chapter 7 quantifying greenhouse gas sources and … · chapter 7: quantifying greenhouse gas...

Author:StephenM.Ogle,ColoradoStateUniversity

Contents:

7 QuantifyingGreenhouseGasSourcesandSinksfromLand‐UseChange.............................7‐37.1 Overview...........................................................................................................................................................7‐37.2 DefinitionsofLandUse...............................................................................................................................7‐47.3 Caveats...............................................................................................................................................................7‐67.4 EstimatingGHGFluxfromLand‐UseChange.....................................................................................7‐6

7.4.1 CarbonPoolsinLiveBiomass,DeadBiomass,andSoilOrganicCarbon..7‐87.4.2 ChangesinSoilCarbon..................................................................................................7‐87.4.3 ChangesinotherGHGemissions.............................................................................7‐13

Chapter7References.............................................................................................................................................7‐14

SuggestedChapterCitation:Ogle,S.M.,2014.Chapter7:QuantifyingGreenhouseGasSourcesandSinksfromLandUseChange.InQuantifyingGreenhouseGasFluxesinAgricultureandForestry:MethodsforEntity‐ScaleInventory.TechnicalBulletinNumber1939.OfficeoftheChiefEconomist,U.S.DepartmentofAgriculture,Washington,DC.606pages.July2014.Eve,M.,D.Pape,M.Flugge,R.Steele,D.Man,M.Riley‐Gilbert,andS.Biggar,Eds.

USDAisanequalopportunityproviderandemployer.

Chapter 7

Quantifying Greenhouse Gas Sources and Sinks from Land-Use Change

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Acronyms,ChemicalFormulae,andUnits

C CarbonCH4 MethaneCO2 CarbondioxideCO2‐eq CarbondioxideequivalentsDOM DeadorganicmatterEPA EnvironmentalProtectionAgencyFIA ForestInventoryandAnalysisGHG Greenhousegasha HectareIPCC IntergovernmentalPanelonClimateChangeN2O NitrousOxideNRI NaturalResourcesInventoryPRISM Parameter‐ElevationRegressionsonIndependentSlopesModelSOC SoilorganiccarbonSSURGO SoilSurveyGeographicDatabaseUSDA U.S.DepartmentofAgriculture

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7 QuantifyingGreenhouseGasSourcesandSinksfromLand‐UseChange

Thischapterprovidesguidanceonestimatingthenetgreenhousegas(GHG)fluxresultingfromchangesbetweenlandusetypes—i.e.,conversionsintoandoutofcropland,wetland,grazingland,orforestland—attheentityscale.Insomecases,itissufficienttoestimatethenetGHGfluxassociatedwiththenewlanduse.Ifchangingfromonelandusetoanotherhasasignificanteffectoncarbonstocks(e.g.,changesinforestcarbonstocks,changesinsoilcarbon),itwillbenecessarytorepresentthatinfluenceassociatedwithaspecificland‐usechange(e.g.,wetlandtocropland,grazinglandtocropland,forestlandtocropland).Table7‐1providesasummaryanddescriptionofthesourcescoveredinthischapter.

Table7‐1:OverviewofLand‐UseChangeSourcesandAssociatedGHGs

SourceMethodforGHGEstimation Description

CO2 N2O CH4Annualchangeincarbonstocksindeadwoodandlitterduetolandconversion

Liveanddeadbiomasscarbonstocksandsoilorganiccarbonconstitutesasignificantcarbonsinkinmanyforestandagriculturallands.Followingland‐useconversion,theestimationofdeadbiomasscarbonstockchangesduringtransitionperiodsrequiresthattheareasubjecttoland‐usechangeontheentity’soperationbetrackedforthedurationofthe20‐yeartransitionperiod.

Changeinsoilorganiccarbonstocksformineralsoils

Soilorganiccarbonstocksareinfluencedbyland‐usechange(Aaldeetal.,2006)duetochangesinproductivitythatinfluencecarboninputs,andtochangesinsoilmanagementthatinfluencecarbonoutputs(DavidsonandAckerman,1993;Ogleetal.,2005;PostandKwon,2000).Themostsignificantchangesinsoilorganiccarbonoccurwithland‐usechange,particularlyconversionstocroplands,duetochangesinthedisturbanceregimesandassociatedeffectsonsoilaggregatedynamics(Sixetal.,2000).

7.1 Overview

Inmanycases,themethodsproposedtoestimatecontributionstotheGHGfluxresultingfromland‐usechangearethesameasthoseusedtoestimatecarbonstockchangesintheindividualchaptersonCroplandandGrazingLand,Forestry,andWetlands;although,inspecificcasesguidanceisalsoprovidedonreconcilingcarbon‐stockestimatesbetweendiscretedatasetsandestimationmethods(e.g.,reconcilingforestsoilcarbonestimatesandcroplandsoilcarbonestimatesforland‐usechangefromforestlandtocropland).Table7‐2presentsthemethodologiesforeachsourceandindicatestheirsection.

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Table7‐2:OverviewofCroplandandGrazingLandSystemsSources,MethodandSection

Section Source ProposedMethod

7.4.1 Annualchangeincarbonstocksindeadwoodandlitterduetolandconversion

Thechangeincarbonstocksindeadwoodandlitterduetolandconversionisestimatedasthedifferenceincarbonstocksintheoldandnewland‐usecategoriesappliedintheyearoftheconversion(carbonlosses),ordistributeduniformlyoverthelengthofthetransitionperiod(carbongains)(Aaldeetal.,2006).

7.4.2 Changeinsoilorganiccarbonstocksformineralsoils

ThemethodologiestoestimatesoilcarbonstockchangesfororganicsoilsandmineralsoilsareadoptedfromIPCC(Aaldeetal.,2006).

Theremainderofthischapterisorganizedasfollows:

Definitions

Caveats

StepsforestimatingGHGfluxfromland‐usechange

Overlaps,issues,andassemblyinstructionsforGHGfluxestimationfromland‐usechange

7.2 DefinitionsofLandUse

Aland‐usecategorizationsystemthatisconsistentandcomplete(bothtemporallyandspatially)isneededtoassesslanduseandland‐usechangestatuswithinanentity’sboundaries.Eachentityshouldensurethatitcharacterizesallofthelandwithinitsboundaryaccordingtothefollowingland‐usetypes:cropland,grazingland,forestland,wetland,settlements(e.g.,residential,farm,andcommercialbuildings),andotherland(e.g.,baresoil,rock).Theland‐usedefinitionsprovidedbelowareexpectedtobeadoptedbyentitiesusingthisreport.Itiscriticalthatindividualparcelareasareestimatedaccuratelyandwhencombinedadduptothetotallandareareportedbytheentitybeforeandaftertheland‐usechange.

CurrentdefinitionsforlandusethatareconsistentwithotherpolicyprogramsrelatedtoGHGestimation(e.g.,IntergovernmentalPanelonClimateChange(IPCC),NaturalResourcesInventory(NRI))areprovidedbelow.ThesedefinitionsarespecifictotheUnitedStatesandarebasedpredominantlyoncriteriausedintheland‐usesurveysfortheUnitedStates.Specifically,thedefinitionofforestlandisbasedontheForestInventoryandAnalysis(FIA)definitionofforest,1whiledefinitionsofcropland,grazingland,andsettlementsarebasedontheNRI.2ThedefinitionsforotherlandandwetlandsarebasedontheIPCC(2006)definitionsforthesecategories.

ForestLand:Aland‐usecategorythatincludesareasatleast36.6meterswideand0.4hectaresinsizewithatleast10percentcover(orequivalentstocking)bylivetreesofanysize,includinglandthatformerlyhadsuchtreecoverandthatwillbenaturallyorartificiallyregenerated.Forestlandincludestransitionzones,suchasareasbetweenforestandnon‐forestlandsthathaveatleast10percentcover(orequivalentstocking)withlivetreesandforestareasadjacenttourbanandbuilt‐uplands.Roadside,streamside,andshelterbeltstripsoftreesmusthaveacrownwidthofatleast36.6metersandcontinuouslengthofatleast110.6meterstoqualifyasforestland.Unimprovedroadsandtrails,

1SeeFIAGlossaryhttp://socrates.lv‐hrc.nevada.edu/fia/ab/issues/pending/glossary/Glossary_5_30_06.pdf2SeeNationalResourceInventoryGlossaryofSelectedTerms(p.9)http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1041379.pdf

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streams,andclearingsinforestareasareclassifiedasforestsiftheyarelessthan36.6meterswideor0.4hectaresinsize;otherwisetheyareexcludedfromforestlandandclassifiedassettlements.Tree‐coveredareasinagriculturalproductionsettings,suchasfruitorchards,ortree‐coveredareasinurbansettings,suchascityparks,arenotconsideredforestland(Smithetal.,2009).

Cropland:Aland‐usecategorythatincludesareasusedfortheproductionofadaptedcropsforharvest;thiscategoryincludesbothcultivatedandnon‐cultivatedlands.Cultivatedcropsincluderowcropsorclosegrowncropsandalsohayorpastureinrotationwithcultivatedcrops.Non‐cultivatedcroplandincludescontinuoushay,perennialcrops(e.g.,orchards),andhorticulturalcropland.Croplandalsoincludeslandwithalleycroppingandwindbreaks,aswellaslandsintemporaryfalloworenrolledinconservationreserveprograms(i.e.,set‐asides3).Roadsthroughcropland,includinginterstatehighways,statehighways,otherpavedroads,gravelroads,dirtroads,andrailroadsareexcludedfromcroplandareaestimatesandare,instead,classifiedassettlements.

GrazingLand:4Aland‐usecategoryunderwhichtheplantcoveriscomposedprincipallyofgrasses,grass‐likeplants,forbs,orshrubssuitableforgrazingandbrowsing.Thiscategoryincludesbothpasturesandnativerangelandsandareaswherepracticessuchasclearing,burning,chaining,and/orchemicalsareappliedtomaintainthegrassvegetation.Savannas,somewetlandsanddeserts,andtundraareconsideredgrazingland.Woodyplantcommunitiesoflowforbsandshrubs,suchasmesquite,chaparral,mountainshrub,andpinyon‐juniper,arealsoclassifiedasgrazinglandiftheydonotmeetthecriteriaforforestland.Grazinglandincludeslandmanagedwithagroforestrypracticessuchassilvopastureandwindbreaks,assumingthestandorwoodlotdoesnotmeetthecriteriaforforestland.Roadsthroughgrazingland,includinginterstatehighways,statehighways,otherpavedroads,gravelroads,dirtroads,andrailroadsareexcludedfromgrazinglandareaestimatesandare,instead,classifiedasSettlements.

Wetlands:5Aland‐usecategorythatincludeslandwithhydricsoils,nativeoradaptedhydrophyticvegetation,andahydrologicregimewerethesoilissaturatedduringthegrowingseasoninmostyears.Wetlandvegetationtypesmayincludemarshes,grasslands,orforests.Wetlandsmayhavewaterlevelsthatareartificiallychanged,orwherethevegetationcompositionorproductivityismanipulated.Theselandsincludeundrainedforestedwetlands,grazedwoodlandsandgrasslands,impoundmentsmanagedforwildlife,andlandsthatarebeingrestoredfollowingconversiontoanon‐wetlandcondition(typicallyasaresultofagriculturaldrainage).Provisionsforengineeredwetlandsincluding

3Aset‐asideiscroplandthathasbeentakenoutofactivecroppingandconvertedtosometypeofvegetativecover,including,forexample,nativegrassesortrees.4Notethatthisdefinitionisthe“grassland”definitionfromtheNIRwith“grassland”replacedwith“grazingland.”5Thejurisdictionaldefinitionofawetlandis“thoseareasthatareinundatedorsaturatedbysurfaceorgroundwateratafrequencyanddurationsufficienttosupport,andthatundernormalcircumstancesdosupport,aprevalenceofvegetationtypicallyadaptedforlifeinsaturatedsoilconditions.Wetlandsgenerallyincludeswamps,marshes,bogs,andsimilarareas”(EPA,1980).The1987CorpsofEngineersWetlandDelimitationManual&RegionalSupplements(U.S.ArmyCorpsofEngineers,1987)isusedtoidentifywetlandsinthefield.

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stormwaterdetentionponds,constructedwetlandsforwatertreatment,andfarmpondsorreservoirsarenotincluded.Naturallakesandstreamsarealsonotincluded.

Settlements:Aland‐usecategoryrepresentingdevelopedareasconsistingofunitsof0.25acres(0.1ha)ormorethatincludesresidential,industrial,commercial,andinstitutionalland;constructionsites;publicadministrativesites;railroadyards;cemeteries;airports;golfcourses;sanitarylandfills;sewagetreatmentplants;watercontrolstructuresandspillways;parkswithinurbanandbuilt‐upareas;andhighways,railroads,andothertransportationfacilities.Alsoincludedaretractsoflessthan10acres(4.05ha)thatmaymeetthedefinitionsforForestLand,Cropland,Grassland,orOtherLandbutarecompletelysurroundedbyurbanorbuilt‐upland,andsoareincludedinthesettlementcategory.Ruraltransportationcorridorslocatedwithinotherlanduses(e.g.,ForestLand,Cropland,andGrassland)arealsoincludedinSettlements.

OtherLand:Aland‐usecategorythatincludesbaresoil,rock,ice,andalllandareasthatdonotfallintoanyoftheotherfiveland‐usecategories,whichallowsthetotalofidentifiedlandareastomatchthemanagedlandbase.

7.3 Caveats

ThemethodspresentedhereforquantifyingGHGfluxfromland‐usechangeareintendedforuseattheentityscaleonlandsmanagedtoenhancetheproductionoffood,feed,fiber,andrenewableenergy.Methodsarecurrentlynotprovidedforestimatingemissionsfromenergyusedwhenconvertinglandusefromonecategorytoanother.Methodsarealsonotprovidedforland‐usechangefromsettlementsorthe“otherland”categorytoforestland,cropland,grazingland,orwetlands.ThesemethodshavebeendevelopedforU.S.conditionsandareconsideredapplicabletoagriculturalandforestryproductionsystemsintheUnitedStates.

7.4 EstimatingGHGFluxfromLand‐UseChange

RationaleforSelectedMethodThismethodisbasedontheIPCC2006Guidelines(IPCC,2006)andrepresentsthemostconsistentmethodforestimatingemissionsfromland‐usechange.Othermethodsareprovidedforlandparcelsthatarenotundergoinglandusechange,andarguablythosemethodsaremorecomprehensiveforestimatingemissionsforthespecificlanduse.However,itiscriticalthatanindividuallandparcelhasaconsistent,seamlessmethodforestimatingcarbonstockchangesthroughoutthetimeseries.Otherwiseartificialchangesinstockscanbeestimatedduetoachange

MethodforEstimatingGHGFluxfromLand‐UseChange

TheGHGfluxassociatedwithland‐usechangeisestimatedbasedonthebalanceofcarbonlossesfromthepreviouslandusefollowingconversionandthecarbongainswiththecurrentlanduse.

Thissectiononlycoversmethodologiesfordeadorganicmattercarbonandsoilorganicmattercarbon.Guidanceonbiomasscarbonmethodsareprovidedintheland‐use‐specificsections(Cropland,Grazingland,ForestLand,andWetlands).

Thechangeincarbonstocksindeadwoodandlitterduetolandconversionisestimatedasthedifferenceincarbonstocksintheoldandnewland‐usecategoriesappliedintheyearoftheconversion(carbonlosses),ordistributeduniformlyoverthelengthofthetransitionperiod(carbongains).

ThemethodologiestoestimatesoilcarbonstockchangesfororganicsoilsandmineralsoilsareadoptedfromIPCC(Aaldeetal.,2006).

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inthemethod.ThemethodsbasedontheIPCC2006Guidelines(IPCC,2006)providethisconsistencyandseamlessintegration.Furthertestinganddevelopmentwillbeneededbeforethemorecomprehensivemethodsprovidedineachlandusesectioncanbeintegratedintoaseamlessapproachforestimatingthecarbonstockchanges.

DescriptionofMethodForinventorypurposes,changesincarbonstockinbiomassshouldbeestimatedfor:(1)landremaininginthesameland‐usecategory;and(2)landconvertedtoanewland‐usecategory.Themethodsprovidedinthissectionarestrictlyforportionsofanentity’soperationthathaveundergonealandusechange.Thesoilcarbonchangesmustbeaddressedovera20‐yearperiod.Abovegroundandbelowgroundbiomassareestimatedonanannualbasis.Notethatthissectiononlyaddressesdeadorganicmattercarbonandsoilorganicmattercarbon.Biomasscarbonmethodsshouldfollowtheguidanceprovidedintheland‐use‐specificsections(Cropland,Grazingland,ForestLand,andWetlands).

Thereportingconventionisthatallcarbonstockchangesandnon‐CO2GHGemissionsassociatedwithaland‐usechangearereportedinthenewland‐usecategory.Forexample,inthecaseofconversionofforestlandtocropland,boththecarbonstockchangesassociatedwiththeclearingoftheforestaswellasanysubsequentcarbonstockchangesthatresultfromtheconversion,arereportedundercropland(IPCC,2006).

TheGHGfluxassociatedwithland‐usechangeisessentiallythesumoftheGHGfluxesassociatedwithprevious(i.e.,old)land‐usecategoriesplusthesumoftheGHGfluxesassociatedwiththecurrent(i.e.,new)land‐usecategoriesforaspecifiedareaundergoingconversionfromtheoldtonewland‐usecategory.GHGemissionsandstockchangesnotresultingfromaland‐usechangeareestimatedwithmethodsintheland‐use‐specificsections.

Foreachland‐usecategoryundergoingaland‐usechange,itisimportanttoestimatetheannualcarbonstockchangeoccurringwithineachstratumorsubdivision(e.g.,carbonpool,managementregime)forthatland‐usecategory.

Equation7‐1:AnnualCarbonStockChangesforaLand‐UseChangeEstimatedastheSumofChangesinAllLand‐UseCategories

ΔCLUC=ΔCLUCo+ΔCLUCn

and

ΔCLUC=ΔCLUCFL+ΔCLUCCL+ΔCLUCGL+ΔCLUCWL

Where:

ΔC=carbonstockchange(metrictonsCO2‐eqha‐1year‐1)

Indicesdenotethefollowingland‐usecategories:

LUC =land‐usechangeo =oldland‐usecategoryn =newland‐usecategoryFL =forestlandCL =croplandGL =grazinglandWL =wetlands

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Forexample,inthecaseofconversionofforestlandtocropland,thecarbonstockchangesassociatedwitheachoftheforestcarbonpoolsplusharvestedwoodproductsshouldbeassessed,aswellasanysubsequentcarbonstockchangesthatresultfromtheconversion(specificannualizedchangesindeadorganicmatter,soilcarbon,etc.).

7.4.1 CarbonPoolsinLiveBiomass,DeadBiomass,andSoilOrganicCarbonLiveanddeadbiomasscarbonstocksandsoilorganiccarbonconstituteasignificantcarbonsinkinmanyforestandagriculturallands.Sector‐specificmethodsforestimatingchangesinbiomasscarbonstocksaredetailedintheindividualsectorchaptersandshouldbeusedwhenestimatingtheeffectofland‐usechange.Inadditiontoestimatingthechangesinbiomasscarbonstocksbeforeandaftertheland‐usechangeusingthesector‐specificmethods,itisalsoimportanttoestimateanyincreaseintheharvestedwoodpoolresultingfromclearing/harvestoftheforestfollowingthemethodsoutlinedinChapter6,Forestry.Anybiomassthatisretainedonthelandduringtheland‐useconversionwillneedtobeincludedintheestimation,suchasconversionofforesttograsslands,wheresometreesarelefttoprovideshadeforgrazinglivestock.

Followingland‐useconversion,theestimationofdeadbiomasscarbonstockchangesduringtransitionperiodsrequiresthattheareasubjecttoland‐usechangeontheentity’soperationbetrackedforthedurationofthe20‐yeartransitionperiod.Forexample,deadorganicmatter(DOM)stocksareassumedtoincreasefor20yearsafterconversiontoforestland.After20years,theareaconvertedbecomesforestandremainingforestland,andnofurtherDOMchangesareassumed.Theconceptualapproachtoestimatingchangesincarbonstocksindeadwoodandlitterpoolsistoestimatethedifferenceincarbonstocksintheoldandnewland‐usecategoriesandtoapplythischangeintheyearoftheconversion(carbonlosses),ortodistributeituniformlyoverthelengthofthetransitionperiod(carbongains).

7.4.2 ChangesinSoilCarbonSoilorganiccarbonstocksareinfluencedbyland‐usechange(Aaldeetal.,2006)duetochangesinproductivitythatinfluencecarboninputs,andtochangesinsoilmanagementthatinfluencecarbonoutputs(DavidsonandAckerman,1993;Ogleetal.,2005;PostandKwon,2000).Themostsignificantchangesinsoilorganiccarbonoccurwithland‐usechange,particularlyconversionstocroplands,duetochangesinthedisturbanceregimesandassociatedeffectsonsoilaggregatedynamics(Sixetal.,2000).Whilethereisconsiderableevidenceandmechanisticunderstandingabouttheinfluenceofland‐usechangeonsoilorganiccarbon,thereislessknownabouttheeffectonsoilinorganiccarbon.Consequently,currentmethodsdonotincludeimpactsoninorganiccarbonuncertaintyassociatedwithestimatesoflanduseandmanagementimpactsonsoilcarbonstocks.

Equation7‐2:AnnualCarbonStockChangesforaLand‐UseChangeasaSumofChangesinEachStratumWithinaLand‐UseChange

ΔCLUC=∑i∆CLUCI

Where:

ΔCLUC =carbonstockchangesforaland‐usechangeasdefinedinEquation7.1(metrictonsCO2‐eqha‐1year‐1)

i =denotesaspecificstratumorsubdivisionwithinthelandusesundergoingland‐useconversion(byanycombinationofspecies,climaticzone,ecotype,managementregime,etc.),i=1ton

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EstimatingchangesinGHGemissions,includingcarbonstocks,requireconsistencyinthemethodsthatareappliedacrossatimeseries.Applyingdifferentmethodstoaccountforchangesincarbonstocksasthelandshiftsfromonelandusetoanotherwillleadtoartificialchangesinthestocksbeyondtheactualchangeoccurringontheland.Thus,inordertoensureconsistency,changesinsoilorganiccarbonstockswillbeestimatedfortheentiretimeseriesbeingreported,usingthemethoddescribedinthissection.Asnotedearlier,estimatesshouldbemadeseparatelyforeachparceloflandthatundergoesachangeinlanduse.However,thestockchangeswillonlybereportedasaland‐usechangeeffectfora20‐yeartransitionperiod.Applyingthesamemethodacrosstheentiretimeserieswilllimiterrorsintheestimationofmineralsoilorganiccarbonstockchangesthatwouldresultfromchangingmethodsafterthe20‐yeartransitionperiod.

7.4.2.1 DescriptionofMethodModelshavebeenadoptedfromtheIPCCmethodstoestimatesoilorganiccarbonstockchange(Aaldeetal.,2006).Formineralsoils,themethodwillrequireestimatesofcarbonstocksatthebeginningandendoftheyearinordertoestimatetheannualchangeusingtheequationbelow.Emissionsoccurinorganicsoilsfollowingdrainageduetotheconversionofananaerobicenvironmentwithahighwatertabletoaerobicconditions(ArmentanoandMenges,1986),resultinginasignificantlossofcarbontotheatmosphere(Ogleetal.,2003).Emissionestimationmethodsfromorganicsoilsshouldbeconsistentwiththeirappropriatesectormethodologies(i.e.,forestry,croplands,grazinglands,orwetlands).

MineralSoils:ThemodeltoestimatechangesinsoilorganiccarbonstocksformineralsoilshasbeenadoptedfromthemethoddevelopedbyIPCC(Aaldeetal.,2006).Thechangewouldneedtobeestimatedseparatelyforeachareaintheentity’soperationthatisconvertedfromonelandusetoanother.Thechangeinstocksforeachareaisestimatedoverfiveyearintervalsfortheentirereportingtimeseries,usingthefollowingequation:

Equation7‐3:AnnualChangeinCarbonStocksinDeadWoodandLitterDuetoLandConversion

ΔCDOM=(Cn‐Co)×Aon÷Ton

Where:

ΔCDOM =annualchangeincarbonstocksindeadwoodorlitter(metrictonsCyear‐1)

Co =deadwood/litterstock,undertheoldland‐usecategory(metrictonsCha‐1)

Cn =deadwood/litterstock,underthenewland‐usecategorymetrictonsCha‐1)

Aon =areaundergoingconversionfromoldtonewland‐usecategory(ha)

Ton =timeperiodofthetransitionfromoldtonewland‐usecategory(year)(Thedefaultis20yearsforcarbonstockincreasesand1yearforcarbonlosses.)

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CarbonstocksareestimatedusingthefollowingequationadaptedfromtheIPCC(Aaldeetal.,2006):

Thestockchangefactors(FLU,FMG,FI)andreferencecarbonstocks(SOCREF)arecountry‐specificvaluesdevelopedfortheUnitedStates(EPA,2011;Ogleetal.,2003;Ogleetal.,2006).ThereferencestocksarebasedontheSOCstocksincroplands(Table7‐3),whiletheland‐usefactorsrepresenttherelativechangeinSOCbetweencroplandandgrazinglands,forestland,andset‐asidecropland(Table7‐4).Themanagementfactorsrepresenttheinfluenceoftillageincroplandsandgrasslandconditioningrazinglands.Theinputfactorsrepresentinfluencesofchangingplantproductivityoncarboninputtosoils.Managementandinputfactorsarenotneededforforestlands(Factorsaresettoavalueof1).

OrganicSoils:ThemethodologyforestimatingsoilcarbonstockchangesinorganicsoilshasbeenadoptedfromIPCC(Aaldeetal.,2006),andisdescribedaccordinglyinChapter4,Wetlands,andChapter3,Croplands,andGrazingLands.Chapter6,Forestry,recommendssoilsamplingincaseswheretherehavebeensignificantchangesinsoilcarbon(e.g.,landconversion).

Equation7‐4:ChangeinSoilOrganicCarbon StocksforMineralSoils

ΔCMineral=[(SOCf−SOCi)×CO2MW]÷D

Where:

ΔCMineral =annualchangeinmineralsoilorganiccarbonstock(metrictonsCO2‐eqyear‐1)

SOCf =soilorganiccarbonstockattheendofyear5(metrictonsC)

SOCi =soilorganiccarbonstockatthebeginningofyear1(metrictonsC)

CO2MW =ratioofmolecularweightofCO2toC=44/12(dimensionless)

D =timedependenceofstockchangefactors(20years)

Equation7‐5:SoilOrganicCarbon StockforMineralSoils

SOC=SOCREF×FLU×FMG×FI×A

Where:

SOC =soilorganiccarbonstockatthebeginning(SOCi)andendofthefiveyears(SOCf)(metrictonsC)

SOCREF =referencesoilorganiccarbonstock(metrictonsCha‐1)

FLU =stockchangefactorforlanduse(dimensionless)

FMG =stockchangefactorformanagement(dimensionless)

FI =stockchangefactorforinput(dimensionless)

A =areaofland‐usechange(ha)

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Table7‐3:ReferenceCarbonStocks(MgCha‐1)(±1SE)ToEstimateSoilOrganicCarbonStockChangesforMineralSoils

SoilTypeUSDA

Taxonomy

CoolTemperate

Dry

CoolTemperateMoist

WarmTemperate

Dry

WarmTemperateMoist

Sub‐TropicalDry

Sub‐TropicalMoist

Highactivityclaysoils

Vertisols,Mollisols,Inceptisols,Aridisols,andhighbasestatusAlfisols

42±1.4 65±1.1 37±1.1 51±1.0 42±2.6 57±13.0

Lowactivityclaysoils

Ultisols,Oxisols,acidicAlfisols,andmanyentisols

45±3.0 52±2.3 25±1.4 40±1.2 39±4.8 47±13.9

Sandysoils

Anysoilswithgreaterthan70%sandandlessthan8%clay(oftenEntisols)

24±4.8 40±3.7 16±2.4 30±2.0 33±1.9 50±7.9

Volcanicsoils

Andisols 124±11.4 114±16.7 124±11.4 124±11.4 124±11.4 128±15.0

Spodicsoils

Spodosols 86±6.5 74±6.8 86±6.5 107±8.3 86±6.5 86±6.5

Wetlandsoils

SoilswithAquicsuborder

86± 89± 48± 51± 63± 48±

Source:EPA(2011)andOgleetal.(2003)Ogleetal.(2006).

Table7‐4:CarbonStockChangeFactors(±1SE)toEstimateSoilOrganicCarbonStockChangesforMineralSoils

FactorWarmTemperateMoist/Subtropical

Moist

WarmTemperate

Dry/SubtropicalDry

CoolTemperateMoist

CoolTemperateDry

Land‐UseFactorLong‐termcultivated 1 1 1 1Forest/grassland 1.42±0.06 1.37±0.05 1.24±0.06 1.20±0.06Set‐aside 1.31±0.06 1.26±0.04 1.14±0.06 1.10±0.05CroplandManagementFulltill 1 1 1 1Reducedtill 1.08±0.03 1.01±0.03 1.08±0.03 1.01±0.03No‐till 1.13±0.02 1.05±0.03 1.13±0.02 1.05±0.03GrasslandManagementa

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FactorWarmTemperateMoist/Subtropical

Moist

WarmTemperate

Dry/SubtropicalDry

CoolTemperateMoist

CoolTemperateDry

Non‐degraded 1 1 1 1Moderatelydegraded 0.95±0.06 0.95±0.06 0.95±0.06 0.95±0.06Severelydegraded 0.7±0.14 0.7±0.14 0.7±0.14 0.7±0.14Improved 1.14±0.06 1.14±0.06 1.14±0.06 1.14±0.06CroplandinputLow 0.94±0.01 0.94±0.01 0.94±0.01 0.94±0.01Medium 1 1 1 1High 1.07±0.02 1.07±0.02 1.07±0.02 1.07±0.02Highwithamendmenta 1.38±0.06 1.34±0.08 1.38±0.06 1.34±0.08GrasslandinputaMedium 1 1 1 1High 1.11±0.04 1.11±0.04 1.11±0.04 1.11±0.04aGrasslandmanagementandinputfactorsarefromthe2006IPCCGuidelines(Verchotetal.,2006)aswellasthehighinputsystemswithmanureincroplands(Lascoetal.,2006).

7.4.2.2 ActivityDataMineralsoilsrequirethefollowingactivityforcroplands:

Cropselectionandrotationsequence;

Residuemanagement,includingharvested,burned,grazed,orleftinthefield;

Irrigation,yesorno;

Mineralfertilization,yesorno;

Limeamendments,yesorno;

Organicamendments,yesorno;

Tillageimplements,whichcanbeusedtodeterminetillageclassification(i.e.,fulltillage,reducedtillage,andno‐till);and

Covercrops,yesorno.Themethodforgrazinglandrequiresthefollowingmanagementactivitydata:

Degradationstatus,non‐degraded,moderatelydegraded,severelydegraded;

Irrigation,yesorno;

Mineralfertilization,yesorno;

Seedinglegumes,yesorno;

Limeamendments,yesorno;and

Organicamendments,yesorno.Themethodforforestlanddoesnotrequireanymanagementactivitydatabecausethemethodprovidedhereassumeslimitedinfluenceonsoilorganiccarbonstockchangesassociatedwithforestmanagementafteraland‐usechange(i.e.,theland‐usechangehasthelargestimpact).

Theactivitydataareusedtoclassifyland‐use,management,andinputclasses.TheclassificationscanbefoundinLascoetal.(2006)forcropland(Figure5.1),andVerchotetal.(2006)forgrassland(Figure6.1).

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7.4.2.3 AncillaryDataAncillarydataincludeclimateregionsandsoiltypes,consistentwiththemethoddevelopedbytheIPCC(Bickeletal.,2006).WeatherdatamaybebasedonnationaldatasetssuchastheParameter‐ElevationRegressionsonIndependentSlopesModel(PRISM)data(Dalyetal.,2008)andareclassifiedaccordingtotheIPCCclassificationasrefinedfortheUnitedStates(Table7‐5).SoilsdatamayalsobebasedonnationaldatasetssuchastheSoilSurveyGeographicDatabase(SSURGO)(SoilSurveyStaff,2011),andareclassifiedaccordingtotheIPCCclassification(Bickeletal.,2006;Figure3A.5.3).However,entitiesmayalsosubstitutefield‐specificsoilsdata,aslongasentitiescharacterizethesoilpedonsnecessaryforuseoftheIPCCclassifications.Thesecharacteristicsincludesandandclaycontent,soilorder,andsuborder(SeeTable7‐3).

Table7‐5:ClimateClassificationfortheSoilOrganicCarbonMethodsAssociatedwithLand‐UseChange

ClimateType MeanAnnualTemperature(°C) MeanAnnualPrecipitation(mm)

Cooltemperatedry <10 <PotentialevapotranspirationCooltemperatemoist <10 ≥PotentialevapotranspirationWarmtemperatedry 10‐20 <PotentialevapotranspirationWarmtemperatemoist 10‐20 ≥PotentialevapotranspirationSubtropicaldry >20 <1000Subtropicalmoist >20 1000‐2000Source:Bickeletal.(2006).

7.4.2.4 ModelOutputModeloutputisgeneratedasanabsolutequantityofemissions.Thechangeinmineralsoilorganiccarbonstocksisestimatedbasedonstockchangesoverfive‐yeartimeperiods(Equation7.4).Inaddition,trendsinsoilorganiccarbonwillbeestimatedfortheentiretimeseriesassociatedwiththeparcelofland,including20previousyearsofhistory,inordertopresentthelongertermtrendsandprovideanadequatebaselineofdataandconsistencyinthetimeseriesforreportingpurposes.

7.4.2.5 LimitationsandUncertaintyThelimitationsofthemineralsoilorganiccarbonmethodincludenoassessmentoftheeffectofland‐usechangeatdeeperdepthsintheprofile(IPCCmethodonlyaddresseschangesintop30cmofsoilprofile;Aaldeetal.,2006),andnoassessmentoferosion,transport,anddepositionofcarbon.Uncertaintiesinthemineralsoilmethodsincludeimprecisionintheemissionfactors,inadditiontouncertaintiesintheactivityandancillarydata.Uncertaintyintheemissionfactorsisprovidedinthisguidance(Ogleetal.,2003;Ogleetal.,2006).Uncertaintyintheactivitydataisbasedontheentityinput,aswellastheancillarydatatotheextentthatthisinformationisprovidedbytheentity.UncertaintiescanbecombinedusingaMonteCarlosimulationapproach.

7.4.3 ChangesinotherGHGemissionsAspreviouslymentioned,changesinotherGHGemissions—i.e.,non‐CO2emissions—associatedwithaland‐usechangeshouldbeincludedinanyestimationoftheGHGfluxstrataassociatedwiththeoutgoingorincomingland‐usechange.WhilechangesinbiomassandsoilcarbonstocksarelikelytodominatetheGHGflux,thereareanumberofactivitiesthatmayoccurduringland‐useconversionthatmightresultinnon‐CO2emission.Forexample,ifforestharvestresidues(andotherdeadorganicmatter)arepiledandburntaspartoftheconversionofforestlandtoanotherlanduse,inadditiontothechangeincarbonstocktheresidueburningwillresultinemissionsofN2OandCH4;andifwetlandsareclearedanddrainedpriortoconversiontoanotherlanduse(e.g.,grazinglands,peatextraction),inadditiontothechangeincarbonstockfromclearing,thedraining

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willresultinareductioninemissionsofCH4,andapossibleincreaseinemissionsofN2O,dependingonthenitrogencontentofthewetlandsoil(i.e.,peat).

Sector‐specificmethodsforestimatingchangesinbiomassburningnon‐CO2emissions(e.g.,forcroplandandgrazinglandsystems)andsoilnon‐CO2emissions(e.g.,forwetlandsystems)aredetailedintheindividualsectorchapters.

Chapter7References

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Armentano,T.V.,andE.S.Menges.1986.Patternsofchangeinthecarbonbalanceoforganicsoil.Bickel,K.,G.Richards,M.Kohl,R.L.V.Rodrigues,etal.2006.Chapter3:Consistentrepresentationof

land.In2006IPCCGuidelinesforNationalGreenhouseGasInventories,S.Eggleston,L.Buendia,K.Miwa,T.NgaraandK.Tanabe(eds.).Japan:IGES.

Daly,C.,M.Halbleib,J.I.Smith,W.P.Gibson,etal.2008.PhysiographicallysensitivemappingofclimatologicaltemperatureandprecipitationacrosstheconterminousUnitedStates.InternationalJournalofClimatology,28:2031‐2064.

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EnvironmentalProtectionAgency.IPCC.2006.IPCCGuidelinesforNationalGreenhouseGasInventories.TheNationalGreenhouseGas

InventoriesProgramme.Hayama,Kanagawa,Japan:TheIntergovernmentalPanelonClimateChange.

Lasco,R.D.,S.Ogle,J.Raison,L.Verchot,etal.2006.Chapter5:Cropland.In2006IPCCGuidelinesforNationalGreenhouseGasInventories,S.Eggleston,L.Buendia,K.Miwa,T.NgaraandK.Tanabe(eds.).Japan:IGES,IPCCNationalGreenhouseGasInventoriesProgram.

Ogle,S.M.,F.J.Breidt,M.D.Eve,andK.Paustian.2003.UncertaintyinestimatinglanduseandmanagementimpactsonsoilorganiccarbonstorageforUSagriculturallandsbetween1982and1997.GlobalChangeBiology,9(11):1521‐1542.

Ogle,S.M.,F.J.Breidt,andK.Paustian.2005.Agriculturalmanagementimpactsonsoilorganiccarbonstorageundermoistanddryclimaticconditionsoftemperateandtropicalregions.Biogeochemistry,72(1):87–121.

Ogle,S.M.,F.J.Breidt,andK.Paustian.2006.Biasandvarianceinmodelresultsassociatedwithspatialscalingofmeasurementsforparameterizationinregionalassessments.GlobalChangeBiology,12:516‐523.

Post,W.M.,andK.C.Kwon.2000.SoilCarbonSequestrationandLand‐UseChange:ProcessesandPotential.GlobalChangeBiology,6:317‐327.

Six,J.,E.T.Elliot,andK.Paustian.2000.Soilmacroaggregateturnoverandmicroaggregateformation:amechanismforCsequestrationunderno‐tillageagriculture.SoilBiol.Biochem.,32:2099‐2103.

Smith,W.B.,P.D.Miles,C.H.Perry,andS.A.Pugh.2009.ForestResourcesoftheUnitedStates,2007.Washington,DC:U.S.DepartmentofAgricultureForestService.

SoilSurveyStaff.2011.SoilSurveyGeographic(SSURGO)Database:NaturalResourceConservationServiceandUnitedStatesDepartmentofAgriculture.

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U.S.ArmyCorpsofEngineers.1987.WetlandDelimitationManual&RegionalSupplementsWetlandsResearchProgramTechnicalReportY‐87‐1:U.S.ArmyCorpsofEngineers,EnvironmentalLaboratory,.http://www.usace.army.mil/Missions/CivilWorks/RegulatoryProgramandPermits/reg_supp.aspx.

Verchot,L.,T.Krug,R.D.Lasco,S.Ogle,etal.2006.Chapter5:Grassland.In2006IPCCGuidelinesforNationalGreenhouseGasInventories,S.Eggleston,L.Buendia,K.Miwa,T.NgaraandD.L.Tanaka(eds.).Japan:IGES.

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