Biome Redistribution Under Climate Change
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CHAPTER 2
Biome Redistribution Under Climate Change
Dominique Bachelet, Oregon State University
Ronald P. Neilson, USDA Forest Service, Pacific Northwest Research Station
Introduction/Background
General warming in the Northern Hemisphere has
been recorded since the end of the 1800s following the
Little Ice Age (Folland et al. 1990). Records of glacier
retreat during the last 100 years over the entire globe
(Oerlemans 1994) independently confirmed the recorded
trend in global temperature rise. Several studies have
illustrated various responses to this climate forcing, i.e.,
the recorded changes in temperature and precipitation
concurrent with the increase in atmospheric CO2 concentration, increases in density of tree populations (Morin
and Payette 1984; Payette and Filion 1985; Scott et al.
1987), declines in tree populations (Hamburg and Cogbill
1988), treeline displacement (Lescop-Sinclair and Payette
1995) or lack thereof (MacDonald et al. 1998), lengthening of the growing season (Mynemi et al. 1997), and
enhanced tree growth (Jacoby et al. 1996). It is critical that
we identify the tools needed to estimate potential consequences of climate change on forest ecosystems (Joyce
and Birdsey this volume) and develop management practices and policies adapted to projected drifts in the geographic distribution of ecosystems.
Emanuel et al. (1985), who used the Holdridge lifezone model (Holdridge 1947), and Box (1981) were among
the first to use correlational models between average climate and vegetation distribution to predict the responses
of vegetation to climate change using general circulation
model (GCM) climate simulations. The Holdridge lifezone classification relates the distribution of major ecosystems to mean annual biotemperature, mean annual
precipitation, and the ratio of potential evapotranspiration to precipitation (Holdridge 1947). It was used by
several authors (Emanuel et al. 1985; Prentice and Fung
1990; Smith et al. 1992) to examine potential global shifts
in major ecosystems with climate change (Dale 1997).
Results from Smith et al. (1992) showed a global decrease
in the extent of tundra and desert, with a concurrent
increase in grassland area, under four different GCM climate change scenarios. Results also showed an increase
in tropical forest area and the replacement of tundra by
boreal forests. These static models offer simplicity and
availability but: 1) they do not take into account seasonality; 2) they have strict climate boundaries which create
problems for representing transitional vegetation; and
3) they cannot include any direct CO2 effect or indicate
changes in vegetation density, runoff, or nutrient fluxes.
18
Over 100 “gap” model studies have also been conducted
to simulate the impacts of global change on forests (Smith
and Shugart 1996; Dale and Rauscher 1994; Smith et al.
1992). These models predict the establishment, growth,
and death of individual trees for all potential species on a
site. They include a wide range of disturbances such as fire,
blowdown, insect defoliation, and drought. Simple rules
are used to simulate succession in most forests. Comparative studies showed that seemingly similar models could
yield totally different projections of future forest composition (for example, Bugmann 1997), since there is considerable uncertainty about the appropriate formulation of
environmental influences on demographic processes. Early
versions of gap models had been developed for current
climate. Their applicability to changing climate conditions
and increasing CO2 concentration was questionable (for
example, Loehle and Leblanc 1996). However, a second
generation of gap models was developed with improved
formulations of key relationships, including physiological
mechanisms, thus allowing more mechanistic calculations
of environmental effects on tree growth. Functional types
were used to reduce the numbers of site-specific parameters required to run the models (Friend et al. 1997). Unfortunately, there has not been enough time yet for results
from climate change research with these newer models to
be widely circulated and published.
Biogeography models such as DOLY (Woodward and
Smith 1994), MAPSS (Neilson 1995), and BIOME2 or 3
(Haxeltine et al. 1996), which are based on ecophysiological constraints and resource limitations, have been considered the next generation of equilibrium spatial models
(Monserud and Leemans 1992). They are capable of simulating impacts on natural vegetation at all scales from
global to continental, regional, and local (Smith et al.
1994) and have been used in several global climate change
studies (IPCC 1996; VEMAP Members 1995; Neilson et al.
1998).
The objective of this chapter is to address the following
question: To what geographic extent will potential ecosystem types change or move across the United States, as
measured in composition and boundary changes? To do
so, we used results from three different studies (Neilson
et al. 1998; VEMAP Members 1995; Neilson and Drapek
1998), which are summarized in table 2.1. Three different
models (DOLY, MAPSS, BIOME2 and its later version
BIOME3) were run at two spatial resolutions (half-degree
latitude × half-degree longitude, and 10 km) for two
geographic extents (North America and the conterminous United States). Older and newer GCM-generated
climate scenarios were used to describe the impacts of
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–59. 2000.
Biome Redistribution Under Climate Change
Bachelet and Neilson
Table 2.1—Summarized description of the three studies used in this article to illustrate the impact of climate change on biome distribution. FAR = First Assessment Report (IPCC 1990) including climate change scenarios from GFDL-R30, GISS, OSU, UKMO; SAR =
Second Assessment Report (IPCC 1996) including climate change scenarios from HADCM2SUL and HADCM2GHG (see table 3 for
details on scenarios).
Region of study
(project)
Biogeography
models
Resolution
Reference
North America
MAPSS
BIOME3
0.5° latitude
× longitude
Neilson et al. 1998
FAR and SAR
Leemans and
Cramer 1991
Conterminous
USA (VEMAP)
MAPSS
DOLY
BIOME2
0.5o latitude
× longitude
VEMAP Members 1995
FAR
Kittel et al. 1995
Regional USA
MAPSS
10 km
Neilson and Drapek 1998;
Borchers and Neilson 1998
FAR and SAR
NOAA-EPA 1997
the improvements made in projecting future climates on
ecological simulation results. The rationale for using this
approach is that: 1) focusing on the entire North American
continent enables us to include entire biomes regardless
of political boundaries; 2) focusing on the U.S. enables
us to address nationally relevant issues and to compare
MAPSS results with other model projections; and 3) a
10 km resolution is a more adequate scale to focus on
regional impacts. A different baseline climatic dataset was
used for each of the three studies, which explains the differences between the North American study and VEMAP,
both of which were performed at the same half-degree
resolution. Using results from these studies increases the
information gain about U.S. forests and also emphasizes
the uncertainties associated with the results.
Methodology
Biogeography Models
Models
Process-based biogeography models simulate the dominance of various plant lifeforms in different environments based on ecophysiological constraints, such as
growing degree days and minimum winter temperatures,
and resource limitations such as available soil water for
plant uptake and available sunlight for the understory
canopy (VEMAP Members 1995). These models simulate
potential “climax” vegetation at steady state under any
climate, past, present, or future (Neilson and Running
1996).
Most of the results presented in this chapter come
from the MAPSS (Mapped Atmosphere Plant Soil System)
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–59. 2000.
Climate change
scenario
Climate data
source
model (Neilson 1995; Neilson and Marks 1994). It includes
a water submodel that calculates plant available water
and a rule-based submodel that determines the climatic
zone, the lifeform, and the plant type as a function of
temperature thresholds and water availability. The maximum potential leaf area index (LAI) a site can support is
calculated iteratively. It uses an aerodynamic approach
sensitive to canopy characteristics to calculate evapotranspiration. Grasses and trees have different rooting
depths in a multi-layer soil and compete for available soil
water, while shading by trees limits grass growth. Vegetation classification in MAPSS is based on the presence/
absence and LAI values of three types of lifeforms—trees,
shrubs, and grasses—with their leaf characteristics, thermal affinities, and seasonal phenology. The woody components, trees or shrubs, are assumed to be dominant and
mutually exclusive. MAPSS includes a fire submodel that
maintains transition zones such as the prairie peninsula.
The model has been run at two different resolutions: 1) 10
km; and 2) half degree latitude-longitude resolution for
VEMAP and the North American study.
BIOME2 and DOLY are two other biogeography models
that have been compared to MAPSS in VEMAP (VEMAP
Members 1995). The newer version of BIOME2, BIOME3,
was later compared to MAPSS in the North American
study (Neilson et al. 1998). BIOME3 builds upon BIOME2
but contains a more process-based canopy physiology,
optimizing carbon gain through photosynthesis with radiation and water balance constraints on stomatal conductance. In BIOME2 and BIOME3 (Haxeltine and Prentice
1996; Haxeltine et al. 1996; Prentice et al. 1992), plant
functional types (PFT) are calculated using a small set
of ecophysiological constraints such as minimum temperature tolerance. Gross primary production (GPP) is
calculated for each PFT as a function of photosynthetically active radiation (PAR) based on the Farquhar photosynthesis equation (Farquhar et al. 1980). GPP is then
reduced by soil water availability and temperature lim-
19
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GENERAL COOLER SCENARIOS TABLE BOTH OVER THE .ORTH
!MERICAN LAND AREAS +ATTENBERG ET AL AND OVER
THE5NITED3TATES4HESULFATEAEROSOLSCENARIOISVERYDRY
OVERTHEWORLDBUTQUITEWETOVERTHE5NITED3TATES!DDI
4ABLE3IMULATEDCHANGESINTEMPERATURE #ANDPRECIPI
TATION PERCENT OVER THE WORLD LAND AREA AND OVER THE CONTER
MINOUS 53 &ROM THE &IRST !SSESSMENT 2EPORT &!2 OF THE
)NTERGOVERNMENTAL0ANELON#LIMATE#HANGE)0##THEATMO
SPHERIC GENERAL CIRCULATION MODELS '#-S USED TO SIMULATE
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'ODDARD)NSTITUTEOF3PACE3TUDIES')33MODELTHE'EOPHYS
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5NITED +INGDOM -ETEOROLOGICAL /FlCE MODEL 5+-/ &ROM
THE3ECOND!SSESSMENT2EPORT3!2OFTHE)0##THEATMO
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ANDWITHOUT(!$#-'('SULFATEAEROSOLFORCING
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NARIOSCANBEFOUNDIN.EILSONAND$RAPEK
2ESULTS
.ORTH!MERICAN)MPACTS
%FFECTSOF#/-!0332ESULTS7ITH
&!23CENARIOS
2ESULTS FROM RUNNING THE EQUILIBRIUM VEGETATION DIS
TRIBUTION MODEL -!033 FOR THE .ORTH!MERICAN REGION
HALFDEGREELATITUDELONGITUDERESOLUTIONWITHANDWITH
OUTA#/EFFECTFORTHREE'#-SCENARIOSAREILLUSTRATEDIN
TABLE-AJORAGREEMENTSCANBEIDENTIlEDDECREASES
IN THE AREA OF BOTH TUNDRA AND TAIGATUNDRA FROM TO PERCENT AND FROM TO PERCENT RESPECTIVELY
INCREASESINTHEAREALEXTENTOFSAVANNASFROMPER
CENT WITH THE #/ EFFECT TO PERCENT WITHOUT AND DECREASESINTHEAREAOFSHRUBLANDSFROMTOPERCENT
7HENTHE#/EFFECTISINCLUDEDPERCENTDECREASEIN
STOMATALCONDUCTANCETEMPERATEEVERGREENANDTEMPER
ATE MIXED FORESTS ARE PREDICTED TO INCREASE IN AREA WITH
THELARGESTINCREASESPREDICTEDUNDERTHE5+-/SCENARIO
PERCENTANDPERCENTRESPECTIVELY
#OMPARISON"ETWEEN")/-%AND-!033
5SING3!23CENARIOS
-!033 SIMULATIONS USING THE (ADLEY #ENTRE SCENAR
IOS (!$#-35,AND '(' ARE COMPARED TO THOSE OF
")/-%INTABLE4HEMODELSPREDICTOPPOSITETRENDS
FOR BOTH THE BOREAL CONIFEROUS FOREST AND THE TEMPERATE
EVERGREENFOREST")/-%GROUPSBOREALFORESTANDTAIGA
TUNDRAINTOONEVEGETATIONTYPEWHILE-!033DOESNOT
-!033PREDICTSLARGEDECREASESINTHETAIGATUNDRAAREA
EASTERN #ANADA AND !LASKA lG WHICH MATCHES
")/-% SIMULATIONS OF BOREAL FOREST AREA INCREASE BUT
-!033ALSOSIMULATESSMALLINCREASESINTHEBOREALFOREST
AREA PROPER 4HUS THE TWO MODELS ARE CONSISTENT WITH
EACHOTHERWITHRESPECTTOHIGHLATITUDEECOSYSTEMSWITH
APPARENT DIFFERENCES ONLY INDICATING DIFFERENT CLASSIlCA
TION SCHEMES &OR ALL SCENARIOS BOTH MODELS AGREE ON
SIMULATINGLARGEDECREASESINTHEAREAOFPURETUNDRA
REPLACED BY THE WARMER TAIGATUNDRA LARGE INCREASES
IN THE TEMPERATE MIXED FOREST TABLE MOVING WEST
WARD IN THE 5NITED 3TATES AND NORTHWARD INTO #ANADA
lGANDLARGEDECREASESINTHEAREAOFARIDLANDS
TABLETHATAREREPLACEDBYGRASSLANDSlG7HEN
THE#/EFFECTISNOTINCLUDEDINTHEMODELSBOTHSIMULATE
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53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"ACHELETAND.EILSON
7ITH THE (!$#-35, SCENARIO -!033 SIMULATES
LARGE SHIFTS OF .ORTHWEST TEMPERATE EVERGREEN FORESTS
TO !LASKA REPLACING THE TAIGATUNDRA AREA lG BUT
")/-% SHOWS A MUCH SMALLER EXPANSION NOT SHOWN
HERElG#ANDIN.EILSONETAL4HEYBOTHSIM
ULATEANEXPANSIONOFTHESOUTHEASTERNTEMPERATEMIXED
FORESTATITSWESTERNEDGE
#ONTERMINOUS53)MPACTS
#OMPARISON"ETWEEN$/,9")/-%AND
-!0335SING&!23CENARIOS
4HREEBIOGEOGRAPHICALMODELS$/,9")/-%AND
-!033WEREUSEDTOSIMULATEVEGETATIONDISTRIBUTION
FORCURRENTCLIMATECONDITIONSANDFUTURECLIMATECONDI
TIONSUNDERTHREEDIFFERENT'#-S4HETHREEBIOGEOGRA
PHYMODELSPRODUCESIMILARMAPSOFCURRENTVEGETATION
DISTRIBUTION7HETHERTHE#/EFFECTISINCLUDEDORNOT
-!033 AND ")/-% SIMULATE A LOSS OF ALPINE TUNDRA
ANDBOREALCONIFEROUSFORESTAREATABLE$/,9SIM
ULATESANINCREASEINALPINETUNDRAWHENTHE#/EFFECT
IS INCLUDED FOR ALL CLIMATE CHANGE SCENARIOS $/,9
ONLY SIMULATES AN INCREASE IN THE EXTENT OF THE BOREAL
CONIFEROUS FOREST UNDER THE /35 SCENARIO WHEN THE
#/ EFFECT IS INCLUDED 7HEN THE #/ EFFECT IS NOT
INCLUDED -!033 SIMULATES A DECREASE IN TEMPERATE
FORESTS ACCOMPANIED BY AN INCREASE IN SAVANNAS AND
GRASSLANDS ON THE OTHER HAND ")/-% SIMULATES AN
INCREASE IN TEMPERATE FORESTS AND TROPICAL BROADLEAF
FORESTAREASATTHEEXPENSEOFSAVANNASSHRUBLANDSAND
ARIDLANDS"OTH$/,9AND-!033SIMULATEINCREASES
INARIDLANDAREA$/,9PRODUCESAGREATEREXPANSION
OFFORESTSINTOTHE'REAT0LAINSANDPRODUCESLITTLEFOREST
DIEBACKUNDERALTEREDCLIMATENOTSHOWNHERE(OW
EVER$/,9ALSOPRODUCESFARMOREDRAMATICINCREASES
INTHEEXTENTOF3OUTHWESTDESERTSTHANEITHER-!033
OR ")/-% TABLE 4HE ONLY GENERAL AGREEMENTS
IN 6%-!0 FOR ALL SCENARIOS AND ALL MODELS ARE THAT
SHRUBLAND AREA DECREASES WHEN THE EFFECT OF #/ IS
INCLUDEDANDWHENITISNOTTUNDRAANDBOREALFOREST
AREASDECREASE!MOREDETAILEDANALYSISOFTHESERESULTS
ISPRESENTEDIN.EILSONAND#HANEY
%FFECTSOF#/-!0332ESULTSWITH
&!23CENARIOS
4HERE ARE LARGE DIFFERENCES BETWEEN -!033 RESULTS
WHETHERTHEEFFECTOF#/ISINCLUDEDORNOT&OREXAMPLE
-!033SIMULATEDLARGEDECREASESnPERCENTINTHE
AREAOFTEMPERATEMIXEDFORESTINTHEEASTERN5NITED3TATES
FOR hWARMERv SCENARIOS SUCH AS THE 5+-/ AND '&$,
WHEN THE #/ EFFECT WAS NOT INCLUDED 4HESE DECREASES
WEREGREATLYREDUCEDnPERCENTWHENWATERUSEEFl
"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
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VEGETATIONTYPEFROMCURRENTCLIMATETOFUTURECLIMATECONDITIONSWITHNO#/EFFECT!ANDWITH#/EFFECT"0ERCENTAGECHANGEIN
VEGETATIONTYPEAREAISCALCULATEDASSCENARIOnCURRENTCURRENT4HEATMOSPHERICGENERALCIRCULATIONMODELSUSEDTOSIMULATECLIMATE
&!2SCENARIOSWERETHE/REGON3TATE5NIVERSITYMODEL/35THE'EOPHYSICAL&LUID$YNAMICS,ABORATORYMODEL'&$,2AND
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/35$
'&$,2$
!7ITHNO#/EFFECT
4UNDRA
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4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
n
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"7ITH#/EFFECT
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
n
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CIENCY WAS INCREASED TABLE 7ITH A MILDER SCENARIO
LIKE/35THESEFORESTSCOULDEVENINCREASEINTHEIREXTENT
BY ABOUT PERCENT IF STOMATAL CONDUCTANCE IS REDUCED
UP TO PERCENT BY ELEVATED #/ CONCENTRATION AS IT IS
ASSUMED IN -!033 TABLE )N THE EARLY STAGES OF
WARMINGWHENTEMPERATUREINCREASESARESMALLA#/
INDUCED INCREASE IN WATER USE EFlCIENCY COULD RESULT IN
ANEXPANSIONOFTEMPERATEFORESTSINTONEIGHBORINGDRIER
AREASANDACONCURRENTINCREASEINFORESTDENSITYTHROUGH
OUTMUCHOFTHECURRENTFORESTDISTRIBUTION(OWEVERAS
THE #/ EFFECTS SATURATE AND TEMPERATURES CONTINUE TO
INCREASE THE ELEVATED EVAPORATIVE DEMAND COULD THEN
OVERWHELM THE INCREASED WATER USE EFlCIENCY AND TEM
PERATE FORESTS COULD CONTRACT IN AREA AND UNDERGO A
DROUGHTINDUCED DECLINE IN VEGETATION DENSITY .EILSON
AND$RAPEK#OMPLEXRESPONSESOFTHEVEGETATION
TO CHANGES IN THEIR CLIMATIC ENVIRONMENT AND IN THE
ATMOSPHERIC#/CONCENTRATIONARETOBEEXPECTED%ARLY
RESPONSESTOTHE#/FERTILIZATIONEFFECTLEADINGTOAGREEN
INGOFTHELANDMAYBEFOLLOWEDBYFORESTDIEBACKSDUETO
INCREASEDWARMINGANDDROUGHTSTRESS
5+-/$
2EGIONAL)MPACTS
2ESULTS&ROM-!033AND/THER-ODELS5SING
&!2AND3!23CENARIOS
-!033SIMULATIONSATTHEKMRESOLUTIONUSINGTHE
(ADLEY#ENTRESULFATEAEROSOLSCENARIOlGANDTABLE
SHOWTHATCONIFEROUSFORESTSINNORTHERN-INNESOTA
7ISCONSINAND-ICHIGANUPPERPENINSULAAREDISPLACED
BYTEMPERATEMIXEDFORESTSEXPANDINGFROMTHEEASTAND
SOUTH &OR ALL &!2 SCENARIOS -!033 SIMULATES LARGE
DECREASESINTHETEMPERATEMIXEDFORESTANDBOREALFOREST
AREAAROUNDTHE'REAT,AKESREGIONWHICHAREREPLACEDBY
SAVANNASANDGRASSLANDSlGSAND7ITHhWARMv
CLIMATE CHANGE SCENARIOS SUCH AS THE 5+-/ AND TO A
LESSEREXTENTTHE'&$,2-!033SIMULATESTHEFRAG
MENTATION OF THE SOUTHEASTERN TEMPERATE MIXED FOREST
WHICHISREPLACEDBYDRIERECOSYSTEMSSUCHASSAVANNAS
AND GRASSLANDS lG 7ITH COOLER SCENARIOS SUCH AS
/35 -!033 SIMULATES AN INCREASE IN FORESTED AREAS IN
AND AROUND THE 7ILLAMETTE 6ALLEY IN THE 0ACIlC .ORTH
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
WESTANDONTHEWESTERNEDGEOFTHESOUTHEASTERNFORESTS
lG -ESQUITEOAK WOODLANDS CURRENTLY IN CENTRAL
4EXAS WOULD SHIFT NORTH INTO THE 'REAT 0LAINS REGION
WHILE THE GRASSLANDS WOULD REPLACE THE SEMIDESERTS OF
EASTERN 4EXAS SOUTHERN .EW -EXICO WESTERN !RIZONA
ANDEASTERN#ALIFORNIA5NDERTHE5+-/SCENARIOlG
AND TABLE SOUTHWESTERN WARMDESERT SPECIES COULD
EXTEND INTO COLDDESERT REGIONS AS FAR NORTH AS EASTERN
/REGON AND 7ASHINGTON OR IN THE CASE OF THE /35 SCE
NARIOlGREMAINABOUTWHERETHEYARETODAY
-EANANNUALTEMPERATURESHAVEINCREASEDGLOBALLYBY
#PERCENTURYANDBY #INTHESOUTHWESTERNDESERT
REGIONOFTHE5NITED3TATESBETWEENAND,ANE
ET AL %MANUEL ET AL SUGGESTED A POSSIBLE
FUTURE INCREASE OF UP TO PERCENT IN DESERT LAND AREA
OF .ORTH !MERICA 0REDICTIONS FROM 6%-!0 -EMBERS
SIMULATIONSHALFDEGREELATITUDELONGITUDERESOLU
TIONINCLUDINGBOTHCLIMATECHANGEANDINCREASED#/
SHOW BOTH DECREASES AND INCREASES IN THE AREAL EXTENT
OF SUBTROPICAL SHRUBLANDS SOUTHWESTERN DESERTS 3INCE
THERMALCONSTRAINTSHAVEKEPTSOUTHWESTERNSPECIESFROM
MOVINGNORTHWARDANINCREASEINTEMPERATUREATHIGHER
LATITUDE AND SUFlCIENT AVAILABLE WATER SHOULD ENABLE
THOSE DESERT SPECIES TO REACH THE 'REAT "ASIN AREA )N
FACT-!033SIMULATESANORTHERNMIGRATIONANDEXPAN
SIONOFSUBTROPICALMIXEDSHRUBSAVANNASINTOTHE'REAT
"ASINREGIONANDASFARNORTHASEASTERN7ASHINGTON9ET
EXPANSION OF DESERT SPECIES DOES NOT NECESSARILY IMPLY
INCREASEDDESERTIlCATION)NFACT-!033SIMULATESUPTO
APERCENTINCREASEINLEAFAREAINDEXPRIMARILYGRASS
LAND IN THE SOUTHWESTERN DESERT REGION OF THE 5NITED
3TATESWHEREGRASSESCANOUTCOMPETESHRUBSUNDERFUTURE
WETTERCONDITIONS
#OMPARISONS BETWEEN -!033 AND THE 0N%4 MODEL
!BER AND &EDERER OVER THE 3OUTHEAST ARE CONSIS
TENTINTERMSOFFORESTDECLINEBUTNOTINTERMSOFRUNOFF
"ORCHERSAND.EILSON0N%4SIMULATEDINCREASESIN
ANNUALRUNOFFFROMTOPERCENTASEVAPOTRANSPIRA
TIONWASALTEREDBYCLIMATECHANGESCENARIOSANDFOREST
DEATHWASOCCURRINGWITHOUTREPLACEMENT-C.ULTYETAL
0N%4DOESNOTINCLUDEANUNDERSTORYTHUSWHEN
FORESTS DECLINE NO OTHER VEGETATION TYPES REPLACE THEM
AND RUNOFF INCREASES )N -!033 WHEN FORESTS DECLINE
SHRUBSANDGRASSESINCREASEANDMAYUSEASMUCHORMORE
WATERPRODUCINGDECLINESINRUNOFF0N%4ALSOSIMULATED
SEVERE REDUCTIONS IN ANNUAL .00 ON LOBLOLLY PINE SITES
IN4EXASnPERCENT-ISSISSIPPInPERCENT&LORIDA
nPERCENTAND6IRGINIAnPERCENTWITHCLIMATESCE
NARIOSBASEDONHISTORICALRECORDSFROMTO!BER
ETAL-C.ULTYETALAANDB
%VENINREGIONSWHERETHEVEGETATIONTYPEWOULDNOT
CHANGE IT COULD EITHER INCREASE IN DENSITY OR DECLINE
7HERE VEGETATION DENSITY CHARACTERIZED IN -!033 BY
LEAFAREAISDECREASINGSOMELEVELOFVEGETATIONDIEBACK
IF FORESTED CAN BE EXPECTED OR AT LEAST A REDUCTION IN
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"ACHELETAND.EILSON
4ABLE0ERCENTAGEOFSIMULATEDAREAFOREACHSIMPLIlEDVEG
ETATIONTYPEUNDERCURRENTCLIMATE!FOR.ORTH!MERICAATAHALF
DEGREELATITUDELONGITUDERESOLUTIONBYTHEBIOGEOGRAPHYMODELS
-!033AND")/-%4OTALAREAISKM0ERCENTAGE
CHANGEINAREAFOREACHVEGETATIONTYPEFROMCURRENTCLIMATETO
FUTURE CLIMATE CONDITIONS WITH NO #/ EFFECT " AND WITH #/
EFFECT#0ERCENTAGECHANGEINVEGETATIONTYPEAREAWASCALCU
LATEDASSCENARIOnCURRENTCURRENT4HEATMOSPHERICGENERAL
CIRCULATIONMODELUSEDTOSIMULATECLIMATE3!2WASTHE(ADLEY
#ENTREMODELWITHOUTAEROSOLS(!$#-'('ANDWITHSULFATE
AEROSOLS(!$#-35,")/-%GROUPSTOGETHERBOREALFOREST
AND TAIGATUNDRA DENOTES A VEGETATION TYPE THAT DID NOT
EXISTINCURRENTCLIMATECONDITIONS.!CORRESPONDSTOAVEGETA
TIONTYPETHATDIDNOTEXISTINEITHERCURRENTORFUTURECLIMATES
!#URRENTCLIMATE
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
4ROPICALBROADLEAFFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
"&UTURECLIMATE
WITHNO#/EFFECT
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREEN
FOREST
4EMPERATEMIXEDFOREST
4ROPICALBROADLEAFFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
-!033
")/-%
.OAEROSOLS
3ULFATEAEROSOLS
-!033 ")/-% -!033 ")/-%
n
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#&UTURECLIMATEWITH#/EFFECT
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREEN
FOREST
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4ROPICALBROADLEAFFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
Bachelet and Neilson
Biome Redistribution Under Climate Change
Figure 2.1–Top: Aggregated potential vegetation classes simulated for the North American region at a half degree latitude-longitude
resolution and for the United States at a 10 km resolution for current climate conditions. Bottom: Areas where new vegetation classes
are simulated in future climate conditions by the MAPSS model using the Hadley Centre climate change scenario including sulfate
aerosols (HADCM2SUL). Areas where there is no change in vegetation type remain white.
26
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–59. 2000.
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
"ACHELETAND.EILSON
THESTANDINGCROP"OTH&!2AND3!2SCENARIOSINDICATE
THAT RELATIVELY LARGE REGIONS OF THE 5NITED 3TATES WOULD
UNDERGOSUCHREDUCTIONSORINCREASES.EILSONETAL
(OWEVERhHOTTERvMORESEVERESCENARIOSSUCHAS5+-/
INDICATE VEGETATION DIEBACK OR STANDING CROP REDUCTION
OVERMOSTOFTHE53
-ORE$ETAILED#ONSIDERATIONS!BOUT
53&ORESTS7ITH&!2AND3!23CENARIOS
.EILSONAND#HANEYTRANSLATEDTHE-!033VEG
ETATIONTYPESINTOFORESTTYPECATEGORIES-!033ASSESS
4ABLE0ERCENTAGEOFSIMULATEDAREAFOREACHSIMPLIlEDVEGETATIONTYPEUNDERCURRENTCLIMATEINTHECONTERMINOUS53ATAHALF
DEGREELATITUDELONGITUDERESOLUTIONFORTHE6%-!00ROJECT!4HREEBIOGEOGRAPHYMODELSWEREUSED-!033")/-%AND$/,9
4OTALAREAISKM0ERCENTAGECHANGEINAREAFOREACHVEGETATIONTYPEFROMCURRENTCLIMATETOFUTURECLIMATECONDITIONSWITH
NO#/EFFECT"ANDWITH#/EFFECT#0ERCENTAGECHANGEINVEGETATIONTYPEAREAISCALCULATEDASSCENARIOnCURRENTCURRENT
4HEATMOSPHERICGENERALCIRCULATIONMODELSUSEDTOSIMULATECLIMATE&!2WERETHE'EOPHYSICAL&LUID$YNAMICS,ABORATORYMODEL
'&$,2THE/REGON3TATE5NIVERSITYMODEL/35ANDTHE5NITED+INGDOM-ETEOROLOGICAL/FlCEMODEL5+-/DENOTES
AVEGETATIONTYPETHATDIDNOTEXISTINCURRENTCLIMATECONDITIONS.!CORRESPONDSTOAVEGETATIONTYPETHATDIDNOTEXISTINCURRENTCLIMATE
CONDITIONSANDDOESNOTEXISTEITHERINFUTURECLIMATECONDITIONS
6EGETATIONCLASSES
!#URRENTCLIMATE
4UNDRA
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"&UTURECLIMATEWITHNO#/EFFECT
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"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
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BYTHEBIOGEOGRAPHYMODEL-!033ANDPERCENTAGECHANGEINAREAFOREACHVEGETATIONTYPEFROMCURRENTCLIMATETOFUTURECLIMATE
CONDITIONSWITHNO#/EFFECT!ANDWITH#/EFFECT"4OTALAREAISKM4HEATMOSPHERICGENERALCIRCULATIONMODELS
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"7ITH#/EFFECT
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MENT CLASSES CORRESPONDING TO AN AGGREGATION OF THE
20!FORESTTYPES7EUSETHESAMEAPPROACHTABLE!IN
!PPENDIX ! TO PRESENT SOME OF OUR RESULTS WITH MORE
DETAILSABOUTSPECIlCFORESTTYPES
7ITH3!2SCENARIOS')33AND'&$,2-!033AT
THEKMRESOLUTIONSIMULATESANOVERALLINCREASEINTOTAL
FOREST AREA AND SMALL DECREASES TO PERCENT WITH
/35AND5+-/SCENARIOSTABLE5SINGEITHER&!2OR
3!2 SCENARIOS THE MODEL SIMULATES DECREASES TO PERCENTINNORTHEASTMIXEDFORESTAREAESPECIALLYMIXED
WOODLANDSPERCENTWHICHAREREPLACEDBYSOUTHEAST
MIXED PINES AND HARDWOOD FOREST TYPE THAT ARE MOVING
NORTHWARDANDEXPANDINGINAREABYTOPERCENTTABLE
7ITH&!2SCENARIOS-!033SIMULATESADECREASEIN
EASTERNHARDWOODFORESTSTOPERCENTWITH3!2SCE
NARIOS IT SIMULATES AN INCREASE EXCEPT IN THE CASE OF THE
OAKHICKORYFORESTSWHICHAREPREDICTEDTODECREASEBY
PERCENTWHENTHE(!$#-35,SCENARIOISUSED
7ITHBOTH&!2AND3!2SCENARIOS-!033SIMULATESA
LARGEDECREASEINTHEAREAOFWESTERNlRANDSPRUCEFORESTS
TOPERCENTANINCREASEINCOASTALSPRUCEHEMLOCK
ANDREDWOODFORESTSTOPERCENTANDANINCREASE
INWESTERNHARDWOODSTOPERCENT7ITH3!2SCE
#-'('
#-35,
NARIOSTHEMODELSIMULATESINCREASESINTHEAREAOFOTHER
TYPESOFWESTERNFORESTSWHILEWITH&!2SCENARIOSRESULTS
ARE LESS CLEAR 7ITH ALL SCENARIOS THE MODEL SIMULATES
INCREASES IN TROPICAL FOREST AREAS REPLACING THE SOUTHEAST
MIXEDPINESANDHARDWOODFOREST-!033ALSOSIMULATES
DECREASESINARIDWOODLANDAREASANDINCREASESIN-EDI
TERRANEANSHRUBLANDSWITH3!2SCENARIOSAND')33
)MPLICATIONSOF"IOME2EDISTRIBUTION
2ESULTSON%COSYSTEM0ROCESSES
#ARBON0OOLS3OURCESAND3INKS
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TROLLEDPROCESSESSUCHASPRODUCTIONANDLITTERDECOMPO
SITION,IFEFORMCHANGESDUETOSHIFTSINCLIMATEALSOAFFECT
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CHANGEISTHEPROJECTEDREDUCTIONOFTUNDRAANDTAIGAECO
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LATITUDESOF.ORTH!MERICAMAYRESULTINASHIFTFROMANET
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
Biome Redistribution Under Climate Change
Bachelet and Neilson
Figure 2.2—Areas where new vegetation classes are simulated in future climate conditions by MAPSS using 3 FAR climate change
scenarios: OSU, GFDL-R30, and UKMO, in the conterminous United States at a 10 km resolution. Areas where there is no change in
vegetation type remain white.
sink (sequestration of carbon) to a net source (release of
carbon) of CO2 (Anderson 1991; Oechel et al. 1993). Soil
warming would also affect methane fluxes from tundra
plant communities directly affected by drier soil surfaces
and the resulting increased surface oxidation. The frozen
soils of boreal forests contain one of the largest pools of
carbon (Dixon et al. 1994; Gorham 1991) in the terrestrial
biosphere: 200–500 Gt of carbon (1Gt = 109 metric tons).
Goulden et al. (1998) used eddy correlation, chamber,
and laboratory techniques to measure carbon balance in
a typical black-spruce boreal forest site in Canada. They
concluded that the deep soil carbon pool was not in equilibrium and discussed the possibility that soil C losses
might be due to climate warming since Oechel et al. (1993)
already reported such findings. Projected shifts in vegetation types due to climate warming would probably accentuate soil carbon losses.
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–59. 2000.
Also see Heath and Smith (this volume), Smith and
Heath (this volume), Birdsey (this volume), and Skog
and Nicholson (this volume) for additional discussions of
carbon sequestration in forests and wood products.
CO2 Impacts on Physiological Processes
Elevated CO2 has been documented to increase productivity, nitrogen efficiency, and water-use efficiency
(IPCC 1996; Bazzaz et al. 1996). Wullschleger et al. (1995)
reviewed 58 studies where a doubling of atmospheric CO2
concentration resulted in a 32 percent average increase
in plant dry mass. Norby (1996) studied seven broadleaf
species under a doubling of atmospheric CO2 concentration over a wide range of conditions, and recorded a
29 percent increase in annual growth per unit leaf area.
Eamus (1991) reported reductions of leaf conductance to
29
"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
4ABLE &OREST AREA IN KM AS DESCRIBED BY ASSESSMENT CLASSES .EILSON AND #HANEY UNDER CURRENT AND FUTURE
CLIMATECONDITIONS4HEATMOSPHERICGENERALCIRCULATIONMODELSUSEDTOSIMULATECLIMATEWERETHE'ODDARD)NSTITUTEFOR3PACE3TUDIES
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(!$#-35,h#URRENTvCORRESPONDSTOCURRENTCLIMATECONDITIONS
!SSESSMENTCLASSES
.%MIXEDCONIFERSANDHARDWOODS
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BY DOWNREGULATING THEIR PHOTOSYNTHESIS "AZZAZ 'UNDERSON AND 7ULLSCHLEGER 7ULLSCHLEGER ET AL
4ESKEY/NTHEOTHERHANDMOSTOFTHEEARLY
RESEARCH ON EFFECTS OF #/ WAS DONE ON JUVENILE TREES IN
POTS AND GROWTH CHAMBERS %VIDENCE NOW SHOWS THAT
ACCLIMATION MAY NOT BE AS PREVALENT WHEN ROOTS ARE
UNCONSTRAINED%AMUS#URTIS-OREOVERLIM
ITINGSUPPLIESOFNUTRIENTSANDWATERTENDTOONLYSLIGHTLY
RESTRICTTHEGROWTHRESPONSEOFTREESTOELEVATED#/CON
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7HILERESULTSFROMCONTROLLEDEXPOSURESTUDIESONSEED
LINGSANDYOUNGTREESAREUSEFULINDESCRIBINGTHERESPONSE
OF INDIVIDUAL TREES THEY CAN ONLY PROVIDE GUIDANCE ON
HOWSUCHDATACANBEEXTRAPOLATEDTOTHESCALEOFMATURE
TREES FOREST STANDS AND ECOSYSTEMS 3IMULATING NATURAL
FORESTRESPONSETOELEVATED#/CONCENTRATIONSREMAINSA
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4HERE ARE NO DATA FROM WHICH TO ASSESS THE EFFECT
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SISOFGROWTHPERUNITLEAFAREA7ULLSCHLEGERETAL
&ORESTSCOULDPRODUCEMORELEAFAREAUNDERELEVATED#/
CONCENTRATION BUT THIS WOULD INCREASE TRANSPIRATION AND
STAND WATER USE %LEVATED TEMPERATURES WOULD INCREASE
/35
5+-/
#-'('
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TRANSPIRATION EVEN FURTHER POSSIBLY INDUCING A DROUGHT
EFFECTONTHESYSTEMBYDRYINGUPTHESOIL%AMUS
4HISNEGATIVEFEEDBACKWOULDTHENREDUCELEAFAREA4HESE
COMPLEX INTERACTIONS ARE DIFlCULT TO IMPLEMENT IN THE
MODELS AND EACH BIOGEOGRAPHY MODEL INCLUDES ITS OWN
SIMPLIlED VIEW OF HOW THE SYSTEM MIGHT BEHAVE FOR
EXAMPLE.EILSONAND$RAPEK
-C'UIREAND*OYCESUMMARIZED#/EFFECTSON
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ASSUMED UNDER ELEVATED #/ WHICH LEADS TO ENHANCED
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3EVERAL STUDIES HAVE DOCUMENTED THIS ENHANCEMENT FOR
MANYTREESPECIES.ORBYETAL.ORBYAND/.EILL
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4ESKEYAND3HRESTHA(OLLINGER4HISEFFECTIS
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AND )DSO -C'UIRE ET AL 0OLLEY ET AL 3IONITETAL4OLLEYAND3TRAIN)TEXPLAINS
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53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
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"ECAUSEOFTHEDIFFERENTWAYSMODELSIMPLEMENT#/
EFFECTSTHEYCANPRODUCEWIDELYDIFFERENTSIMULATIONSFOR
THE SAME CLIMATE CHANGE SCENARIOS "ECAUSE -!033 IS
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,!) IT PREDICTS THE MOST DRAMATIC CHANGES IN MOISTURE
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INCLUDES AN EFFECT OF #/ ON THE COMPETITIVE BALANCE
BETWEEN#AND#PLANTSITSIMULATESANEXPANSIONOF
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NARIOSPREDICTINGONLYSMALLINCREASESINTEMPERATURENOT
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7ATER"UDGET
7ATER USE BY VEGETATION IS A COMPLEX INTERACTION
BETWEEN LIFEFORM WATER USE EFlCIENCY SOIL CHARACTERIS
TICS SNOW DYNAMICS AND CLIMATE $ALE )T IS THUS
DIFlCULT TO PREDICT A GENERAL RESPONSE OF HOW IT WILL BE
AFFECTEDBYCLIMATECHANGE7ITHINCREASEDTEMPERATURES
AND LONGER GROWING SEASONS VEGETATION WILL TRANSPIRE
MOREWATERTHUSMAKINGLESSWATERAVAILABLEINTHEFORM
OF RUNOFF FOR IRRIGATION OR DOMESTIC USES 4HUS IT IS NOT
SURPRISINGTHATINLARGEAREASOFTHECONTERMINOUS5NITED
3TATES-!033SIMULATESADECREASEINRUNOFFUNDERALLCLI
MATECHANGESCENARIOSANDINSOMEREGIONSQUITEDRASTI
CALLY.EILSONAND-ARKS&OREXAMPLEATTHEKM
RESOLUTION IN THE TUNDRA AND TAIGATUNDRA AREA -!033
SIMULATESLARGEDECREASESINRUNOFFnPERCENTOFTHE
TOTALAREAUNDERGOESADECREASEINRUNOFFUNDERBOTHTHE
'&$,2ANDTHE(ADLEY#ENTRE(!$#-35,SCENAR
IOSTABLES!AND!IN!PPENDIX!THATCORRESPONDTO
LARGE INCREASES IN ,!) TABLES ! AND ! 3IMILARLY IN
GRASSLANDSTHEDECREASEINRUNOFFPERCENTOFTHETOTAL
AREAISDUETOANINCREASEIN,!)PERCENTOFTHETOTAL
AREATABLES!!!!-!033SIMULATESSIGNIlCANT
AREASnPERCENTOFTHETOTALAREAOFDECREASEDRUNOFF
FORTEMPERATEMIXEDFORESTSEASTERN5NITED3TATESWHICH
AREVERYSENSITIVETOWATERLOSSES-!033ALSOSIMULATES
LARGEAREASnPERCENTOFTHETOTALAREAOFINCREASED
RUNOFFFORTEMPERATEEVERGREENFORESTS
3IMULATION5NCERTAINTIES
#URRENT#LIMATE3OURCE
4HE #RAMER AND ,EEMANS DATASET DERIVED FROM ,EE
MANS AND #RAMER USED FEWER 53 STATIONS AND
A DIFFERENT PRECIPITATION INTERPOLATION THAN THE 6%-!0
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"ACHELETAND.EILSON
DATASET!SARESULTTHE.ORTH!MERICANVEGETATIONSIMU
LATIONSDONOTCAPTUREMOUNTAINOUSVEGETATIONASWELLAS
SIMULATIONSUSINGTHE6%-!0OR6%-!0DERIVEDKM
DATASETS-OREOVERSOMEDISTORTIONOFVEGETATIONBOUND
ARIESALSORESULTFROMTHEDIFFERENTCLIMATOLOGY
#LIMATE3CENARIO
#ONSIDERABLE UNCERTAINTY REMAINS IN THE DIFFERENCES
AMONG THE '#- CLIMATE SCENARIOS )0## #IRET
AND(ENDERSON3ELLERS(OWEVERTHECAPABILITIESOF
'#-SHAVEIMPROVEDSIGNIlCANTLYFROMTHEOLDER)0##
TO THE NEWER )0## SCENARIOS RESULTING IN
LOWERESTIMATESOFCLIMATESENSITIVITY.EVERTHELESSSOME
OFTHEIMPROVEMENTSSUCHASTHEINCLUSIONOFACOOLING
EFFECTBYAEROSOLSMAYPROVETOBELESSIMPORTANTTHAN
ASSUMED BY THE CLIMATE MODELERS 4AYLOR AND 0ENNER
3CIENTISTS GENERALLY AGREE ON THE LIKELY RISE IN THE
AVERAGE GLOBAL TEMPERATURES OVER THE NEXT CENTURY AND
THATANNUALWORLDWIDEPRECIPITATIONANDEVAPORATIONWILL
INCREASEAFEWPERCENTFOREVERYDEGREEOFWARMING(OW
EVER PROJECTIONS OF CLIMATE CHANGE IN SPECIlC AREAS ARE
NOT FORECASTS BUT ARE REASONABLE EXAMPLES OF HOW THE
CLIMATE MIGHT CHANGE "Y ANALYZING DIFFERENT SCENARIOS
FROM SEVERAL DIFFERENT '#-S THE OBJECTIVE IS TO INCLUDE
AWIDERANGEOFSCIENTIlCUNCERTAINTY"UTITISIMPORTANT
TOREMEMBERTHATCLIMATICINPUTSDERIVEDFROMTHE'#-S
HAVEBEENINTERPOLATEDTOTHEHIGHERRESOLUTIONANDMAY
NOTCORRESPONDTOREALISTICREGIONALSIMULATIONS
!TMOSPHERICCIRCULATIONISSTRONGLYAFFECTEDBYmUXES
OFENERGYANDWATERFROMTHELANDSURFACE4HESEmUXES
DEPENDONVEGETATIONCHARACTERISTICSSUCHASALBEDO,!)
AND VEGETATION HEIGHT #HANGES TO LAND SURFACE CHAR
ACTERISTICS EVENTUALLY FEED BACK TO THE ATMOSPHERE 4HE
CURRENTGENERATIONOFCLIMATEMODELSINCLUDETHEBIOPHYS
ICALINTERACTIONSBETWEENLANDSURFACEANDATMOSPHEREIN
A hLAND SURFACE MODULEv 3ENSITIVITY STUDIES HAVE NOW
SHOWN THE IMPORTANCE OF THE FEEDBACK PROCESSES FOR
EXAMPLE "ONAN ET AL 8UE AND 3HUKLA "ETTS
ETAL&OLEYETALANDTHATUSINGAlXEDGEO
GRAPHICDISTRIBUTIONOFVEGETATIONTYPESLIMITSTHEIRUSEIN
GLOBALCHANGESTUDIES5NFORTUNATELYALLTHEASSESSMENTS
TODATEHAVEBEENUSINGECOSYSTEMMODELSTHATSIMULATE
CHANGESINVEGETATIONSTRUCTUREWITHNOFEEDBACKTOCLI
MATE MODELS THAT PRODUCE THE CLIMATE CHANGE SCENARIOS
THEYARESODEPENDENTUPON2ESULTSTODATEMUSTTHUSBE
TAKENWITHCAUTIONSINCETHEATMOSPHEREISTOTALLYDECOU
PLED FROM THE LAND SURFACE CHANGES #URRENT RESEARCH IS
NOWFOCUSINGONCOUPLINGFULLYDYNAMICREPRESENTATIONS
OF TERRESTRIAL ECOSYSTEMS WITH CLIMATE MODELS 3OME OF
THE NEW GENERATION OF BIOGEOGRAPHY MODELS DYNAMIC
GLOBALVEGETATIONMODELSOR$'6-SHAVEALREADYBEEN
DESIGNED TO BE FULLY COUPLED WITH CLIMATE MODELS FOR
EXAMPLE&OLEYETAL
"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
4ABLE0REDICTEDPERCENTOFTHETOTALAREAOF.ORTH!MERICAANDOFTHECONTERMINOUS5NITED3TATESOCCUPIEDBYTHEVARIOUSSIMPLI
lED VEGETATION TYPES AND PERCENTAGE CHANGE WHEN THE '&$,2 SCENARIO IS APPLIED AND THE #/ EFFECT IS INCLUDED IN -!033
2ESULTSCORRESPONDTOTHREEPROJECTSTHE.ORTH!MERICANPROJECTFROMTHE-EXICANBORDERTONORTHERN#ANADAATAHALFDEGREE
LATITUDELONGITUDERESOLUTIONTHE6%-!0PROJECTATTHESAMERESOLUTIONASTHE.ORTH!MERICANPROJECTBUTCONCENTRATINGONTHE
CONTINENTAL53THELASTPROJECTCONCENTRATINGONTHECONTERMINOUS53ATAKMRESOLUTION0ERCENTAGECHANGEINVEGETATION
TYPEAREAISCALCULATEDASSCENARIOnCURRENTCURRENT
IN6%-!0THECATEGORYTAIGATUNDRAWASNOTUSEDSINCETHE")/-%MODEL
DIDNOTSEPARATEITFROMTHEBOREALFORESTCOMPONENT
-ODELRESOLUTION
6EGETATIONCLASSES
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
#URRENTCLIMATE
HALFDEGREE
HALFDEGREE
.ORTH!MERICA 6%-!053 KM53
3PATIAL2ESOLUTION
7E COMPARED SIMULATION RESULTS FROM -!033 AT TWO
DIFFERENT SCALES KM AND HALF DEGREE LATITUDELONGI
TUDERESOLUTIONANDFORTWOREGIONS.ORTH!MERICAAND
THECONTINENTAL5NITED3TATES&IRSTWECOMPAREDRESULTS
FROMKMRESOLUTIONRUNSANDRESULTSFROM6%-!0AT
APPROXIMATELY KM RESOLUTION TABLE AND lG FORTHECONTINENTAL5NITED3TATESUSINGTHE'&$,2SCE
NARIO 4HE #/ EFFECT WAS INCLUDED IN -!033 !SMALL
AREAINCREASEPERCENTINGRASSLANDSISSIMULATEDATTHE
KMSCALEWHILEADECREASEOFPERCENTISSIMULATEDAT
THE6%-!0SCALE,ARGERCHANGESINTHEEXTENTOFTEMPER
ATE EVERGREEN FORESTS ARE SIMULATED AT THE 6%-!0SCALE
WITHSMALLERCHANGESINTHEEXTENTOFSAVANNAS3IMULA
TIONRESULTSAGREEINTHEDIRECTIONOFCHANGEFORRUNOFFPAT
TERN IN THE 5NITED 3TATES WITH THE EXCEPTION OF TUNDRA
AREAS AND ANTICIPATE INCREASES IN RUNOFF IN FOREST AREAS
SAVANNASANDSHRUBLANDSTABLE!$ECREASESINRUNOFF
ARE SIMULATED IN GRASSLANDS AND ARID LANDS 4HE MODEL
ALSO SIMULATES AN INCREASE IN ,!) INDEX OF VEGETATION
DENSITYINTUNDRAAREASSAVANNASSHRUBLANDSANDARID
LANDSBUTADECREASEIN,!)INTEMPERATEMIXEDFORESTS
TABLE!
3ECONDLYWECOMPAREDRESULTSOBTAINEDFORTHE.ORTH
!MERICAN REGION INCLUDING #ANADA AND THE 5NITED
3TATES AND FOR THE CONTINENTAL 53 6%-!0 BOTH AT A
HALFDEGREELATITUDELONGITUDERESOLUTION#HANGESDUETO
THECLIMATECHANGESCENARIOSAREGENERALLYCONSISTENTBOTH
FORRUNOFFAND,!)ESTIMATESTABLES!AND!
'&$,2
HALFDEGREE
.ORTH!MERICA
n
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n
n
HALFDEGREE
6%-!053
n
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n
n
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KM53
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n
n
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&INALLY WE COMPARED RESULTS OBTAINED FOR THE .ORTH
!MERICANREGIONATAHALFDEGREELATITUDELONGITUDERES
OLUTION WITH THOSE OBTAINED FOR THE CONTINENTAL 5NITED
3TATES AT A KM RESOLUTION 4HERE IS GOOD AGREEMENT
BETWEEN SIMULATIONS EXCEPT FOR THE TUNDRA AREA SINCE
COARSERESOLUTIONRESULTSREmECTLARGECHANGESOCCURRINGIN
#ANADABUTNOTINTHE5NITED3TATESTABLE4ABLES!
AND! ILLUSTRATE THE AGREEMENT BETWEEN SIMULATIONS OF
,!)ANDRUNOFFCHANGES4HEONLYDISAGREEMENTOCCURSIN
THETUNDRAANDTHEBOREALFORESTAREAS
)NSUMMARYRESULTSFROMCLIMATECHANGEIMPACTSIM
ULATIONSHAVETOBECAREFULLYANALYZEDTHEAREAOFINTER
EST MUST BE WELL DELINEATED AND THE SCALE OF RESOLUTION
SPECIlED4RENDSINTHEEXPANSIONORREDUCTIONOFCERTAIN
SYSTEMSCANCHANGEDRAMATICALLYBETWEENREGIONS3MALL
CHANGES THAT CAN BE CAPTURED AT HIGH RESOLUTION CAN
COLLECTIVELY MODIFY THE DIRECTION OF TRENDS #AUTION IS
NEEDEDWHENANALYZINGMODELRESULTSFORCOARSERRESOLU
TIONREGIONALSIMULATIONS
4EMPORAL2ESOLUTION5NCERTAINTY
#URRENTCLIMATECONDITIONSUSEDTORUNTHEMODELSCOR
RESPOND TO LONGTERM AVERAGE CLIMATE DATA THAT IGNORE
EXTREMEEVENTSANDYEARTOYEARVARIABILITY)NREALITYTHIS
VARIABILITYGREATLYAFFECTSVEGETATIONDYNAMICS3IMILARLY
'#-GENERATEDFUTURECLIMATESCENARIOSFORANhAVERAGEv
YEARAREONLYSNAPSHOTSOFFUTURECLIMATEATEQUILIBRIUM
WITH A DOUBLED ATMOSPHERIC #/ CONTENT 4HEY DO NOT
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
Biome Redistribution Under Climate Change
Bachelet and Neilson
Figure 2.3—Aggregated potential vegetation classes simulated by MAPSS for current conditions (top) and areas where new vegetation
classes are simulated by MAPSS using the GFDL-R30 climate change scenario (bottom) at a 10 km resolution (right) and at a halfdegree resolution (VEMAP) (left) in the conterminous United States. Areas where there is no change in vegetation type remain white.
accurately represent the constantly evolving interactions
between atmosphere, ocean, and land. In reality, there is
no “average” year and thus equilibrium models such
as MAPSS simulate vegetation distributions that do not
and will not have an exact analog in nature (Borchers
USDA Forest Service Gen. Tech. Rep. RMRS–GTR–59. 2000.
and Neilson 1998). The value of equilibrium projections,
however, is that they depict theoretical equilibrium states
or potential natural “climax” that the vegetation might
evolve toward, a concept that has guided decision-making
in forest management and silviculture for many years.
33
"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
4ABLE0REDICTEDPERCENTOFTOTALAREAOFEITHERTHE.ORTH!MERICANREGIONORTHECONTERMINOUS5NITED3TATESOCCUPIEDBYTHE
VARIOUSSIMPLIlEDVEGETATIONTYPESANDPERCENTAGECHANGEINAREAWHENTHE(ADLEY#ENTRESULFATEAEROSOLSCENARIO(!$#-35,
ISAPPLIEDANDTHE#/EFFECTISINCLUDEDIN-!0332ESULTSCORRESPONDTOTWOPROJECTSUSINGTHE-!033EQUILIBRIUMBIOGEOGRAPHY
MODELONECONCENTRATINGONTHE.ORTH!MERICANREGIONFROMTHE-EXICANBORDERTONORTHERN#ANADAATAHALFDEGREELATITUDELONGITUDE
RESOLUTIONTHEOTHERCONCENTRATINGONTHECONTERMINOUS53ATAKMRESOLUTIONDENOTESAVEGETATIONTYPETHATDIDNOTEXIST
INTHECURRENTCLIMATESCENARIO.!CORRESPONDSTOAVEGETATIONTYPETHATDIDNOTEXISTINEITHERCURRENTORFUTURECLIMATES0ERCENTAGE
CHANGEINVEGETATIONTYPEAREAISCALCULATEDASSCENARIOnCURRENTCURRENT
-ODELRESOLUTION
#URRENTCLIMATE
HALFDEGREEn.ORTH!MERICA
6EGETATIONCLASSES
4UNDRA
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"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
4ROPICALBROADLEAFFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
! NEW GENERATION OF MODELSTHE DYNAMIC GLOBAL
VEGETATION MODELS OR $'6-IS NOW EMERGING 4HESE
MODELS COUPLE VEGETATION STRUCTURE AND BIOGEOCHEMICAL
mUXESANDSIMULATETHEIRDYNAMICCHANGESASARESPONSE
TO CHANGES IN CLIMATE AND DISTURBANCE REGIMES .EILSON
AND 2UNNING &OLEY ET AL &RIEND ET AL ,ENIHAN ET AL (OWEVER OTHER CONSTRAINTS TO THE
TRANSIENTRESPONSEOFVEGETATIONARESTILLMISSINGSUCHAS
SOIL DEVELOPMENT AND SEED DISPERSAL 4HESE MODELS ARE
BEING DEVELOPED AND SHOULD SOON BECOME THE ESSENTIAL
TOOLSOFFUTUREASSESSMENTS
-ODEL,IMITATIONS
.ITROGEN"UDGET
.ITROGENLIMITATIONISTHOUGHTTOMODERATELONGTERM
RESPONSES TO ELEVATED #/ +IRSCHBAUM ET AL -C'UIREETAL%AMUS#LIMATECHANGEAFFECTS
TEMPERATURE AND MOISTURECONTROLLED PROCESSES SUCH AS
NUTRIENTUPTAKEMINERALIZATIONANDVOLATILIZATION5NLESS
#/ STIMULATES AN INCREASE IN NITROGEN MINERALIZATION
#URTISETAL6%-!0-EMBERSPRODUCTIVITY
GAINS WITH HIGH #/ CONCENTRATION WILL BE CONSTRAINED
BY THE AVAILABLE NITROGEN +ÚRNER .ITROGEN LIMI
TATIONS MAY CONSTRAIN CARBON GAINS TO STRUCTURAL TISSUE
RATHER THAN LEAVES #URTIS ET AL ,IFEFORM CHANGES
(!$#-35,
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n
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DUE TO SHIFTS IN CLIMATE WILL ALSO AFFECT NUTRIENT INPUTS
0ASTORAND0OST.ITROGENlXATIONHASBEENPOORLY
QUANTIlEDANDHASYETTOBESIMULATEDACCURATELY!NTHRO
POGENICNITROGENlXATIONFAREXCEEDSNATURALNITROGENlX
ATION6ITOUSEK)NAREASRECEIVINGLARGEAMOUNTSOF
NITROGEN DEPOSITION A DIRECT #/ RESPONSE COULD RESULT
IN LARGE INCREASES IN LEAF AREA 4HIS INCREASED ,!) COULD
INCREASE TRANSPIRATION AND POSSIBLY PROVOKE RAPID SOIL
WATERDEPLETIONTHUSINCREASINGTHESYSTEMSENSITIVITYTO
DROUGHT.ITROGENDEPOSITIONHASLIKELYCAUSEDCONSIDER
ABLE ACCUMULATION OF CARBON IN THE BIOSPHERE SINCE THE
LASTCENTURY6ITOUSEK4OWNSENDETAL(OW
EVERNITROGENSATURATIONINSOILSCANALSOBEDELETERIOUS
ANDPOSSIBLYCAUSEFORESTDIEBACKINSOMESYSTEMS&OSTER
ETAL4HISEFFECTISNOTINCLUDEDIN-!033
$ISTURBANCE
$ISTURBANCE INTENSITY FREQUENCY AND DURATION ARE
LIKELYTOCHANGEWITHCLIMATE/VERPECKETAL$ALE
.ATURAL lRE FREQUENCY DURATION AND INTENSITY
ARE CLOSELY TIED TO STORM OCCURRENCES AND PRECIPITATION
REGIMESWHICHWILLBEAFFECTEDBYGLOBALCLIMATECHANGE
$ALE &UTURE CLIMATE COINCIDENT WITH CHANGES IN
lREMANAGEMENTPRACTICESANDPOSSIBLEFORESTDECLINEOR
DIEBACK COULD BRING LONGER lRE SEASONS AND POTENTIALLY
MORE FREQUENT AND LARGER lRES IN ALL FOREST ZONES EVEN
THOSE THAT DO NOT CURRENTLY SUPPORT lRE &OSBERG &LANNIGANAND6AN7AGNER+INGAND.EILSON
7OTTON AND &LANNIGAN 0RICE AND 2IND &OS
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
BERG AT AL &IRE SUPPRESSION DURING MUCH OF THE
THCENTURYHASALLOWEDBIOMASSINMANYINTERIORFORESTS
TOINCREASECONSIDERABLYOVERHISTORICLEVELS!GEE
7ITHINCREASEDBIOMASSFORESTSTRANSPIREALMOSTALLAVAIL
ABLESOILWATERANDBECOMEVERYSENSITIVETOEVENSMALL
VARIATIONSINDROUGHTSTRESS&ORESTSARETHENHIGHLYSUS
CEPTIBLETOCATASTROPHIClRESEVENWITHOUTGLOBALWARM
ING .EILSON ET AL 3TOCKS 3TOCKS ET AL &ORESTSINTHEINTERIOROF.ORTH!MERICAAREEXPERIENCING
INCREASEDFREQUENCIESOFDROUGHTSTRESSPESTINFESTATIONS
AND CATASTROPHIC STANDREPLACING lRES !GEE 4HIS
SEQUENCEOFEVENTSISAREASONABLEANALOGFORWHATCOULD
HAPPEN TO FORESTS OVER MUCH LARGER AREAS IN THE ZONES
INDICATEDBYTHEBIOGEOGRAPHYMODELSTOUNDERGOALOSS
OFBIOMASSORLEAFAREADUETOTEMPERATUREINDUCEDTRAN
SPIRATION INCREASES AND DROUGHT STRESS /VERPECK ET AL
+INGAND.EILSON"ECAUSElREMEDIATESRAPID
CHANGEVEGETATIONCHANGECOULDBESIGNIlCANTLYAFFECTED
BYCHANGESINlREFREQUENCY
4HEABILITYTOPREDICTCHANGESINTHEFREQUENCYORINTEN
SITYOFEXTREMEWEATHEREVENTSSUCHASDROUGHTmOODING
HAILHURRICANESANDTORNADOESUSINGGLOBALANDREGIONAL
MODELSISLIMITEDBYTHEIRLACKOFSMALLSCALESPATIALAND
TEMPORAL RESOLUTION AND UNCERTAINTIES ABOUT REPRESENTA
TIONOFPROCESSES)0##
#ONCLUSIONS
#URRENTPUBLISHEDASSESSMENTSOFBIOSPHERICRESPONSES
TO CLIMATE CHANGE ARE BASED ON EQUILIBRIUM MODELS OF
THE TERRESTRIAL BIOSPHERE SUCH AS -!033 ")/-% OR AND $/,9 4HESE MODELS SIMULATE THE COMBINATION OF
PLANT LIFEFORMS THAT ARE IN STEADY STATE WITH A GIVEN CLI
MATEGIVENAPARTICULARSOILENVIRONMENT4HESEMODELS
WHENRUNWITHVARIOUSSCENARIOSOFCLIMATECHANGESHOW
ASERIESOFSTRONGRESPONSES
"OREAL FOREST AND TAIGATUNDRA REGIONS ARE PREDICTED
TO MOVE NORTHWARD OR UPWARD IN ELEVATION AT THE
EXPENSEOFTHE#ANADIANORALPINETUNDRABOREALFOR
ESTSAREALSOSIMULATEDTOEXPERIENCEDIEBACKSOFVARI
OUS DEGREES ALONG THE SOUTHERN OR LOWER ELEVATIONAL
LIMITSUNDERALLCLIMATECHANGESCENARIOS4HEBOREAL
FOREST SIMULATED IN -INNESOTA FOR CURRENT CLIMATIC
CONDITIONS TOTALLY DISAPPEARS WITH EVEN MILD CLIMATE
CHANGE SCENARIOS SUCH AS THE (!$#-35, 5PPER
ELEVATIONAL OR NORTHERN BOUNDARIES ARE PREDICTED TO
SHIFTUPSLOPEORNORTHWARD
7ARMERSCENARIOSPRODUCETHELARGESTIMPACTSONTHE
BOREALFORESTBUTAREALSORESPONSIBLEFORFORESTDIEBACK
INTHECONTERMINOUS5NITED3TATES
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
"ACHELETAND.EILSON
.ORTHWESTANDSOUTHEASTFORESTSMIGHTINITIALLYEXPAND
THEN LATER CONTRACT IN AREA &OR THE WARMER CLIMATE
CHANGE SCENARIOS -!033 SIMULATED EXTENSIVE FRAG
MENTATION OF THE EASTERN TEMPERATE MIXED FORESTS
WHICHAREVERYSENSITIVETOCHANGESINAVAILABLEWATER
ANDTHUSTOANYPOSITIVEEFFECTOFELEVATED#/
3OUTHWESTERNDESERTSPECIESMAYMOVEINTOTHE'REAT
"ASIN REGION GIVEN ADEQUATE THERMAL AND HYDROLOGIC
CONDITIONS
4HETREATMENTOF#/EFFECTSINEACHOFTHETHREEBIO
GEOGRAPHY MODELS STRONGLY INmUENCES THEIR SIMULATIONS
ANDEXPLAINSSOMEOFTHEDIFFERENCESAMONGTHEM2ESULTS
FROMTHESEEQUILIBRIUMMODELSALSOCLEARLYDEPENDONTHE
CLIMATECHANGESCENARIOTHATWASUSEDFORTHEASSESSMENT
!LTHOUGHTHEREISAGROWINGCONSENSUSABOUTTHEINCREASE
INFUTUREGLOBALAVERAGETEMPERATURETHEREISLITTLEAGREE
MENT ON THE MAGNITUDE AND TIMING OF THE CHANGES IN
THE HYDROLOGICAL CYCLE IN VARIOUS REGIONS OF THE WORLD
-OREOVER LARGE UNCERTAINTIES REMAIN ABOUT THE REGIONAL
CHANGES OF THE VARIOUS CLIMATE VARIABLES +ATTENBERG ET
AL4HEREFOREASSESSMENTSOFFUTUREVEGETATIONDIS
TRIBUTION CARRY THE UNCERTAINTY INTRINSIC TO THE CLIMATE
CHANGE SCENARIOS AND SHOULD NOT BE CONSIDERED AS SOLID
PREDICTIONS %QUILIBRIUM MODELS BY DElNITION DO NOT
SIMULATE DYNAMIC OR TRANSIENT CHANGES IN VEGETATION
ASSEMBLAGES4HERATEOFCHANGEPREDICTEDBYTHECLIMATE
MODELS MAY EXCEED HISTORICAL RATES OF CHANGE +IRSCH
BAUM ET AL 3IMULATION RESULTS MAY THUS BE USED
TO INDICATE THE DIRECTION OF POSSIBLE CHANGE BUT NOT TO
ESTIMATETHETIMEITMIGHTTAKEAPARTICULARPLANTTYPETO
REACHANEWSITE#RAMERAND3TEFFEN
-OVEMENTOFTHEVARIOUSECOSYSTEMSMAYALSOBECON
STRAINED AFTER THEIR INITIALLY RAPID EXPANSION BY VARIOUS
FACTORS SUCH AS LACK OF SEED DISPERSAL OR ESTABLISHMENT
LACKOFSEASONALTHERMALREQUIREMENTSFORESTABLISHMENT
POORSOILSORUNFAVORABLELANDUSESUCHASURBANIZATION
OR CULTIVATION &OR EXAMPLE THE EXTENT OF THE TEMPERATE
MIXED FOREST ZONE NEAR THE 'REAT ,AKES INCREASES OR
DECLINESDEPENDINGINPARTONSOILPROPERTIES0OSTAND
0ASTOR -OREOVER VEGETATION TYPES WILL PROBABLY
NOTBEDISPLACEDHOMOGENEOUSLY$IFFERENTASSEMBLAGES
MAY APPEAR AND DISAPPEAR OVER LONG PERIODS OF TIME
(UNTLEYETAL,ENIHANAND.EILSONANDTHEIR
COMPOSITIONWILLBESTRONGLYAFFECTEDBYCHANGESINDIS
TURBANCEREGIMES
#HANGESINBOUNDARIESLIMITEDBYWATERBALANCEAREDIFl
CULTTOPREDICTBECAUSEOFTHECOMPLEXINTERACTIONSBETWEEN
CHANGESINTEMPERATUREPRECIPITATIONAND#/ CONCENTRA
TION )NCREASES IN RAINFALL ARE IN SOME CASES SUFlCIENT TO
BALANCE INCREASES IN EVAPORATIVE DEMAND AND IN OTHER
CASESTHEYARENOT#/INDUCEDCHANGESINWATERUSEEFl
CIENCYCOULDREVERSEAPOTENTIALDROUGHTRESPONSEFORCER
TAINPLANTS.ORTHERNSTATESSUCHAS-INNESOTA-ICHIGAN
AND 7ISCONSIN WOULD ENDURE DISPLACEMENT OF FORESTS BY
"ACHELETAND.EILSON
GRASSLANDSUNDERALLSCENARIOSlGSANDATRANSI
TION THAT WOULD BE MEDIATED BY DROUGHT AND lRE &UTURE
CLIMATE CHANGES COINCIDENT WITH CHANGES IN lRE MANAGE
MENTPRACTICESANDPOSSIBLEFORESTDECLINEORDIEBACKCOULD
BRINGLONGERlRESEASONSANDPOTENTIALLYMOREFREQUENTAND
LARGERlRESINALLFORESTZONES$ROUGHTANDFORESTDIEBACK
COULDINCREASETHEFUELLOADANDTRIGGERMOREFREQUENTAND
LARGERlRESWHILEINCREASEDGROWTHGIVENCLIMATICOSCILLA
TIONSWOULDALSOINCREASETHEFUELLOAD4HEIMPORTANCEOF
lREONVEGETATIONCHANGECOULDINCREASEANDMEDIATERAPID
CHANGES-OREOVERINTHEEARLYSTAGESOFWARMINGWHEN
TEMPERATUREINCREASESARESMALLA#/INDUCEDINCREASEIN
WATERUSEEFlCIENCYCOULDRESULTINANEXPANSIONOFTEMPER
ATE FORESTS INTO NEIGHBORING DRIER AREAS AND A CONCURRENT
INCREASEINFORESTDENSITYTHROUGHOUTMUCHOFTHECURRENT
FOREST DISTRIBUTION &OR EXAMPLE -!033 SIMULATES THE
EXPANSIONOFTHETEMPERATEEVERGREENFORESTINTO#ANADA
WHERE IT REPLACES THE TAIGATUNDRA )T ALSO SIMULATES THE
EXPANSIONOFTHEEASTERNTEMPERATEMIXEDFORESTWESTWARD
INTOTHECENTRAL5NITED3TATESATTHEEXPENSEOFSAVANNAS!
SIMILAR SHIFT OF NORTHWESTERN FORESTS INTO DRIER AREAS IS
SIMULATEDUNDERTHEMODERATEWARMINGSCENARIOS!STHE
#/EFFECTSATURATESANDTEMPERATURESCONTINUETOINCREASE
HOWEVER THE ELEVATED EVAPORATIVE DEMAND COULD OVER
WHELMTHEINCREASEDWATERUSEEFlCIENCY4EMPERATEFORESTS
COULDTHENCONTRACTINAREAANDUNDERGOADROUGHTINDUCED
DECLINEINVEGETATIONDENSITY.EILSONAND$RAPEK
#OMPARINGTHEhWARMERvCLIMATECHANGESCENARIOSWITH
COOLERONESILLUSTRATESWHATMIGHTHAPPENTOTHESOUTHEAST
ERN MIXED FOREST WHERE EXTENSIVE FRAGMENTATION IS SIM
ULATED TO OCCUR WITH HIGHER TEMPERATURES 4HE BENElCIAL
EFFECTSOFELEVATED#/COULDMAKEALARGEDIFFERENCEINTHE
RESPONSEOFTHESOUTHEASTERNFORESTSTOTHEWARMING
&INALLYWEWANTTOEMPHASIZETHATIMPORTANTFACTORS
SUCHASGRAZINGBYHERBIVORESINVASIONSBYWEEDSDIS
EASESANDPESTSANDCHANGESINLANDUSEDUETOHUMAN
DEVELOPMENTCOULDDRASTICALLYALTERTHERESPONSESOFVEG
ETATIONTOCLIMATICCHANGES4HEREISCURRENTLYNOMODEL
THATINCORPORATESALLTHESEFACTORSANDADDINGSUCHCOM
PLEXITYTOCURRENTLYEXISTINGMODELSWOULDALSOINCREASE
THEMARGINOFUNCERTAINTYINTHERESULTINGPREDICTIONS#LI
MATECHANGEASSESSMENTSSHOULDTHUSINCLUDETHESEFAC
TORSBUTNEWMETHODSNEEDTOBEDEVELOPEDTORETAINTHE
USEFULNESS OF MODEL SIMULATIONS BY KEEPING THE UNCER
TAINTYMANAGEABLE
!CKNOWLEDGMENTS
4HISWORKWASSUPPORTEDBYTHE53$!&OREST3ERVICE
0.7.%3%3TATIONS0.7ANDTHE53'3"2$
#!
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
4HIS PAPER COULD NOT HAVE BEEN WRITTEN WITHOUT THE
HELPOF2AY$RAPEK/REGON3TATE5NIVERSITYWHOSESKILLS
IN UNEARTHING ARCHIVED DATA AND MAPS ARE UNEQUALED
4HE AUTHORS WANT TO THANK THE REVIEWERS OF THE EARLY
DRAFT OF THIS CHAPTER 3TEVE 7ONDZELL #HRIS $ALY ,INDA
(EATH2ICHARD"IRDSEYAND,INDA*OYCE4HEYALSOWANT
TO THANK THE FOLLOWING REVIEWERS FOR THEIR HELPFUL COM
MENTSONTHElNALDRAFTOFTHECHAPTER,LOYD)RLAND"RENT
3OHNGEN-ARK(ARMON%RIC6ANCEAND#RAIG,OEHLE
,ITERATURE#ITED
!BER*$&EDERER#!!GENERALIZEDLUMPEDPARAMETERMODEL
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INTEMPERATEANDBOREALFORESTECOSYSTEMS/ECOLOGIAn
!BER *$ /LLINGER 36 &EDERER #! ;ET AL= 0REDICTING THE
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$ECREASE
)NCREASE
6EGETATIONCLASSES
4UNDRA
4AIGA4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
KMn53
"ACHELETAND.EILSON
"IOME2EDISTRIBUTION5NDER#LIMATE#HANGE
4ABLE!0REDICTEDPERCENTAREAOFINCREASEDORDECREASED,!)EITHERINTHE.ORTH!MERICANREGIONORTHECONTERMINOUS5NITED
3TATESFORTHEVARIOUSSIMPLIlEDVEGETATIONTYPESWHENTHE'&$,2SCENARIOISAPPLIEDANDTHE#/EFFECTISINCLUDEDIN-!033
2ESULTS CORRESPOND TO THREE PROJECTS USING THE -!033 EQUILIBRIUM BIOGEOGRAPHY MODEL THE .ORTH !MERICAN PROJECT FROM THE
-EXICANBORDERTONORTHERN#ANADAATAHALFDEGREELATITUDELONGITUDERESOLUTIONTHE6%-!0PROJECTATTHESAMERESOLUTIONASTHE
.ORTH!MERICANPROJECTBUTCONCENTRATINGONTHECONTERMINOUS53THELASTPROJECTCONCENTRATINGONTHECONTERMINOUS53ATA
KMRESOLUTION$ECREASECORRESPONDSTOTHEAREASWHERE,!)DECREASESWHILE)NCREASECORRESPONDSTOAREASWHERE,!)INCREASES
-ODELRESOLUTION
6EGETATIONCLASSES
4UNDRA
4AIGAn4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
HALFDEGREEn.ORTH!MERICA
HALFDEGREEn6%-!053
KMn53
$ECREASE
)NCREASE
$ECREASE
)NCREASE
$ECREASE
)NCREASE
4ABLE!0REDICTEDPERCENTAREAOFINCREASEDORDECREASED,!)WHENTHE(ADLEY#ENTRESULFATEAEROSOLSCENARIO(!$#-35,
ISAPPLIEDANDTHE#/EFFECTISINCLUDEDIN-!0332ESULTSCORRESPONDTOTWOPROJECTSUSINGTHE-!033EQUILIBRIUMBIOGEOGRAPHY
MODELONE CONCENTRATING ON THE .ORTH !MERICAN REGION FROM THE -EXICAN BORDER TO NORTHERN #ANADA AT A HALF DEGREE LATITUDE
LONGITUDERESOLUTIONTHEOTHERCONCENTRATINGONTHECONTERMINOUS53ATAKMRESOLUTION$ECREASECORRESPONDSTOTHEAREASWHERE
,!)DECREASESWHILE)NCREASECORRESPONDSTOAREASWHERE,!)INCREASES
-ODELRESOLUTION
6EGETATIONCLASSES
4UNDRA
4AIGA4UNDRA
"OREALCONIFEROUSFOREST
4EMPERATEEVERGREENFOREST
4EMPERATEMIXEDFOREST
3AVANNAWOODLAND
3HRUBWOODLAND
'RASSLAND
!RIDLAND
HALFDEGREEn.ORTH!MERICA
KMn53
$ECREASE
)NCREASE
$ECREASE
)NCREASE
53$!&OREST3ERVICE'EN4ECH2EP2-23n'42n
