofien considered tobe the 'best' approach. Nonetheless, it may have anumber of limitations both in principie and,particularly, in practice:• there is sometímes a tendency for data acquisition not tobe focused upon specific questions, but to be part of a'wish-list' of 'useful' information, or to be seen as away of identifying the specific questions that need to beanswered; sometimes the aequisition of such data,although of interest, may have Iittle direct relevance tothe development of a restoratíon plan and may even becounter-productive because:• data acquisition is frequently expensive and in mostcases this constrains the amount of information that canbe callected; Ihis usually results either in inadequatesample replication or inadequate site coveragc. Thclatter may be of particular importance in large raisedbogsites and can lead to lack of information about quitelarge parts of the mire; it is quite common experiencethat even elaborate investigations do not generate thelevel ofdetail required for sorne restoration purposes;• data interpretatíon may sometimes be difficult. Thisreflects both lack of knowledge and understandingspecific to sorne areas of peatland ecology together withthe more general problems of data interpretatíon. Forexample, it is simple to, measure high concentrations ofammonium in the peat of 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 provide the level ofpredictive accuracy required for the exact formulation ofrestoration objectives. For example, there are variousprocedures available for modelling the behavíour ofwater table in peatlands, but they may have limitedcapacity to predict accurately the position of the watertable with respect to the peat surface, especially in peatcuttingsites. This is because of intrínsíc límitations ofsorne models; because the more sophisticated models are'data-hungry'; and beeause ofthe difficulty afobtaíningmeaningful estimates of certain parameters for themodels. Restoration initiatives may, ofcourse, provide avaluable opportuníty to develop 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 provide the only realist option when dataacquisition is inadequate or of limited predictivereliability. To yield maximum benefits for restoration,data acquisition should be: (a) focused upon answeringspecific, defined questions that are critical to particularaspeets of restoration; (b) sufficientIy well resourced toensure that reliable and usable data are col1ected; and(c) performed by experienced practitioners who areaware ofthe inherent problems and likely límitations oftheir studies. These comments are not ¡ntended todiscourage acquisition ofsite data, but to emphasise theneed for relevant and reliable data and for a eonsideredappraisal, at the outset of planning a restorationstrategy, ofthe salient questions and data that are likelyto be required to answer them. The acquisition ofinformation of limited relevance or reliability (e.g.because of inadequate replication) may ultimatelyprovide little more than a loss ofmoney17.2.2 Feasibility studyIn view of the various sources of informationpotentially available and varying conditions at differentsites, it is recommended that the formulation ofrestoration schemes should be preceded by a feasibilitystudy which will provide the basis for choice ofspecific objectives for a site and the nature of anyrestoration work required. For sites currently underextraetion, a restoration scheme should be formulatedas soon as possible, before extraction ceases, eventhough this wiIJ involve an element of prediction (e.g.final topography, peat depths etc.).The primary functions of the feasibility study are:(i)(ii)lo determine lhe practica! and financia! feasibility ofrestoration;to determine the most suitable techniques for rctainingand enhancing any existing wildlífe or archaeologicalinterest within or on a site (in particular raised-bogelements);(iii) (o determine 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 consider thepotential of the site for education and research and itspotential for interpretation and public access.Assessments will be based on information derived from(a) a preliminary 'desk study' by collation of existinginformation and (b) from on-site investigations. Thelatter, together with interpretation of the information,may require the expertise of specialists from severaldisciplines, although an indication of the importanceand usefulness of the information is given in theappropriate sections below. Collection of supertluousinformation should be minimised by careful scoping ofthe site assessment programme; a reasonable balancemust be achieved between collection of adequate datato facilitate informed decisions and the cost ofcollecting such data. The latter is likely to be a majorlimiting factor in peatland restoration. An example ofthe potential scope of 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 of a restoration scheme. They relateboth to the process of choosing the most appropriaterestoration objectives for each site and the realisationof the specified objective. It will particularly help toidentify at an early stage· any known potentialconstraints on development. The main interestedparties are given in Table 7.2. Key consultees includethe 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 provide advice orinformation on various aspects of the site and proposedrestoration schemes, sorne of whom may wish to bedirectly involved. Some ofthese are Iisted in Table 7.3.Table 7.1 Potential scope of a feasibility study concerning the restoration of a cut-over or damaged peatland site.1. Site description1.1 Site location, landscape selling, and boundary information1.2 Soils and geology (including peat types and depths)1.3 General topography (within site, and in relation to surroundings)1.4 Flora and fauna (past, present and potential) (including features of special interest or conservalion value)1.5 Hydrology (including climate, regional and local water resources, 'undesirable' 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 of land and minerals ownership of site and adjoining land which may be affected by any restoration scheme4. Restoration options4.1 Objectives4.2 Constraints and opportunities4.2.1 Potentiallegal and land-use constraints on development (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 of restoralion work including:4.3.1 Conservalion of existing features of importance4.3.2 Optimisation of working practices to achi€we optimal starting conditions for restoration4.3.3 Work needed to improve hydrological water balance (and water quality, if appropriate)4.3.4 Reconfiguration of topography4.3.5 Proposed schedule of restoration work (including phasing of the work, taking climatic, management and practicalconstraints .into consideration)4.3.6 Proposals for on-going maintenance and management4.3.7 Proposals for monitoring progress6. Costed options


132RESTORATION OF DAMAGED PEATLANDSThe focus of the consultations may depend upon the¡nitiator ofthe 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 of relevance to MPA's in assessing theinformation provided in any applications submitted.7.3 Financial considerations7.3.1 IntroductionThe feasibility of the various restoration options maydepend on financial Iimitations, as well as practical andlegal constraints. Unless funding for restoration workhas been agreed in advance, an important part of theinitial feasibility study will be to determine thepotential for financial or practical assistance that maybe available from different sources, including bothstatutory and non-statutory conservation bodies. Thelatter may be able to provide help with past records forthe site, reconnaissance and recording. The costs ofrestoration are inevitably site specific, depending onsuch factors as the size of the site, the degree ofdamage, the extent of the remedial action necessary toachieve the stated management objectives (includingarchaeological mitigation), availability of materials,and the technical difficulties in carrying out the work.Sorne typical ranges of costs for different techniquesare given in Table 7.4.Table 7.2 Primary interested parties* in the formulation of a restoration scheme.OrganisationPeat extraction companiesLand and mineral owners involved with the siteor adjacent land (if different from aboye)Mineral Planning AuthorityEnglish Nature, Countryside Council for Wales.Scottish Natural Heritage, DoE(NI), CountrysideCommission.National Rivers Authority (NRA) and InternalDrainage Boards (IDB); River PurificationBoards (Scotland) ; DoE(NI).The Ministry of Agriculture Fisheries and Food(MAFF), Department of 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 of machinery etc.Details of 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 of site leases.Future plans for land following cessation of extraction.Guidance on planning and conservation issues (e.g. in development plans)Planning constraints relating to the site (e.g. existing conditions, rights ofway); Site history (planning).Statutory designations, e.g. Local Nature Reserves (LNR), common land,Scheduled Ancient Monuments (SAM).Non-Statutory designations e.g. Local Nature Reserves.Possible financial support for restoration work.Statutory designations e.g. National Nature Reserves, Sites of SpecialScientific Interest (SSSI's), Areas of Special Scientific Interest (ASSI's),Areas of Outstanding Natural Beauty (AONB), National Parks, SpecialProtection Areas (SPA's) and Ramsar sites.Occurrence or likely occurrence of scheduled species e.g. adder, badger,great crested newt.Wildlife value of 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 defences.Location of any nearby water abstraction points.Pollution potential of 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 of Environmentally Sensitive Areas (ESA's)Agriculturalland quality (of site and/or surrounding areas)Advice on archaeological interest and survey.Location and details of Scheduled Ancient Monuments (SAM).Possible practical and I or financial support for restoration work.The relevant participants will depend 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 of afishing lake; (b) eompensation payments are made; or(e) publie aeeess and finaneial eontribution iseneouraged. The major investments are likely to oeeurat the start of a projeet, but ongoing maintenaneemanagement may be essential for a long time. It iselear that the most eost-effeetive means of earrying outthe work will be earried out by or in eo-operation withthe Peat Industry, where the maehinery and expertiseare already on site. Sorne of the most reliable guides toeosting come from NW Germany, where a number ofbogs have now been prepared for restoration. Thesesuggest that preparation eosts of eut-over surfaees arein the region of 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 under the following headings:• Land - e.g. purchase ofsite or adjacent land.• Restoration procedures and management:(a)(b)(e)personnel;specialist advice;management operations;Table 7.3 Useful consultees in the formulation of 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 ofEngland; Royal Commission on Historieal Monumentsof Wales; Royal Commission on Historical Monumentsof Seotland; Historie SeotlandJoint Nature Conservation CommitleeThe Wildlife Trust Partnership RSNC; Seotlish WildlifeTrust; Ulster Wildlife TrustCouneil for the Proteetion of Rural England; Couneilfor the Proteetion of Rural Wales.Royal Society for the Proteelion of 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 of HydrologyScientific literature, local journals etc.Local schools and colleges etc.Nature of informationCounty Series Ordnance Survey maps. Estate plans. Earlydocuments relating to peat extraction.Site history.Statutory designations e.g. Scheduled Ancient Monuments.Information and advice on archaeological interest and value of 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¡ncludes the National Record of 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 of sites.Advice on restoration methods used in existing restoration schemeson Trust reserves.Landscape, wildlife, and historical details 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 wide range of groups. Speciesevaluation.Health and safety issues of the site.Location of 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 of 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 considered 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 of purchasing or leasing land has been amajor consideration in the conservation of several ofthe raised-bog sites in England and Wales, althoughobviously this wil1 not be a consideration where thework is to be carried out by existing owners oroccupiers, unless the scheme requires control ofadditional land. For example, the National NatureReserve at Fenns and Whixal1 was bought in 1990 at acost of f 1.7m (for 137 ha) and f 20,000 is spentannual1yl on rent for the leased land (302.3 ha). Costsof land purchase in the Somerset Levels were estimatedto vary from c. f 2,800 to f 10,700 ha-¡ depending onthe amount of peat remaining (Hancock, 1991).7.3.3 Restoration procedures andmanagement(a) PersonnelMost of the major restoration projects in the UKcurrently undertaken by the statutory conservationagencies involve a full time warden (site manager),with assistance from varying numbers of estateworkers. Sorne sites are managed as nature reserves bythe local Wildlife Trusts. Volunteer labour is ofienused but it is general1y considered 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,considerable time investment by site managers isusual1y needed 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 inorder, for example, to carry out survey work(topographical, biological, hydrologicaI, archaeological);perform chemical analyses of water, peat ormineral substrata; interpret the results; assist in thepreparation of an appropriate restoration scheme withdetailed specifications, and perhaps occasionally toprovide 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, depending on the type ofwork, and experience necessary to carry it out. Theinformation required should therefore be careful1yidentified before any such work is commissioned.(e) Management operationsApproximate ranges of costs have been summarised fordifferent management operations [Table 7.4], based oninfonnation provided by site managers, the peatindustry and published information (e.g. Beets, 1993;Edgar, 1993). From these, the approximate potentialcosts ofsorne restoration measures have been estimatedfor a hypothetical situation of 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 depend heavily on the extent ofthe remedial action required.Machinery, equipment and materialsA variety of 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 choiceof machine depends 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 of restoration alongside ongoing peatextraction, while the machinery is on site. In theabsence of 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 of inexperienced contractors, although sometimescheaper, is not recommended as practical experiencesuggests that these lack appropriate expertise andrequire more supervision.For construction of peat dams and bunds, the mostcost-effective option is to use the peat in situ, wherethis is available and judged to be sufficiently wel1decomposed. Excavation and transport of peat fromone area to another substantial1y increases costs. It mayalso be necessary to reinforce the dams with animpermeable care, either of polythene, plastic-coatedmetal or wood.Irrigation using pumps and piping requires purchase ofhardware, plus instal1ation and running costs.It may be appropriate to provide boardwalks at sornesites, for example, to facilitate management andmonitoring or to provide public access.


CHAPTER 7: RESTORATION PLANNING135Vegetatíon managementScrub control is ofien a major problem of 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 , depending on theamount ofscrub.Grazing is only practised rarely in bog restorationprojects in the UK, and is not generally considered tobe economical (i.e. it costs more to maintain andsupervise the tlock than is recouped from sale of thewool or meat) although it could be considered 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 of cut-over areas, by transplantationof vegetation etc. [see Chapter 9] should beincluded 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 of monitoring and maintenance will mainlyconsist of personnel time, in terms of establishing andexecuting the work and taking appropriate remedialaction (which may involve sorne machinery). The costswill depend on the options taken and methods used,and whether the work can be carried out 'in house' ornecessitates the engagement of suitably qualifiedspecialists. Assessment of monitoring costs shouldinelude provision for regular data analysis andinterpretation. [see also Chapter 11].7.3.4 Financial assistanceFinancial assistance with the costs of restoration of cutoverbogs may be available from a variety of sources.These should be investigated as part of the feasibilitystudy, as they may have considerable bearing on whatis financially practicable. Eligibility for assistancedepends on such factors as ownership; details ofplanning conditions; conservation status (whether SSSIetc.); proximity to water or impact on water resources;presence of specially-protected species or habitats;whether located within designated areas etc. The applicabilityof each scheme will depend on the precise circumstances,and will usually be considered on merit.Specific details 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 of revenue from a site, forexample as a consequence of terminating peatextraction before a previously agreed limit; orprevention of 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 of costs for selected restoration techniques used on lowland peatlands. These aremainly based on examples from a survey carried out in 1991-1992, using information provided by site managersand the peat industry.Operation Methods Range of costs Example potential costs for50 ha site with 45 ha cutover(milled) + 5 ha remnant*Bunding of 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 (includes Wide, palisade 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 of peal and compacling,(may include transport of peal)Scrub conlrol By hand or machine (may include f. 400-2,500 ha- 1 as approprialechemicallrealments)Transplanlalion of < f. 2,000 ha- 1 < f. 100,000vegetation• Assuming division of lhe cul-over ¡nlo 9 polders of 5 ha, and 1200 m perimeler of remnanl; wilh some damming of drainagedilches.


136 RESTORATlüN 01' DAMAGED PEATLANDSTable 7.5 Possible sources of 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 ownersCountryside CommissionMAFF I DANII DAFSEuropean UnionType of assistance possibly availableManagement agreements (on SSSl's I ASSl's)Grant aid (under the Wildlife and Countryside 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 provide help with specific projects, for example survey and monitoring.May provide help with specific projects (including volunteer labour)Potential for co-operative ventures, help with machinery etc.Possibility of contributions from developers to longer-term management throughSection 106 obligations under the Town and Country Planning Act, 1990.Countryside Stewardship Scheme-offers incentives for positive conservationmanagement in selected landscapes, including waterside landscapes. May beapplicable to enhancement of existing vegetated areas (on and off site), but wouldnot be applicable to restoration under planning conditions. Individual casesconsidered on merit.Environmentally Sensitive Areas scheme (ESA). The designation is designed toensure that traditional farming practices are continued within the area concerned,with financial incentives offered to farmers not to intensify their agricultural practice.Although not directly applicable to restoration of recently cut-over bog, the schemecould include the raising of water levels on adjacent agriculturalland.Funding may be available for selected restoration projects; relevant schemes mayvary annually.·7.4 Preliminary collation ofinformation (desk studies)7.4.1 Cartographic detailsExamination of maps will help to put a peatland siteinto its overall topographical, historical, industrial,geological and land-drainage setting. Features whichmay be determined by examination of various mapsinelude the following:• geology and soils;• topography;• main land drainage pattems and water courses(detailed site drainage will not normally be shown);• infrastructure, buildings, access roads etc.;• information on the historic and industrial landscapeand structures;• natural features ofthe site boundary.Sources include Ordnance Survey, Soil Survey andGeological Survey maps.Examination of a series of maps of different ages canbe valuable in helping to establish the history of thesite, particularly with respect to land-use changes.These include Tithe Maps, 1st edition OrdnanceSurvey, Enelosure Maps, Manorial Maps. 1t should,however, be noted that cartographers have not alwayssurveyed peatland areas in detail and sorne maps ofpeatlands may have limited accuracy. Moreover,successive Ordnance Survey revisions do not alwaysinelude changes to the character ofsorne peatland sites.Soil and geology maps may help to put the site in aregional and local context, for example, in establishingthe original extent of the peat body, of which the sitemay form only a small parto This may influencedecisions on the best restoration strategy, for examplewhether it would be desirable or feasible to try tomanage the entire peat area as a whole. At sorne sites,information shown on these maps may proveinsufficiently detailed, and, if required, plotting aprecise boundary of the peat body is likely to requirefurther investigation in the field.The amount of information that can be obtained frommaps with direct value to peatland restoration is ofienstrictly limited. For example, geological and soil mapsmay provide some useful background information onpossible factors that may influence restorationmanagement (e.g. . type of bedrock surrounding andunderlying the site), but in general do not provideinformation concerning, for example, the nature of thesubstratum beneath the bogo In these situations it isimportant to substantiate the information derived frommaps with chemical analyses of 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 ofaerial photographsAerial photographs are important aids to sitecharacterisation and, when time-series photographs areavailable, may perrnit determination of the effects ofrecent activities on site. They are also useful inupdating cartographic information and for locatingfeatures not readily evident on the ground, such as oldpeat cuttings and forrner drainage ditches, whichalthough occluded, may still retain sorne drainagefunction. Aerial photographs are also useful inidentifying vegetational features and boundaries. Forexample they may help to locate open areas otherwisehidden within dense scrub. They thereby provide animportant aid to ground survey work and if possiblerecent photographs should be made available to fieldworkers.7.4.3 Ownerships and tenanciesLocal occupants of the site and adjoining land shouldbe consulted and involved at an early stage in theplanning of any restoration project, particularIy wheretheir land may be affected by the restoration scheme.They may also provide a valuable source of 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 details (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 of the site so that these canbe incorporated into the restoration strategy, whereappropriate, or possible constraints on developmentidentified.Inforrnation on the land use history of a site, includingprevious management regimes, can sometimes begleaned by examination of maps, aerial photographs,literature and local sources etc. Although not criticalfor assessing restoration options, the inforrnation canprovide valuable insights into the site. For example itcan be used to chart the changing layouts of peatextraction operations, and help to date different cutoverareas. Such data are crucial to the archaeological,historical or industrial background ofa site.7.4.5 Hydro/ogical informationAvailable existing information relating to climate,regional and local water resources, 'undesirable' 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 of meteorologicaldata to individual bog sites is related to theproximity of the recording station, but in many cases itwill be adequate to provide a broad outline ofthe 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 of potential effects onboth water inputs and outputs, for example,considering availability of water for supplementarysupply, possible constraints imposed by flood defenceor 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 ofpeatland sites can be collated from the sourcesidentified in Tables 7.2 and 7.3. Available data arelikely to vary considerably in quantity and quality, butmay provide sorne useful background inforrnation andinsights, for example concerning former conditions orspecies on the site.7.4.7 PotentiaI legal and land-useconstraints on deve/opmentThe relevant legislation (international, national andlocal) which may affect development should beinvestigated and its implications for restoration optionsset down. The most important areas to be consideredconcern legislation relating to planning, conservationand water resources. Further details are provided inAppendix 2.Planning legislationPeat is classed as a mineral under 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 details of any planningpermissions are known, including the preciseboundaries of the area affected and the implications ofany specified conditions.Wildlife and conservation legislationAlthough one of the main aims of the restorationschemes considered in this document will usually be tomaintain and enhance the conservation 'value' of 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 ofconservational interest needs to be resolved (forexample, where a statutorily-protected species of 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 of thefollowing:• Species specially protected under the Wildlife andCountryside Act 1981 (as updated and amended);• National Nature Reserves;• Sites or Areas of Special Scientific Interest (SSSI /ASSI);• SpeciaI Areas ofConservation (SAC sites)• Ramsar sites;• Special Protection Areas (SPA's);• Environmentally Sensitive Areas (ESA's);• National Parks;• . Areas of Outstanding Natural Beauty;• Heritage Coasts;• Public Rights OfWay;• Scheduled Ancient Monuments;• Listed Buildings;• Local Nature Reserves;• Any further sites of environmental, archaeologicaI orgeological interest, such as those identified 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 of water; bloeking or divertingwater eoursesA water impoundment licence is required to impoundwater, for example if 'on-stream' water is impoundedor an existing water course is blocked or diverted toprovide 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 of water aboye the'natural level' ofany part ofthe adjoining land or havea dam higher than 4.5 m. The intention of this is toensure that there is no potential danger to Jife orproperty through the sudden release of water due to thecatastrophic failure of the retaining structures. Thevolume of water specified is equivalent to c. 4.5 hat100ded to 50 cm depth. lt is therefore possible thatparts of sorne restoration schemes may fall under theprovisions of the legislation, where the intention is tocreate large lagoons, in which case it is recommendedthat advice is sought from a qualified engineer.(b) Abstraetion ofwaterConsent is needed to abstract water either from water .courses or groundwater.(e) Diseharge of waterIn sorne circumstances it will be necessary to makeprovision for the discharge of water from a bogo Thiswill usually require a certificate giving the Consen! !oDischarge, unless drainage rights already exist.Situations where this may apply include the provisionof specific outfalls from a bog and pumping ofenriched water from a lagoon. It is necessary to providedetails ofthe quality ofthe water to be discharged.(d) Works affeeting land drainageAny works which interfere with existing drainagerequire Land Drainage Consent. This includes thebuilding of any constructs on or adjacent to watercourses, the diversion of any streams around a bog andthe potential for causíng t100ding of land not within thesite. Details of 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 ofthe proposals.


CHAPTER 7: RESTORATION PLANNING139Miscellaneous legislationAdherence to health and safety legislation should forrnpart of the requirements for any work carried out inconnection with restoration works.Searches should also be made for possible constraintssuch as cO,mmon land, turbary rights, rights of way,riparian rights, mineral rights, shooting rights, grazingrights, location of public utilities such as gas pipes,electricity pylons etc. The implications of any suchconstraints for the project should be assessed.7.4.8 SummaryA preliminary examination and summary assessmentshould be made of the inforrnation gathered by thedesk study in order to identify its nature and usefulnessand where further details are needed, in order tofacilitate the planning offurther work.7.5 Field investigations7.5.1 IntroductionThe aim of field investigations is to build on datagathered in the preliminary desk-study, enabling aH therelevant options to be considered in the forrnulation ofan appropriate restoration strategy. Suggestions of thetype of inforrnation which may be gathered is outlinedin Table 7.1 and considered in further detail below.This is intended as a guide to possible field investigationsthat may be needed at sorne sites, rather than aprescriptive list. It is recommended that 'hard' dataacquisition is focused upon inforrnation that is specificaHyneeded, rather than upon a general 'wish-Iist' ofinforrnation that may be of interest, and that it issufficiently well resourced and perforrned byexperienced practitioners who, when appropriate, areaware ofthe likely limitations oftheir studies [see 7.2].Appropriate field investigations are an essentialrequirement of site assessment and may require theservices of 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 of the site.Locations of aH transects, sample points etc. should berecorded on the base maps. Assessments of any healthand safety measures which need to be taken should bemade and action implemented to protect field workersprior to field work commencing.Surveys of the site must necessarily gather inforrnationon a wide range of topics, but these inter-relate to alarge extent. For example, inforrnation on thetopography of the site would be required to assess thecurrent and future hydrological regimes; in theplanning of any earth-works and as an archaeologicalrecord. It is thus desirable to co-ordinate the efforts ofdifferent interested parties into an integrated approachto the site investigation. The advantages of this includethe foHowing:• avoids unnecessary duplication and overlap (andtherefore reduces costs);• optimises the information gathered by each survey team,to provide input for other specialisms;• minimises disturbance or damage to sensitive areas of thesite;• promotes on-site discussions between various specialistsof the various restoration options and means ofachievement;• allows the early identification of any potential problemsor areas ofconflict of interests.7.5.2 Site physical characteristicsA broad survey of the topography and physicalcharacteristics of the site should be carried out toobtain inforrnation on the following factors, whenconsidered necessary and if not already -available insufficient detail from existing documentation:• general size and shape; extent of site in relation to wholepeat body;• surface and subsurface topography; peat depths;• geology and soils underlying and surrounding the site;• access for machinery and equipment;• location of existing tracks, pathways, boundaries,buildings and other structures; location of potentialhaúrds (e.g. rubbish tips).These aspects are discussed below. A general plan ofthe site should be made, and relevant features mapped.General size and shape; extent of site inrelation to whole peat body.In most cases the exact boundaries of the site underconsideration will have already been established, butoccasionaHy there may be a need for sorne verificationand accurate mapping. The establishment of at least theapproximate boundaries ofthe 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 of reasonably accurate mapsof 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; peatdepths(a) Disposition ofpeat fie/ds in re/ation to eaehother and any upstanding areasIdeally, the detailed topography of the peat fields andany uncut areas should be carefully mapped andlevelled to Ordnance Datum to facilitate the planningof a detailed restoration scheme. For example, it willhelp to identify any 'massif areas [2.1]; identify theneed and potential for any buffer zones [8.3]; allowpredictions to be made of the movement or collectionof water; facilitate the optimal siting of water controlmeasures such as dams and bunds and provide a recordof the historical and industrial land surface. Thepotential value of existing baulks etc. as water-holdingstructures should be assessed l .It may also be important to determine 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 professional 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 of Iíne transects andgrids, plus examination of profiles where, for exampledrains have already been cut into the sub-soil. This willalso provide the necessary information on peat depths.(b) Re/ationship to surroundingsThe general disposition of the site in relation to thesurrounding land is important in assessing possibleimpacts both from and on the adjoining land. Forexample, the potential for inputs of minerotrophic orpolluted water is greater if any of the exposed peatsurfaces líe below the level ofthe 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 of waterretention, and potential for flooding of adjoining land,but ensure that the only water inputs are atmospheric.(e) Peat depthsThe data available from the survey of the surface andsubsurface contours will allow identification andassessment of:• depth ofpeat remaining;• areas with the most complete peat stratigraphical andpalaeoenvironmental record;I The efficacy of the baulks as bunds will depend on their size,intactness, degree of dehydration and humification of the peat, andits bulk density.• areas where drains or peat extraction has exposed mineralsoil;• potential availability of peat for bunding, ditch blockingetc.Where possible the recording of peat depths should beaccompanied by sorne assessment of the peat types[7.5.5].Geology and soils underlying and surroundingthe sitePublished geology (solid and drift) and soil mapsprovide sorne information to put a site into its regionaland local context [7.4.1] but often the amount ofinformation of direct value to restoration is strictIylimited and, in those situations where it is consideredimportant, it may be necessary to supplement theinformation derived from maps by on-site survey.Consideration of 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 detailed survey may also help to indicate thepotential for mineral enrichment of water supplies(although this should also be substantiated by chemicalanalyses of the soils) and provide locational informationof palaeochannels for palaeoenvironmentalanalysis.Access for machinery and equipmentFor most restoration schemes it will be necessary tomaximise the use of machinery and equipment incarrying out management operations such as ditchblocking, bund building and scrub clearance. The fieldreconnaissance should therefore:• identify access routes for machinery of different types (atleast those potentially available) including light railways;• identify areas where passage of machinery would bedamaging to biological interest.The strategy adopted should take into account theaccessibilíty of different areas of a site to differentequipment, both before and after rewetting. Theplanning of operations will also need to take intoaccount the possible climatic constraints on the use ofmachinery at different times ofthe yearLocation of existing featuresFeatures such as tracks, pathways, boundaries,buildings and other structures, location of potentialhazards (e.g. rubbish tips) should be carefulIy recordedon the base maps, where not already documented.


CHAPTER 7: RESTORATION PLANNING1417.5.3 Land useWhere information has not been available from thepreliminary 'desk 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 of nutrient enrichment from agricultural actívitíes(either through water or air) and assessment of possibleremedial action that may be necessary (e.g. catch·waterdrains, shelter belts, diversion of polluted streams);• potential damage to adjoining land caused by raisingwater levels in the bog;• possible constraints on restoration options and potentialfor change of land-use in adjacent areas to onesympathetic to wetland conservation and restoration, orthe provision of buffer zones (through purchase,management agreements, ESA schemes etc.).7.5.4 HydrologyIntroductionThe maintenance of an ombrotrophic environmentrequires that the input of water from precipitation mustequal or exceed the water losses (at least on an annualbasis). The major problem for the restoration of mostdamaged raised bogs is the lack of an adequate andconsistent ombrotrophic water supply at or near thepeat surface to sustain the growth of peat-buildingSphagna.In sorne situations a mainly empirical approach torestoration of suitable hydrological conditions may besufficient for effective restoration [7.2]. However, inorder to formulate the most appropriate and costeffectiveremedial strategy it is important to determinethe main causes of dry conditions [see Chapter 2], toidentify the main factors which affect the water inputsand outputs in different areas ofthe mire and to put thesite into its local and regional hydrological context.Available information collated as part of the desk study(see aboye) can be supplemented as required by furtherinvestigations and measurements, as outlined below.It is recommended that expert hydrological advice issought on the level of detail required for an adequatehydrological assessment of a site. Information whichmay be required could include the following (at leastthose items marked * are likely to be needed for mostprojects):• c1imatic information*;• details ofwater courses* (type, distribution, slope, degreeoffunctíoning);• water outputs*;• topographical disposition of peat fields*and remnants*;peat depths* and sub-surface contours;• peat hydraulic conductivity;• vegetation characteristics;• distribution and stability of open water*;• potential for water supply;• local and regional context ofthe site.(i) Climatic informationConstruction of detailed water budgets for a site orhydrological modelling may require more localisedinformation than that available from publishedmeteorological records, as conditions on site may varyfrom those recorded sorne distance away, particularlyin situations of varying topography. The most relevantdata includeseasonal variations in rainfall, temperatureand evapotranspiration.(U)Reconnaissance of drains and watercourses. A reconnaissance survey should be carried out of alldrains and water courses impacting upon the site(including those outwith the site), and a map producedshowing direction of flow; slope; degree offunctioning; main outfalls and inputs; whether cutthrough to mineral subsoil and whether thought to beintroducing minerotrophic or polluted water on to thesite. This should include drains which are apparentlyalready occluded by vegetation and also a generalassessment of any 'buried' cross drains (usually slitdrains or mole drains) across peat fields or cuttings.Aerial photographs can be an invaluable source ofdetail, particularly when trying to trace old drains andwater courses. Potential impacts of external drains andwater courses on the site should be noted, in terms ofboth water outputs and as potential sources of 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 ofwater around the site. Note, however, that operatives ofthe peat industry often have a good workingknowledge ofthe characteristics of the drainage systemand consultation may be advantageous.Measurement ofthe mean altitude ofthe water levels inthe main drains and around the margins of the site canhelp to predict possible water draw-down effects.(iii) Water outputsReconnaissance of water cour.ses (see aboye) shouldprovide information conceming the most obvious waterlosses from the sites. However, where appropriate, andpossible, more indirect causes of dehydration shouldalso be identified and assessed. This includes possibleconnectivity between the perched water mound andregional water tables; leakage through the base of 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 testsunder different conditions.(iv) Dispositíon ofpeat fields and remnants,peat depths and subsurface contoursThese features should be identified by the topographicsurvey (see aboye) and will be useful in detennininglikely pattems ofwater 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 identified and the infonnationincorporated into the design of any 'engineering'works (constrllction of bunds etc.). Although suchareas may be identified 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 evident after a period ofheavy rainfal!.(v) Peat hydraufic conductivityMeasurements of peat hydraulic conductivity can beuseful in several different contexts associated withhydrological modelling [Box 7.1]:• prediction of (potential) perched water mounds withinrellllively 'inlact' peat remnanls [Chapter 1];• prediction of the rates at which water is lost tllrough peatin different areas (e.g. edges of remnants, through baulksor lhe basallayer ofpeal);• prediction of the draw-down in potential buffer zones,and hence calculation ofan appropriate buffer zone width[8.3];• prediction of the effects of different peat extraction ormanagement operations.For such measurements and predictive hydrologicalmodeIling [Box 7.1], it will usually be necessary toemploy the services of a competent hydrologist. Itshould, however, be recognised that good-qualityhydrological data (such as meaningflll estimates ofactual values of hydraulic conductivity) may be bothdifficlllt and expensive to obtain.(vi) Vegetation characteristics anddistribution of open waterA field survey of the vegetation [7.5.6] wiII provideinfonnation on the distribution of different vegetationtypes across the site, together with open water and bareground. This may facilitate some assessment of 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 modellingVarious hydrological models are available which can be usedto explore the hydrodynamics of peatlands, including: anassessment of the hydrological relationships between bogremnants and their surroundings; hydrological relationshipsbetween different areas on a site; inler-relalionships belween.the hydrodynamics of the bog and local and regional walertables; calculation of the appropriate width of buffer zones andprediclion of lhe outcome of various operations (including peatextraction and management techniques) bolh on sile and onadjacent land.Sorne of lhe available hydrological models are mostappropriate to relatively simple, uniform bog sites such aslhose which retain much of lheir original dome. In suchsituations 'simple' 'groundwater mound' mOdels can, subject lovarious constraints, help to predict, for example (a) the effectsthat reduction of the area of 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., often at various altitudes and perhaps withvarying (and usually unknown) hydraulic conduclivilies). Hereapplication of 'simple' models is particularly difficull, nol leastbecause the assumptions of sorne models are inapplicable orbecause 'calibration' of sorne of their parameters may nol befeasible. In such circumslances, finile element groundwalermodels may potenlially be more useful than lhe simpler'groundwater mound' models, as they are more flexible, canlake into accounl more easily variabilily in paramelers andmay be able to predict changes as a result of differentdisturbance or management activities. In addition, sorne canconsider variables such as the acrolelm properties and, inparticular, run-off and overland-f1ow elements that representlarge losses lo raised-bog syslems in winter. Such models are,however, very 'dala hungry' and have not been widely testedin peatlands.11 is beyond the scope of this report to provide guidelines onthe most appropriale models and methods, not least becauselhese are still being refined. The choice of model largelydepends on the purpose of lhe modelling, lhe level of detailrequired, lhe resources available and the amount (and quality)of data available (Schouwenaars, 1995; Bromley & Robinson,1995). In general, jI may be suggested thal al present theapplication of hydrological models is Iimited more by thedifficulties of obtaining sufficient and accurale field estimatesof sorne of lheir parameters than by deficiencies of lhe modelsthemselves.There can be little doubt thal, in principie, hydrological modelsmay be able to provide exact solutions to sorne critical aspectsof lhe hyorooynamics ano rewet\ing of pea\\am:ls, bu\,depending on lhe questions asked, at present there is Iittlereason lo suppose lhal lhey necessarily have sufficienlprediclíve accuracy lo provide more Ihan a broad basis forpraclical peatland resloration and that empírícal solutjons willconlinue to be important. Nonetheless, further development ofhydrological models, and of techniques for better estimatingsorne of their terms, may be expected to make an importantfulure contribution to peatland restoralion.Specific advice on lhe use of hydrological models 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 ofcomparative information currently available.ldentification of areas which are permanentlyinundated will also be useful in assessing approaches torevegetation, for example where there ís exístíngpotential for establishment offloating rafts.(vii) Potential for water supplyThe potential for supplementary water supply tospecific areas may be an important consideration insorne sÍtes. The quality of such supplíes is of criticalimportance [4.4.3] and needs to be established at anearly stage ifthis approach is considered desírable.7.5.5 Substratum characteristics andwater qualityThe chemical properties of water and peat wíll have aprofound influence on the plants that will colonise agiven area of peatland, and on the likely course ofsubsequent succession [1.9; 4.4]. They may also affectthe long-term preservation of sorne archaeologicalstructures. Thus sorne basic chemical data may beneeded to make decisions on the most appropriatestrategies and outcomes.Simple measurements of pH and the conductivity(corrected for pH) of water inputs, including rainfall,made in a representative selection of peat fields canprovide valuable ínformation. Comparison betweenresults (and with published values) will allowidentification of anomalous values [see also Table 2.1].Where sorne pollution or inappropriate minerotrophícinput is suspected, it may be necessary to carry outfurther analyses to identify the nature and source of theproblem. Analysis of the water (including the common'heavy' metals), followed by comparison of theproportions ofvarious ions with those in localrainwater inputs will give an indication of which ionsmight be coming in from sources other than rainfall.It will also be important to establish the water qualityofany potential supplementary water supplies [4.4.3].Knowledge ofthe type of peat that is, or will be,present when restoration management commences isvery important in assessing the potential and optionsfor restoration. One of the most important consideratíonsis whether the exposed peat is ombrotrophic(bog) peat or minerotrophic (fen) peat. Usually, thiscan be easily determined by simple measurement ofpH, or by examination of the plant remains preservedin the peat (macrofossils) [see Chapter 1]. The degreeof decomposition of the peat is also of importance asthis will help to determine the water storagecapabilities and permeability of the peat, and itssuitability for use in the construction of dams andbunds etc. Table 1.3 gives the basic details of the vonPost scale of hum ification.7.5.6 Survey and assessment ofbiological interest - flora andfaunaIntroductionA survey and assessment of the existing biologicalinterest of any site is an important component in theformulation of a restoration strategy. Where possible,field survey should build on the information collatedduring the initial desk study [7.4].The aíms of the survey should ideally include thefollowing:• identification and assessrnent of any areas with existingbiological interest;• identification of any species or cornrnunities with specialconservation status (e.g. statutory protection) eitherpresent on, or using the site; for the less cornrnon species,sorne assessrnent ofthe population size should be made;• identification of any potential conflicts between existingconservation interest and airns of restoration strategy;• assessrnent of the potential for 'natural' and 'assisted'recolonisation of darnaged or rewetted areas (i.e. theavailability of inoculurn etc.);• identification of areas with 'undesirable' species orcornrnunities (e.g. scrub etc.);• identification of potential 'threats' to the existing floraand fauna;• provision ofbase-line data for rnonitoring.FloraA broad survey of the vegetation and main habitattypespresent should be carried out. Various surveymethodologies are available, but it is recommendedthat 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 identify the specificfeatures outlined aboye. It is particularly important toidentify species and areas of existing conservationinterest, and those areas which may provide a reservoirof bog species for recolonisation of the cut-over areas.These species and specific areas should form the focusofthe restoration scheme for the whole site.An extensive cover of Sphagna, with a variety ofSphagnum species (including semi-aquatic species,lawn and hummock species) may help to identify arefugium as providing a good reservoir of bog specíes.However, good refugium areas need not necessarilytake the form of a residual, uncut block of peat; old,


144RESTORATION OF DAMAGED PEATLANDSrevegetated peat cuttings can fulfil a similar role. Thepresence of a cover of birch should not be considereddetrimental to the assessment of interest, providing theground layer is still relatively Sphagnum-rich.In sorne sites, existing wildlife interest of certain areasmay not be as a refugium for bog species but forspeejes of replaeement habitats (dry heath, fen, birehwoodland etc.). The róle and future of sueh areas mustbe elosely considered in relation to the strategy for thewhole site; adviee should be sought from the statutorynature eonservation bodies.As part of the field investigations, it would be desirableto initiate sorne fixed point photography, to illustratekey features, both as an aid to off-site diseussions andas the basis of a monitoring programme [Chapter 11].FaunaInvertebratesAssessment of the invertebrate interest of a site willideally eomprise referenee to existing reeords, speeieslists, etc., supplemented as neeessary by field survey,together with expert appraisal of the likely habitatrequirements ofany rare or notable taxa.Given the diversity of invertebrates and the diffieultyand expense that would be assoeiated with identifyingall speeimens in any reasonably-sized sample, fieldsurvey work will neeessitate restrietion to a limitednumber of groups and the partieipation of expertseapable of aeeurately identifying material and ofreeognising notable and rare groups. Survey work ofthis sort is very prone to adverse effects of weathereonditions and sampling technique. To overeome suchbias, surveys should employ several samplingprocedures and be carried out on several occasions.Methodologieal problems include the difficulties ofaccurately censusing the populations of different typesof invertebrates (Beukeboom, 1986). The larger,actively flying, diurnal species such as dragonflies andbutterflies are usually counted along line transects, anderrant ground dwellers are usually sampled using pitfalltraps. Undoubtedly a major problem with interpretingthe abundance and distribution of invertebrates inraised bogs, and in particular in intact Sphagnumcarpets, are practical difficulties of sampling fromthese low vegetation types. Nearly al1 studies haverelied heavily on pitfall trapping ancl/or water pan trapsand net sampling of water beetles [see Table 7.6].These wil1 undoubtedly tend to be biased in favour oferrant species sueh as carnivorous beetles (e.g.Carabidae, Staphylinidae) and spiders, and will tend tounderestimate more sedentary, phytophagous and sapsuekinggroups (Coulson & Butterfield, 1985). ThusKirby (1992a) notes that several species of delphacidbugs occurring in bogs seem to be difficult to find (andhence record), and though they may be caught in pitfalltraps, these will undoubtedly miss many of thesespecies unless very intensive sampling is carried outand quantifying more sedentary 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 of invertebrates on cut-over peatlands.Survey methodAquatic nettingTransect walks with visualcountingWaterpan trappingPilfall trappingU.V. Iight trappingSweep-nettingHand searchingExtraction of 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 spiders; 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 orders (e.g. Neuroplera, Trichoplera)Insecls may be attracled from a dislance and therefore derive from habilals olher thanwhere the trap is localedAppropriate for a wide range of errant and more sedentary insects and spiders of the herband scrub layer; can be difficult under 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 of surveying soil fauna though it may underestimate 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 widely employed. These aresummarised in Table 7.6. No one sampling method isIikely to be adequate to make a thorough and usefulassessment of the invertebrate interest of a site. Themethods selected will no doubt normally reflect theavailability of taxonomic expertise. However, pitfalltrapping and.UV light trapping should be used ifpossib\e as they have been the two most wide\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 UKinclude a mosaic of 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 ofien unc1earwhat aspects of the bog system may need to beprotected in order 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 ofrecovery from certain forms of peat extraction, notablyfrom traditional hand-cutting, do provide importantsites for a number of species of high conservationpriority. Taxa which fall into this category inelude 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 ofhabitat.BírdsAssessment of the omithological status of a site mayrequire field survey to supplement the informationderived from the collation of existing records, togetherwith expert appraisal of the Iikely habitat requirementsofany rare or notable species.A survey of 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 undertaking an assessment ofpopu\ations of wintering birds, but methods involvingtransects, point counts or grid surveys may beappropriate. Basic details are provided by Bibby,Burgess and HiIl (1992). However, bird censustechniques are currently receiving much attention, andit is recornrnended that the British Trust forOmithology (BTO) are contacted for up to dateinformation on preferred methods.Assessrnent of breeding and wintering birds will needto be carried out over a mihimum of one year andshould aim to provide an assessment of bird habitatsnot only within but also surrounding the site in order toput the site into its local context..Non-avían vertebratesNon-avian vertebrates (mammals, amphibians, reptiles)usually form a relatively minar part ofthe conservationinterest of raised-bog sites, but efforts should be madeto collate and review existing records so that thepotential impact of restoration measures can beassessed. Records from raised-bog sites have inc1udedsuch species as otter, mountain hare, deer and adder.Bogs roay a\so constitute important feeding areas forbats, especially around marginal habitats.Assessment of wildlife 'value'Following the reconnaissance surveys, an overalleva\uation of the wildlife of the site shou\d be carriedout, in consultation with the statutory conservationagencies, in particular to identify key areas or specieswhich require special protection. This should becoupled with an assessment of how such areas can bestbe maintained and, where possible, the ecologicalrequirements of the relevant species.Sites may be conservationalIy valuable either throughthe presence of 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 consider which sort of interest they consider to bemore important [see Chapter 3].7.5.7 Survey of archaeological andpalaeoecological interestThe palaeoecological record contained within peat(pollen, plant macrofossils, fossil beetles etc.) can beused to reconstruct vegetation history, landscapedeve\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 of interest, and maywarrant recording before remedial action is undertaken.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 hiddenor destroyed artefacts or may have exposed features notpreviously recorded. Contact should be made at leastwith the local authority or county archaeologists andthe statutory archaeological bodies to seek advice onthe potential archaeological interest ofthe site.


146RESTORATION OF DAMAGED PEATLANDSWhere further evaluation is considered desirable,assessments of archival value can be made by wetlandarchaeologists or palaeoecologists. Archaeologicalinvestigations can include topographical and structuralsurvey, palaeo-environmental analyses and siteinspection, coupled with evaluation and mitigation.Sorne exploratory excavations may be required.Specific points which should be considered during anarchaeological investigation include:• the 'value' of the site both in terms of the individualstructures and artefacts and the site as a whole;• the importance of the site in the context of others in thearea;• the historical and industrial landscape;• the palaeoenvironmental record contained in the peat(pollen and macrofossil stratigraphy);• the conservation needs of any finds and sites, and thepotential for conflict with wildlife conservation aims (andrestoration methods).In sorne sites it may also be appropriate to consider thepotential of 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 needed,particularly where there is evidence of extensivearchaeological interest or conflicts are identifiedbetween the archaeological and biological conservationneeds. Any areas which would be affected byrestoration proposals may need to be properly recordedprior 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 offireFire is a potential hazard on any bog, and can causeextensive damage if uncontrolled. Provision should bemade for the prevention and control of fires in theformulation of 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 identified.Where these are considered to be inadequate, 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 intended to carry out restoration workthrough the building of bunds, movement ofconsiderable amounts of peat etc., it may be advisableto carry out an engineering assessment of the site, aspart of the feasibility study for any particularrestoration strategy. This would centre on the natureand properties of the materials available on site, theexisting topography, the condition of structures, thepotential for building water-retaining constructs andthe movement ofwater through the site.Particular attention should be paid to the followingpoints:• acccss for machinery - existing availability vsrequirements;• hydrology;• impoundment of water may bring the constructs underthe provisions of the Reservoirs Act 1975 and thus besubject to inspections and remedial works [Appendix 2];• design of 'new' landforms must take into accountstability considerations.7.5.10 SafetyassessmentSafety assessments should consider:(a)(b)physical hazards;chemical hazards.Physical hazards will be principally related to old orcurrent peat workings and structures, and should berecorded during the field reconnaissance surveys. Theymay include:• old peat cuttings with unstable, floating rafts ofvegetation;• unstable or unsafe buildings;• drainage ditches - both extant and occluded;• peat works machinery, light railway etc;• debris from tipping.Chemical hazards may be encountered where the sitehas been used for tipping (either official1y or for flytipping).Where a potential problem is identified, theLocal Authority should be contacted for guidance ondisposal.Consideration will need to be given to the safety ofworkers on site and the general public (if applicable,e.g. if rights of way exist). Adherence to other healthand safety legislation should form part of therequirements of 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 of 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 of bare ground, and to blend withits surroundings.


CHAPTER 7: RESTORATION PLANNING147Where a site is c10se to housing, potential detrimentaleffects of rewetting to householders should beconsidered. For example, in at least one instance in TheNetherlands,increased populations of biting insects, asa consequence of 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 ofrewetting peat extraction complexes in the UK arerelated: (i) maintaining a consistently high water levelin the peat; (ii) providing adequate water storage; and(iii) preventing lateral water loss. The solutions to theseproblems will depend upon the topography anddisposition of the peat fields, the nature of the exposedpeat; and the climatic context.The retention of water in peat extraction complexes ispartly a function of their topography and capacity forwater storage. The latter is a property of the peat type[2.3.2]. Where the exposed peat has limited storagecapacity, increase of storage may be possible only bystoring water above-ground, by creating sorne form ofreservoir on part or all of 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 of water management operations is partlydetermined by c1imatic considerations - in areas ofhigh rainfall the desired 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 of 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 dischargesof water), and to conservation interests (includingarchaeological or palaeoecological interest in theresidual peat deposit). Possible constraints should beidentified and resolved at an early stage in the planningofany restoration scheme [Chapter 7].Sorne reconfiguration of the peat surfaces prior torewetting may be needed to optimise the conditionsprovided for water retention and recolonisation, forexample removal of existing vegetation; manipulationof the macro- or micro-topography through reductionor increase in the number or height of baulks, creationof lagoons for retention of 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 deliver peak discharges from the bog otherwiseerosion of the regenerating peat surface, damageto the dam network and bunds or to the recolonistvegetation may occur. Even in undisturbed raised bogs,high run-off occurs in autumn through to spring whenprecipitation exceeds evaporation. In designing thewater level control system for a regenerating mire, highwater flows must therefore be catered for and this mayinvolve the installation ofweirs or sluices.Rowell (1988) deals with the general principies andpractical aspects of control of water in peatlands.Brooks (1981) also gives practical advice, particularlyon the building of dams and sluices or weirs. Thetechniques available to reduce hydrological changewithin refugia and rewetting cut-over sites include:• ditch blocking;• bunding;• provision ofsupplernentary 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,occluded 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 ofhigh permeability;• slit drains or mole drains in abandoned cut-over areasmust be identified, and blocked if thought to befunctioning (in sorne cases they will be effectivelyblocked by retention of water in the main drains);• for large scale operations it is necessary to use machinery(rather than hand methods) to build the dams, butconsideration must be given to potential damage toexisting vegetation;• in most cases, peat dams will be adequate if buiUcorrectly, but they may need to have an impermeablecore of plastic, metal sheeting, wood etc.• careful attention should be paid to the re-routing of 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 of dams will largely depend onthe size, fall and orientation ofthe drain;• on-going maintenance of dams is essential to correet assoon as possible any damage through faetors sueh asshrinkage, slumping and erosion;• adequate provision must be made 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 desirable to prevent too much vegetation colonisationand preserve the linear pools created by blockingditches at intervals, which can provide an attractivehabitat for wetland fauna (e.g. Fox, 1986a, b) and mayhelp to temporarily provide 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 of upstanding bogremnants, to reduce run-off from remnants, to impoundwater within existing peat cuttings or to create newlagoons. Depending on location and availability ofsource material, these may be constructed frommaterials such as c1ay, peat and plastic membranes, andusually involve the use of machinery. Note that c1aybunds may help to enrich the mire water, although thesignificance of this to bog restoration is not wellknown. The construction material may be won in si/u,or brought in from outside. The latter may only beappropriate in sites with existing infra-structure frompeat cutting operations, for example tramways orroadways that permit the transport of materials insufficient quantities, and would substantially increasecosts. In many cases, existing tramways and roadwaysmay act as bunds, and can be utilised or extended,although they may not necessarily be watertight. Theefficacy of the baulks as bunds will depend on theirsize, intactness and degree of dehydration of the peat.Use of bunding techniques is illustrated in Plates 8.2and 8.3.PeatThe construction of bunds raises several problems fromthe engineering point of view, as, although manyembankments have been constructed from, and on,peat, there is still no accepted procedure fordetermining the engineering properties of these typesof structure or standard engineering criteria on whichto base a designo 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 of water aboye the'natural level' of any part of the adjoining land or havea dam higher than 4.5 m; requiring that theconstruction be undertaken in accordance with thedesign and under the supervision of a qualified civil.engineer [see Appendix 2].For an effective bund, the peat recommended by mostpractitioners is wet, strongly-humified peat, although itshould retain some fibrous structure (for example, peatof humification value H6-H8\). Where sufficientquantities of 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 ofwet 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 of 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 anadequate layer of strongly-humified, wet peat. Suchbunds may be used to seal the edges of 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 of 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 ofpeat, 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 wide drainage ditch; WedholmeFlow (Cumbria).(e) Sheet-metal dam across narrow drainage ditch,Glasson Moss (Cumbria).(d) Sheet metal dam across wide fire-break;Moss (Cheshire).Risley(e) Simple plywood-sheet dam across narrow ditch;Danes Moss (Cheshire).(f) Palisade 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 of shallow, internal bunds: (a) by replacement of upper, weakly-humified peat with importedstrongly-humified peat 1 ; (b) by interchange of 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 of 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 depth remains. Sorne compaction of thepeat in the construction of 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 provide sorne protection from erosion through windand waves using wooden baffles. Provision of a 'shelfarea would aIso help to dissipate the wave energy, thusprotecting the main bund, and may help to provide aplatform for the initiation of rafting vegetation.Plastic membranesThese have been used in situations where there is somedoubt about the permeability of the peat available forbunding. The plastic used is a heavy duty polythene(such as is available from builders 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 of massifs, asexpense may prohibit their extensive use within peatcutting complexes. However, the material can also beused to improve the water retention of existingstructures (dams or bunds) which are thought to beleaking.Plastic membranes are non-biodegradable and have anindefinite (although unknown) life-span. The mainpotential problems suggested include damage by1 The source of the strongly-humified peat may be from clsewhereon the site, or from a treneh dug along the inside of the position ofthe proposed bund.burrowing animaIs, in particular rats and moles, andthe potential formation of a vertical 'slip plane' downthe outer face of the plastic membrane, particularly ifthe peat on the 'outside' becomes dry. Neither problemseems to have happened so far, although the possibilitycannot be excluded. The plastic does not necessarilyneed to go down to the base of 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 of pressure behind themembrane, although this should be monitored. lt maybe possible to reduce the potential for a zone ofenhanced water movement at the base of themembrane, which could lead to leakage and weakeningof the bund structure, by inserting lengths of the plasticto different depths.Mineral substrataEmbankments on peat or estuarine clay for river floodcontrolare usually constructed from peat or sandymaterials around a c1ay coreo Sorne of 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 design and methods, and size. Wheremineral materials are used, attention must also be givento the potential problem of leaching of 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 constructionof a trench on the remnant side of the bund to ensurethere is a supply of 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 orderto help counteract drying, part of the length ofthe bundhas been constructed with a water trap half-way downthe outside-slope, intended to contain water and release


CHAPTER 8: WATER MANAGEME T 153Construction of a bund around old peat cuttings on the SE bog at Cors Caron (Dyfed). The lines of dams acrossditches on the remaining 'dome' ofthe 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 of water deficit (Wynne & O'Oonnell,1993) [Plate 8.3]. As this project is new, there hasbeen no opportunity to assess the effectiveness of 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 of the bunds. An adjustable collar-overflowpipe system laid through the bund, or a sluice can beused for this. An overflow system also has theadvantage of providing specific discharge points forthe water, whether into another lagoon or externaldrainage system as appropriate. The latter will help toavoid any potentially undesirable impacts on adjoiningland. Careful consideration must be given to thematerials and methods used for over-flow provision, sothat lines of weakness are not created, and regularchecks made for correct functioning.On-going management of the bunds is necessary toensure that any problems are dealt with promptly, forexample rectifying slumping and removal of shrubseedlings. The height of the bunds around bogremnants may need to be increased periodically as thepeat within swells. Maintenance of 'internal' bundswhich subdivide peat fields in less important, once thecuttings have started to renature.8.2.4 Provision ofsupplementarywaterSupplementary water provision should only beconsidered 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 inelude Shapwick Heath (Somerset) andThorne Waste (S. Yorkshire).8.3 Buffer zonesOn the European mainland an attempt has been made,in sorne cases, to surround uncut remnants, and regeneratingcut-over areas with 'buffer zones', designed tohelp protect the sites against adverse influences ofsurrounding 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 of water from the bottom of the bog;or (e) reduce oxidation of underlying impermeable layersor of the basal peats that might oeeur should anunsaturated zone develop 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 order 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 of trees(a non-invasive speeies) may be ineorporated into thebuffer zone.• A buffer zone to provide an impermeable barrier aroundthe margins of a peat-extraetion eomplex to preventingress of 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 of semi-naturalvegetation adjoining the bogoB. Buffer zone Oll the peat body:• A buffer zone whieh eorresponds to the maximum widthof the water drawdown zone at the margin of anupstanding peat block.The principIe of the establishment of buffer zonesaround both uncut remnants and cut-over mires ise1early an important one. The width of the buffer zonedepends on such factors as climate, hydraulicconductivity of the peat, height differences and thedistance to (and depth ot) active drains. However,although the width of buffer zone required in differentsituations can be calculated using standardhydrological data and equations (see e.g. Eggelsmann,1982; van der Molen, 1981; Robinson el al, 1992; vanWalsum, 1992), the accuracy and value of suchdeterminations have been little tested in practice, andmay be limited by difficulties of obtaining meaningfulestimates of sorne key hydrological variables. Moreresearch is needed to refine the modelling approach tocalculate the appropriate buffer zone widths fordifferent situations before it is possible to provideprecise guidelines by such methods.Widths of between 30 m and 100 m have beensuggested to provide a sufficient hydrological buffer.However, work by Robinson el al (1992) suggestedthat in sorne circumstances, a buffer zone of 500 mmight be needed to minimise the effect of peatextraction on an adjacent upstanding peat block, unlesshydrological management measures were taken (e.g.ditch blocking or installation of an impermeablebarrier).Raising of water levels in a buffer zone within theadjoining land, while probably not sufficient in itselftoeffect much rewetting of an upstanding bog remnant(unless there is a very low hydraulic gradient) mayprovide the opportunity for the establishment ofsympathetic management, for example in the creation


156RESTORATION OF DAMAGED PEATLANDSof wet meadows. Thís would have the addítionalbenefit of reducíng the potentíal for agriculturalpolIutíon impinging on the site, either from watercourses or aeríal sources.8.4 Practical implications ofrewetting for adjoining landAs the major aim of 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 depend on such factors as thehydraulic conductivity of the peat, the difference inheight between site and surroundings, distance todrains, permeability ofthe underlying substratum etc.Use of bunds should alIow relatively índependentcontrol of water levels 'inside' 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 ofthe bog and bounded by a second ditch within whichwater levels can be lowered. The width of buffer zonenecessary would depend largely on the permeabiJity ofthe substratum and the required drainage capacity ofthe outer ditch. However, clearly thís could haveímplications in terms of loss of the land for agriculture,and requires further investigatíon.There is sorne evidence to suggest that in certain mires,partjcularly those underlain 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 of the bag (e.g. Paelman &loosten, 1992);b) the role of ground water recharge cannot be ignored,especially where the mire has been extensively cut-overand a relatively thin veneer of 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] andeither elevated aboye or retumed to formergroundwater levels. 5uch strategies may involvefurther substantial infrastructural works, which, besidesdirect costs ofconstruction and maintenance, may alsohave obvious financialimplications in terms of landpurchase or compensation etc. Considerable problemsin achíeving such rewetting are Iikely to beencountered where the adjoining land is under 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 ofthe restoration measures for increasíngthe buffering capacity of the mire in terrns of fioodcontrol of adjoining land should be consídered as thismay be perceived as beneficial by the water resourcesagencíes and would enhance the 'value' of therestoration scheme. However, there is conflictingevidence in the literature conceming the role ofundamaged, drained and rewetted peatlands in the'dampíng' ofpeak fiows folJowing storms.


Chapter. 9Facilitation ofrevegetation9.1 IntroductionNatural recolonisation of cut-over bogs by plants maytake place quite readily where there are local refugia oftypical bog species. However, where these do not exist,or have a sparse range of species, or where sites areparticularly large, it may be necessary to consider'inoculation' of damaged areas with suitable plantspecies, either by transplantation or by seeding.Before areas are inoculated, it is important that otherstages ofthe restoration scheme have been successfullycarried out, and that any remedial work can beundertaken without damage to the vegetation. Forexample, if appropriate vegetation is to re-establish, itis important that the hydrological conditions, in termsof quality, quantity and stability of water supply, areappropriate [see Chapters 4 and 5]. Conversely, therestoration scheme developed should take into accountthe availability ofplant inoculum.9.2 Inoculation with Sphagnumspecies9.2.1 IntroductionThe main feature of the vegetation of an undamagedraised bog is the extent of the Sphagnum cover, which,besides being characteristic, may play various importantroles in the functioning ofthe mire [1.7]. The restorationof a mire to a self-sustaining system requiresthe reinstatement of an acrcJíelm which is comparableto that ofa little-damaged bbg surface. Thus, one ofthemost important considerations in the restoration of adamaged bog is the question of how to regain theSphagnum cover. A characteristic of many damag\j.dbogs is the lack of or limited areas of Sphagnum-richrefugia, which may hinder 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 considered least 'sensitive', ensuring thatdamage is minimised. Donor sites should preferably bein the same geographic area to avoid undesirabletranslocation of 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 ofSphagnum will regenerate more readily if a template ofaquatic Sphagna is first created, than from direct'broadcasting' ofplants into open water pools.For larger scale restoration, removal of large quantitiesof Sphagnum from donor sites is likely to beinappropriate. In these situations the availability ofpropagules may be increased by Sphagnum 'farming'.9.2.2 Sphagnum 'farming'AII Sphagnum species can reproduce vegetatively andtechniques have been investigated to increase theamount of 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' of aquatic Sphagna on which toregenerate [9.2.3]. Further work is needed to formulateadequate guidelines for optimal conditions for sustainablefarming of Sphagna to allow for harvesting on aregular, rotational basis. It may be recommended that'nursery' poois'are established as soon as possible in arestoration programme (if possible alongside ongoingextraction), so that inoc.m is available as required.9~2.3 Propagation ofSphagnum fromsma/l vegetative fragments~ ~Effective inoculation of the extensive areas presentedby commercial peat workings with whole Sphagnumplants would require large amounts of source material.Techniques have therefore been investigated foroptimising the use of available plant material. It is


158RESTORATION 01' DAMAGED PEATLANDSknown from numerous observations that S. cuspidatumregenerates remarkably well from fragments and alsothat the growth of lateral buds of Sphagnum can bestimulated by damage to the plant apex, for example,by decapitation. Small-scale trials have shown goodregeneration of S. cuspidatum plants in pools intowhich fragments of plants in a suspension of waterwere 'broadcast' (Money, 1994, 1995). Regenerationfrom fragments will depend on provision of a suitablewater regime as periodic desiccation on a dry peatsurface inhibits regeneration, while regeneration alsoseems to be inhibited if fragments are introduced intodeep water (>50 cm), unless sorne provision is made toassist flotation [9.2.5]. Colonisation ofdeep water by S.cuspidatum tends to occur by lateral spread from plantsanchored to the edges of pools, thus regeneration islikely to be most successful initially at the peat-waterinterface and in shallow water (Money, 1994, 1995).The regenerative capacities of 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 & Pfadenhauer,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 of 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 considerinoculation as whole plants in c1umps, to the edges ofpools, or on to artificial rafts.9.2.4 Regeneration ofSphagnum fromsporesRegeneration of Sphagnum from spores is potentiallyan important process for recolonisation of damagedpeatland as it would enable long-distance inoculationof areas devoid of a local source of propagules forcertain species. However, the contribution to dispersalmade by sexual reproduction of Sphagnum is poorIyunderstood. Spores have regenerated successfullyunder laboratory conditions (e.g. Boatman & Lark,1971; Sabotka, 1976; Baker & Boatman, 1985; Clymo& Duckett, 1986), but under nutrient poor conditions inthe field it would appear that regeneration from sporesmay be less important than vegetative reproduction.9.2.5 Facilitation ofSphagnumestablishment and raftingThere is evidence that the establishment and spread ofSphagnum within embryonic bogs may be facilitated insorne situations by the presence of 'nurse species' suchas Molinia caerulea, Eriophorum vaginatum andJuncus ejJusus (Joosten, 1992; Meade, 1992; Grosvernieret al. 1995). These may (i) afford protectionagainst wind and wave action in flooded sites; (ii)provide a 'climbing frame' for Sphagnum; and (iii)provide a more suitable microclimate for Sphagnum.Joosten (1992) refers to this as 'tussock buffering'.However, a possible limitation of this approach is thata critical balance may exist between conditions thatfavour extreme dominance of species such as E.vaginatum and M caerulea and those which pennitthese species to act as nurse species to Sphagnum.The provision of '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. bunkerde - see 9.6) or particles floatingin the pools, either washed in from the sides, ordetached and lifted from the base of the cuttings(probably due to the formation of gas bubbles).9.3 Inoculation with vascularplantsCommercial supply of seed of bog species is unlikelyto be available, although seed mixtures are availablefrom specialist seed merchants which could be used forthe creation of 'wet meadows' at the margins of 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 of a range of plantspecies, as well as invertebrates, which would beabsent from specially raised sources.There is little information available on the Iikelysuccess of transplanting vascular bog species, but it isunlikely to be too problematic under a suitablehydrological regime and could be considered wherethere is no nearby source of propagules. However, it islikely to be practicable only over small areas, usualIybeing restricted by the availability of suitable plantmaterial and intensity of ¡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 provide fragments of vascular plants andmosses, and a seed source (Bayfield et al., 1991),although this technique is likely to be of 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 density of 2-4


CJlAPTER 9: FACILlTATION OF REVEGETATIO159turves m- 2 can be used to provide a good source ofinoculum (at least on blanket bog).Some of 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 of theproblems of transplanting into open water such asusing log or board baffles to help break the force ofany waves and using bio-degradable cotton mesh ornetting to hold the plants in position until established.Planting should ideally be carried out in the autumn orearly spring so that vegetation can establish before anyonset of dry periods in summer. Plant material shouldbe transplanted as soon as possible after collection ­drying out in transit must be avoided. Maintenance ofhigh and stable water levels are crucial for thesuccessful establishment of 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 made.9.4 Legal aspects oftransplantationConcem is sometimes expressed about the use of intersitetransplants, as disturbance of regional gene pools isconsidered undesirable, as is the possible introductionof 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 made as to whether or not such speciesare a desired component of restoration (this is partlydeterrnined by the restoration objectives for the site).While there is no specific legislation which coverstransplantation, under the Wildlife and Countryside Act(1981) it is illegal to uproot any plant without theowners' consent and consent is required from thestatutory conservation agencies for the removal oforganisms from, or introduction to a Site (or Area) ofSpecial Scientific Interest as this may be considered apotentially damaging operation. It is recommended thatguidance on intra-site translocations of both flora andfauna is sought from these agencies, as the generalguidelines are currently under review.9.5 Mitigation of 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 of 'typical'bog species, due to particularIy high acidity or lownutrient availability. The use of phosphorus has beenshown experimentally to assist in the short-term establishmentof certain Sphagnum species in peat cuttings(applied at arate of 30 g NaH 2 P0 4 in c. 4m 3 of water)(Money, 1995). However, to date, this has only beencarried out on a very small scale; large scale trials areundoubtedly needed before firm guidance andrecommendations can be made as to the use of fertiliserin facilitating revegetation. Any application of fertilisershould be regarded as experimental, and the resultscarefully documented. There is likely to be a finedividing line between the stimulation of the growth of'desirable' vegetation and the encouragement of'undesirable' species, including algae. The potential forthe stimulation of the microbiota and henceacceleration of peat decomposition must also be takeninto account. The latter is an important consideration interms of the preservation of the pollen record andarchaeological artefacts. Note that similar commentsapply to the use of 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 decomposition.9.5.2 Base- or nutrient-enrichmentExcess inputs of bases or nutrients (from telluric water,bird droppings etc.) may have an adverse impact uponredevelopment of bog vegetation, depending on theloadings in question. In most situations, the onlymethod of mitigating any adverse effects will be toidentify the source(s) and attempt to stop or reduceinputs, for example by diversion of polluted streams,providing flood-protection banks, scaring off 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 ofvegetation rafting can help to initiate the hydrosere,and provide a buffer against the influence of poorqualitywater [4.3].9.6 Importance of 'bunkerde' torevegetation'Bunkerde' is a Gerrnan terrn for the surface layer ofvegetation 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 of'natural' vegetation, or upon such recolonist vegetationthat ha redeveloped between cutting episodes, togetherwith variable amounts of different types of peat. [nGermany bunkerde is considered to be of greatimportance in the restoration of abandoned peatworkings and there is a legal requirement for thismaterial to be stored [P[ate 9.1] so that a 30 cm thicklayer can' be replaced afier extraction has ceased, toas isl in the restoration. As slorage necessitates theformation of quite thick layers which may remainundisturbed for a considerable period, the material isessentially composted, although it may be mixed withremnants of living vegetation before being spread backon to the bare peat surface.The evidence for the general importance of bunkerde isinconclu ive, perhap due to the extremely variablenature of the material in question. There is littleevidence that bunkerde necessarily improvesrestoration pro pecl , and in some cases may even bedetrimental. Some bunkerde (that derived from anatural bog surface) can retain viable diaspores of awide range of typical bog species (Poschlod, 1995).Other types contain few diaspores (or sometimes seedof 'undesirable' species such a Molinia caerulea andin this case any value of bunkerde may be morethrough amelioration of growing conditions byphysical properties than as a source of propagules.Bunkerde may provide a mulch, greater water storage,better rooting conditions and provide an importantsource of nutrients, particularly compared withstrongly-humified peat (see, for example, Roderfeld,1992). It may al so Ooat when Oooded, thus providing a'platform for vegetation coloni ation. Its role may beto accelerate revegetation, but this is likely to dependupon the water regime. It may be of greater value insite where the water is not kept at a high leve!.The use of bunkerde may be derived from the practiceof 'shoeing' of peat cuttings with the living turf ofvegetation which is removed from the bog urface priorto cutting. This occurs widely in small-scale peatoperations in the UK, and was probably once morewidespread. 1t encourages rapid regeneration andretains the vegetation resource (although this may havebeen an unforeseen beneficial consequence of thepractice at the time). The use of bunkerde or living turfis unlikely to be relevant to the current context in theUK, as there has been no requirement for this type ofmaterial to be stored. However, should such materialbe available, its use should be carefully considcrcd,particularly with respect to its quality and thehydrological conditions that will pertain in the rewettedareas.Plate 9.1. Storage of bunkerde, alongside current peat extraction, for future use in bog restoration. SteinhuderMoor (Lower Saxony, Germany)


Chapter 10Vegetation management and after-care10.1 IntroductionOne of the main objectives of raised-bog managementand restoration schemes is to maintain or restore asufficient area of actively-growing raised bog to enablethe site to become a self-sustaining system, needingonly minimal management inputs. However, someforro of on-going management is ofien necessary forthis to be achieved (which could amount to scores ofyears, depending on the rewetting strategy), in order tomaintain or enhance the species composition and toreverse the adverse effects of damage. Vegetationmanagement should forro part of the restorationstrategy for the bog, and should be planned to coincidewith the phasing of peat extraction operations, andopportunities for rewetting.One of the main problems associated with theabandonment of large, relatively dry, bare surfaces, isthe colonisation by 'weedy' species [4.2]. In situationswhere cut-over areas are abandoned before adequateprovision can be made to elevate water levelssufficiently to provide 'natural' weed control, othertypes of control may be necessary, for example, toprevent the establishment of species which may not beeasily controlled by subsequent elevation of waterlevels. Mowing, grazing and buming or even the use ofsurface rotavation or chemical herbicides may need tobe considered, both within and around revegetatingmires. Consideration will also have to be given to thevegetation management of refugia. Clearly, theapplicability of such management will be site specific,and depend on the overall restoration strategy adopted.The most commonly used methods for the control ofwater levels are discussed in Chapter 8; here commentis made on the practices used widely in themanagement of vegetation on damaged bogs. Certaincommon principies can be identified:• vegetation management is necessary to reduce theinvasion and spread of 'undesirable' species, which arenorrnally checked by high water levels;• scrub invasion and its control is a major problem;• there are few circumstances in which mowing or grazingare likely to be appropriate techniques if attempts arebeing made to restore raised 'bog, except as an interimmeasure;• it may be necessary to consider the use of herbicides tocontrol 'undesirable' species;• adequate provision for control of fire is essential;• ongoing maintenance of bunds and dams may berequired.Clearly, appropriate management techniques willdepend on the restoration objectives for any particularsite [see Chapter 3]. Rowell (1988) deals with thegeneral principies and practical aspects of managementof peatlands. Brooks (1981) also gives practical advice,particularly on aspects such as scrub control andbuilding of dams and sluices. The frequency ofmanagement operations necessary will depend onfactors such as water levels and nutrient status. Sitespecificpractical advice should be sought from thestatutory conservation agencies.10.2 Scrub controlDrying-out of a bog remnant, cuttings or baulkstypically results in an invasion of woody species, mostcommonly birch, but also species such as pine andRhododendron (Chapter 2]. This is generally thought tobe detrimental to the bog vegetation due to shading,both from living leaves and smothering as litter;increasing water loss through evapotranspiration;reduction of water input through interception ofrainfall; nutrient enrichment through leaf fall; provisionof roosting posts for birds and a positive feedbackthrough the production of seeds. In some circumstances,it is possible that a small amount of scrub mayhelp to provide a more humid micro-cIimate whichcould help to promote Sphagnum growth in the earlystages of regeneration, although this positive influencemay cease once the canopy cIoses (TUxen, 1976).Where the peat is fairly thin, it is possible that treesmay root through the peat into the mineral subsoil,thereby increasing the nutrient status of the peat bytaking up nutrients, with subsequent release and recycIingthrough the litter. Roots may also penetratedams and bunds, thus causing leaks. In dry sites, treeroots may exacerbate the effects of dehydration bycreating cracks and fissures in the peat.Even with adequate control of water leveIs on a site,the control of scrub is likely to remain a major


162E TORATION OF DAMAGED PEATLANDSmanagement fe ture in restoration w r [Plate 10.1]until the bog can be returned to a self-sustaining systemin which birch colonisation is naturally kept in check.crub removal should precede rewetting operations.After the initial learance (by hand or machinery), andrewetting, sufficiently increased water levels shouldPlate 10.1 Scrub cutting at Roudsea Moss (Cumbria).Plate 10.2 Birch trees killed by deep flooding;Neustadter Moor (Germany).Plate 10.3 Die-back of birch trees attributed to flooding;Thorne Waste (S. Yorkshire). [Photo: P. Roworth]help to keep the birch in check. Deep flooding willprevent initial establishment, and in some cases, maystunt or even kili quite large birches r oted in the baseof cuttings [Plate 10.2]. Tt has been suggested that thein si/u dying or dead trees may help to reduce damagethrough wave action and facilitate the colonisation bySphagnum [9.2]. Ho ever, birch can establish onfloating rafts, and deep flooding is unli ely to kili thesetrees. It is also not clear whether raising the water tableto below the level ofthe peat surface is sufficient to kilie tablished birch trees, althougl it may help to reducenew colonisation and retard growth [Plate 10.3].Disposal of the cut wo dy material is commonly aproblem, particularIy in areas inaccessible to vehicles.Brashings may be left or bumt in si/u (usually on metalsheeting raised aboye the bog surface to avoid damageto the peat), or removed. Bulk may be reduced bychipping. In ome circum tances, jt may be possible topush the brashing into cuttings or drains to helpreduce any flow of water, and to act as a 'climbingframe' for the Sphagnum (Chapter 9). It may also bepossible to use the brashings in inundated area toreduce wave action and facilitate raft forrnation. Fearshave been expre sed o er the possible nutrientenrichmenteffect from decomposing plant material,and undoubtedly this occurs, although it seems that thephenomenon may only be short-lived, and the pulse ofnutrients may ometimes be beneficia!.Regrowth can be treated with chemical, such as'K.renite' although thi sometimes has limited success(e.g. Ruckley & Doar 1991). Use of chemicals shouldbe carefully controlled, following the appropriateHealth and afety regulations.In ome site it may be con idered important to retain aband of tree a part of a buffer zone around a site, inorder to pr vide a shelter-belt to reduce transport andpollution from an aerosol of sprayed agro-chemicals.This may also help to create a more humid microclimateon small site by redl1cing wind effects. Rowell(1988) recommend that any helter belt should besited off the main pe t body. Planned estab ishment ofscrub at the margins of a site could be phased with theremoval of crub from the centre in o der to maintainsorne continui of habitat for birds and invertebrates,but it should be recognised that marginal scrub can actas a seed source for invasion of 'undesirable' speciessuch as birch onto the bog - removal of trees (both onand off the site) has the advantage of removing theseed sources.It should be noted that concem has been e pressed byarchaeologists over the potential damage caused to thearchaeological and palaeoecological record by variousscrub control methods. Advice should be sought fromEnglish Heritage on the most appropriate methodswhich will cause least damage.


CHAPTER 10: VtGETATlON MANA(;EMENT AND A~,En-cARE16310.3 MowingBog vegetation is sometimes mown to control growthof Cal/una and birch. The benefits of mowing are alsothought to include retarding growth of Molinia;rejuvenation of Cal/una and breaking-up and spread off?phagnum hummocks over the bog surface (Eigner &Schmatzler, 1980). Molinia tussocks may be removedby brush-cutters in sites unsuitable for mowing(Rowell, 1988). It has also been suggested that it maybe possible to accelerate the process of development ofraised-bog vegetation through mowing and removal ofvegetation in sites where nutrient levels are too high(see Joosten & Bakker, 1987). However, it should benoted that although mowing may be valuable inmanaging vegetation of a fairly dry or 'enriched' site,or as a 'holding-operation' on sites where rewettingcannot be achieved soon after abandonment of cut-oversurfaces, it would not be appropriate in an adequatelywet site, as the passage of the machinery is likely tocause more damage than benefits gained. Mowing oftirebreaks and to control vegetation on bunds may alsobe appropriate in certain circumstances.10.4 GrazingFew raised bogs are grazed, other than on the claimedbog margins or cut-over areas, although ít ís not clearto what extent this occurred in the past [see Chapter 1].In Germany, a special breed oE sheep ('Moorschnucke')are used at sorne sites to control the heatherand scrub and maintain conditions suitable for thegolden plover. However, as with mowing, this isprobably only really appropriate on sites which aredrier than required for good growth or regeneration ofSphagna.The main fears conceming grazing of bogs are theproblems of damage by poaching and nutrient enrichmentfrom dung. Sheep may do more harm than good,particularly on fairly wet sites, but could be useful tocontrol scrub invasion or domination by heather wherethese are a problem. If used, the breed of sheep shouldbe carefully selected, as modem breeds tend to be tooheavy and not suited to the poor diet. The animalsshould be carefully shepherded, for example, drivenacross the bog during the day to spread the dung, andtaken off the site at night to reduce dung inputs.Controlled shepherding also means that the moresensitive areas (e.g. breeding birds, rare plants), couldbe avoided. However, shepherding is costly, with ¡¡ttleretum from the poor-quality sheep products. Grazing issometimes used inconservation management forcertain moorland birds, such as Golden Plover, toatneed short, treeless vegetation. However, although itkeeps the vegetation open, grrazing may still notprovi


164RESTORATION OF DAMAGED PEATLANDS(usually grazing and mowing). Such managementregimes are 'traditional' and have shaped the characterof the vegetation. Abandonment of such managementusually means a loss of floristic diversity and 'quality'as the vegetation becomes overgrown, first by coarseherbaceous species and then by invading trees andshrubs. Attempts to recreate such seral vegetation-typesin abandoned peat workings must therefore makeprovision for ongoing management to maintain them.In flooded peat workings, continued growth of plants,and accumulation ofpeat, makes these pits increasinglycomparable with areas of solid peat and is generallyassociated with a waning floristic interest. In this context,the Broads Authority and English Nature haverecognised the need for cyclical excavation of peat insorne East Anglian mires, aimed at periodically rejuvenatingthe hydrosere. Various studies, including experimentalpits, have been established with this in mind.One of the major problems encountered is the excavationand, particularly, disposal ofthe unwanted peat.Floristic and ecological parallels with the Broadlandpeat pits occur in sorne of the extensive peat workingsin The Netherlands, particularly those in North-westOverijsel. In these mires, similar ongoing successionalprocesses have been identified (e.g. Segal, 1966) includingthe acidification and replacement of rich-fencommunities with a Sphagnum-dominated vegetation,which may provide the basis for the re-development ofombrotrophic vegetation. However, as this leads to theloss of prized plant species and communities, it is notuniversally welcomed; and sorne attempts are beingmade to manipulate the peat workings to maintainbase-rich conditions (e.g. Beltman et al., 1995). InBroadland, similar acidification and expansion ofSphagnum has occurred over (and mostly only over)the old turf ponds (Giller & Wheeler, 1988), but as yetits scale is sufficiently small, and its association withrare plants such as Dryopteris cristata (and, in thiscontext, Sphagnum species) is sufficiently great for itnot yet to be perceived as a 'problem'.10.7 After-care of water controlstructuresProvision must be made in the restoration strategy forregularly monitoring the condition and maintaining allwater control structures, although this will probably beat diminishing time intervals as the project progresses.10.7.1 DitchesIn most situations, it will not be necessary to maintainditches, as occlusion by vegetation is to be encouraged.However, situations in which this may need to beconsidered include:• maintenance of outfall ditches adjacent to peat workingsor agricultural land;• maintenance of ditches carrying mineral- or nutrientenrichedwater through the site;• maintenance of open water habitat for invertebrates (e.g.dragontlies) (where this does not contlict with the mainaims of restoration).10.7.2 DamsMaintenance of dams is essential to correct as soon aspossible any damage through factors such as shrinkage,slumping and erosiono Checks should also be made forerosion channels around the dams and for scouring ofthe base of ditches caused by strong overflows. Conversely,during dry weather, checks should be made forevidence of shrinking and cracking of dams and ditchchannels, and remedial action taken where possible toprevent subsequent loss of water due to preferentialflow though these cracks. As rewetting progresses, itmay prove necessary to increase the height of thedams, for example, ifthe adjacent peat swells.10.7.3 BundsIn general, bunds should be kept as wet as possible,and, as for dams, regular checks must be made toidentify and remedy any problems caused byshrinkage, settlement, slumping, erosion, cracking etc.The height of the bunds may need to be increasedperiodically as the peat within swells. Maintenance of'internal' bunds which sub-divide peat fields is lessimportant than for 'external' bunds, particularly oncethe cuttings have started to revegetate.Vegetation growth on the bunds may help to bind thesurface peat together, but tree growth should beprevented, as this may increase problems ofdrying andcracking. Control of vegetation growth will also bebeneficial as bunds are likely to be useful for accesspurposes for personnel and machinery. In certaincircumstances this may be achievable using grazinganimals, but in general, mowing is likely to be the mostappropriate method.


Chapter 11Recording and monitoring11.1 IntroductionThere are several reasons why it is important to recordand monitor procedures and progress in bogrestoration:• alI schemes must be regarded as essentialIy experimental,and therefore recording is important in increasing theknowledge oftechniques etc.• provision of 'base-line' data so that progress can beassessed and changes lo lhe programme made wherenecessary;• provision of 'hard' dala so lhat current and fuluremanagers (and other interested parties) know the startingconditions, exactly whal has been done and can continuelo assess the degree of success, in order to formulateappropriate further management strategies;• provision of information that can be used to assess theapplicability and potential of similar schemes al othersites.Without adequate monitoring it may be difficult toleam both from past mistakes or successes.Monitoring procedures need to be set up with c1earlydefinedobjectives and with identified yardsticks bywhich the direction and extent of change can bemeasured. In setting up a monitoring strategy, thequestions which need to be addressed include thefollowing (Usher, 1991):• Purpose: what is the aim ofthe monitoring?• Method: how can this be achieved?• Analysis: how are the data, which wilI be colIectedperiodically, to be handled?• Interpretation: what might the data mean?• Fulfilment: when will the aim have been achieved?The questions are, of course, inter-related, each largelydepending on the one aboye. To this list, perhaps asixth question should be added - what resources areavailable for monitoring?Monitoring can be approached at two levels:1. provision of hard and detailed evidence of change inresource or conditions (or lack of it);2. provision of casual data to give a broad indication ofchange.Any preliminary surveys of the topography, hydrologyand biological interest ofthe site made prior to the startof restoration measures [Chapter 7] can act as a baseline for monitoring, and should be set up with this inmind. The information gathered will help to determinean appropriate monitoring strategy, for example byidentifying areas, species, communities etc. to bespecifically targeted.Whereas detailed monitoring is considered to bedesirable, in practice it is usually time-consuming andexpensive. It may be difficult to carry out and tointerpret it in a meaningful way. When detailedmonitoring schemes are impractical, it should bepossible to determine simple key factors such aswhether water levels are responding to management,whether Sphagnum is expanding or Molinia and birchdeclining [see Table S4].Where possible, it is recommended that a monitoringprogramme should be set up taking the followingaspects into account:• careful recording of management operations undertaken(including time taken and costs);• base-line data on flora, fauna and water levels (based onfield in\restigations, but with additional detail ifpossible);• selected species or priority areas (e.g. those identified asrefugia), plus species of special conservation statusshould be identified for regular monitoring checks toassess response to management operations;• the hydrological and biological response within arepresentative selection of cut-over areas to be regularlymonitored;• dipwelIs or staff gauges inserted at key points formonitoring water levels;• photographic record, for example:(i) 'fixed point' photographic records of selectedrepresentative areas, including 'before' and 'after'pictures and regularly thereafter;(ii) selected management operations (such as bundand dam construction).• regular checks to be made on any water control structures(dams etc.) and remedial action taken as necessary;• records should be made of events beyond the control ofsite managers (e.g. heavy storms, fires, vandalism etc.)which may influence the future interpretation of 'success'ofthe project;• annual review of results to alIow assessment of anychanges needed to management programme.


166RESTORATION OF DAMAGED PEATLANDS11.2 MethodsVarious methods are available for monítoring change.Selection of an appropriate technique and themonitoríng intensity will depend on the objectives, thefeatures being monitored and the level of detailrequired. It is Iikely that the monítoríng protocol wíllllave to be adapted as rewetting and renaturationprogress. Similarly, the frequency of monítoring willneed to be adjusted according to the response, and alsothe perceived success. Annual appraísal should allowresults to be assessed, and the necessary changes toeíther the restoration programme itself, or themonitoring procedures to be implemented. Suggestionsare made here of what and how to monitor - morespecific discussion, details and advice should be soughtin the literature (e.g. Goldsmith, 1991) and fromspecialists and practitíoners, such as the natureconservation agencies (statutory and non-statutory) andthe Institute ofHydrology.11.2.1 HydrologyHydrological monitoring can be divíded into (í)monitoring of hydrological change and (ii) inspectionofthe integrity ofwater-control structures.Monitoring hydrological changeEquipment used for monitoring hydrological changecan vary from simple, 'home-made' deVices tosophisticated automated installatíons usingcomputerised equipment. The former can providesufficient information for basic monitoring of thesuccess and effects of management (11.3.1], althoughthe latter may be more appropriate for sorne specificapplications. Advice on hydrological monitoring'hardware' and techniques is available from thestatutory conservation agencies or hydrologicalspecialists such as the Institute ofHydrology.A series of dipwells I installed across a site (pieferablyalong a transect), or targetted on specific areas, wouldallow assessment of water table tluctuations. Wherepossible, the tubes should be anchored to preventmovement, either by direct installation into theunderlying mineral ground, or by attachment to anchorposts. The tops of the tubes should be levelled to afixed datum (preferably Ordnance Datum) to enable an.absolute comparison of water levels between dipwells,as well as assessment of trends in water levels relativeto the peat surface. lo tlooded areas, water levels canbe assessed using graduated staff gauges, againpreferably fixed .in~o the mineral subsoíl to mioimisemovement, and levelled to OD. Water discharges canI Usually made from perforated plastic piping.be measured usíng weirs. Fortnightly monitoriog ofwater levels in selected areas allows assessment ofgeneral response and tluctuations. A oew, low-costfield instrument, known as aWALRAG (WAter LevelRAnge Gauge), is currently being developed (Bragg etal., 1994). This records the highest and lowest waterlevels attaíned between site visits and thus providesmore informatíon on water table movements than thesimple dipwells for the same recordiog intervaI.It will be important to make at least sorne visits to thesite during (or immediately following) heavy rain, asthis may help to identify prevíously unrecognised wateroutlets.Peat anchors 2 fixed in to the mineral subsoil wil\ helpto determine the degree of swelling of the peat surfacein response to water level measurements, andultimately the accrual of peat (note, however, that aelear distínctíon must be made between increase in peatvolume and peat mass).If there is no suitable local weather station from whichrecords can be obtained, it may be desirable to set up asimple weather station to give basic climatic recordsfor precipitation, potential evaporation, wind andtemperature if such informatíon is required for detailedhydrological monitoring.Integrity of water-control structuresThe functioning of drains, dams and bunds should beregularly checked, particularly following heavy rainevents, so that any remedial action can be taken torepair damage etc. [10.7].11.2.2 VegetationDiscussion of various methods for monitoringvegetation changes are given by Goldsmith (1991) andadvice may be obtained from the statutory conservationbodies. Appropriate methods inelude permanentquadrats, random quadrats and photographic records(fixed point photography) following selection ofappropriate areas. Records should be made of plantspecies and theír relative abundance. Recording theamount of bare ground (or open water) within theselected areas will allow assessment of the generalrates of recolonisation.It may be possible to devise a scheme whereby theresponse of selected indicator species only aremonitored. Species selected for this will depend on theobjectives of the restoration, and thestage ofcolonisatíon at which recording begins. Tables 11.1and 11.2 give suggestions for sorne species which it2 The movement of a metal plate buried just below the surface ismeasured relative to a datum post fixed in to the mineral substratum.


CHAPTER 11: RECORDING AND MONITORING167would be appropriate to monitor when the objective isrestoration ofraised-bog vegetation.After the initial base-line recording, it is suggested thata monitoring programme is set up to record thevegetation at intervals of3-5 years.Inoculated plant material: Careful records should befiade of any transplants or inoculations, includingsources, species concemed (and amounts), methodsand locations. Monitoring protocol should aim toassess 'success' through recording vegetative expansionof individuals, f10wering / seed setting andseedling establishment. Photographic records are alsorecommended.11.2.3 Invertebrates.Few UK lowland raised-bog habitats offer large,uninterrupted areas of Sphagnum carpet or even justhand-cut areas in various stages of regeneration.Damaged peatlands often contain a complex mosaic ofhabitats which have their own distinct invertebratefaunas. Detailed invertebrate surveys are timeconsumingand expertise-intensive, and consequentlycan be costly. It is therefore desirable to considerwhether the overall invertebrate conservation value ofasite could be estimated by more selective screening,employing indicator species for habitat conditions orindices of species diversity and rarity (see e.g. Ball'1992; Holmes el al., 1993b).Species of special conservation statusLowland raised bogs in the UK support a number ofRed Data Book (RDB) species (see Chapter 1), thoughall of these are assóciated with habitats other than bog­Sphagnum carpets (Shirt, 1987; Bratton, 1990; Falk,1991a, b; Wallace, 1991; Kirby, 1992a, b), and only afew appear to be confined to the set ofhabitats that areassociated with little-damaged lowland raised bogs inTable 11.1 Suggested plant indicator species tor monitoring progress towards a raised-bog objective.SpeciesSphagnum cuspidatum, S. recurvumS. papilfosum, S. magelfanicum, S. capillifo/iumEriophorum angustifoliumErica tetra/ix I Scirpus cespitosus I Calfuna vu/garisOther 'desirable' species include: Vaccinium oxycoccos,Narthecium ossifragum, Drosera spp., Rhynchosporaalba, Andromeda po/ifolia, Sphagnum subnitens, S.pu/chrum, (S. fuscum, S. imbricatum)'Weed' species, including birch I pine I MoliniaNotesOften colonise areas with open I standing waterIndicate satisfactory development of bog speciesMay invade precursor floating Sphagnum carpets, or root directlyinto peat (± inundated).These are only indicators of 'success' if associated with peatformingSphagna (e.g. S. papillosum) as they are also constantspecies of wet heath communities.Reduction in vigour and spread of these species (through rise inwater levels ± vegetation management) would be generallyregarded as indicative of 'success'.Table 11.2 Vegetational indicators of potential problems with respect to revegetation with bog species. Note that Inmany cases it should be possible to mitigate the effects of adverse conditions through management and it shouldnot be assumed that these are necessarily irreversible [see Chapters 9 and 10].Juncus effususSpeciesBirch I pine I Calfuna I Molinia / RhododendronSphagnum recurvum, S. fimbriatum, S. squarrosum'Heathy' Sphagna (e.g. S. tenelfum, S. compactum, S.molfe); plus other bryophytes (e.g. P/eurozium schreberi,Dicranum scoparium, Hypnum cupressiforme).Fen species (e.g. Typha, Phragmites, Salix, A/nus.)'Weed' species, e.g. bracken, Rumex acetosella,Chamerion angustifolium, Graminae (e.g. Ca/amagrostiscanescens).Potential problemMay indicate a eutrophication problem (e.g. from bird excrement orpolluted drain) andl or disturbance.Extensive invasion probably indicates conditions are too dry.May indicate some base or nutrient enrichment (possiblyatmospheric pollution)Although these species may be present in smail quantities inM18a vegetation, their establishment and spread in the absenceof the aquatic or main peat-building Sphagna would suggest thatconditions are not generally sufficiently wet.Indicates minerotrophic water source ± nutrient enriched.Suggests that conditions are too dry and possibly disturbed.


168RESTORATION OF DAMAGED PEATLANDSthis country. However, monitoring the response of suchspecies to management may be desirable.Monitoring response of different invertebratesspecies or groups to various managementoptionsChanges in management regimes (e.g. water tablelevel, scrub removal, peat extraction, creating orenlarging areas of open water) are liable to havesignificant effects on the population levels and evensurvival of many invertebrate species. It is thereforedesirable to monitor effects such that they may beadjusted if necessary. In the case of dragonflies andbutterflies, counting along transect walks has proved auseful monitoring procedure at sorne sites. For othergroups it will be necessary to use one or more of thesurvey methods outlined in Table 7.6. However, it mustbe recognised that management that is appropriate forone species or group may not be so for another.Particular care should therefore be taken if amanagement action is likely to adversely affectpopulations of any RDB or notable species - anypotential conflict between existing interest andmanagement objectives should be identified at an earlystage [Chapters 3 and 7].11.2.4 BirdsA periodic survey of breeding and wintering birdscould be carried out appropriately using methodsdescribed in Chapter 7 [7.5.6]. It will be particularlyimportant to evaluate the relative density of thosespecies characteristic of the various stages of habitattransition from relatively undamaged and extensivebogs to those which are more characteristic ofdamagedbogs [1.11; 2.2; 2.3.6]. Based upon data from the initialsite assessment, changes of numbers of breedingterritories and wintering populations can be assessedand related to changes in habitats.Based on information derived from initial base-linesurveys, it should be possible to monitor populations ofselected target species only, for example, species ofspecial conservation status, together 'with other specieswhich are likely to be particularly responsive to changein habitat, for example a decrease in scrub / woodlandor increase in open water. Appropriate species willclearly be site-specific, but suggestions include teal,snipe, raptors (hobby, hen harrier, merlin), lapwing,skylark, whinchat, stonechat, tree pipit, nightjar,willow warbler, general numbers ofwaders and ducks.11.2.5 Water chemistryIn circumstances where 'undesirable' inputs of base ornutrient enrichment have been identified, it may benecessary to carry out sorne ongoing monitoring ofwater chemistry [7.5.5], to assess the success of effortsthat have been made to change the conditions.11.3 Assessment of 'success'The ultimate test of success is, of course, whether thedesired objectives have been achieved. However, inview of the long time-scales over which restoration islikely to occur, it is important that a series oftargets beidentified so that progress towards the goal can beassessed, and adjustments to management operationsetc. be made where necessary. In general, for themanagement operations considered in this report, themost immediate response is likely to be hydrological,followed by biological changes and ultimatelyregeneration of peat growth. Specific factors which canbe assessed are outlined below.11.3.1 HydrologyMonitoring of water levels and regular checks on thecondition of water control structures should allow theassessment of the success of water managementoperations, by assessing the answers to the followingquestions:• Are water leveIs maintained at the levels required by theobjectives?• Have water leveIs stabilised and fluctuations beenreduced sufficiently?• Are water levels consistently higher in the ditches thanpreviously?• Are the dams or bunds damaged or Ieaking?Note that assessment must be made with due regard tothe actual and prevailing weather conditions.Interpretation of the data collected can be carried outmost easily using graphical techniques, for example byplotting the water levels recorded over time, and inrelation to the peat surface (e.g. Mawby, 1995). Onesimple method for assessing water level fluctuations isto use 'duration lines', i.e. the number of days themeasured water level is between certain limits, over agiven time periodo11.3.2 Swelling and growth ofpeatIncreasing water retention within a formerly partlydehydratedpeat mass can be expected to cause'swelling' of the peat mass, which will result in anincrease in the relative height of the peat surface. Thiscan be measured using peat 'anchors' [11.2.1]. Theremay be a relatively rapid response (for example, at theMeerstalblok, The Netherlands, the surface of parts ofthe remnant is thought to have risen sorne 50 cm in 5


CHAPTER 11: RECORDlNG AND MONITORING169years), and can be distinguished from the potential forlonger term renewal of peat growth and subsequentaccumulation, which is likely to be less than amillimetre per year. Swelling of the peat mass mayresuIt in the necessity for dams or bunds to be raised.11.3.3 VegetationWhether the management measures have been trulysuccessful in returning the site to a self-sustaining,growing raised bog will only be apparent after a longperiod oftime (probably centuries), but it is possible inthe short-term to assess the response by the vegetation,which will indicate whether the hydrological andvegetation management operations have beenappropriate for the given objectives - for example,whether the vegetation is progressing towards bog orwet / dry heath. It is difficuIt to recommend preciseindicator species through which to measure 'success',as most species found in MI 8a are also commonlyfound in other bog or even fen communities (e.g.blanket bog, wet heath or poor fen)3 . It is the particularcombination and relative abundance of differentspecies which makes up each different community,rather than the presence of certain species. However,the establishment of Sphagnum species is one of themajor objectives, particularly the aquatic andhummock-forming species, if a site is to be returned toa self-sustaining raised-bog system. Joosten & Bakker(I987) suggest that 'raised-bog regeneration' can beconsidered successful in the short term when 'durable'communities (i.e. stable over a period of about 10years) have formed, which are able to form the basisfor raised-bog development in the current c1imaticconditions; these include communities dominated by S.papillosum, S. magellanieum and S. eapillifofiul11.Table 11.2 suggests certain plant species which mayhelp to indicate the presence of specific problems onthe site. However, in many cases it should be possibleto mitigate the effects of adverse conditions throughmanagement [see Chapters 9 and 10] and it should notbe assumed that these are necessarily irreversible. Forexample, aIthough Juneus effusus may be consideredan 'undesirable' speéies, and perhaps indicate sornenutrient enrichment, its presence does not necessarilypreclude the invasion of Sphagna and eventualprogression through to raised bog (providing steps aretaken to reduce the nutrient source, and to preventflooding of the Sphagnum with poor-quality water). It3 Constant species of the E. tetra/ix - S. papi/losum raised andblankct mire (MI8a) are: Cal/una vu/garis, E. tetra/ix, E. angustifo/ium,S. papil/osum, E. vaginatum, S. capil/ifo/iul/1, S. tene/llun,Odontoschisma sphagni. Cal/una, E. vaginatul/1 and Scirpuscespitosus are usually associated with (he drier areas (Rodwell,1991).may even have a beneficial role in acting as a 'nurse'species [9.2.5].Inoculated plant materialIn most cases, it will be evident fairly quickly whethertransplants have initially 'taken' as under particularlyunfavourable conditions the plants will just die!Successful establishment can be measured throughvegetative expansion of individuals, or tlowering / seedsetting, followed by establishment of seedlings. ForSphagna inoculated by 'hydro-seeding' methods, thegrowth and establishment of new capitula should bemeasured in relation to the amount and distribution ofthe initial inoculum.Rates of changeVegetation of sorne sort can be expected to start tocolonise abare, abandoned surface within a fewmonths (depending on the seed supply and season).Colonisation and establishment will progress until littleor no bare ground remains, the rates (and species)depending on the prevailing hydrochemical conditions[Chapter 4]. Colonisation of open water is likely to beslower than bare peat, unless inoculated with plantmaterial. For transplanted material, it should be evidentwithin the first two growing seasons whether the plantsare putting on new growth, and in the case of Sphagna,producing new capitula. In minerotrophic or nutrientenrichedconditions, revegetation can be expected toprogress at a faster rate than under purely ombrotrophicconditions (particularly by non-bog species).A floating raft of vegetation is likely to take manyyears to develop, unless positive steps are taken tospeed up the process through provision of artificialconstructs, inoculation with plant material ele. [seeChapter 9]. Evidence from the recolonisation of oldhand peat cuttings suggests that the redevelopment ofM18 -type vegetation may occur within 50-100 yearsgiven appropriate hydrochemical conditions (Smart, elal., 1989; Money, 1994). van Wirdum, den Held &Schmitz (1992) showed colonisation of typical bogspecies (including Andromeda polifofia) within 100years, from a rich-fen starting point.11.3.4 InvertebratesAs for other factors outlined aboye, assessment of'success' in terms of invertebrate species orpopulations will clearly depend on the objectives setfor the restoration programme. However, it is possibleto identify sorne species characteristic of little-damagedraised bogs [Table 11.3] or those of high conservationimportance associated with sites which have sufferedsmall-scale damage (e.g. by hand cutting) whilst


170RESTüRATlüN üF DAMAGED PEATLANDSmaintaining (or regaining) a generally high water table[Table 11.4].Coulson and Butterfield (1985) further note thatlowland raised-bog invertebrate faunas are character­¡sed by the absence ofa number ofspecies ofwhich thefollowing are probably most relevant froll1 the point ofview of assessing their status: Dyschirius globosus,Bradycel/us ruficollis, Olisthopus rotundatus, Trichocel/lIscognatus, Ormosia pseudosimilis, Cicadulaquadrinotata, Agonum juliginosum, Tipula subnodicornis,Moliphilus ater. However, it should be emphasisedthat all these are generally common (at leastlocally) and therefore are all [iable to tum up occasionallyeven on little-damaged lowland raised bogs.An altemative view that ll1ight be taken with specificsites is to base the assessment of success on a definedspecies or group, for example sites might be managedso as to favour numbers and diversity of dragonflies(Odonata). Within a particular group, any change in theproportion of species typicalIy associated with 'wet' or'dry' habitats could be monitored at specific points onthe bog, chosen in relation to the management. Assessmentof success with such arbitrary objectives isrelatively straightforward.Maintenance of a high water table (with associatedSphagnum carpet development) seems vital to ensuresurvival of most if not all notable bog associatedinvertebrates even though ll1any of these [see Table1.6] require an interface situation between Sphagnumand/or bare peat and drier zones. For example, dryingout has been strongly intimated in the decline of therare fly Phaonia jaroschewskii (= crinipes) onHumberhead Levels sites. Loss of open water poolsdue to plant (including Sphagnum) growth, will bedetrimental to dragonflies (Odonata). Regularmonitoring should enable such adverse trends to berecognised in time for remedy (if this does not conflictwith the main restoration aims).Rate of recolonisation is Jikely to be stronglyinfluenced not only by the development of a Sphagnumcarpet and associated flora, but also by the proximity ofrefugia for 'desirable' invertebrate species. Nothing isknown about the potential to seed (inoculate)regenerating areas with appropriate invertebrates in theabsence of nearby refugia. Available data for areas oflowland raised bog that were subjected to traditionalTable 11.3 Invertebrate species associated with little-damaged raised bogs, which may be useful in theassessment of 'success' of restoration initiatives.SpeciesPterostichus diligens, P. nigrita andAgonum ericetiDolichopus atratusMolophilus occulatusJassargus sursumflexusOrderColeopteraDipteraDipteraHemipteraNotesIndividuals sampled in proportion 2:4:3 (Mossakowski, 1970);AbundantAbundantShould be absent or rare on little-damaged bogs because itsfoodplant is MoliniaTable 11.4 Invertebrate species associated with partly-damaged raised bogs, which may be useful in theassessment of 'success' of restoration initiatives.SpeciesLeucorrhinia dubiaLimnephilus elegansAgonum ericetíBembidion humeraleCurimopsis nigritaAcilius canaliculatusSorhoanus xanthoneurusDolichopus atratusMolophilus occultusHercostomus aerosusOchthera mantísCoenonympha tulliaOrderOdonataTrichopteraColeopteraColeopteraColeopteraColeopteraHemipteraDipteraDipteraDipteraDipteraLepidopteraNotesPresent and abundantPresentPresent and abundant relative to Pterostichus diligens and P. nigrita(Mossakowski, 1970)At present only on Humberside levels; occurrence elsewhere wouldbe a significant sign of successAt present only on Humberhead levels; occurrence elsewherewould be a significant sign of successPresent (an RDB 3 species)Present; associated with Molinia; tends to avoid uplands (Kirby1992a).Present (Coulson, 1992)Present (Coulson, 1992; Coulson & Butterfield, 1985)Abundant (Coulson & Butterfield, 1985); generally associated withwet, acid placesPresent; also occurs in rich fens.Present; associated with Molinia and I or Eriophorum; tends toavoid uplands


CIIAPTER 11: RECORDING AND MONITORING171hand peat cutting but subsequently allowed torecolonise from adjacent uncut and other areas suggestthat invertebrate faunas of considerable conservationinterest can reassemble within a period of 20 years(Heaver & Eversham, 1991) though the communitiesthat exist at this time are undoubtedly still transitional.11.3.5 BirdsRe-establishment of a bird community typical of littledamagedand extensive raised-bog habitats may be anultimate objective of the restoration programme, butthis is unlikely to be achievable in the short-term. Mirerestoration is likely to produce substantially changedconditions for birds, and is Iikely to dramaticallychange the existing bird community. For example,during rewetting, if large areas of open water arecreated initially, the site may become attractive to largenumbers of wetland birds. If the ultimate aim is torestore a bird community which is characteristic oflittle-damaged raised bog, it is likely that such specieswould subsequently be displaced in the long term asthe renaturation progresses. Progress towards such agoal could be assessed by comparison with birdassemblages characteristic of relatively undamagedraised-bog habitats and monitoring populations ofspecies likely to be particularly responsive to changesin habitat such as woodland / scrub or open water [see11.2.3].11.4 General commentsIt has been suggested that areas should be monitoredfor at least 18 months before deciding on the optimumsurface configurations (e.g. where to put the bunds forlagoons), particularly where the water table fluct-uations are known to be erratic, although this may notbe practicable in all cases. Similarly, once the lagoonsare constructed, a further period of at least ayearshould elapse for water levels to stabilise beforemaking decisions on any planting operations so thatappropriate areas can be targeted, and any adjustmentscan be made without fear of damage to the vegetation.It is recognised that monitoring of mire sites doespresent considerable problems, particularly in view ofthe sensitivity of sorne of the plant and bird species todisturbance. Once a site has started to rewet, there arealso likely to be considerable practical difficulties (e.g.access) in effectively monitoring the redevelopment ofthe flora and fauna. In some situations it may bepossible to overcome sorne of these problems, forexample, providing chest waders, aluminium ladders oreven an inflatable raft or boat! Clearly, however,adequate attention must be given to Health and Safetyconsiderations at all times.Even where monitoring data are collected, there maybe problems in their analyses. Careful considerationmust be given to developing an appropriate monitoringstrategy with specific objectives, that will providemeaningful data, and provision made in the restorationprogramme for adequate analysis, interpretation andevaluation.An important part of the monitoring of restorationoperations is the provision of information that can beused to assess the applicability and potential for similarschemes at other sites. Thus it is important that thedetails and outcome (whether positive or negative)should be disseminated to others, either throughpublication in conservation and technical journals orthrough the production of regular reports, which can bemade available on request to others with an interest inrestoration.


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Appendix 1Glossary of termsAcrotelmActive porosityAllochthonousAllogenicAnoxicAquiferAutochthonousAutogenicBaulksBlock-cuttingBogBog speciesBog vegetationBog-SphagnumvegetationBorrow pitBulk densityBundBunkerdeThe tenn 'acrotelm' refers to the surface layer ofa peatland that is aboye the limit ofpennanent saturation (e! catotelm). In a little-damaged raised bog, it refers to theuppennost, 'active layer' [see Box lAJ, comprising the living plant cover passingdownwards into recently-dead plant material and thence to fresh peal. It fonns the largelyoxygenated surface layer with high hydraulic conductivity;within which the water tablefluctuates and the main water movement oecurs. Strictly speaking, cut-over bogs also havean acrotelm, but this lacks sorne ofthe distinctive features ofthe acrotelm layer ofa Iittledamagedbog surface, such as its apparent eapacity for hydrological self-regulation. In thisreport, unless qualified, the tenn 'acrotelm' is restricted to refer to the 'fully-functional'surface layers such as characterise little-damaged bogs.Tenacity with which water movement occurs within the peat matrix (comprises the amountofloosely-bound inter-particle (interstitial) water).Ofimported origin (e! autochthonous). (e.g. allochthonous deposits are those fonned frommaterial brought in from outside, such as inwashed silts).Caused by external factors (e! autogenic).Lacking oxygen.Water-bearing substratum, at full moisture capacity.Fonned in situ (e! allochthonous).'Self-made'. [caused by reactions oforganisms themselves, J (e! allogenic).Upstanding blocks ofpeat between peat cuttings or fields.Method ofpeat extraetion in which the peat is cut in blocks from a vertical face [2.3.1]General tenn for ombrotrophie mires (but sometimes used colloquially for other types ofwetland).Any speeies typicaIly found on bogs. [Many ofthese also oceur in fens or other habitats.JRefers to any species / vegetation-type typical of, or elosely resembling, that found on Iittledamagedraised bogs. .This eategory accommodates vegetation in which 'bog-Sphagnum' species are prominent,often dominant, components. It ineludes NVC mire expanse community Ml8 and the bogpoolcommunities M2 and M3. These latter may occur as a mosaic with M 18 vegetation,fonning the so-called 'regeneration complex'. This vegetation is particularly characteristicofthe surface of Iittle-damaged raised bogs.A pit from which 'construction' material (e.g. peat) is removed.The amount ofsolid material per unit volume.Used here to mean an embankment used to pond baek water, to a greater extent than a dam,which in this context has been confined to use for structures built to block linear watercourses. Elsewhere, sueh structures have been variously referred to as dams, embankmentsand dykes.There is no standard definition of 'bunkerde' - it is a Gennan tenn for the surface layer ofvegetation and peat which is removed prior to peat cutting, at each cutting phase, andsubsequently returned to the peat cuttings / fields. [see 9.6J


182RESTORATION OF DAMAGED PEATLANDSCatotelmClimax ecosystemCut-over surfacesI1epressionDiasporeDiplotelmicDraw-downEdge effectsEricoid / ericaceousEurytopicEutrophicEvapotranspirationFeedertankFenFlatsFloodingFlux densityForbGradient feedingGrowth lagoonGuanotrophicationHaplotelmicHerbHumification (vonPost scale)Hydraulicconductivity[K; K sat ]Hydraulic gradientHydraulic headHydrosere(hydroseral)HydrostaticpressureThe lower 'inert' layer ofthe peat ofan undamaged raised bog [see Figure 1.1]. Thecatotelm underlies the acrotelm, and is perrnanently saturated, mainly~and of lowhydraulic conductivity.The mature or stabilised stage in a successional series ofcommunitiesGeneral terrn used to refer to the peat surface remaining after extraction (by any extractionmethod).Effectively refers to areas that have been cut for peat and which forrn hollows or flatsurfaces in relafion to adjoining bloeks. They tend to have an overall eoneave or waterholding profile. [el massif]. [2.1]Any spore, seed fruit, or other portion ofa plant when being dispersed and able to produce anew plant.'Two-layered'. In raised bogs, this refers to the typical occurrence ofan upperrnost 'activelayer' (the acrotelm) and lower 'inert layer' (the catotelm) [1.7].Refers to the faH in water level caused by a steepened hydraulic gradient, for example as aresult ofwater movement to drains or ditches.Effects associated with the transition between habitat types; for example, the tendency tohave greater variety and density oforganisms in the boundary zone between communities orhabitats.Pertaining to plant species ofthe Heath family (Ericaceae).Used to refer to invertebrates having a wide range ofgeographical distribution (e!stenotopic).Nutrient-enriched (not necessarily base-rich).Loss ofwater from the soil by evaporation from the surface and by transpiration from theplants growing thereon; the volume ofwater lost in this way.Lagoon constructed to help soak adjoining baulks of peat.General terrn for minerotrophic mires.The base ofthe peat cuttings, in a block-cut system.Inundation ofthe peat surface, with water levels usually at least > + 10 cm.Flow per unit area per unit time.A non-graminoid herb [an herbaceous plant, other than a grass or grass-like plant].The gravity flow ofwater through a system of lagoons constructed across a slope.Lagoon constructed primarily for direct plant colonisation.Nutrient enrichment owing to bird droppings.A diplotelmic mire from which the upper surface layer (acrotelm) has been removed orotherwise destroyed.A vascular plant with a green, non-woody stem.Degree ofdecomposition (of peat) [production ofhumus from the decay oforganic matteras a result ofmicrobial action] [see Table 1.3].The rate at which water moves through a material. K sat denotes saturated hydraulicconductivity - i.e. the rate at which water moves through a saturated material.The change in hydraulic head or water surface elevation over a given distance.The difference in pressure-head between two hydraulically-connected points.Autogenic terrestrialisation of open water.The pressure created by the weight ofwater acting upon itself.


ApPENDlX 1: GLOSSARY 183LaggLevelling (levelled)MacrofossilsMassifMeteoric waterMillingMineralisationMinerotrophicMinerotrophic mireMireMire macrotopeMire mesotopeMire microtopeMonophagousNiedersachsenOligophagousOligotrophicOmbrotrophicOmbrotrophic bogPalaeoecologyPaludification(paludosere)Para-bogvegetationSwedish term for the outer margin ofa raised bog, typically with a water course and / or fen(usually poor fen or fen woodland), into which water from the bog drains. [Few 'natural'examples remain in the UK as most sites have suffered at Jeast sorne degree ofmarginaldamage].(a) Measurement ofthe surface topography using surveying equipment.(b) Configuration ofthe peat surface