Lecture6:EffectofGlobalChangeonTerrestrialCarbonCycle1.Globalclimatechange(temperature,precipitation,CO2)2.Interactionofclimatechange,terrestrialecosystemsandcarboncycle3.Effectsofclimatechange4.EffectsofincreasingatmosphericCO25.Effectsoffiredisturbance6.EffectsofchangesinlanduseandlandmanagementIPCCThirdAssessmentReport(TAR)WMO,(2001)“Globalwarmingcontinues”(Hansenetal.,2002;Science,295,275)ClimateChangeDisturbancesEcosystemStructureEcosystemFunctionCarbonandEcosystemSustainabilityEcosystemServicetoHumansSpeciesCompositionVegetationTypeCyclingofC,N,P,SandwaterInterrelationsofClimateChange&TerrestrialEcosystems

3.EffectsofClimateChange(IPCC2001)

GlobalwarmingmayincreaseNPPintemperateandarticecosystems,but,itmaydecreaseNPPinwater-stressedecosystemsasitincreaseswaterlossSoilandrootsrespirationhavegenerallybeenshowntoincreasewithwarmingintheshorttermChangesinrainfallpatternaffectplantwateravailabilityandlengthofgrowingseason,particularlyinaridandsemi-aridregionsChangingclimatecanalsoaffectthedistributionofplantsandtheincidenceofdisturbancesuchasfire,wind,andinsectattacks,leadingtochangesinNBPHighlatitudeecosystems(tundraandtaiga)containabout25%ofglobalsoilcarbonpoolandaresensitivetochangesintemperatureandwatertabledepthLargeareasofthetropicsarearidandsemi-arid,andplantproductionislimitedbywateravailability(e.g.,hot,dryconditionsoftypicalElNiňoyears)4.EffectsofIncreasingAtmosphericCO2

IncreasingCO2concentrationinatmospherehastwoeffectsonthecarbon-fixingenzyme(Rubisco)reactions:increasingtherateofcarboxylationanddecreasingtherateofoxygenationIncreasedCO2concentrationallowsthepartialclosureofstomata(adecreaseinstomatalconductance),restrictingwaterlossduringtranspirationthatresultinanincreaseinplant’swateruseefficiencyTheresponsesofC3andC4plantstoincreasingtheCO2concentrationinatmospherearedifferent:

-C3plantsshowanincreasedrateofphotosynthesis -C4plantsshownodirectphotosyntheticresponseorlessresponsethanC3plants

ThedirecteffectsofCO2fertilization(underadoublingCO2):-C3cropsshowanaverageincreaseinNPPofaround33%-Grasslandandcropsstudiescombinedshowanaveragebiomassincreaseof14%-Fieldstudiesonyoungtreeshaveshownastimulationofphotosynthesisofabout60%Reference:Saxeetal.(1998).TreeandforestfunctioninginanenrichedCO2atmosphere.NewPhytologist,139:395-436.5.EffectsofFireDisturbanceFireaffectscarboncycleinterrestrialecosystemsinsixways:Firedirectlyreleasecarbonintotheatmospherethroughthecombustionofbiomass(2)Fireconvertsplantmaterialintocharcoal,whichisaninertformofcarbonanddoesnotbreakdownviadecomposition.(3)Theeffectsoffiresignificantlyalterthethermalregimesoftheorganicandmineralsoillayers,which,inturn,alterstheratesofdecompositionwithintheselayers

(4)Throughthereductionofplantbiomasstoash,themeltingofthepermafrostlayer,andincreaseddecomposition,fireincreasetheamountofsoilnutrientavailableforplantgrowth(resultinginanincreaseofNPP)(5)Thedirectandindirecteffectsofburningstronglyinfluencethepatternssecondarysuccessiononfire-disturbedlandscape,which,inturn,controlthepatternsoflivebiomass/carbonstorage.Thefrequencyoffireinagivenregionwilldirectlyinfluencethestandagedistributionofforests,which,inturn,affectsthetotalamountofcarbonstorageinthoseforests6.EffectsofChangesinLandUseandLandManagementReadingassignment:IPCC2001(#–Pages193-194)(http://www.grida.no/climate/ipcc_tar/wgl/095.htm)Reference:Kasischkeetal.(1995).Fire,globalwarming,andthecarbonbalanceofborealforests.EcologicalApplication,5:437-451.ThreeMainApproachestoInvestigatingEffectofClimateChangeonEcosystemsLong-termobservationExperimentalmanipulationModelsimulation(J.M.Melillo,1999,Science,283:183)ChanghuiPengModelingtheEffectsofClimateChangeandFireDisturbanceonProductivityandCarbonDynamicsinCanadianBorealForestsOneCaseStudyinCentralCanadaStudyareaTheBorealForestsTransectCaseStudy(BFTCS)MethodsCENTURY4.0(Partonetal.1987;Metherelletal.1993)DataClimateSite-specifictreesSoilResultsPengetal.1998;PengandApps,1998,GlobalBiogeochem.CyclesPengandApps,(1999),Ecol.Modell.Priceetal.(1999),JofBiogeographyVEGETATIONDISTRIBUTION(BFTCS)WhatistheCENTURY?CENTURY,asdevelopedbyPartonetal.(1987,1993),isaprocess-basedecosystemmodelofplant-soil,whichsimulatesthelong-termbiogeochemicalcyclesofC,N,P,andSforvariousecosystems,includinggrassland,agriculturalland,savannasandforests.Website:/projects/century/nrel.htmCENTURY4.0Submodelsforestproductionsoilorganicmatter/decompositionwaterbudgetgrassland/cropmanagementandeventsschedulingfunctionsTimestep:monthlyCarbonpools(boxes)andfluxes(arrows)inCENTURY4.0ATMOSPHERELeafFineBranchesLargeWoodCoarseRootFineRootVEGETATIONSurfaceLitterMetab.Struc.DeadLargeWoodDeadFineBranchesDeadCoarseRootSurfaceMicrobeActiveSOMSlowSOMPassiveSOMLITTERSOILNPPASSIMILATIONLeachedCPlantRespirationMicrobialRespirationSoilRespirationCO2CO2CO2CO2CO2RootLitterMetab.Struc.(Pengetal.1998)CENTURY4.0InputVariablesmonthlymean,max,andminairtemperaturemonthlytotalprecipitationsoiltexture:clay(%),silt(%),sand(%),andbulkdensityatmosphericandsoilnitrogeninputsforesttypesSimulationStrategy(1)Modelvalidationsimulatedabove-groundbiomassvs.observeddatasimulatedsoilcarbonvs.observeddata(0-20cm)(2)Effectsofclimatechange(CC)alterationtomonthlymeantemperatureandprecipitationbasedon2xCO2scenariowiththeGISSGCMEffectsofCO2fertilization(CO2)20%decreaseintotalPETanda20%increaseinnutrientuseefficiency(NUE)associatedwith2xCO2EffectsofCCandCO2combined(3)Effectsoffiredisturbances-changesinfiredisturbanceintervalValidationofCENTURY4.0(Pengetal.1998)ValidationofCENTURY4.0024681012Soilcarbon(0-20cm)(kg/m^2)TH1TH2TH3FF2PA2FF1FF3FF4PA130-50<Sand(%)>60-80ObservationSimulationNORTHSOUTH(Siltanenetal.1997)(Correlation:R2=0.92)RelativeEffectsonNPPAsprojectedbyCENTURY4.0forGISS2xCO2scenario-100102030405060%changeTH1TH2TH3FF1FF2FF3FF4PA1PA2CCCO2CC+CO2Netprimaryproductivity(gm-2yr-1)NORTHSOUTH(PengandApps1998)RelativeEffectsonSoilDecomposition0102030405060%changeTH1TH2TH3FF1FF2FF3FF4PA1PA2CCCO2CC+CO2Decomposition(gm-2yr-1)AsprojectedbyCENTURY4.0forGISS2xCO2scenarioNORTHSOUTH(PengandApps,1998)(a)(b)Relationships(a)and(b)areSimulatedbyCENTURY4.0Under“CC+CO2”ClimateChangeR2=0.89R2=0.98(PengandApps1999)RelativeEffectsonBiomassCarbonStorage01020304050%changeTH1TH2TH3FF1FF2FF3FF4PA1PA2CCCO2CC+CO2TotalBiomass(gm-2)AsprojectedbyCENTURY4.0forGISS2xCO2scenarioNORTHSOUTH(PengandApps1998)RelativeEffectsonCarbonStorage-20-15-10-5051015%changeTH1TH2TH3FF1FF2FF3FF4PA1PA2CCCO2CC+CO2Soilorganicmatter(gm-2)AsprojectedbyCENTURY4.0forGISS2xCO2ScenarioNORTHSOUTH(PengandApps1998)(PengandApps1999)EffectsofFireIntervalsonNPPBiomassDynamicsUnderFireDisturbance(Jiang,Peng,andApps1999)SoilCarbonDynamicsUnderFireDisturbance(Jiang,PengandApps1999)SummaryClimatechangewouldresu