Baseline Land-Use and Land-Cover Changes in the Western ... · Baseline Land-Use and Land-Cover ....
Transcript of Baseline Land-Use and Land-Cover Changes in the Western ... · Baseline Land-Use and Land-Cover ....
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.)
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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
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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
Area
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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
30,000
35,000
20052004200320022001200019991998199719961995199419931992
Area
, in
squa
re k
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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
Dev
elop
ed
Mec
hani
cally
dis
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ed (n
atio
nal f
ores
t)
Mec
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pub
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Mec
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riva
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Min
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Dec
iduo
us fo
rest
Ever
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rest
Mix
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rest
Gra
ssla
nd
Shru
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ture
Hay
/pas
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Woo
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etla
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Her
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Ice/
snow
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.