Baseline Land-Use and Land-Cover Changes in the Western United States Between 1992 and 2005

By Terry L. Sohl, Benjamin M. Sleeter, Tamara S. Wilson, Michelle A. Bouchard, Rachel R. Sleeter, Kristi L. Sayler, Ryan R. Reker, Christopher E. Soulard, and Stacie L. Bennett

Chapter 2 ofBaseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United StatesEdited by Zhiliang Zhu and Bradley C. Reed

Professional Paper 1797

U.S. Department of the InteriorU.S. Geological Survey

U.S. Department of the InteriorKEN SALAZAR, Secretary

U.S. Geological SurveyMarcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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Suggested citation:Sohl, T.L., Sleeter, B.M., Wilson, T.S., Bouchard, M.A., Sleeter, R.R., Sayler, K.L., Reker, R,R,, Soulard, C.E., and Bennett, S.L., 2012, Baseline land-use and land-cover changes in the Western United States between 1992 and 2005, chap. 2 of Zhu, Zhiliang, and Reed, B.C., eds., Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the Western United States: U.S. Geological Survey Professional Paper 1797, 12 p. (Also available at http://pubs.usgs/gov/pp/1797.)

iii

Contents

2.1. Highlights..................................................................................................................................................12.2. Introduction..............................................................................................................................................12.3. Input Data and Methods ........................................................................................................................22.4. Results and Discussion ..........................................................................................................................6

2.4.1. Baseline LULC Mapping and Modeling—Results for the Western United States ...........62.4.2. Regional Results .........................................................................................................................8

2.4.2.1. Western Cordillera ........................................................................................................102.4.2.2. Marine West Coast Forest ...........................................................................................102.4.2.3. Cold Deserts ..................................................................................................................102.4.2.4. Warm Deserts ...............................................................................................................122.4.2.5. Mediterranean California ............................................................................................12

Figures 2.1. Timeline for LULC change mapping and modeling for both the baseline and

scenario-based projections …………………………………………………… 2 2.2. Map showing how data from LANDFIRE’s vegetation change tracker (VCT)

provided information on ecosystem disturbances ……………………………… 4 2.3. Chart showing the declining trend of forest clearcutting in the Western

United States between 1992 and 2005 ………………………………………… 7 2.4. Chart showing the increasing trend in the areal extent of urban development

in the Western United States between 1992 and 2005 ………………………… 8 2.5. Map showing the spatial variability of land-use and land-cover change in

the Western United States between 1992 and 2005 …………………………… 9 2.6. Map showing the spatial variability of forest clearcutting in the Western

United States from 1992 to 2005 ………………………………………………… 9 2.7. Charts showing the proportions of land use and land cover (LULC) at the end

of the baseline periodand the net change in the mapped and modeled LULC classes between 1992 and 2005, by level II ecoregion ………………………… 11

Tables 2.1. Thematic land-use and land-cover classes used in this assessment, the

corresponding ecosystems defined for this assessment, percent area (from 1992) of the Western United States, and the source of the input data …… 3

2.2. Mapped and modeled land-use and land-cover (LULC) change (in square kilometers) indicating trends in mapped and modeled LULC classes for the Western United States for the baseline period (1992–2005) …………………… 7

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Chapter 2. Baseline Land-Use and Land-Cover Changes in the Western United States Between 1992 and 2005

By Terry L. Sohl1, Benjamin M. Sleeter2, Tamara S. Wilson2, Michelle A. Bouchard3, Rachel R. Sleeter2, Kristi L. Sayler1, Ryan R. Reker3, Christopher E. Soulard2, and Stacie L. Bennett4

2.1. Highlights

• Annual,250-mresolutionland-useandland-cover(LULC)mapswereproducedforthebaselineperiodof1992to2005.

• Observeddataderivedfromremotelysensedsourceswereusedwhenpossibleforthebaselinemapproducts.

• Whenannual,observeddatawerenotavailable,aspatialLULCmodelbasedoninputdataderivedfromLULCstudieswasusedtoproducetheannualLULCmaps.

• ThebaselineLULCchangewasrelativelylowbutvariablebetweenecoregions;someecoregionsexperiencedsignificantamountsofchangeandsomeecoregionsexperiencedverylittlechange.

• LULCchangeassociatedwithforestrywasthemostcommonformofLULCchange,followedbyurbandevelopment.

2.2. IntroductionAsindicatedinfigure1.2(agraphicrepresentationofthe

overallmethodologyforthisassessment)ofchapter1ofthisreport,themappingandmodelingofLULCdescribedinthischapteraresomeofthespatialfoundationsofthisregionalassessmentandhelpdefinetheboundariesandcompositionsoftheassessedecosystems.TheresultsoftheLULCmappingandmodelingcomponentfeedintoothercomponentsoftheassessment,particularlychapter5(baselineterrestrialcarbonstorageandgreenhouse-gasfluxes)andchapter6(developmentoffutureLULCscenarios).

TheLULCintheWesternUnitedStatesisdiverse;vastforests,shrublands,andgrasslandsareinterspersedwithhumanagriculturalactivities,mining,andsomeofthelargesturbanareasintheUnitedStates.Topography,soils,climate,andwateravailabilityinteracttodeterminethelandscapepotentialandanthropogeniclanduse,producingamosaicofdifferentLULCtypesacrosstheWest.Silviculture,agriculture,urbandevelopment,mining,andnaturaldisturbancessuchaswildlandfireshavedramaticallyalteredportionsoftheWesternUnitedStates,buttheLULCchangeisfragmented;someareashaveexperiencedlittlechangeoverthelastcenturyandothershaveexperiencedrapidandfrequentchanges.

TheannualLULCmapsfortheWesternUnitedStatesserveasthespatialandtemporalfoundationforassessingthebaselinecarbonstorageandfluxesforterrestrialecosystems(chapter5).Theclassificationscheme(asdiscussedbelow)isacombinationofland-useandland-coverclassesthatcloselyfollowstheclassesusedbythe1992NationalLandCoverDatabase(NLCD)(Vogelmannandothers,2001).Thedisturbanceofecosystemsbywildlandfiresisdiscussedseparately(chapter3).Land-managementactivities(forexample,croptillage,croprotation,andfertilization)arealsodiscussedseparately(chapter4).InordertoprovideapartitionedspatialframeworkfortheWesternUnitedStates,theregionwasdividedintofivelevelIIecoregions(modifiedfromU.S.DepartmentofEnvironmentalProtection(EPA),1999):WesternCordillera,MarineWestCoastForest,ColdDeserts,WarmDeserts,andMediterraneanCalifornia.ThefiveecoregionsweremappedandmodeledtocreateannualLULCmapsforthebaselineperiodof1992to2005.ThefollowingsectionsdiscussthedatasourcesandmethodologiesusedtomapandmodelannualLULCchangeandthebaselineLULCresults.

1U.S.GeologicalSurvey,SiouxFalls,S.D.2U.S.GeologicalSurvey,MenloPark,Calif.3ArcticSlopeRegionalCorporationResearchandTechnologySolutions,SiouxFalls,S.D.4U.S.GeologicalSurvey,Sacramento,Calif.

2 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

Integrated model to assess the global environment (IMAGE 2.2)

IPCC-SRES scenarios—A1B, A2, B1

Baseline

Figure 2.1.

USGS Land Cover Trends project

Vegetation change tracker19

92

2000

2006

2010

2020

2030

2040

2050

National Land CoverDatabase

Figure 2.1. Timeline for LULC change mapping and modeling for both the baseline and scenario-based projections. The baseline period runs from 1992 to 2005; the modeled scenarios (from the Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios (IPCC–SRES; Nakicenovic and others, 2000) were run from 2006 to 2050. The data sources at the top of the graphic were used to support the analysis of baseline, scenarios, or both. USGS, U.S. Geological Survey.

2.3. Input Data and MethodsThebaselineperiodforthisassessmentwasdefinedas

theperiodfrom1992to2005.ThebaselineperiodallowedforanexaminationofrecentLULCchangeandforthecalibrationofboththeLULCandbiogeochemicalmodelingframeworksbeforebeginningthesimulationsoffutureLULC.Theyear1992waschosenasthestartofthebaselineperiodbecauseitmarkedtheearliestyearforwhichconsistent,nationwide,high-spatial-resolutionLULCdatawereavailable.Amodifiedversionofthe1992NationalLandCoverDataset(NLCD)(Vogelmannandothers,2001)servedastheinitialLULCdataforthiswork;theNLCDdatahadbeenextensivelyassessedforaccuracy(Stehmanandothers,2003;Wickhamandothers,2004).Theyear2005waschosenastheendpointforthebaselineperiod.Thechoiceofthebaselineyears1992to2005thusmaximizedtheuseofconsistent,spatiallyexplicit,nationwide,observedLULCdataavailablewhenworkontheassessmentbegan.Scenario-basedprojectionsofpotentialfutureland-coverchangewerecreatedtocover2006through2050(seechapter6ofthisreport)(fig.2.1).

TheNLCDthematicclassificationsystemprovidesalevelofthematicdetailthatallowsforanexaminationoftheeffectsofLULCchangeonfluxesofcarbonandgreenhousegases,buttheclassificationsystemcanalsobedirectlycollapsedtotheprimaryecosystemtypesthatwereanalyzedforthisassessment(table2.1).Theoriginalresolutionofthe1992NLCDwas30meters,butthedatawereresampledto250metersforthisassessmenttoreducethevolumeofdataandholdthemodelingrequirementstoamoremanageablelevel.Severaladjustmentsweremadetothethematicclassesinordertofacilitatethisassessment,includingthecollapsing

ofthefoururbanclassesfromthe1992NLCDintoone“urban/developed”class.Similarly,threeagriculturalclassesfromthe1992NLCD(rowcrop,smallgrains,andfallow)werecollapsedintoone“agriculture”classthatrepresentedcultivatedcrops.

The1992NLCDdatasetwasalsoaugmentedbyincorporatinginformationfromLANDFIRE’svegetationchangetracker(VCT)data(ChengquanHuangandothers,2010)(fig.2.2).TheVCTdatamappednaturalandanthropogenicdisturbancesbyanalyzinghistoricallayersofLandsatThematicMapper(TM)data.PolygonsofclearcutforestderivedfromVCTdatawereusedtopopulate“mechanicallydisturbed”classes3,4,and5(table2.1)for1992.Thethreemechanicallydisturbedclassesrepresentedclearcutsthatoccurredonlandownedbythreedifferententities:(1)nationalforest,(2)otherpublicland,and(3)privateland.Giventhateachoftheseownershiptypeshavevaryingmanagementstrategies,theProtectedAreaDatabaseoftheUnitedStates(PAD–USPartnership,2009)wasusedtospatiallydistinguishownershipforthethreedisturbanceclasses.ThePAD–USdatabaseincludesFederal,State,andlocalprotectedlands,aswellasinformationfromnationalnonprofitorganizations.Thedatabasedoesnotcoverallprotectedlands(suchasconservationeasements),butitisthemostcomprehensiveandaccurateprotectedlandsdatabaseavailablefortheUnitedStates.ThematicallydistinguishingclearcuttingbythesethreedifferentclassesofownershipresultedinanimprovedabilitytomapandmodelLULCchangerelatedtoforestryandthusimprovedtheabilitytoexaminetheeffectsofforestryoncarbonandgreenhouse-gasfluxes.

Chapter 2 3

Table 2.1. Thematic land-use and land-cover classes used in this assessment, the corresponding ecosystems defined for this assessment, percent area (from 1992) of the Western United States, and the source of the input data.

[LANDFIRE,LandscapeFireandResourceManagementPlanningToolsProject(Rollins,2009);NLCD,NationalLandCoverDataset(Vogelmannandothers(2001);VCT,vegetationchangetracker(aproductofLANDFIRE;ChengquanHuangandothers,2010)]

Land-use and land-cover (LULC) class

EcosystemArea

(percent)Source

Openwater Aquaticecosystems 1.5 NLCD—Openwater.Urban/developed Otherlands 1.0 NLCD—Low-intensityresidential.

NLCD—High-intensityresidential.NLCD—Commercial/industry/transportation.NLCD—Urban/recreationalgrasses.

Mechanicallydisturbed—Nationalforest Forests 0.4 LANDFIREVCT.

Mechanicallydisturbed—Otherpublicland Forests 0.1 LANDFIREVCT.

Mechanicallydisturbed—Privateland Forests 0.1 LANDFIREVCT.

Mining Otherlands 0.1 NLCD—Quarries/stripmines/gravelpits.

Barren Otherlands 3.8 NLCD—Barerock/sand/clay.

Deciduousforest Forests 2.0 NLCD—Deciduousforest.

Evergreenforest Forests 23.9 NLCD—Evergreenforest.

Mixedforest Forests 1.4 NLCD—Mixedforest.

Grassland Grasslands/shrublands 13.9 NLCD—Grassland/herbaceous.

Shrubland Grasslands/shrublands 45.1 NLCD—Shrubland.

Cultivatedcrop Agriculturallands 3.6 NLCD—Rowcrops.NLCD—Smallgrains.NLCD—Fallow.

Hay/pasture Agriculturallands 2.5 NLCD—Pasture/hay.

Herbaceouswetland Wetlands 0.1 NLCD—Emergentherbaceouswetlands.

Woodywetland Wetlands 0.3 NLCD—Woodywetlands.Ice/snow Otherlands 0.1 NLCD—Perennialice/snow.

Themodified1992NLCDdataservedastheinitiallandcoverdatasetfortheassessment.AnnualLULCmapsforthebaselineperiodwererequiredtoadequatelyportraygrosschangesbetweenLULCclassesthatcouldbemissedbyawidertemporalintervalandthuscouldaffectcarbonandGHGcalculations;however,therewerenoannual,nationallyconsistent,spatiallyexplicitLULCdataavailablefortheentirebaselineperiodof1992to2005.NLCDdatawereavailablefor1992,2001,and2006(Vogelmannandothers,2001;Homerandothers,2007;Xianandothers,2009),butdifferentclassificationsystemsanddifferentmappingmethodologiesbetweenNLCDversionsprecludedtheuseofNLCDaloneforprovidingLULCdataforthe1992to2005period.TheVCTdatawereavailableonanannualbasis,butonlyprovidedinformationonareasofdisturbancesuchasforestclearcutsandfires(ChengquanHuangandothers,2010).TheUSGSLandCoverTrendsproject(Lovelandandothers,2002)providedhistoricalLULCdata,butonlysample-baseddatawereavailablefor1992and2000.Eventhoughtheindividual

datasetscouldnotprovidetheconsistent,annual,wall-to-wallLULCmapsneededfortheassessment,theycouldbeusedtodirectlyinformaspatialmodelingframeworktoproduceannualLULCmapsfrom1992to2005.

Thespatialmodelingframework,“forecastingscenariosofland-coverchange”(FORE–SCE),wasusedtoproduceannualLULCmapsfrom1992to2005.FORE–SCEwassuccessfullyusedtomodelannualLULCmapsforlargegeographicregions(SohlandSayler,2008;Sohl,Sleeter,Zhu,andothers,2012;Sohl,Sleeter,Sayler,andothers,2012).TheFORE–SCEmodelusedseparatebutlinked“Demand”and“SpatialAllocation”componentstoproducespatiallyexplicit,annualLULCmaps.The“Demand”componentprovidedaggregate-levelquantitiesofLULCchangeforaregion,ora“prescription”fortheoverallregionalLULCproportions.The“SpatialAllocation”componentingested“Demand”andproducedspatiallyexplicitLULCmapsusingapatch-basedallocationprocedure.

4 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

121°30'W121°45'W122°00'W

47°00'N

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46°40'N

121°30'W121°45'W122°00'W

47°00'N

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EXPLANATION

Year of vegetation change(forest cutting}

[Part C]

Ownership of land

1986198719881989199019911992199319941995

Mount Rainier National ParkNational forestOther public landPrivate land

0 5 10 MILES

0 5 10 KILOMETERS

1996199719981999200020012002200320042005

Figure 2–2.

N

WaterDevelopedMiningBarrenDeciduous forestEvergreen forestMixed forest

GrasslandShrublandAgricultureHay/pastureHerbaceous wetlandWoody wetlandIce/snow

Land cover[Parts A and B]

A B

C

Mount Rainier National Park boundary

Figure 2.2. Map showing how data from LANDFIRE’s vegetation change tracker (VCT) provided information on ecosystem disturbances. In this assessment, the VCT data were used to identify polygons that represented forest clearcuts for the baseline period (1992–2005). A, Land-use and land-cover map of a portion of the Western United States. B, Inset map showing land use and land cover of Mount Ranier National Park and the

surrounding national forest, other public land, and private land. C, Inset map showing vegetation changes in the same area as part B. The small colored polygons outside of the national park boundary (national forest, other public land, and private land) represent forest clearcuts, color-coded by the year in which the clearcutting occurred. LANDFIRE, Landscape Fire and Resource Management Planning Tools Project.

Chapter 2 5

The“Demand”forthebaselineLULCchangewassplitintotwotimeperiodstotakeadvantageoftemporallyspecifichistoricaldata.Demandfrom1992to2000wasprovidedbyUSGSLandCoverTrendsdata(U.S.GeologicalSurvey,2012a).TheUSGSLandCoverTrendsprojectusedasamplingapproachandthehistoricalarchiveofLandsatMultispectralScanner(MSS),ThematicMapper(TM),andEnhancedThematicMapperPlus(ETM+)datatoproduceestimatesofLULCchangeforeachofthe84levelIIIecoregions(modifiedfromEPA,1999)intheconterminousUnitedStates(Lovelandandothers,2002).Althoughthecoarser-scalelevelIIecoregionframeworkwasusedfortheoverallassessmentintheWesternUnitedStates,thefiner-scalelevelIIIecoregionframeworkservedastheprimaryframeworkforallFORE–SCE-basedLULCmodeling,thusimprovingtherepresentationofspatialLULCchangepatternsintheveryheterogeneousWesternUnitedStates.Asaresult,the“Demand”informationfromtheUSGSLandCoverTrendsprojectwasprovidedseparatelyforeachlevelIIIecoregion,andthe“SpatialAllocation”componentofFORE–SCEwasparameterizedindividuallyforeachlevelIIIecoregion.Forthe1992to2000period,USGSLandCoverTrendsdataprovidedbaselineregionalproportionsofLULCchange(“Demand”)foreachlevelIIIecoregion;however,thesedatawerethematicallylessdetailedthantheLULCclassesusedforthisassessment(table2.1).Forexample,USGSLandCoverTrendsonlyestimatedoneaggregate“forest”class,whilethisassessmentdifferentiatedbetweendeciduous,evergreen,andmixedforesttypes.ToobtainthethreeforesttypesandtheirtransitionsfromtheUSGSLandCoverTrendsdatafor1992to2000,proportionsofthethreeforesttypesfromthe1992NLCDwereusedtodisaggregatetheUSGSLandCoverTrendssingleforestclassforeachlevelIIIecoregion.AsimilardisaggregationofUSGSLandCoverTrendsclassesusingthe1992NLCDwasperformedtosplittheclass“grass/shrub”intothe“grassland”and“shrubland”classes,split“wetland”intothe“herbaceouswetland”and“woodywetland”classes,andsplit“agriculture”into“hay/pasture”and“cultivatedcrop.”Finally,the1992to2000estimatesbyecoregionwereannualizedtoproduceannualratesofchangethatservedasannual“Demand”fortheFORE–SCEmodel.

Asimilarmethodologywasusedtopopulatethe“Demand”componentofthemodelfor2001to2005.The“Demand”forthisperiodwasprovidedbythe2001to2006NLCDchange-productdata(Xianandothers,2009).The2001and2006NLCDdataprovidedaLULCchangeproductthatprovidedconsistent,wall-to-wallLULCdatafortheUnitedStates.Thelevelofthematicdetailwascompatiblewiththisassessment,and,unliketheUSGSLandCoverTrendsdatafor1992to2000,nodisaggregationtoafinerthematicscalewasnecessary.The2001to2006NLCDchangedatawereannualizedtoproduceratesofchangethatservedasyearly“Demand”for2001to2005fortheFORE–SCEmodel.

The1992to2005annual“Demand”forLULCservedasinputtothespatialmodelingcomponentofFORE–SCE.FORE–SCEusedlogisticregressiontoquantifyempiricalrelationshipsbetweenLULCandspatiallyexplicitbiophysicalandsocioeconomicvariables.SuitabilitysurfaceswereproducedforeachuniqueLULCclassthatwasmodeled(table2.1)foreachlevelIIIecoregion.ThesuitabilitysurfaceswereusedtoguidetheplacementofindividualpatchesofLULCchange;thecharacteristicsofthepatcheswereparameterizedusinghistoricalLULCdatafromtheUSGSLandCoverTrendsproject.TheUS–PADdatawereusedtorestricttheplacementofspecificformsofLULCchangeoncertaintypesofprotectedlands(forexample,restrictingurbandevelopmentinnationalparklands).IndividualpatchesofLULCwereplacedonthelandscapeforagivenannualmodelrununtil“Demand”wasmetforthatyear.Theprocessingthencontinuedtothenextyearuntilthebaselineperiodof1992to2005wascomplete.AdditionaldetailsontheFORE–SCEmodelstructuremaybefoundinSohlandSayler(2008);Sohl,Sleeter,Zhu,andothers(2012);andSohl,Sleeter,Sayler,andothers(2012).

Theageofforeststandswasalsotrackedspatiallyandtemporallyandwasestimatedinthemodelingenvironment.Dataaboutforest-standageswereusedtoensurerealisticclearcuttingcycles(basedonthetypicalagewhenaforeststandisreadyforharvesting)foragivengeographicarea,andprovidedinformationonforeststructurethatcouldbeusedforbiogeochemicalorclimatemodeling.Aninitialmapofforest-standageswasgeneratedfortheregionusingacombinationofdatafromLANDFIRE’sVCTandtheU.S.ForestService’s(USFS’s)ForestInventoryandAnalysis(FIA;USDAForestService,2012b).WheretheLANDFIREVCTmeasuredadisturbance,theforest-standagewasdirectlycalculatedfortheinitialyearof1992.InareaswherenodisturbancewasmeasuredbytheLANDFIREVCT,theFIAdatapointswereusedtocreateaninterpolated,continuoussurfaceofforest-standage.TheFORE–SCEmodeltrackedforest-standageforeachyearlymodeliterationandresetthestandageto“0”wheneveranewforestareawasgeneratedorwheneveraforestwasclearcut;however,toensuretheuseofasmuchobservedspatialdataaspossibleforthebaselineperiod,theclearcuttingofforests(classes3,4,and5)intable2.1wasnotmodeledusingtheproceduresoutlinedabove;instead,themodelswereextractedfromtheLANDFIREVCTdata.AllareasofforestthattheVCThadidentifiedasclearcutbetween1992and2005were“burnedin”totheappropriatelydatedLULCmapsproducedfromtheFORE–SCEmodel(forexample,all1994clearcutareasidentifiedbytheVCTwereburnedintothe1994LULCmapproducedfromtheFORE–SCEmodel).Theforest-standagewasappropriatelyupdatedthroughoutthebaselineperiod,mimickingmeasureddatesofforestclearcutsfromtheVCT.

6 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

Theresultofthemappingandmodelingeffortsfor1992to2005LULCwereannual,250-meter-resolutionLULCmapsdepictingtheLULCclasses(shownintable2.1)andannual,250-meter-resolutiondataonforest-standage.Giventhelimitationsofavailable,spatiallyandthematicallyconsistentLULCdatafor1992to2005,thecombinedmappingandmodelingtechniqueensuredthattheoverallproportionsofthe1992to2005LULCmapswereasrepresentativeaspossibleofthereal,measuredLULCchangedistributionsthatwereprovidedbytheUSGSLandCoverTrends,NLCD,andLANDFIREVCTprojects.ThelocationofLULCchangeaftertheinitial1992yearwasamixofactualmappedchangeandmodeledchange.TheVCTprovidedtheactuallocationsofclearcutforestpatchesbetween1992and2005,awelcomedatasetgiventhatforestclearcuttingrepresentedthelargestLULCchangeintheWesternUnitedStatesperunitofarea(BenjaminM.Sleeter,USGS,unpub.data,2012).ForotherLULCtypes,the“SpatialAllocation”componentforLULCchangewasmodeledusingtheFORE–SCEmodel.

Thevalidationofthebaseline1992to2005LULCmapswasaccomplishedthroughacombinationofqualitativeandquantitativeassessment.Aquantitativeassessmentofthemodel’sperformancewasobviouslypreferred.ThequantitativevalidationofLULCmodeloutputcouldbeperformedbyexaminingmeasuresofquantitydisagreementandallocationdisagreementthatreflectedthemodel’scapabilitytomapthecorrectquantityandlocationofLULCchange,respectively(PontiusandMillones,2012).Anexaminationofquantitydisagreementwasunnecessaryforthisassessment,however.ThequantityofLULCchangewasdictatedbytheUSGSLandCoverTrendsprojectfor1992to2000andbytheNLCD2001to2006changeproductfor2001to2005.TheFORE–SCEmodelwasdesignedtopreciselymatchprescribedproportionsofLULCchangeasdictatedbythe“Demand”componentofthemodel.GiventhedesignoftheFORE–SCEmodel,quantitydisagreementwas,therefore,notanissuebecausethemodelmatchedtheannual,prescribedLULC“Demand”for1992to2005onaregionalbasis.

GiventhatalllevelIIIecoregionswereparameterizedandmodeledindependently,theallocationdisagreementwasalreadypartiallymitigatedbecausetheproportionsofchangewerespatiallydistributedtotheecoregionlevel.TheallocationdisagreementwasonlyanissuewithinalevelIIIecoregion.Theallocationdisagreement(whereLULCchangewasmapped)wasnotanissuefortheclearcuttingofforests(themostprevalentformofLULCchangeintheWesternUnitedStates)becausethe1992to2005polygonsofforestchangeweremappedbytheLANDFIREVCT,notmodeledbyFORE–SCE.AlloftheothertypesofLULCchange,however,weremodeledbyFORE–SCEandwerethussubjecttoallocationdisagreement.Thereweredifficultiesinperforminganassessmentofallocationdisagreement,however,giventheinabilitytodirectlycompareUSGSLandCoverTrends,the1992NLCD,andthe2001and2006NLCDdata.The

2001and2006NLCDdatawereproducedusingaconsistentmethodologyandcouldtheoreticallybeusedtoevaluatetheallocationdisagreementofthemodeledLULCchangeforthatperiod;however,outsideofthedominantLULCchangeintheWesternUnitedStates(forestclearcuttingandassociatedforestregeneration,mappedbyVCTandnotmodeled),otherLULCchangewasveryminorasonly0.76percentoftheregionchangedbetween2001and2006.Anassessmentofthemodel’sperformancebyexaminingsmallamountsofLULCchangeoververyshorttemporalintervalsisofquestionablevalue(Sohl,Sleeter,Zhu,andothers,2012).Allocationdisagreementforclassesotherthanforestclearcuttingwasthusevaluatedthroughqualitativeassessment.Duringthemodelingprocess,theperformanceofthemodelfrom1992to2005wasevaluatedindependentlyforeachlevelIIIecoregionusingavisualassessmentoftheLULC-changedistribution.AnunacceptabledistributionofLULCchangeresultedinare-parameterizationoftheFORE–SCEmodelandasubsequentnewmodelwasrununtilthemodelperformancewasdeemedacceptable.

2.4. Results and Discussion

2.4.1. Baseline LULC Mapping and Modeling—Results for the Western United States

Atthebeginningofthesimulationperiodin1992,theWesternUnitedStatesasawholewasdominatedbyshrubland(45.1percent),evergreenforest(23.9percent),andgrassland(13.9percent)—threeLULCclassesthatcoverednearly83percentoftheWesternUnitedStates.ThelesscommonbutsignificantLULCclassesincludedcultivatedcrop(3.8percent),barren(3.8percent),hay/pasture(2.5percent),anddeveloped(1.0percent).Thethreemechanicallydisturbedclasses,derivedfromtheLANDFIREVCTdataandrepresentingclearcutforest,coverednearly1.0percentoftheregion.

Between1992and2005,2.9percentofthelandareaintheWesternUnitedStateschangeditsLULCclassatleastonce.MostLULCclassesexperiencedrelativelysmallnetchangesduringthestudyperiod(table2.2).ThethreelargestLULCclasses—shrubland,evergreenforest,andgrassland—changedby−2,854km2,+5,201km2,and−1,426km2,respectively.Althoughthearealchangemayseemlargeforthethreemajorclasses,theamountofnetchangewaslessthan1percentofthetotalareaforeachLULCclassduringthetimeperiod.

ThemostdynamicchangestoLULCclassesintheWesternUnitedStates,bothintermsofabsolutenetchangeandintermsofrelativechangeforagivenLULCclass,werechangesrelatedto(1)forestclearcuttingand(2)urbandevelopment.Theareacoveredbythethreemechanically

Chapter 2 7

Table 2.2. Mapped and modeled land-use and land-cover (LULC) change (in square kilometers) indicating trends in mapped and modeled LULC classes for the Western United States for the baseline period (1992–2005).

[km2,squarekilometers;LULC,landuseandlandcover]

LULC class1992 (km2)

2005 (km2)

Change (km2)

Percent change

Water 39,289 39,744 455 1.2Urban/developed 27,430 32,486 5,056 18.4Mechanicallydisturbed—Nationalforest 9,227 3,888 −5,339 −57.9Mechanicallydisturbed—Otherpublic 2,544 1,909 −635 −25.0Mechanicallydisturbed—Private 11,580 8,103 −3,476 −30.0Mining 1,329 2,032 703 52.9Barren 100,658 100,783 125 0.1Deciduousforest 52,088 53,791 1,704 3.3Evergreenforest 636,190 641,391 5,201 0.8Mixedforest 36,286 37,289 1,003 2.8Grassland 369,279 367,853 −1,426 −0.4Shrubland 1,199,764 1,196,910 −2,854 −0.2Cropland 95,943 95,893 −50 −0.1Hay/pasture 65,573 64,820 −753 −1.2Herbaceouswetland 6,913 6,890 −22 −0.3Woodywetland 2,913 3,223 310 10.7Ice/snow 1,521 1,521 0 0

disturbedclassesofforestclearcuttingexperiencedatotalnetdeclineofnearly9,500km2by2005,whichwasareductionofover40percentinarealextentsince1992(fig.2.3).The5,201km2increaseinevergreenforestduringthesametimeperiodwasstronglytiedtothereductioninoverallclearcuttingrates.Althoughclearcuttingdeclinedinallclassesofmechanicallydisturbedlands,thesharpestdeclineinclearcuttingwasonnationalforestlands,whichdeclinedby58percentbetween1992and2005.Clearcuttingonprivatelyheldforestedlandalsodeclinedsharply(by30percent),butatamuchlowerratethantheclearcuttingonNationalForestland.

AnumberoffactorsdrovethelowerratesofforestclearcuttingintheWesternUnitedStatesduringthebaselinetimeperiodof1992to2005.FederalenvironmentalpolicystronglyaffectedclearcuttingpracticesinthePacificNorthwest.OnJune23,1990,theNorthernSpottedOwl(Strix occidentalis caurina)waslistedas“threatened”undertheEndangeredSpeciesAct.OnMay21,1991,aU.S.DistrictCourtblockedfurtherclearcuttingonnationalforestlandsintheregion.ThoserestrictionshelduntilthepassingoftheNorthwestForestPlanin1993,anagreementwhichlimitedtheclearcuttingofforestedpubliclandsto1billionboardfeetannually,whichwasroughlyone-fourthoftheclearcuttingratesduringthe1980s.Thosetimberharvestingconstraintsrippledthroughtheglobaltimberexportmarkets;thehigherpricesleadAsianimporterstolookforcheapertimberfromNewZealand,Chile,Russia,andelsewhere(Daniels,2005).

Figure 2–3.

0

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20052004200320022001200019991998199719961995199419931992

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EXPLANATIONMechanically disturbed land

National forest

Other public

Private

Year

Figure 2.3. Chart showing the declining trend of forest clearcutting in the Western United States between 1992 and 2005. The areal extent of mechanically disturbed (clearcut) land declined significantly over the baseline study period of 1992 to 2005. The strongest declines were noted on national forest lands.

8 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

TheAsiandemandfortimberproductsfromtheWesternUnitedStatesdeclinedevenfurtherinresponsetotheAsianeconomiccrisisin1997(Daniels,2005).PredictionsofthedeclineinforestclearcuttingratesintheWesternUnitedStates,however,hadbeenmadefarinadvanceofthepassageoftheNorthwestForestPlanortheAsianeconomiccrisisinthe1990s,asstudiesnotedthattheratesofforestclearcuttinginpartsoftheWesternUnitedStatesbeforethe1990swereunsustainable(Beuterandothers,1976).Thedeclineinclearcuttingnotedinthisassessmentwasprecededbyadditionaldeclinesbefore1992.TimberharvestsinthePacificNorthwestdeclinedby87percentfrom1988to1996(Warren,1999;Daniels,2005).

UrbandevelopmentwastheothermostactiveLULCclassintermsofabsolutenetchangerelativetoinitial1992LULCconditions.UrbandevelopmentintheWesternUnitedStatesincreasedbyover5,000km2from1992to2005,whichwasan18.4percentincreaseinarea(fig.2.4).Althoughtherateofincreaseindevelopmentwasrealistic,theinitialextentofurbandevelopmentinthe1992LULCdatawaslikelyanunderestimationoftheactualurbanextentbecauseitwasdifficulttoidentifyandmaplow-densityresidentialareasusingLandsatdata(Claggettandothers,2004;McCauleyandGoetz,2004).Inaddition,the2001NLCDdatahadsignificantlymoreurbanlandmappedthanthe1992NLCD,whichwaslikelyduetoimprovedsourcedataandmethodologiesjustasmuchasactualurbanexpansion.Althoughurbandevelopmentwaslikelyunderestimatedintheinitial1992map,urbanlandsstillrepresentedonlyasmallportionoftheWesternUnitedStateslandscape,andthe“story”ofurbangrowthwasrepresentedthroughthemeasuredratesofurbandevelopmentbetween1992and2005.

ThenetchangeofotherLULCtypesintable2.2wasrelativelyminor.Theevergreenforestclassincreasedbyover5,200km2(0.8percent)from1992to2005,asdiddeciduousforest(+1,704km2,or3.3percent)andmixedforest(+1,003km2,or2.8percent).Asnotedabove,theincreaseinareaofthethreeforestclasseswasprimarilyrelatedtothereductionintheratesofforestclearcutting,whichresultedinmoreareacategorizedasforestin2005becauseoftheregenerationofforestinformerlyclearcutareas.OthernotableLULCchangesincludedanincreaseof700km2ofminingby2005,whichwasa60percentincreasefrom1992.Thetwoagriculturalclasses,cultivatedcropandhay/pasture,eachdeclinedwithanegligibledeclineforcultivatedcropandadecreaseof1.1percentinhay/pasturefrom1992to2005.Grasslandandshrublandbothdeclined,withgrasslandlosing1,426km2andshrublandlosing2,854km2.GiventhevastexpansesofgrasslandandshrublandintheWesternUnitedStates,however,thisonlyrepresentedanetlossof−0.39percentand−0.24percent,respectively,fromtheinitial1992extentsofgrasslandandshrubland.

25,000

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20052004200320022001200019991998199719961995199419931992

Area

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Figure 2–4.

Year

Figure 2.4. Chart showing the increasing trend in the areal extent of urban development in the Western United States between 1992 and 2005. The data were derived from the USGS Land Cover Trends project for the 1992 to 2000 period and from the National Land Cover Dataset (NLCD) 2001 to 2006 change product for the 2001 to 2005 period. A consistent annual rate of change was modeled between 1992 and 2000, and again for 2001 to 2005, on the basis of the USGS Land Cover Trends and NLCD data, respectively. The measured rate of urban development for those two periods was nearly constant.

2.4.2. Regional Results

Althoughtable2.2indicatesoverallnetchangesintheprimaryLULCtypesfortheWesternUnitedStatesfrom1992to2005,regionalvariabilityresultedinaheterogeneouspatternofLULCchangeduringthestudyperiod.WithinthelevelIIIecoregionswheresignificantamountsofforestclearcuttinghadoccurred,20percentormoreofthelandareachangeditsLULCclassatsomepointbetween1992and2005,whereaswithintheecoregionscoveredprimarilybydesert,1percentorlessoftheareachangeditsLULCclass(fig.2.5).Thetotalspatialchangecloselymimickedthespatialvariabilityofforestclearcutting,whichwasthemostprevalentformofLULCconversionintheWesternUnitedStates(fig.2.6).Forestclearcuttingwasonlyonepartofthestory,however.EachecoregionhadgreaterinternalhomogeneitythantheWesternUnitedStates’landscapeasawhole,andeachhadaunique“story”aboutitsbaselineland-coverchangefrom1992to2005.ThefollowingsectionsdescribethebasiccharacteristicsofeachlevelIIecoregionanddiscusstheprimaryLULCchangesfrom1992to2005,includingabriefdiscussionofthemajordrivingforcesofthechanges.

Chapter 2 9

0 5 10 15 20

100 2000 300 400 500 MILES

2500 500 KILOMETERS

Spatial variability of land-use and land-cover change in the Western United States, by level III ecoregion, in percent

EXPLANATION

Level II ecoregion

Level III ecoregion

Figure 2.5.

N

Figure 2.5. Map showing the spatial variability of land-use and land-cover change in the Western United States between 1992 and 2005. The spatial change (the percent of area that changed at least once from 1992 to 2005) varied greatly between the ecoregions. See figure 1.1 in chapter 1 for ecoregion names.

100 2000 300 400 500 MILES

2500 500 KILOMETERS

EXPLANATION

0 5 10 15 20

Level II ecoregion

Level III ecoregion

Figure 2.6.

N

Spatial variability of forest clearcutting in the Western United States, by level III ecoregion, in percent

Figure 2.6. Map showing the spatial variability of forest clearcutting in the Western United States from 1992 to 2005. Given that forestry activity was the primary driver of measured land-use and land-cover (LULC) change in the region, the distribution of clearcutting by ecoregion was very similar to the overall pattern of LULC change of Western United States. See figure 1.1 in chapter 1 for ecoregion names.

10 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

2.4.2.1. Western CordilleraTheWesternCordilleraecoregioncoversmostofthe

forestedlandsintheinterioroftheWesternUnitedStatesandconsistsofanumberofgeographicallydisparateregionsstretchingfromtheCanadianborderinWashingtontothe“skyislands”ofNewMexicoandArizona.TheWesternCordilleraischaracterizedbygenerallyruggedtopography(includingmountainrangesthathavethehighestelevationsintheWesternUnitedStates)andpredominantlynaturallandscapes.In1992,forestcover(evergreen,mixed,anddeciduousforest)alonecovered60.8percentoftheecoregion.The“natural”land-coverclasses(forestedclasses,grassland,shrubland,wetlandclasses,andwater)coveredover95.9percentoftheecoregionwhereasanthropogeniclanduses(urbandevelopment,forestcutting,mining,andagriculture)coveredonly4.1percentoftheecoregion(fig.2.7).

Approximately4.4percent(38,447km2)oftheecoregionexperiencedLULCchangeatleastonceduringthebaselineperiod(1992–2005).Althougharelativelysmallproportionoftheecoregionchanged,thiswasthesecondmostactivelevelIIecoregionintheWesternUnitedStatesforthisperiod.Between1992and2005,thevastmajorityofLULCchangewasassociatedwithforestryactivity;87.8percent(33,739km2)ofthechangedpixelswereassociatedwitheitherclearcuttingfortimberortheregenerationoftheclearcutareas.AswiththeWesternUnitedStatesasawhole,thenetchangesinLULCclassesweresmall,andthelargestchangesbyabsoluteareaandbypercentagelossorgainwereassociatedwiththetimberindustry(fig.2.7).Between1992and2005,clearcuttingactivitydeclinedsharplyinallthreemechanicallydisturbedclasses(nationalforests,otherpublicforests,andprivateforests).Thecuttingratesonnationalforestlandexperiencedboththelargestabsolutechange(−5,130km2)andrelativechange(−57.7percent)from1992to2005.Forestedlands(evergreen,deciduous,andmixedforest)increasedby1.4percent(7,335km2),whichwasprimarilyduetothedeclinesinclearcuttingrates.Thedevelopedlandsexperiencedamodestincreaseof367km2,oranincreaseof16.2percent,between1992and2005.

2.4.2.2. Marine West Coast ForestTheMarineWestCoastForestecoregioncovers

themaritimeforestsalongtheWestCoastoftheUnitedStates.ThisecoregionwasthemostheavilyforestedofthefivelevelIIecoregionsintheWesternUnitedStateswithapproximately70percentofthelandareacoveredbyoneofthethreeforestclassesin1992.ThisecoregionwassimilartotheWesternCordilleraecoregioninthatthe“natural”land-coverclassescoveredthemajorityoftheecoregion,andasmallerpercentage(24.8percent)ofthelandareaofthisecoregionwascategorizedbyanthropogeniclandusesin1992.In1992,theterrestrialportionoftheMarineWestCoast

Foresthadhigherproportionsofclearcutland(7.9percent),ahigherproportionofdevelopedlands(4.5percent,mostlyaroundthePugetSoundandaroundtheWillametteValley),andsignificantlymoreagriculturalland(12.4percent,themajorityofwhichwashay/pasture)thantheWesternCordillera(fig.2.7).

ThespatialfootprintofLULCchangebetween1992and2005wasmuchhigherinthisecoregionthaninanyotherlevelIIecoregionintheWesternUnitedStates.Approximately19.7percent(16,850km2)ofthelandscapechangedLULCclassesatleastoncebetween1992and2005withthevastmajorityofthechangerelatedtoforestryactivity(aspatialfootprintof15,061km2).AswiththeWesternCordilleraecoregion,forestclearcuttingdeclinedfrom1992to2005,althoughnotassharplywithatotaldeclineof24.9percent(1,671km2).ForestclearcuttingonNationalForestlanddroppedbynearly70percent;however,mostoftheforestedlandinthisecoregionwasprivatelyheld,andthemoremodestdeclinesinclearcuttingratesonprivatelandmitigatedthedeclineintheecoregion’soverallrateofclearcutting.Despitetheoveralldeclineinclearcuttingrates,theamountoflandinthethreeforestclassesonlyincreasedslightly—by0.5percent(520km2)—between1992and2005.TheincreaseinforestedlandwaslessthanthatintheWesternCordilleralargelybecausethedecreasesinforestclearcuttingwerepartiallyoffsetbyclearingforestedlandforurbandevelopment.EventhoughtheMarineWestCoastForestecoregionissmallerinareathantheWesternCordilleraecoregion,ithad1,563km2moredevelopedlandin1992andmorenewurbandevelopmentbetween1992and2005(893km2intheMarineWestCoastForestcomparedto367km2intheWesternCordillera).ThenetchangewithintheotherLULCclasseswasminor;nolandareacategorizedbythoseclasseschangedbymorethan200km2between1992and2005.

2.4.2.3. Cold Deserts TheColdDesertsecoregionencompassesthetemperate

andcooleraridlandsoftheinteriorWesternUnitedStates.Grasslandandshrublandwerethemostcommonland-covertypesintheecoregion;in1992,theycovered61.9percentand14.5percentoftheecoregion,respectively.In1992,forests(evergreen,deciduous,andmixed)covered9.2percentoftheecoregionandwerefoundthroughouttheecoregioninscatteredpocketsoflandwithsuitablesoils,moisture,andclimate.In1992,agriculturallands(cultivatedcropandhay/ pasture)covered7.7percentoftheecoregion;themajoritywasirrigatedagriculturallandlocatedintheColumbiaPlateauandtheSnakeRiverPlainlevelIIIecoregions.TheColdDesertsecoregionhadalowpopulationdensitywithonlyafewlargeurbanareas,includingSaltLakeCity,Utah,andAlbuquerque,NewMexico.Urbandevelopmentcovered5,085km2oftheecoregionatthebeginningofthebaselineperiodin1992.

Chapter 2 11

Open water

Developed

Mechanically disturbed (national forest)

Mechanically disturbed (other public land)

Mechanically disturbed (private land)

Mining

Barren

Deciduous forest

Evergreen forest

Mixed forest

Grassland

Shrubland

Agriculture

Hay/pasture

Woody wetland

Herbaceous wetland

Ice/snow

EXPLANATION

Figure 2–7.

Land-use or land-cover class

[Pie charts represent data for 2005]

Ope

n w

ater

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Dec

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rest

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ssla

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Western Cordillera ecoregion

1992 (area, in km2) 7,827 2,260 8,896 1,557 5,987 266 14,916 30,213 483,704 16,541 110,982 166,953 4,977 12,289 2,229 1,176 1,507

2005 (area, in km2) 7,939 2,627 3,767 1,113 3,889 393 15,004 31,104 489,702 16,987 110,983 166,892 4,778 11,944 2,303 1,353 1,507Net change in area (in km2) 111 367 –5,130 –444 –2,099 127 88 891 5,998 446 1 –61 –200 –346 74 177 0Change in area (in percent)

1992 (area, in km2)

2005 (area, in km2)

Net change in area (in km2)Change in area (in percent)

1992 (area, in km2)

2005 (area, in km2)

Net change in area (in km2)Change in area (in percent)

1992 (area, in km2)

2005 (area, in km2)

Net change in area (in km2)Change in area (in percent)

1992 (area, in km2)

2005 (area, in km2)

Net change in area (in km2)Change in area (in percent)

1.4 16.2 –57.7 –28.5 –35.1 48.0 0.6 2.9 1.2 2.7 0.0 0.0 –4.0 –2.8 3.3 15.0 0.0

Marine West Coast Forest ecoregion

9,964 3,823 290 953 5,471 32 505 10,082 38,077 10,880 2,846 1,367 2,561 8,042 182 347 0

10,004 4,715 89 783 4,170 52 499 10,888 37,345 11,326 3,037 1,507 2,516 7,902 223 364 0

40 892 –201 –170 –1,301 20 –6 806 –732 446 191 140 –45 –140 41 17 0

0.4 23.3 –69.3 –17.8 –23.8 62.5 –1.2 8.0 –1.9 4.1 6.7 10.2 –1.8 –1.7 22.5 4.9 0.0

Cold Deserts ecoregion

12,804 5,085 11 20 61 645 48,201 6,089 89,580 1,499 152,950 653,289 51,675 29,562 3,538 1,037 10

12,924 6,237 2 4 11 937 48,284 6,098 89,552 1,513 152,684 651,974 51,865 29,325 3,458 1,177 10

121 1,153 –9 –16 –50 291 84 9 –28 14 –267 –1,315 190 –237 –80 139 0

0.9 22.7 –80.0 –81.0 –81.8 45.2 0.2 0.2 0.0 1.0 –0.2 –0.2 0.4 –0.8 –2.3 13.4 0.0

Warm Deserts ecoregion

2,424 4,618 16 7 19 322 33,539 497 7,120 466 55,915 348,558 7,168 4,286 129 205 0

2,446 5,747 12 3 3 507 33,450 499 7,100 466 55,806 347,586 7,097 4,240 135 191 0

21 1,129 –3 –4 –16 185 –89 2 –20 0 –109 –972 –71 –46 6 –14 0

0.9 24.4 –21.9 –52.3 –83.4 57.6 –0.3 0.4 –0.3 0.0 –0.2 –0.3 –1.0 –1.1 4.8 –6.8 0.0

Mediterranean California ecoregion

6,270 11,645 14 7 42 64 3,498 5,207 17,709 6,901 46,586 29,598 29,562 11,393 835 149 3

6,431 13,160 18 6 31 144 3,547 5,202 17,692 6,997 45,343 28,951 29,638 11,409 772 139 3

162 1,515 4 –1 –11 80 49 –5 –17 96 –1,243 –646 76 16 –64 –10 –0

2.6 13.0 25.9 –16.5 –26.5 123.5 1.4 –0.1 –0.1 1.4 –2.7 –2.2 0.3 0.1 –7.6 –6.4 –4.0

Land-use or land-cover class

Figure 2.7. Charts showing the proportions of land use and land cover (LULC) at the end of the baseline period (pie charts for 2005) and the net change in the mapped and modeled LULC classes between 1992 and 2005, by level II ecoregion.

12 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in Ecosystems of the Western United States

ThespatialfootprintofLULCchangebetween1992and2005wasonly1.1percentoftheecoregionarea.Commercialforestryactivityandotherforestclearcutting,whichweremajorsourcesofLULCchangeintheWesternCordilleraandMarineWestCoastForestecoregions,werenegligibleintheColdDesertsecoregionbecauseoftheabsenceofsuitableforestresources.UrbandevelopmentwasresponsibleforthelargestnetchangesinLULCtypes,asshowninfigure2.7.Anestimated1,153km2ofnewurbanlandsweredevelopedby2005,whichwasanetincreaseof22.7percentoverthe1992urbanextent.Thelargestabsolutenetchangebyclasswasa1,315km2lossofshrubland,whichwasprimarilyduetotheconversionofshrublandtourbandevelopmentandirrigatedagriculture;however,giventheprevalenceofshrublandinthisecoregion,thearealextentofshrublanddeclinedbyonly0.2percentfrom1992to2005.TheabsolutenetchangesinallotherLULCclasseswereminor.Nolandareacategorizedbythoseclasseschangedbymorethan300km2from1992to2005.Mininglands,however,increasedby291km2from1992to2005,anincreaseof45.2percent.

2.4.2.4. Warm Deserts TheWarmDesertsecoregioncoversthewarmer

desertsandaridregionsoftheinteriorSouthwesternUnitedStates.ThreeLULCclassesalonecovered94.1percentoftheecoregionin1992:shrubland,74.9percent;grassland,12.0percent;andbarrenland,7.2percent.Forestsandagriculturallandswereonlyfoundinafewscatteredlocationsintheecoregion.Theforestedlands(evergreen,deciduous,andmixed)wereprimarilyfoundinafewareasofhigherelevationandnearwatersourcesandtogethercovered1.7percentoftheecoregionin1992.Theagriculturallands(cultivatedcropandhay/pasture)wereprimarilyfoundinareaswhereirrigationsourceswereavailable,suchasneartheSaltonSeainCaliforniaandnearPhoenix,Arizona;in1992,theycovered2.5percentoftheecoregion.Urbandevelopmentonlycovered1.0percentoftheecoregionin1992,yetseverallargeurbancentersarelocatedinthisecoregion,includingPhoenixandTucsoninArizona,andLasVegas,Nevada.

ThespatialfootprintofLULCchangebetween1992and2005wasonly0.8percentoftheWarmDesertsecoregion,makingittheecoregionwiththeleastamountofLULCchangeintheWesternUnitedStates.Urbandevelopmentincreasedby1,129km2,a24percentincreasefrom1992.Shrublanddeclinedby972km2,adeclineof0.3percent,with

mostofthelossattributedtotheconversionofshrublandtourbandevelopment.OtherLULCchangesintheecoregionwereminor.Commercialforestrywasnegligibleintheecoregion.Mininglandsexpandedby185km2,anincreaseof57.6percentfrom1992.

2.4.2.5. Mediterranean CaliforniaTheLULCoftheMediterraneanCaliforniaecoregionis

moreheterogeneousthantheotherecoregionsintheWesternUnitedStates.Thisecoregionistheonlyonewhereforests(evergreen,mixed,anddeciduous)orshrublandalonedidnotcoveramajority(>50percent)oftheecoregionarea.Grassland(27.5percent),agriculturalclasses(24.2percentforthetwoclasses),forest(17.6percentforthethreeclasses),shrubland(17.5percent),andurbandevelopment(6.9percent)eachrepresentedthedominantLULCclassforspecificportionsoftheecoregionin1992.GrasslandwasscatteredthroughouttheecoregionbuttherewasahighconcentrationaroundtheperipheryoftheCentralCaliforniaValleylevelIIIecoregion.AgriculturallandwasconcentratedintheCentralCaliforniaValley,althoughthereweresmaller,scatteredpatchesinwesternandsouthernCalifornia.ForestedlandswereconcentratedintheSouthernCaliforniaMountainslevelIIIecoregionandalongtheedgesoftheSouthernandCentralCaliforniaChaparralandOakWoodlandslevelIIIecoregion.Thevastmajorityofshrublandwasfoundinthefarsouthernthirdoftheecoregion,andareasofdenseurbandevelopmentwerefoundthroughouttheecoregion.

ThespatialfootprintofLULCchangebetween1992and2005was3.5percentoftheecoregionarea.Thegreatestamountofchangebyareawasassociatedwiththegrosschangebetweenthecultivatedcropandhay/pastureclasses.Thenetchangeinthosetwoclasseswasverysmall,withcultivatedcropincreasingby76km2(0.3percent)andhay/ pastureincreasingby16km2(0.1percent).Underlyingthesmallamountofnetchange,however,werelargeamountsofgrosschangewithnearbalancesofcultivatedcropconvertingtohay/pastureandviceversa.ThehighestnetchangesinLULCclasseswereassociatedwithurbandevelopment.Over1,500km2ofnewurbandevelopmentoccurredbetween1992and2005,whichwasa13.0percentincreaseoverthe1992extent.Grasslanddeclinedby1,243km2(2.7percent)andshrublanddeclinedby646km2(2.2percent),withthemajorityofthedeclinescausedbyconversiontourbandevelopment.OtherLULCchangesintheecoregionwereminor.