Carnivores and Omnivores
928
WILDFIRE EFFECTS ON BLACK BEAR DEMOGRAPHY
Effects of wildfire on black bear
demographics in central Arizona
Stan C. Cunningham and Warren B. Ballard
Abstract Little is known about the effects of wildfire on black bears (Ursus americanus). Following
a wildfire in Arizona, we hypothesized that the local black bear population would decline
due to direct mortality or reductions in food and cover. We also hypothesized that
remaining bears would have larger home ranges than bears in unburned areas because of
decreased food resources and cover. To test our hypotheses, we studied short-term effects
of a wildfire on black bear demographics in the Mazatzal Mountains, central Arizona,
from 1997–2000 and compared these parameters to those in an unburned area. We also
compared density estimates, survival, cub production and survival, and home-range sizes
in the same area prefire (1973–1978) to postfire (1997–2000). We captured 31 adult
bears within the burn perimeter on Four Peaks and 15 on unburned Mt. Ord during
1997–2000. Adult sex ratio within the burn perimeter on Four Peaks was more skewed
toward males (4 M:1 F) than in the unburned area on Mt. Ord (1.7 M:1 F), or the same
area prefire (1.4 M: 1 F). Subadults comprised 20% of captured bears in both study areas.
The largest apparent impact of the wildfire was lack of recruitment of cubs to the yearling
age class. Five adult females produced 16 cubs within the burn perimeter on Four Peaks
during 1997–1999, but none survived to 1 year of age. Four females in the unburned area
produced 13 cubs, and 36% survived to 1 year of age; in a prefire study, 48% of cubs survived to 1 year on Four Peaks. Hunting was the greatest cause of adult mortality in both
areas. Estimated black bear superpopulation size within the burn ranged from 27–36; a
simultaneous density estimate of the 120-km2 area was 13.3/100 km2. Because the
majority of activity occurred in the 26.2 km2 of unburned area within the burn perimeter, the density could have been as high as 73.8 bears/100 km2. Superpopulation size in
the 120-km2 unburned study area ranged from 21–30; density was estimated at 12.5
bears/100 km2. Female home-range sizes were similar between pre and postburn and
unburned Mt. Ord. Managers should be aware of possible negative short-term consequences of wildfire on black bear populations and manage to increase cub survival.
Key words age ratio, Arizona, black bear, chaparral, density, fire, home range, Madrean evergreen
forest, reproduction, sex ratio, sky island, wildfire
Fire-history studies (circa 1650–1900) indicate
that forests in the southwestern United States
burned every 2–10 years, many times more frequently than during recent decades (Swetnam and
Betancourt 1990). This historical fire regime
ensued from an annual cycle of wet winters
(November–February), arid foresummers (April–
June), and isolated lightning storms before the
onset of summer monsoonal rains (July–
September). Baisan and Swetnam (1990) described
Address for Stan C. Cunningham: Research Branch, Arizona Game and Fish Department, 2221 W. Greenway Road, Phoenix, AZ
85023, USA; e-mail: [email protected]. Address for Warren B. Ballard: Department of Range, Wildlife, and Fisheries
Management, Texas Tech University, Box 42125, Lubbock, TX 79409, USA; e-mail: [email protected].
Wildlife Society Bulletin 2004, 32(3):928–937
Peer refereed
Wildfire effects on black bear demography • Cunningham and Ballard
the historical fire regime from 1697 to 1860 on an
Arizona sky-island desert mountain range (for this
study defined as Madrean evergreen woodlands and
coniferous forests on higher elevations surrounded
by interior chaparral and Sonoran desert scrub).
These areas were dominated by large-scale (>200
ha), early season (May–July) surface fires every 1–13
years. Fires in the Southwest have become less frequent due to changes in land use, removal of fine
fuels by livestock grazing, and fire suppression
(Swetnam and Betancourt 1990). With fire exclusion, dead fuels accumulated continuously and
dense thickets formed in interior chaparral and
invaded open ponderosa pine (Pinus ponderosa)
stands. This increased hazards for crown fires or
stand-replacing fires (Fule and Covington 1994).
Stand-replacing fires have occurred only relatively
recently (<1 century) and will continue because of
fuel accumulation (Fule and Covington 1994).
On 28 April 1996 a wildfire (the Lone Fire) was
started by campers on Four Peaks Mountain, a
Southwest desert sky island, in the southern
Mazatzal Mountains, Arizona. This fire burned 237
km2 in 16 days and destroyed >90% of the vegetation. A fire resulting in high mortality of vegetation
(catastrophic) could be considered ecologically
unnatural because historical fire regimes burned
mountaintop forests without causing mortality of
mature trees (Fule and Covington 1994). The Lone
Fire provided a unique opportunity to determine
the effects of an ecologically unnatural wildfire on
black bear (Ursus americanus) populations.
The only literature describing the impacts of a
catastrophic wildfire on bears was the study by
Blanchard and Knight (1990). They recorded
behavior of radiocollared grizzly bears (U. arctos
horribilis) up to 6 months after a 1988 wildfire in
Yellowstone National Park, Wyoming. Thirteen
bears moved immediately into the burned areas
after the fire front passed, 3 remained within the
burn perimeter as the fire progressed, 3 stayed outside the burned areas at all times, and 2 were
believed to have died during the fire. Bears that
moved into the burned areas after the fire fed on
ungulate carcasses. Frequency of occurrence of
ungulates in grizzly bear scat postfire was significantly higher the year of the burn than in any other
year of study in Yellowstone National Park
(Blanchard and Knight 1990).
Fires can have positive effects on black bear diet
by creating early-successional stages in northern
coniferous forests. Black bear cub production and
929
survival were higher in populations living in recent
burns (<10 years) versus middle-aged burns (>25
years) on the Kenai Peninsula, Alaska due to
increased food supply, primarily moose (Alces
alces) calves (Schwartz and Franzmann 1991).
Black bears used recently burned areas heavily
(2–20 years) in western United States forests when
mast-producing plants were more available (Patton,
D. R., and J. Gordon. 1995. Fire, habitats, and
wildlife. United States Department of Agriculture
Forest Service, Coconino National Forest, Flagstaff,
Arizona, unpublished report). However, these studies were conducted in relatively homogenous coniferous forests, not in the Southwest where suitable
black bear habitats occur in sky-island patches. We
hypothesized that a hot wildfire in a desert skyisland environment would have short-term negative
effects on black bears. We hypothesized that black
bear density would be reduced either by direct
mortality or by emigration. We also hypothesized
that loss of food and cover would result in reduced
postfire survival and recruitment and that remaining bears would have larger home ranges than
bears in unburned areas because bears would have
to traverse larger areas to acquire necessary
resources for survival.
Availability of demographic data on black bears
prefire (LeCount 1982) allowed us to compare
population demographics before and after the wildfire. There were 32 adult black bears in the area of
the Lone Fire from 1973–1978 with an equal sex
ratio and an average age of 8.1 years (LeCount
1982). The population was lightly exploited, and
numbers were regulated by habitat quality, nutrition, subadult dispersal, and cannibalism of younger
bears by resident adults (LeCount 1982). In our
study we compared black bear sex and age ratios,
reproduction, survival, density, and movements collected after the Lone Fire to findings of LeCount
(1982) recorded before it. We also compared those
parameters with black bears on an unburned adjacent sky island (also postfire), Mt. Ord, located 26
km to the north.
Study area
The study region was located 80 km northeast of
Phoenix, Arizona in the southern portion of the
Mazatzal Mountains and included the Four Peaks
and Mt. Ord sky islands (Figure 1). We divided the
region into the Four Peaks study area—120 km2
within the burn perimeter on Four Peaks, which
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Wildlife Society Bulletin 2004, 32(3):928–937
ature gradient of 1°C per
100 m in elevation (Sellers
and Hill 1974).
Variations in elevation,
temperature, and precipitation resulted in a mosaic
of vegetation types. The
primary type was interior
chaparral (900–1,850 m;
Brown and Lowe 1974), a
complex association of
shrubs and small (<2 m)
trees, which intergraded
with Arizona Sonoran
desert scrub and semidesert grassland at lower
elevations (<900 m). Overstory was dominated by
Madrean evergreen woodland pine (Pinus spp.) and
oak (Quercus spp.) and
ponderosa pine coniferous forest on higher elevations (>1,850 m). Major
drainages were riparian
communities consisting of
both deciduous and evergreen forest types.
The fire did not burn 2
areas of Madrean evergreen forest (16 and 10.2
km2) in the Four Peaks
study area, and the differFigure 1. Location of Mt. Ord and Four Peaks study areas with respect to the Lone Fire perimeence between burned and
ter in the Mazatzal Mountains, Arizona, 1997–2000.
unburned areas was evident. Within burned sites,
included LeCount’s (1982) study area—and Mt. most vegetation that could shelter a black bear was
Ord, which was unburned and outlined by the destroyed. In wet periods forbs and grasses were
home ranges of 4 radiocollared female bears that abundant but vegetation >40 cm tall was minimal.
The trunks and large branches of trees and shrubs
we monitored during the study (120 km2).
Elevations in both study areas ranged from were charred but intact. There were no leaves on
700–2,300 m, with steep, rocky topography and these branches, but most species, excluding ponmany slopes >45%. Annual precipitation at derosa pine, regenerated at the base. Daytime cover
Roosevelt, Arizona (720 m), on the eastern edge of requirements for black bears were not available in
the Four Peaks study area, averaged 63 cm, and burned areas as late as 2000, and known black bear
occasional snows usually melted within a week. foods were not available within the burn until 1998
Average temperatures (1976–2000) ranged from (Cunningham et al. 2003).
39oC in July to 15oC in December (National
Oceanic and Atmospheric Administration
Methods
1976–2000). From Roosevelt Lake there was an
We captured black bears using Aldrich foot
increasing precipitation gradient of 1.3 cm per 310
m in elevation and a decreasing altitudinal temper- snares at baited sites from 19 April–23 June 1997 (n
Wildfire effects on black bear demography • Cunningham and Ballard
= 350 trap-nights), and 27 April–29 June 1998 (n =
370 trap-nights). After 2 years of using baited
snares, we suspected some bears became trap-shy.
To reduce bias in mark–recapture population estimates, we began using trail sets along bear “trails”
and continued baited snare sets from 1 May–29
June 1999 (n = 285 trap-nights), and 1 May–7 July
2000 (n=336 trap-nights). On Four Peaks trapping
was conducted on or near 3 snare lines established
by LeCount (1982) within the unburned area.
Prefire demographic estimates were based on snare
lines placed throughout the 120-km2 study site on
Four Peaks (LeCount 1982). However, we could not
use other known lines because there was not adequate shelter for captured bears in these areas
because of the wildfire damage to vegetation.
We immobilized captured black bears with
Telazol (5.0 mg/kg) and examined them for
injuries, gender, and reproductive condition. We
extracted a premolar for age estimation based on
number of cementum annuli (Stoneburg and Jonkel
1966). We attached a numbered plastic tag to each
ear and fit adult bears with MOD-500 radiocollars
(Telonics, Mesa, Ariz.) with mortality sensors. No
more than 25 bears were monitored at a time in
both areas combined. We conducted aerial radiotracking flights every 7–10 days from 15 April–1
November, 1997–2000. We conducted bimonthly
tracking flights during the denning period (2
November–14 April, 1997–2000). We assumed that
telemetry error was 80 ± 40 m (Carrel et al. 1997).
We conducted flights during the first 2 hours of
daylight, so locations primarily indicated crepuscular activity. From 1 July–15 September 1997–1999
we ground-tracked bears 16 days/month to midday
bedding and feeding locations. All relocation data
for each telemetered bear were combined (n =
18–36/year) to calculate annual home-range size
(convex polygon; Mohr 1947). We used convex
polygon estimates because small location sample
sizes inflated kernel estimates, and it allowed comparisons with other studies.
For all analyses except mean ages, we classified
black bears into 3 age classes: cubs (<1 year),
subadults (1 year <3 years),and adults (>3 years). We
determined reproductive activity of radiocollared
females by entering female bear dens and searching
for cubs and by teat condition in the subsequent
year’s recapture. We assessed differences between
mean ages of male and female bears using the MannWhitney U test. We used a chi-square contingency
test to evaluate differences in age and sex ratios.
931
We generated 2 superpopulation (i.e., residents
and visiting bears with completely random movements; Kendall 1999) estimates for each study area.
We used the Leslie Index and the Lincoln-Petersen
estimate so we could compare data with LeCount
(1982). We also used a modified Petersen estimator
suggested by Garshelis (1992), which uses animal
equivalents based on proportional occupancy to
reduce the bias of geographic closure and provides
a simultaneous estimate of the population at a
given time (a simultaneous estimate was defined as
the number of bears estimated in the area over a 10day sampling period; Garshelis 1992, Doan-Crider
and Hellgren 1996).
We determined annual and overall survival rates
of radiocollared bears equipped with mortality sensors using Kaplan-Meier procedures (Pollock et al.
1989). Because of limited sampling, sexes were
combined. We determined survival of cubs by visiting dens; we considered cubs dead if they were
not with their mother in the den the following year
(i.e., as yearlings).
We determined size of burned and unburned
“patches” using ARC-INFO GIS from a Landsat
Thematic Mapper image taken immediately after the
Lone Fire. Black bear density within the burn
perimeter on Four Peaks was estimated by dividing
the superpopulation estimate by the size of the
study area (120 km2) and by the amount of area
with unburned vegetation within the burn perimeter (26.2 km2).We determined the area and proportion of each vegetation association within each
study area from the Arizona GAP vegetation map
produced in 1995 (Halvorson and Kunzmann 2000).
We evaluated our hypotheses by assuming that if
bears had lower densities, cub production and survival, and adult survival, and larger home-range sizes
than in prefire conditions and on the unburned
area, the fire had negative impacts on bear demography.
Results
We captured 31 bears (>1 year old) 71 times in
889 trap-nights (8.0% trap success) within the Four
Peaks study area. On Mt. Ord we captured 16 individuals 23 times in 207 trap-nights (11.1%). Three
bears died during capture (2 yearlings were killed
and eaten by another bear in snares overnight, and
a >10-year-old male died due to injuries sustained in
falling from a tree). These bears were not included
in mortality estimates.
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Wildlife Society Bulletin 2004, 32(3):928–937
Table 1. Sex ratios of adult and subadult black bears captured
in the Mazatzal Mountains Arizona, 1973–2000. All chi-square
tests have df = 1.
Study area
No.
individuals
captured
χ2 value
(P value)
Four Peaks, 1973–1978 (LeCount 1982)
Adultsa
Male
21
na
Female
19
Subadultsb
Male
13
na
Female
3
Total
34:22
Four Peaks, 1997–2000 (this study)
Adults
Male
20
9.0
Female
5
(0.003)
Subadults
Male
4
0.67
Female
1
(0.41)
Total
24:6
9.3 (0.002)
Mt. Ord, 1997–2000 (this study)
Adults
Male
8
0.7
Female
5
(0.41)
Subadults
Male
2
0.33
Female
1
(0.56)
Total
10:6
1.0 (0.31)
% of
category
captured
51.3
48.7
81.3
18.7
80.0
20.0
80.0
20.0
61.5
38.5
66.6
33.3
a Adults = >3 years.
b Subadults = >1 to <3 years.
1.1 years. Both sexes had similar mean ages (M=5.4
and F=5.5 years) on Mt. Ord. No bears on Mt. Ord
were >10 years, but 8 of 24 of the males on Four
Peaks were >10 years.
Reproduction. None of 4 breeding-age females
(4, 5, 9, and 10 years) captured within the burn
perimeter on Four Peaks in 1997 showed signs of
having had cubs that year based on teat condition.
However, all 4 produced at least 2 cubs (1 litter of
3) during winter 1997–1998 (Table 2). Two of 4
females had cubs again in 1998–1999, which indicated an early loss of cubs for at least these 2
females in summer of 1998. The 3 other females did
not have cubs or yearlings, and changed dens >2
times as determined from aerial telemetry. In winter 1999–2000, we checked 3 denned females; 1
had 2 cubs. Overall, litter size averaged 2.3 cubs,
and 5 reproductive females produced 16 cubs in 3
years (Table 2).
On Mt. Ord none of 4 breeding-age females captured had cubs present and they showed no signs
of lactation in 1997. Three of 4 females produced 6
cubs in winter 1997–1998. In winter 1998–1999, 2
females had 5 cubs, and a yearling accompanied 1.
In winter 1999–2000, 1 female had 2 cubs, and yearlings accompanied the 2 others. Overall, average litTable 2. Production and survival of black bear cubs in the
Mazatzal Mountains, Arizona, 1973–2000.
Demography
Sex and age structure. Sex ratio of captured
bears >1 year old in the Four Peaks study area was
significantly skewed toward males (4M:1F;Table 1),
whereas the sex ratio on Mt. Ord was not different
from 1:1. On the Four Peaks study area, we captured new adult males each year: 8 initial males in
1997, 4 of 11 individuals in 1998, 3 of 8 individuals
in 1999, and 5 of 9 individuals in 2000. Conversely,
we captured 4 original adult females in 1997, and 1
new female of the 2 individuals captured in 1998,
but all 9 female captures in 1999–2000 were recaptures. On Mt. Ord we captured 4 females and 5
males in 1997; the following year we captured 2
new females and 5 new males. We did not run capture lines on Mt. Ord in 1999 and 2000.
Subadults comprised 20% of captured black
bears on both the Four Peaks and Mt. Ord study
areas, which is the same value LeCount (1982) estimated. The mean age of males at Four Peaks was
7.9±1.0 (SE) years, whereas females averaged 5.2±
Study area
No.
breeding
age
females
Four Peaks (LeCount 1982)
1973
2
1974
1
1975
1
1976
5
1977
9
1978
7
Total
25
Four Peaks (this study)
1997
4
1998
5
1999
3a
Total
12
Mt. Ord (this study)
1997
4
1998
3b
1999
3
Total
10
% of
females
producing
cubs
No. cubs
produced
% of cubs
surviving
to 1 year
of age
50.0
0.0
100.0
100.0
11.1
71.4
3
0
2
9
2
9
25
0.0
0.0
100.0
44.4
0.0
66.7
48.0
100.0
40.0
33.3
9
5
2
16
0.0
0.0
0.0
0.0
75.0
66.6
33.3
6
5
2
13
16.6
60.0
na c
36.4
a No. F reduced from 5 to 3 due to radio failure.
b No. F reduced from 4 to 3 due to mortality.
c Na indicates data were not collected.
Wildfire effects on black bear demography • Cunningham and Ballard
ter size was 2.2 cubs and 3 females produced 13
cubs in 3 years (Table 2).
Survival and mortality. None of the 16 known
cubs born within the burn perimeter on Four Peaks
survived to the yearling age class (Table 2). We captured 5 yearlings (4 M and 1 F) within the burn
perimeter on Four Peaks but their origin was
unknown. Cub survival to 1 year of age on Mt. Ord
was 16.6% in 1997–1998, and 60% in 1998–1999
(Table 2).
The primary cause of adult mortality among
radiocollared bears during this study was legal
hunting. Hunters in or near the Four Peaks study
area killed a 4-year-old female and 4 males between
3 and 7 years old; a 13-year-old male was killed in an
automobile collision. On Mt. Ord legal hunters
killed 2 males, and a 5-year-old female was killed
and eaten by another bear.
Overall, survival rate (averaged over 43 bearyears) of radiocollared black bears (sexes combined) on Four Peaks was 0.836±0.11 while annual survival was estimated at 0.964 ± 0.03. Overall,
survival on Mt. Ord was 0.714 ± 0.17 in 28 bearyears and annual survival was 0.941±0.06. Annual
survival prefire was 0.982 (LeCount 1982).
Population estimates and movements
Population Estimates. Population estimates (not
including CIs) within the Four Peaks study area
ranged from 16–36 adults, depending on the estimator used (Table 3). There were 32 adults in the
same area during prefire (LeCount 1982). We captured 31 adult black bears within the burn perimeter over 4 years. Simultaneous density was 13.3
bears/100 km2 in the 120-km2 Four Peaks study
area (Table 3). In early morning hours bears used
areas with burned vegetation, but >2 hours after
sunrise they were primarily (90.1%) in unburned
vegetation (Cunningham et al. 2003), so daytime
density could have been as high as 73.8 bears /100
km2 within the 26.2 km2 of unburned islands within the burn perimeter. We captured 16 bears on Mt.
Ord; population estimates ranged from 15–30
adults, and a simultaneous density estimate was
12.5 bears/100 km2 (Table 3).
Home Range. Mean home-range size of Four
Peak’s female bears differed (F=3.48, df=3, P=0.05)
among years (Figure 2). However, female bear
home-range sizes did not differ from 1997 through
1999 and ranged from 11–15 km2, with a high
degree of home-range overlap. Home-range sizes of
females were larger in 2000 (125.3 km2) due to
933
Table 3. Population estimates and density based on modified
Petersen estimates (Garshelis 1992) of adult (>3 years) black
bears in the Mazatzal Mountains, Arizona, 1973–2000.
Study area (km2)
Estimation method
No. bears
Population marked
estimatea in area
Four Peaks, 1973–1978
(LeCount 1982: 120 km2)
Leslie method
32
Petersen estimate
32(±16)
Four Peaks, 1997–2000
(this study)
Leslie method
27(±20)
Petersen estimate
36(±18)
Modified Petersen
16
Mt. Ord, 1997–2000
(this study; 120 km2)
1997–1998
Leslie method
21(±11)
Petersen estimate
30(±23)
Modified Petersen
15
Density
estimate
(No. bears/
100 km2)
28
30
13.3 bears/100km2
15
12.5 bears/100km2
a 95% Confidence intervals in parentheses.
movements to lower elevations by all females, and
2 moved 29 km northeast to another mountain
range. Prefire female home ranges were 17.9 km2
(LeCount et al. 1984). Male bears at Four Peaks had
larger home-range sizes (= 115.8, t=–2.72, P=0.01)
than females, but they did not differ among years.
Although there were no differences in annual
female home-range sizes among years on Mt. Ord
(Figure 3), male bears had larger home ranges than
females (34.9 vs. 17.4; t=–2.2, df=9, P=0.05). Males
Figure 2. Mean (±SD) annual and overall home-range sizes of
male and female black bears captured in the Four Peaks study
area in the Mazatzal Mountains, Arizona, 1997–2000.
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Wildlife Society Bulletin 2004, 32(3):928–937
Figure 3. Mean (±SD) annual and overall home-range sizes of
male and female black bears captured in the Mt. Ord study area
in the Mazatzal Mountains, Arizona, 1997–1999.
captured in the burn area of Four Peaks had larger
mean annual home-range sizes than males captured
on Mt. Ord (115 km2 vs. 35 km2; t = 2.3, df=11, P =
0.04), but female home-range sizes were similar
(14.4 km2 vs. 17.4 km2; t =–0.6, df=24, P=0.59) in
burned and unburned habitat.
Discussion
The sex ratio of captured adults (4 M:1 F) within
the burn area was skewed more toward males than
other bear populations in the Southwest (LeCount
1982, Waddell and Brown 1984, LeCount and
Yarchin 1990, Doan-Crider and Hellgren 1996).
Within the burn area we captured unmarked males
from 1–17 years of age through 2000; however, we
did not capture any unmarked females after June
1998. The sex ratio at Mt. Ord was equal. Prior to
the burn there were 19 adult females in the Four
Peaks area (LeCount 1982), whereas we captured
only 7. Male bias in trap samples has often been
attributed to their larger home-range sizes (Jonkel
and Cowan 1971, Lindzey and Meslow 1977).
However, given our trapping effort within the burn
perimeter, we doubt that many more females were
present, indicating a large drop in the female population since LeCount’s (1982) study, apparently as a
result of the wildfire. LeCount (1982) also captured
34 males as opposed to the 24 males we captured.
The primary differences in number of males was
the lack of the subadult proportion of the population in our captures (13 to 4), probably influenced
by lack of local reproduction. We can not rule out
the possibility that the bear population had
changed prior to the wildfire, but we assumed it
had been stable since LeCount’s (1982) study. We
documented a difference in sex ratio for the Four
Peaks study area, even with small sample size and
corresponding weak power. We do not know
whether adult females died directly as a result of
the fire or whether they emigrated from the area
due to a shortage of food or cover or for some other
reason. Adult females normally have strong site
fidelity (Rogers 1987).
That we captured so many more adult males than
females was interesting, but we can only speculate
on the reasons. We suspect the number of males
we captured was a realistic figure of adult males
that inhabited or visited the area and not an
increase in numbers. LeCount (1982) captured 21
adult black bear males in the Four Peaks study area,
while we captured 20. Any male that lived in or
repeatedly visited any part of the study area (e.g.,
breeding) most likely would have been forced to
visit the smaller unburned islands if they returned
because no other suitable habitats were available.
Females were located in the unburned habitats 90%
of the time, so most breeding activity probably
occurred there. Scant cover and food resources in
the burn (Cunningham et al. 2003) also probably
forced black bears of both sexes into the unburned
islands or out of the study area.
The age structure at Four Peaks during our study
was similar to that reported by LeCount (1982). A
20% subadult capture rate may be indicative of a
lightly exploited population with respect to hunting mortality (LeCount 1982, Beecham 1983,
Kolenosky 1986). It also may indicate low recruitment to the yearling age class before and during
our study (Doan-Crider and Hellgren 1996). We
failed to find evidence of recruitment to the yearling age class within the burn area. Since subadult
females usually stay in their natal territory (Elowe
and Dodge 1989, Schwartz and Franzmann 1992),
we suspected that few or no cubs survived.
However, subadult females may have dispersed
away from the Four Peaks area and we may have
failed to detect such dispersals.
Even with the high bear density within the burn
postfire, females still produced cubs, indicating
adequate food quantity and nutrition for reproduction (Rogers 1976, LeCount 1982, Schwartz and
Franzmann 1991). The number of cubs produced/female over the study period was similar
Wildfire effects on black bear demography • Cunningham and Ballard
between our 2 study areas (1.3 cubs/females). Prior
to the burn, there was 1 cub/female in Four Peaks.
Several potential explanations exist for the low cub
survival in the burn area. First, cannibalism of cubs
by adult male black bears has been documented in
other bear populations in Arizona (LeCount 1982,
1987). The high proportion of males and the high
black bear density in the unburned patches may
have made cubs more vulnerable to predation.
Females on Four Peaks prior to the burn avoided
males by using higher elevations (LeCount et al.
1984). After the Lone Fire, females did not use
higher elevations, and we assume this was due to
limited cover and food. Second, it was also possible
that cubs dispersed during autumn and were no
longer in the study area. Black bear cubs in some
eastern North American populations separate from
their mothers during autumn and subsequently
have denned and survived on their own (Jonkel
1978). Although we cannot totally dismiss this
explanation, the fact that cub survival was 36%,
based on yearling counts in dens on unburned Mt.
Ord, suggests this may have been a secondary factor. Also, it may have been possible that food
resources were adequate for cub production but
insufficient for sustained lactation and cubs
starved.
The lack of black bear recruitment for 4 years
suggested that the Lone Fire had a negative effect
on the Four Peaks population. We documented
immigration by subadults and older animals, but all
but one were males. Replacement of the female
portion of the population likely will depend on the
reestablishment of thermal and escape cover along
with recovery of food-producing vegetation.
Replacement of females rarely results from immigration of subadult females, because few female
subadults disperse from their place of birth (Rogers
1987, Schwartz and Franzmann 1992).
Chaparral reestablishment post-wildfire in the
Four Peaks area generally took up to 11 years
(Hibbert et al. 1974), so we expect that habitat conditions will improve. However, the forested island
on Four Peaks was reduced in size from 51.0 km2
to just 2.2 km2 of ponderosa pine and 11.9 km2 of
Madrean evergreen woodland. We did not observe
ponderosa pine reproduction, and ponderosa pine
is not adapted to recolonize after a fire this severe
(Swetnam et al. 1999). We did document resprouting and reproduction of Gambel’s (Q. gambelii) and
Emory oak (Q. emoryi). Black bears in Arizona
depend on large coniferous trees for escape, bed-
935
ding, and food, and often bed in brushy areas near
large pines (>74 cm diameter at breast height;
Mollohan 1987; LeCount and Yarchin 1990). The
resprouting oak trees, which are generally smaller
than ponderosa pine, may not be sufficient to provide black bears adequate cover and thus may not
allow recovery to previous densities.
Annual adult survival in both study areas
(0.941–0.964) was relatively high compared to
other black bear populations in southwestern
North America (LeCount 1982,Waddell and Brown
1984, LeCount and Yarchin 1990). Although adult
survival was high, if lack of recruitment continues,
the population could decline. However, we expect
that if vegetative recovery was not too prolonged,
recruitment could return to preburn levels in a
short period of time.
Arizona manages black bear hunting on a unit
basis (areas bounded by topographic features), with
a kill quota of females set for each unit. When the
maximum allowable number of females has been
killed in a unit, the unit is closed to bear hunting.
Management plans allow for an annual harvest of
no more than 5% of females within a unit. Given
the small proportion of marked black bears (7 of
51; 13.7%) that were killed in a 4-year period, hunting effects were minimal. However, if the reproductive potential of the bear population is significantly reduced within the burn, harvest may reduce
female recruitment. Fortunately, a female harvest
quota system allows for quick readjustments.
Home-range sizes of female bears captured within the burn were only slightly smaller than mean
female home-range size (17.9 km2) prior to the
burn (LeCount et al. 1984). The study areas experienced a drought during 2000 that may have
explained why home ranges were relatively large
(125.3 km2) that year. Probable lack of food from
the Lone Fire and drought caused females to move
to lower elevations and into other mountain ranges.
Larger home-range sizes for males captured in the
burn over those captured on Mt. Ord indicated they
may have been looking for females for breeding
that were displaced or killed as a result of the fire
or had to travel farther to find food.
Our results suggested that the female and
subadult portion of the bear population did decline
following a wildfire in Arizona. Density estimates,
adult survival rates, and cub production were similar pre and postburn and similar to those on an
unburned area (postburn). However, cub recruitment was lower. Home-range sizes also were simi-
936
Wildlife Society Bulletin 2004, 32(3):928–937
lar pre and postfire and to the unburned area.
Although we could not determine causes of cub
mortality, the indirect effects of the wildfire probably were a significant factor. Consequently, our
hypotheses were partially supported in the short
term. Continued poor cub recruitment ultimately
could result in a population decline if regeneration
of vegetation is prolonged.
Management implications
Given the lack of recruitment in the Four Peaks
Study area for at least 4 years following the wildfire,
it may be prudent for managers to consider reducing the harvest of females following a catastrophic
fire. Maintenance and perhaps further restrictions
on the current quota system for female harvest may
be needed. Managers also may have to increase harvest of males to reduce cub mortality and increase
subsequent bear recruitment. To reduce the number of males in the population, we suggest a spring
hunt with restrictions against harvesting bears with
cubs. The period of time needed by a black bear
population to recover from a catastrophic wildfire
is unknown, but short-term impacts on recruitment
appear severe. A hunting strategy that favors male
harvest appears desirable. Long-term studies are
needed to determine the full impacts of wildfire on
black bears.
One primary sky-island management effort by
resource agencies should be to maintain species
composition and diversity of vegetation stages.
One way to accomplish this may be to reduce the
constantly accumulating fuels by controlled burning or thinning.We suspect the effects of a cool fire
or tree thinning would be less dramatic than was
documented for the Lone Fire. However, black bear
reactions to different levels of fire are unknown and
should be studied.
Acknowledgments. Funding was provided by
the Federal Aid to Wildlife Restoration Act Project
W-78-R. Many individuals from the Arizona Game
and Fish Department and volunteers helped with
capturing, handling, and radiotracking bears. The
field assistance of L. Kirkendall, R. Vega, and L.
Monroe and the administrative assistance of J.
deVos and R. Ockenfels was appreciated. D. L.
Doan-Crider, D. L. Garshelis, P. R. Krausman, C.Ticer,
L. Monroe, D. White, Jr., and 2 anonymous referees
provided constructive comments on earlier drafts
of this manuscript.
Literature cited
BAISAN, C. H. AND T. W. SWETNAM. 1990. Fire history on a desert
mountain range: Rincon Mountain Wilderness, U.S.A.
Canadian Journal of Forest Restoration 20: 1559–1569.
BEECHAM, J. J. 1983. Population characteristics of black bears in
west central Idaho. Journal of Wildlife Management 47:
405–412.
BLANCHARD, B. M., AND R. R. KNIGHT. 1990. Reactions of grizzly
bears, Ursus arctos horribilis, to wildfire in Yellowstone
National Park, Wyoming. Canadian Field Naturalist 104:
592–594.
BROWN, D. E., AND C. H. LOWE. 1974. A digitized computer-compatible classification for natural and potential vegetation in
the southwest with particular reference to Arizona. Journal
of Arizona Academy of Science Volume 9: Supplement 2.
CARREL,W. K., R.A. OCKENFELS, J.A.WENNERLUND, AND J. C. DEVOS, JR.
1997. Topographic mapping, Loran-C, and GPS accuracy for
aerial telemetry locations. Journal of Wildlife Management
61: 1406–1412.
CUNNINGHAM, S. C.,W. B. BALLARD, L. M. MONROE, M. J. RABE, AND K. D.
BRISTOW. 2003. Black bear habitat use in burned and
unburned areas, central Arizona. Wildlife Society Bulletin 31:
786–792.
DOAN-CRIDER, D. L., AND E. C. HELLGREN. 1996. Population characteristics and winter ecology of black bears in Coahuila,
Mexico. Journal of Wildlife Management 60: 398–407.
ELOWE, K. D., AND W. E. DODGE. 1989. Factors affecting black bear
reproductive success and cub survival. Journal of Wildlife
Management 53: 962–968.
FULE, P. Z., AND W.W. COVINGTON. 1994. Fire-regime disruption and
pine-oak forest structure in the Sierra Madre Occidental,
Durango, Mexico. Restoration Ecology 2: 261–272.
GARSHELIS, D. L. 1992. Mark–recapture density estimation for animals with large home ranges. Pages 1098–1111 in D. R.
McCullough and R. H. Barrett, editors. Wildlife 2001:
Populations. Elsevier Applied Science, London, United
Kingdom.
HALVORSON, W. L., AND M. R. KUNZMANN. 2000. Assessment, correction, and augmentation of the Arizona GAP vegetation
data. Report Number HAB-96–0017. United States
Geological Survey, University of Arizona,Tucson, USA.
HIBBERT,A. R., E.A. DAVIS, AND D. G. SCHOLL. 1974. Chaparral conversion potential. Part I:Water yield response and effects on
other resources. Report Number RM-129. Rocky Mountain
Forest and Range Experimental Station, Fort Collins,
Colorado, USA.
JONKEL, C. 1978. Black, brown (grizzly), and polar bears. Pages
227–248 in J. L. Schmidt and D. L. Gilbert, editors. Big game
of North America, ecology and management. Stackpole
Books, Harrisburg, Pennsylvania, USA.
JONKEL, C. J., AND I. M. COWAN. 1971. The black bear in the sprucefir forest. Wildlife Monograph 27.
KENDALL, W. L. 1999. Robustness of closed capture-recapture
methods to violations of the closure assumptions. Ecology
80: 2517–2525.
KOLENOSKY, G. B. 1986. The effects of hunting on an Ontario
black bear population. International Conference on Bear
Research and Management 6: 45–55.
LECOUNT, A. L. 1982. Characteristics of a central Arizona black
bear population. Journal of Wildlife Management 46:
861–868.
LECOUNT, A. L. 1987. Causes of black bear cub mortality.
Wildfire effects on black bear demography • Cunningham and Ballard
International Conference on Bear Research and Management
7: 75–82.
LECOUNT,A. L., R. H. SMITH, AND J. R.WEGGE. 1984. Black bear habitat requirements in central Arizona. Arizona Game and Fish
Department Special Report 13, Phoenix, USA.
LECOUNT,A. L., AND J. C.YARCHIN. 1990. Black bear habitat use in
east central Arizona. Arizona Game and Fish Department
Technical Report 4, Phoenix, USA.
LINDZEY, F. G., AND E. C. MESLOW. 1977. Population characteristics
of black bears on an island in Washington. Journal of Wildlife
Mangement 41: 408–412.
MOHR, C. O. 1947. Tables of equivalent populations of mammals.
American Midland Naturalist 37: 223–249.
MOLLOHAN, C. M. 1987. Black bear habitat use in northern
Arizona. Final Report, Work Plan 2, Job 22. Arizona Game
and Fish Department, Phoenix, USA.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION. 1976–2000.
Climatological data: Arizona annual summaries. National
Climatic Data Center, Asheville, North Carolina, USA.
POLLOCK, K. H., S. R. WINTERSTEIN, C. M. BUNCK, AND P. D. CURTIS.
1989. Survival analysis in telemetry studies: the staggered
entry design. Journal of Wildlife Management 53: 7–15.
ROGERS, L. L. 1976. Effects of mast and berry crop failures on survival, growth, and reproductive success of black bears.
Transactions North American Wildlife Natural Resource
Conference 41: 431–483.
ROGERS, L. L. 1987. Effects of food supply and kinship on social
behavior, movements, and population growth of black bears
in north-eastern Minnesota. Wildlife Monograph 97.
SCHWARTZ, C. C., AND A.W. FRANZMANN. 1991. Interrelationship of
black bears to moose and forest succession in the northern
coniferous forest. Wildlife Monograph 113.
SCHWARTZ, C. C., AND A. W. FRANZMANN. 1992. Dispersal and survival of subadult black bears from the Kenai Peninsula,
Alaska. Journal of Wildlife Management 56: 426–431.
SELLERS, W. D., AND R. H. HILL. 1974. Arizona climate. University
of Arizona Press,Tucson, USA.
STONEBURG, R. P., AND C. J. JONKEL. 1966. Age determination of
black bears by cementum layers. Journal of Wildlife
Management 30: 411–414.
SWETNAM,T. W., AND J. L. BETANCOURT. 1990. Fire-southern oscillation relations in the southwestern United States. Science
262: 1017–1020.
SWETNAM,T.W., C. D.ALLEN, AND J. L. BETANCOURT. 1999. Applied historical ecology, using the past to manage for the future.
Ecological Applications 9: 1189–1206.
WADDELL, T. E., AND D. E. BROWN. 1984. Exploitation of two subpopulations of black bears in an isolated mountain range.
Journal of Wildlife Management 48: 933–938.
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Stan Cunningham (left) has been working as a research biologist with the Arizona Game and Fish Department since 1982,
with a brief 4-year stint as the education officer, when he coordinated Project WILD. Stan’s research interests include fire
ecology, carnivore–prey interactions, and ungulate habitat use.
He still is very active in environmental education and teaches
at least 4 WILD workshops for teachers each year. He received
his B.S. degree from the University of Wyoming and his M.S.
from Arizona State University. Warren Ballard (right) is professor of wildlife science and Associate Chair within the
Department of Range, Wildlife, and Fisheries Management at
Texas Tech University. He received his B.S. from New Mexico
State University, M.S. from Kansas State University, and Ph.D.
from the University of Arizona. He has been a member of The
Wildlife Society since 1967.
Special editor: Krausman