Runoff in Afforestations and in Established Forests in ... - ForeStClim

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Runoff in Afforestations and in Established Forests in ... - ForeStClim

ForeStClimTransnational Forestry Management Strategies in Response toRegional Climate Change Impactswww. forestclim.euRunoff in Afforestations and inEstablished Forests in SW-Germany:Process Identification by Sprinkler-Irrigation ExperimentsGebhard Schüler 1 ; Marco Hümann 2 ; Christoph Müller 2 ; Raimund Schneider 2 ; Margret Johst 21Research Institute for Forest Ecology and Forestry Rheinland-Pfalz2University Trier2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


The Sciences of the causes of floodsadmits uncertainty and imprecision inthe prediction of land use impacts onthe flood regime.The interaction between forests andsoils remains a particularly ‘grey‘ areain our knowledge.Ian Calder, 20052 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Within the European INTERREG-projects - ForeStClim andWaReLa - water retention functions are being investigated thatdepend on landscape features and land-use. The results of ourinvestigations lead to digital maps identifying sensitive forestsites to adapt forestry measures to a changing climate in view offlood mitigation.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Aim of the investigations: “digital map with the runoff generationafter storm rainfall in forest catchments”catchment areaphysical soil conditionshydrological behaviourgeomorphology2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Project Area= INTERREG NWE2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


I. Investigation sites in the headwater catchment of the“Frankelbach”1. 1-year old afforestation (with Alder,Linden, Maple and Oak on formerpasturage)2. 30-years old afforestation (with oak andhornbeam on former agricultural land)3. established deciduous forest with oak,beech and hornbeam4. 40-years old Douglas fir afforestation(on former agricultural land)5. established coniferous forest stand2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Site conditions in the „Frankelbach“headwater catchmentThe headwater catchment area of theFrankelbach is about 8 km 2 large.The height above sea level is 210m to 430m.Precipitation: 700 - 800 mm/year with acumulation of storm rainfalls duringsummertime in the last decade.Average temperature: 9° CelsiusAverage temperature during vegetationperiod: 14° CelsiusGeology: Permian era (296 – 258 Mio years);New Red, so-called “Rotliegendes”Sediments were deposited during semiarid andsubtropical conditions and later bulged byvolcanismSoils: Brown earth / colluvia from sand-loam,silt-loam, partly relocated, (in the valleys loamyfloodplains)2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


I. Investigation sites in the headwater catchment of the“Holzbach”1. old Beech stand on the upper slope2. old Beech stand on the middle slope3. old Spruce stand on the upper slope4. old Spruce stand on the middle slope2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Site conditions in the „Holzbach“headwater catchmentThe headwater catchment area of the Holzbachis about 4.2 km 2 large.The height above sea level is 400m to 650m.Precipitation: 950 - 1200 mm/yearAverage temperature: 6° CelsiusAverage temperature during vegetationperiod: 10° CelsiusGeology: Paleozoic era with series fromDevonian (290 Mio years);Soils: Podsols / brown earths / gleysols fromquartzite-loam, gleyic quartzite-loams,periglacial loams above Quartzite-loams,2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Sprinkler-Irrigation MethodSprinkler-irrigation experiments havefound a widespread use for explanationof runoff processes and to differentiatethe runoff behavior of different sites.Slope scale simulations were carriedout on moderately sloped test areas of5 x 10 m (effective 3 x 10 m). Per day anamount of 40 mm rainfall was appliedduring a period of 3 days in 4 intervalsof 15 min duration, resulting in rainfallintensities of approx. 10 mm 15 min -1 .Surface and subsurface water flow werecollected and measured for the middle3 x 10 m to exclude lateral losses ofwater.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Discharge of different forest types in the Frankelbach catchmentdischarge [% irrigation]403530251. Tag[%]202. Tag153. Tag1050reafforestation30 years oldreafforestationestablisheddeciduous f.40 years oldDouglas firestablishedconiferiuous f.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Runoff types in the Frankelbach catchment100%90%80%70%60%50%40%30%20%10%0%HOF/SOFSSFDSSFreafforestation30 years oldreafforestationestablisheddeciduous f.40 years oldDouglas firestablishedconiferiuous f.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Discharge of different forest types in the Holzbach catchmentdischarge [% irrigation]2520[%]15101. Tag2. Tag3. Tag50beechupper slopebeechmiddle slopespruceupper slopesprucemiddle slope2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Runoff types in the Holzbach catchment100%90%80%70%60%50%40%30%20%HOF/SOFSSFDSSF10%0%beechupper slopebeechmiddle slopespruceupper slopesprucemiddle slope2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Statements1. From theoretical considerations it would be expected that theinterception of the tree crowns and the transpiration of trees willregulate flood events;But the interception (with a moistening capacity of 2 – 6 mm and asaturation capacity of up to 10 mm) is nearly of no relevance, comparedwith the magnitude of flood producing storm rainfalls (> 40 mm/event)2. The transpiration of the tree stands (4-10 mm/day) increases soilmoisture deficits, and by this, increases the absorption capacity of thesoil;• the benefit of forests in mitigating runoff and reducing flood peaks ismost pronounced for small, frequent flood events.But the transpiration of a closed layer of grass vegetation (up to 8 mm/day)is comparable to that of forest stands.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Conclusions (1)1. The recent physical soil conditions are the crucial factor for mitigatingfast runoff and reducing flow peaks.But, the history of land-use often teaches us that forests were left on soilswith bad soil conditions, e.g. shallow or hydromorphic soils with less fieldcapacity, whereas the better soils were allocated by agricultural land-use.• thus, the less benefiting soil conditions under forests may havedetrimental effects on the runoff behaviour, at least as SSF / DSSF.2. Nonetheless the soils under established forests are not secondarilycompacted. Thus, they tend to be relatively porous with high infiltrationand water conductivity rates and consequently reduced incidence ofsurface runoff and low rates of subsurface runoff.But, this is not necessarily the case for afforestations:• whereas the soils under established forests may take centuries toevolve and to develop an increasing water storing pore-system, the soilsunder afforestations still have the soil physical conditions of the formergrassland or agricultural soils.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Conclusions (2)3. Adverse effects on runoff in forsts are often related to managementacitivities. They may result e.g. from• the forest road network2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Conclusions (2)3. Adverse effects on runoff in forsts are often related to managementacitivities. They may result e.g. from• the forest road network• bad logging techniques which compact the soil and increase surfaceflow2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Conclusions (2)3. Adverse effects on runoff in forsts are often related to managementacitivities. They may result e.g. from• the forest road network• bad logging techniques which compact the soil and increase surfaceflow• pre-planting drainageactivities have a greatimpact on the runofffrom forest catchmentssince they increase thedensity of water channels.This can increase floodflows and decrease thetime to peak and thuscause local floodingproblems.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


Getting better understanding of theinteractions between forest, soil andwater as well as of impacts ofdifferent land-useson floodsremains an important scientific task.2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA


www.forestclim.euThank you for your attention2 nd International Conference on Forests and Water in a Changing EnvironmentSeptember 14 – 16, 2009 Raleigh NC, USA

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