MODELSFOR PREDICTINGOCCUPIEDBLACKBEAR HABITAT
IN COASTAL
NORTHCAROLINA
MARKD. JONES,1 Department of Forestry, Wildlife and Fisheries, University of Tennessee, P.O. Box 1071, Knoxville, TN 379011071, USA
GORDON S. WARBURTON, North Carolina Wildlife Resources Commission, 4470 Hidden View Loop, Marion, NC 28752, USA,
email: [email protected]
MICHAELR. PELTON, Department of Forestry, Wildlife and Fisheries, University of Tennessee, P.O. Box 1071, Knoxville, TN
37901-1071, USA, email: Pelton@ utkvx.utcc.utk.edu
Abstract: Black bears (Ursus americanus)are restrictedto approximately10% of their historical range in the Southeast. While the southern
Appalachian mountains contain a relatively contiguous black bear population, southeasterncoastal plain populations are fragmented across
several states. Some bearpopulationsin southeasterncoastal areasare declining or threatened,yet occupied bear habitatin coastal NorthCarolina
has increased from 667,000 ha (1971) to 2.2 million ha (1991). These contrasting situations in the Southeast warrantthe development of
quantifiabletechniquesfor determiningsuitableblack bear habitaton a regional scale. Predictingblack bear distributionis a critical first step in
determiningsuitablehabitat. We tested 12 habitatvariables,using 6 backwardeliminationmultipleregressionequations,against occupied range
and changes in occupied range in coastal North Carolina. Human density and percentof a county in total forest land, loblolly-shortleaf (Pinus
taeda-P. echinata),oak-gum-cypress (Quercusspp.-Nyssa spp.-Taxodiumdistichum),wheat, and soybeans were accuratepredictors(a = 0.05)
of currentblack bear distribution. Only changing human density and changing percent forest land accuratelypredictedchanges in distribution
throughtime. The black bear range expansion in eastern North Carolina,coupled with the results of these models, points to the adaptabilityof
black bears and the complicatednatureof bear-habitatrelationshipsin areas influencedby majorlandscapechanges. Managersin other regions
may wish to develop similar models for the specific habitatcharacteristicsof their areas. Such models may be used to predictthe suitabilityof
areas for restorationor the long-term consequences of habitatalterations. We recommendthat bear managersin the southeasterncoastal plain
consider the juxtapositionof contiguous forested areas and oak-gum-cypress forests with areas of suitablebear food crops on a landscape scale
and develop cooperativeefforts with the forest industryto enhance habitatmanagement.
Ursus 10:203-207
Key words: black bear, distribution,habitat,models, North Carolina,statistics, Ursus americanus.
Black bearshistoricallyrangedthroughoutthe forested
habitatsof North America occupying all 49 continental
states, all Canadianprovinces and territories,and much
of northernMexico (Hall 1981). As a result of humanrelated mortality and habitatloss, black bears are now
relegatedto approximately10%of their historicalrange
in the Southeast (Pelton 1982, Maehr 1984, Garshelis
1990), where they are found in the AppalachianMountains and the Atlantic Coastal Plain. The Appalachian
populations are relatively contiguous and concentrated
on 2 nationalparksand 6 nationalforests (Maehr 1984),
yet coastalpopulationsareseparatedinto sub-populations
centeredon privatelands (Wooding et al. 1994). Pelton
(1990) documentedthe existence of at least 30 disjunct
black bear populationsin the southeasterncoastal plain
with varyingdegreesof isolationandvulnerability.However, occupied bear habitatin coastal North Carolinais
relativelycontiguousand has increasedfrom 667,000 ha
in 1971 to 1.5 million ha in 1981 to 2.2 million ha in
1991 (Jones 1996) (Fig. 1). Analyses of black bearmortalitycharacteristicsalso supportthe conclusionthatNorth
Carolina'scoastal bear populationshave expandedover
1Presentaddress:North CarolinaWildlife Resources
Commission,P.O. Box 1231, Bridgeton,NC 28519-1231, USA,
email: [email protected].
the past 10-15 years (Warburtonet al. 1993). The black
bear range expansion in coastal North Carolinahas occurreddespite a markedincrease in human density and
activity. Manyof the characteristicsassociatedwithblack
bears may need to be reviewed and modified based on
the occurrencesin easternNorth Carolina. Habitatconditions, in which we will include human-relatedactivities, requiredfor sustainingblack bears in easternNorth
Carolinaaremuchmorecomplicatedthantraditionalideas
of contiguousareasof forestedlands. The unpredictable
responsesof blackbearsto increasinghumandensityand
activity in the NorthCarolinacoastal plain make quantification of importanthabitatvariablescritical for sound
bearmanagement.Wildlife managerswouldbenefitfrom
the developmentof quantifiablemodels for predictingthe
percentof a given area (e.g., a county) suitable for sustainingblackbearpopulationsgiven a set inputof habitat
variables(e.g., totalareaof forest,humanpopulationdensity, and areaof specific habitats). Predictionsregarding
futurehumaneffects on black bearpopulationscould be
made and management efforts guided accordingly.
Furthermore,the models could be used to identify suit-
204
Ursus 10:1998
by observationsof females with cubs. The currentoccupied range and range changes indicated on maps by
NCWRCbiologists were supportedwith observationsby
huntersand farmersand with NCWRC harvestand nui.;.''
' '
d'~
sance informationover the same periods. A dot grid was
*k
F ~used to measurethe hectaresof occupiedhabitatfor 1981
d
and 1991 in each of 30 coastal plain counties. Dot grid
were ?5% (n =15) based on comparisonsbetween
results
:
estimates
of county size and official measuredareas of
yP
counties.
Estimated occupied range from 1981 and 1991 and
percentchangesin occupiedrangebetween 1981 and 1991
were the dependentvariables(Y) in 6 separatemultiple
1991
regressionanalyses. Dependentvariableswere regressed
against 2 sets of independentvariables. The first set of
independentvariablesconsisted of human density, percent of county forested, and percent of county in cropland. The second set included percent of a county in
loblolly-shortleaf,longleaf-slash(P. palustris-P. ellioti),
oak-gum-cypress, oak-hickory (Quercus spp.-Carya
spp.),oak-pine (Quercusspp.-Pinus spp.),corn,peanuts,
soybeans,andwheat. A backwardeliminationprocedure
with a SLS (significance level for staying in the model)
of 0.05 was used to determinesignificantsubsetsof independent variables (SAS Inst., Inc. 1982). Therefore,3
models (1981, 1991, and 1981-91) assessed the predictive significance of human density, percent forest, and
percentcroplandvariables(HFC),and 3 models assessed
Fig. 1. Occupied black bear habitat in North Carolina,1981
the habitat-typevariables(HT) over the same periods.
and 1991 (Jones 1996).
Humandensitiesfor 1980 and 1990 were obtainedfrom
habitat
and
to
restoration
the
U.S. Bureauof the Census(1994). Forest-relateddata
but
able,
justify
unoccupied
were obtainedfromforest statisticspublishedby the U.S.
efforts.
Forest Service (Tansey 1983, Davenport 1984, Johnson
We wish to thankNorth CarolinaWildliffe Resources
Commission (NCWRC)biologists for assistting with the
1990, Thompson1990), andagriculturaldatawere issued
collection of occupiedrangedata. We also vvish to thank cooperativelyby the NorthCarolinaandU.S. Departments
of Agriculture(N.C. Agric. Stat. 1985, 1992). All forest
F. van Manen for reviewing an early sum]mary of this
and agriculturalstatistics were converted from acres to
B.
Marchinton
for
ideas
and
<
and
sharing
assisting
paper
with data entry. Finally, appreciationis exltended to D.' percentagesto accountfor differencesin county sizes.
Martorellofor advice and assistance designiing maps of
occupied black bear range in 1981 and 19911.
1981
4a
A%I
.
'A
I
I
0
250
o500
RESULTS
STUDYAREAAND METHODS
Black bear range maps for the North Carolina coastal
plain counties were preparedin 1981 and 1991 by the
NCWRC. Occupiedblackbearhabitatwas dcrawnon U.S.
Geological Surveytopographicmaps andNc)rthCarolina
Departmentof Transportationcounty mapis by district
biologists who were knowledgeableaboutb)eardistribution in theirareas. Occupiedhabitatwas defined as areas
havingreproducingblack bear populations<as evidenced
No HFC variables successfully predicted occupied
rangein 1981 (Table 1). Occupiedhabitatwas predicted
using HT variables (percent loblolly-shortleaf, percent
longleaf-slash, percent oak-gum-cypress, and percent
wheat, R2= 0.61). However,in 1991, the following HFC
variables were significant:human density, percent forest, the quadraticfunctionsof both variables,and an interactiontermbetweenthe variables(R2= 0.53, Table 1).
Significant HT variableschanged little in 1991, as percent loblolly-shortleaf, percent oak-gum-cypress, and
FORPREDICTING
MODELS
OCCUPIED
BLACKBEARHABITAT * Jones et al.
percent wheat remainedfrom the 1981 model, and percent soybeansreplacedpercentlongleaf-slash(R2= 0.60).
The quadraticfunctionof changes in humandensity and
an interactionterm between changes in human density
andpercentforest were significant(R2= 0.21) in predicting changes in occupied rangefrom 1981-91 using HFC
variables. No HT variables predicted changes in bear
distributionfrom 1981 to 1991. Equationsfor predicting
occupied habitatare based upon the synergisticrelationship of all significantvariables,and positive or negative
values for individualvariablescannot be equatedwith a
directpositive or negative effect on bear distribution.
DISCUSSION
The 1981 results indicatedthat only the relationships
between HT variablesaccuratelypredictedbear distribution, as no variables were significant in HFC models
(Table 1). However, in 1991, occupied black bear habitat was predictedusing the relationshipsbetween human
density and total forest-croplandand by the use of habitat variables. Changing significance of the variables
over the 10-year period emphasized the dynamic relationship of these variables and the complicated process involved in predicting suitable black bear habitat
at a given time. The variation not explained by the
models may be related to local circumstances, nonhabitat variables such as NCWRC regulations and
human attitudes, or spatial relationships between habitat variables.
Predictingchanges in occupied habitat(1981-91) using changes in the variableswas only possible with HFC
variables. The insignificance of HT variables may be
relatedto the fact thatchangesin HT variableswere relatively small (usually <1%), while bear range increased
205
markedly. Perhapsonly variablesthatchange by a critical magnitudeor reacha certainthresholdwill be significant for predictingchanges in bear distributionthrough
time. Another possibility is that predictingchanges in
beardistributionwith these types of models is unreliable
due to variablesthatcannotbe quantifiedsuch as human
toleranceand the effects of managementregulations.
The complicatednatureof the 1991 HFC model was
expected in coastal North Carolinadue to the expansion
of bearrangethatoccurredwith increasesin humandensity and landscapeactivity. The validity of these models
dependson the interactionof all significantvariablesin a
multiple regressionequation,and conclusions regarding
the individualvariablesare limited. However, some inferences regardinghabitatare warranteddue to the results of various habitat use and food habits studies in
easternNorth Carolina(Landerset al. 1979, Hellgren et
al. 1991, Lombardo1993, Maddrey1995, Jones 1996).
Loblolly-shortleaf, oak-gum cypress, and wheat
provedsignificantin both 1981 and 1991. Loblolly-shortleaf makesup 40% of all forestedlandsin the 30 counties
studied(Johnson1990, Thompson1990). Therefore,the
importanceof loblolly-shortleaf may be a result of the
dominanceof this forestcover type in areasof large,contiguous blocks of forest (i.e., bears are concentratedin
contiguousforestedhabitat,and loblolly-shortleaf is importantonly because it constitutesmuch of that forest).
Furtherevidenceof this was foundby Jones(1996); based
on rankingsof blackbearhabitatutilization,loblolly pine
habitatsrankedno higherthanfourthamonghabitatschosen by males or females in spring, summer, or fall.
Landerset al. (1979), Hellgren et al. (1991), Lombardo
(1993), and Jones (1996) demonstratedthe importance
of oak-gum-cypress forests for black bears, specifically
in fall as bears prepareto den. The significance of oak-
Table 1. Equations for predicting occupied black bear habitat in the counties of eastern North Carolina based on backward
elimination multiple regression, 1981-91.
Occupiedrange(Y) modelsa
Year
Humandensity-%forest-%cropland
Habitat
types
1981
No significant variables
Y = -33.67 + 1.46(%LB)+ 1.71(%LL)+ 1.09(%OG)+ 3.4(%WT)
1991
Y = 453.11 - 1.87(HD) - 11.76(FR) +
0.001(HD2) + 0.09 (FR2) + 0.02(HF)
Y = -23.56 + 1.75(LB) + 2.04(OG) - 4.45(SY) + 12.73(WT)
Changein Y
1981-91b
Y = 26.95 - 0.02(HD2) - 0.1(HF)
No significant variables
FR = % forest, HD = humandensity, HF = FR x HD, lB + % loblolly-shortleaf, LL =
longleaf-slash, OG = oak-gum-cyress, SY = soybeans,
WT = wheat.
b
Change in occupied range was predictedby change in significant variablesover approximatelythe same time.
a
206
Ursus 10:1998
gum-cypress in our models furtheremphasizedthe importanceof this forest cover type because it constitutesa
relatively small componentof availableblack bear habitat in the coastalregion. We hypothesizethatthe importance of wheat is related to the lack of alternatefood
sources in spring just after den emergence. Maddrey
(1995) foundwheatto be the dominantfood item in scats
duringspringin the centralcoastal plain of North Carolina. Wheat is the only agriculturalfood crop available
to bearsat thattime, and springis the season outside the
denningperiod when bear foods are most scarce.
The significance of soybeans in the 1991 HT model
may be evidence of bear adaptationto changingcrop rotationpatterns. Many farmersin easternNorth Carolina
have reportedthat bear depredationon soybeans is a recentphenomenon(Jones,pers.obs.), andMaddrey(1995)
was the first to reportthat soybeans were a major fall
food item. The absence of corn from the models was
unexpectedbecause bear depredationon corn was common in many areasof the coastal plain. However, many
extensive areas of corn arejuxtaposed with fragmented
forests in areas of low percent occupied habitaton the
westernperipheryof coastal bearhabitat. This variation
that occurs in local areasis evidence of the need to perform these types of habitatanalyses on a broadregional
scale. Furthermore,the 1991 model's conclusions are
supportedby evidence from Jones (1996) where cropland rankedsecond in use among 7 habitatsfor females
in 1 coastal studyareain the spring(wheatseason) andin
the fall (soybean season).
Finally,total areaof clearedland appearsto be a limiting factorfor blackbears. The westwardlimits of coastal
beardistributioncoincide with the boundarybetweenthe
easterncoastal plain's contiguousforests (largelyowned
by private timber companies) and the western coastal
plain's more intensively farmed and cleared areas and
higher humanpopulationdensities.
IMPLICATIONS
MANAGEMENT
Rudis and Tansey (1995) characterizedcourse habitat
elementsof occupiedblackbearrangeon a broadregional
basis throughoutthe SoutheasternUnited States. Our
models used a more detailedapproachto determinespecific habitatvariables(includinghumandensity) thatare
sometimes significant for predicting occupied habitat
within a distinctareaof a state. Both approachesidentified the importanceof large contiguous blocks of forested habitat and areas of bottomland hardwoods for
maintainingblackbearpopulationsin the Southeast. Our
models, which may be sensitive to local habitatcondi-
tions, also indicatedthat area and type of croplandwas
importantto bearsin easternNorthCarolina. Cropfoods
may substitutefor hardwoodmast in areas of sufficient
forestedhabitatwith escape cover anddenning. Because
estimatesindicatethatbottomlandhardwoodswill experience the greatestproportionalloss among southernforest types in the future (19% in 1952 to 15% in 2030,
Hughes 1990), managers in the Southeast should consider the juxtapositionof remainingcontiguousforested
blocks, oak-gum-cypress forests, and areasof important
crop foods. Because trendspredicta significantincrease
in forestindustryownershipof southernforestland (17%
in 1952 to 25% in 2030, Hughes 1990), coordinationof
managementefforts between wildlife managersand the
forestindustrywill becomeincreasinglyimportant.Landscape scale managementand cooperationbetween major
landownersis imperativeto ensureblackbearviabilityin
the rapidlydeveloping Southeasterncoastal plain. Models such as these may prove useful for developing landscape scale managementplans and identifying suitable
but unoccupied habitat for restoration. However,
unquantifiedvariablessuch as harvestrate, depredation
kill, effects of regulations,and otherhuman-relatedfactors must be carefully consideredby managersin conjunction with these types of habitatmodels.
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