WILDFIRES ON BIG SAGEBRUSH/
ANTELOPE BITTERBRUSH RANGE
IN NORTHEASTERN CALIFORNIA:
IMPLICATIONS FOR DEER
POPULATIONS
Douglas R. Updike
Eric R. Loft
Frank A. Hall
winter forage and thermal cover are reduced, the period
of time that deer can energetically maintain themselves
is also reduced (Hobbs 1989).
From September through December, bitterbrush
(Purshia spp.) has historically been the most important
winter range food in Lassen and Washoe Counties of
northeastern California and northwestern Nevada for
mule deer on winter range (Hormay 1943; Lassen and
others 1952; Dasmann and Blaisdell 1954; Leach 1956).
From January to March, sagebrush (Artemisia spp.) has
historically been the dominant forage source (Leach 1956;
Tueller 1979). The alien cheatgrass (Bromus tectorum)
has become important in the diet during spring and during the fall if wet, mild weather produces a "green-up"
(Bentley and Talbot 1951; Young and others 1987).
Hobbs (1989) developed a simulation model that predicted that mortality of deer would increase as shrub
forage digestibility decreased in severe winters. In the
model, digestibility is influenced by the availability of
shrub and herbaceous vegetation as modified by snow
depth. Herbaceous forage becomes less available as snow
depth increases. During mild winters when herbaceous
forage is available, declines in herbaceous forage digestibility increased mortality more than declines in shrub
digestibility. Hence, in severe winters, mule deer in
shrub-steppe communities must rely heavily on browse,
while in mild winters, both shrub and herbaceous forages
are important. The model assumes that, over time, both
shrub and herbaceous vegetation are present on the winter range, but in Lassen and Washoe Counties that is
increasingly not the case. Analogous to decreasing digestibility of shrub forage is to severely decrease the
availability of shrub forage resulting from fire.
Fires in the Lassen-Washoe range occur primarily during summer months due to lightning storms. Humancaused fires along highways and railroad rights-of-way
are also common, but are more likely to be kept small
because of their accessibility. Some prescribed fires during summer have been used to reduce sagebrush and
juniper (Juniperus occidentalis) abundance and increase
the production of herbaceous vegetation for livestock
(Bureau of Land Management, Eagle Lake Resource Area
files). The primary result of summer fire in the Great
Basin is the eradication of big sagebrush (A tridentata)
for a period of time (Pickford 1932; Blaisdell 1953). N atural regeneration ofbitterbrush following summer fire is
also poor on these western Great Basin ranges (Hormay
ABSTRACT
Between 1983 and 1988, wildfires burned more than
159,000 acres (64,300 ha) of big sagebrush (Artemisia
tridentata)!antelope bitterbrush (Purshia tridentata)
winter range used by mule deer (Odocoileus hemionus)
in Lassen County in northeastern California and Washoe
County in northwestern Nevada. As in much of the Great
Basin, these burned areas are frequently recolonized by
cheatgrass (or downy brome) (Bromus tectorum) and some
native perennial grasses, to the detriment of sagebrush
and bitterbrush regeneration. Recently burned areas provide no browse, thermal cover, or hiding cover for deer.
In the early 1950's, deer in the area consumed 63 percent
(by volume) browse and 28 percent grass during December.
In December 1987, dry cheatgrass comprised 80 percent by
volume while bitterbrush was almost nonexistent in deer
diets. Many deer died in winter 1987 because of storms
that made high-quality herbaceous forage unavailable and
because there was little browse available as a result of fire.
The deer population has been in a downward trend since
1964, and is down 28 percent since 1983. Management
options are suggested to help mitigate the modification
of deer habitat and consequent loss of deer.
INTRODUCTION
Winter is a maintenance or survival period of the
year for deer and their behavior and activities are directed towards maintaining a balance between energy
intake and expenditure (Hobbs 1989). High-energy
forage and thermal cover are important for mule deer
(Odocoileus hemionus) survival on Great Basin winter
ranges (Leckenby and others 1982). Because winter forage is usually insufficient for maintaining deer condition,
the duration and severity of the season is considered a
pnmary factor determining how long deer survive on
the winter range (Wallmo and others 1977). As quality
Paper presented at the Symposium on Cheatgrass Invasion, Shrub DieOff, and Other Aspects of Shrub Biology and Management, Las Vegas, NV,
April 5-7, 1989.
Douglas R. Updike is associate wildlife biologist and Eric R. Loft is
wildlife biologist, California Department ofFish and Game, 1416 Ninth
St., Sacramento, CA 95814; Frank A. Hall is wildlife biologist, California
Department ofFish and Game, 728-600 Fish and Game Road, Wendel, CA
96136.
41
This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
1943; Blaisdell1950; Nord 1965). One consequence of
summer fires has been the proliferation of cheatgrass,
which reduces natural bitterbrush seedling recruitment
(Holmgren 1956; Hubbard and Sanderson 1961; Young
and others 1972). Efforts to rehabilitate these ranges
may be difficult if not done before cheatgrass establishes
itself, or if herbivores are not controlled for the first few
years (Evans and Young 1978). In this paper, we develop
the hypothesis that summer fires on these ranges are
detrimental to the energy balance of wintering deer and
their survival because of the extensive conversion of
shrubland to grassland and associated loss of browse
and thermal cover.
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METHODS
The study area is located on the east side of the Sierra
Nevada between Reno, NV, and Susanville, CA (fig. 1).
Deer migrate to the area from summer ranges in the
Sierra Nevada. Fire records from 1957 to 1988 within the
winter range boundaries of the Doyle deer herd in southern Lassen and Washoe Counties were obtained from the
Susanville and Carson City Bureau of Land Management
offices and the California Department of Forestry. Polygons of fire occurrences were plotted on topographic maps.
Only fires over 300 acres (121 ha) were included, because
smaller fires were generally delineated with only a symbol
by the agencies and did not have a detailed map. Occurrence of repeat fires, those areas that have burned more
than once in the study years, was calculated to determine
whether those areas are predisposed to burn because of
the recent burning and presence of flammable herbaceous
vegetation (Young and others 1987).
""inter Range Boundar)
Figure 1-Mule deer winter range boundary.
Shaded areas represent polygons of wildfire
boundaries from 1957 to 1987 in Lassen
County, CA, and Washoe County, NV.
Acres (x 1000)
200~------------------------------------~
Food Habits-We compared mule deer food habits
data collected during December of 1951 and 1952 (n = 30)
and December 1987 (n = 16). Deer were collected during
both periods on winter ranges in Washoe County, NV, and
were analyzed by the same researcher (Leach 1956; Leach
1988). Deer collected in 1987 were from an area that had
burned many years previously and is adjacent to the site
of the 1951-52 collections. Mean frequency of occurrence
and percent volume of plant species in the stomach contents were determined for each deer.
150
100
Deer Population Estimates-Estimates of deer population numbers in the affected area were determined using a Lotus 1-2-3 (Lotus Development Corp.) simulation
of the POP-II population model (White 1985). The model
was considered valid when a 25-year simulation of the
annual harvest and herd composition agreed with field
data, and when the simulated population trend agreed
with an i~dependent method used to estimate the population (Fowler and others 1985).
50
RESULTS
o~~~~~~~~~~~~+-~~~~~~~~
1962
Fires burned about 49,000 acres (19,800 ha) of winter
range between 1957 and 1982 (figs. 1 and 2). From 1983
through 1988, fires burned at least an additional159,000
acres (64,300 ha). Repeat fires, those areas that burned
at least two times between 1957 and 1988, comprised
about 7,000 acres (2,830 ha) (about 3 percent of the total
burned area).
1967
1972
1977
Year
Figure 2-Cumulative acreage of burned (fires
> 300 acres in size) mule deer winter ranges in
Lassen and Washoe Counties from 1962 to
1988.
42
1982
1987
Food Habits-Diets of mule deer collected during
December 1951 and 1952 consisted of 28 percent grass,
63 percent browse, and 9 percent forbs (table 1). Cheatgrass was the only grass species found in the stomachs,
and the majority of it was green. The major browse species consumed were big sagebrush, antelope bitterbrush
(P. tridentata) and curlleafmountain-mahogany (Cercocarpus ledifolius ). Arrowleaf balsamroot (Balsamorhiza
sagittata) was the dominant forb eaten.
Diets of deer collected during December 1987 consisted
of 80 percent cheatgrass, almost all of it dry, and about
20 percent browse (table 1). Less than 1 percent of the
diet was forbs. Sagebrush and rabbitbrush (Chrysothamnus spp.) were the principal browse foods eaten.
No bitterbrush was found in the diet. The mix of forages
in the diet was less in 1987 than in the 1950's (fig. 3).
Body fat indices of 31 deer collected in 1987 indicated
that 28 were in poor to fair condition, three were in good
condition, and none were in excellent condition (Shor
1988).
Deer Population Estimates-Between 1962 and the
present, the December deer population in the study area
peaked at about 15,500 animals in 1964 and has declined
since (fig. 4). Between 1983 and 1988, the December
population estimate dropped about 28 percent to a new
low in recent decades of about 7,100 deer.
Dry Cheatgrass
6
Green Cheatgrass
20
1951-52
Green Cheatgrass
1
Other Browse
20
1987
Figure 3-Mix of dietary items eaten by mule
deer in December 1951 and 1952 compared
to December 1987.
Deer (x 1000)
Table 1-Volume of plants (percent) in stomach contents
of mule deer collected in December on mule
deer winter range in Washoe County, NV
18~---------------------------------,
16
Plant species
Years
1951 and 52
1987
(n = 30)
(n = 16)
14
12
- - - - Percent - - - Grasses
Cheatgrass (dry)
Cheatgrass (green)
Total grass
Browse
Big sagebrush
Antelope bitterbrush
Rabbitbrush •
Curlleaf mountainmahogany
Other browse
Total browse
Forbs
Balsam root
Alfalfa (Medicago sp.)
Filaree (Erodium sp.)
Other forbs
Total forbs
10
6
__gQ_
28
27
21
1
5
79
__
1
8
80
6
13
0
6
trace
4
2
_ _9_
63
trace
20
o~~~~~~~~~~~~~~~~~~
1962
5
2
trace
_ _2_
9
0
trace
<1
trace
<1
1967
1972
1977
1982
Year
Figure 4-Mule deer population trend (December
estimates) in Lassen and Washoe Counties from
1962 to 1989.
43
1987
DISCUSSION
has a winter crude protein content of about 8 percent
(Shaw and Monsen 1986). However, crude protein levels
for grasses in winter are generally lower than the maintenance requirement (Welch and others 1986). Poor body
condition and mortality of study deer in 1987 were most
likely attributable to a negative energy balance from consuming dry cheatgrass of low digestibility and low crude
protein.
The condition of deer and carrying capacity for deer has
been reduced because of the decrease in shrub vegetation
on the Lassen-Washoe winter ranges. This has made
deer much more susceptible to an energy deficit and subsequent mortality in severe winters when herbaceous forage is covered by snow, and in winters when there is no
fall greenup of herbaceous vegetation. When deer condition and range carrying capacity are reduced, the effect
should be reflected in reduced numbers of deer if the
winter range is a limiting factor. Prior to the extensive
fires, the summer ranges of these deer was considered
the most limiting factor (Fowler and others 1985). Since
1983, however, the winter range appears to have become
more limiting because of the cumulative loss of shrub
vegetation. The declining deer population reflects these
limiting conditions.
Since the 1951-52 study, the available forage for mule
deer in Lassen and Washoe Counties has been modified
by fire. Past research and current observations suggest
that summer fires in sagebrush-steppe communities
eliminate valuable browse used by mule deer in winter.
To a limited extent, small openings created by fire in
dense sagebrush communities would be desirable to deer
by increasing the patchiness of a given area. However,
on the scale of the extensive wildfires in the 1980's, large
areas of winter range have become a fairly homogeneous
stand of herbaceous vegetation. Adequate thermal and
hiding cover for deer are lacking on these burned ranges.
Although deer were not collected from exactly the same
sites, browse in the diet has decreased from about 60
percent to about 20 percent. Browsing pressure on remaining bitterbrush stands is high. Almost no forbs were
found in the diet in 1987 and the volume of green and dry
grass increased about three-fold.
Weather conditions from September to November determine the availability of green annual grasses and forbs
(Bentley and Talbot 1951). If a germinating rain and mild
temperatures do not occur, the only herbaceous forage
available may be dry vegetation from the previous spring.
From November to the following spring, snow depth also
determines availability of herbaceous vegetation. Hence,
annual herbaceous forage is an unreliable source of energy for wintering deer in some years.
Leach (1956) and Tueller (1979) considered grass consumption by deer in winter to be proportional to availability. Studies of wintering mule deer food habits indicate
an average diet consisting of 74 percent shrubs and trees,
15 percent forbs, and 11 percent grass (Kufeld and others
1973).
Deer in this study had a higher proportion of grass in
the diet than in any of the studies summarized by Kufeld
and others (1973). They assigned rankings to indicate the
relative importance of plant species to mule deer diets in
winter (fig. 5). Sagebrush and bitterbrush were among
the most important species. Cheatgrass was also important in mild winters that ensured its availability. By
comparison, squirrel tail (Sitanion hystrix), which is one
of the most abundant postfire species on prescribed-burn
sites in the Lassen-Washoe range, was considered a poor
source of winter forage for deer. Squirrel tail is one of the
most successful native species at coming back after fire
(Wright 1971), but we are not convinced that its abundance alone is justification for using summer fire as a
range improvement technique. Longhurst and others
(1977) concluded that conversion of shrubland to grassland, and grass seedings, were generally unsuitable for
wildlife.
Forage of dry matter digestibility less than 50 percent
may not provide sufficient energy for deer to maintain
their body weight (Ammann and others 1973). Succulent
green grass is typically of high digestibility; however,
cured grass has a higher lignin content and lowered
digestibility (Carpenter 1976). The minimum crude protein requirement to maintain deer condition is about
7 percent of the dry matter content (Welch and McArthur
1979). The 'Lassen' antelope bitterbrush shrub variety
SUGGESTED PRESCRIPTIONS
We suggest the following management prescriptions to
help mitigate the decline in deer habitat quality and deer
numbers:
Relative Importance to Deer in Winter
2
0
Squirreltail Cheatgrass Bitterbrush
Figure 5-Histogram of relative importance of
common winter forages to mule deer in the study
area (adapted from Kufeld and others 1973).
44
Sagebrush
(a) Quantify pre- and postburn vegetation composition.
Because of the 1950's-1960's research efforts in the area,
many vegetation and deer use transects exist for monitoring trends. Those in unburned as well as burned areas
should be examined again in anticipation of future wildfires to assess their impacts. For prescribed fires, prebum data on stand characteristics should be required.
Bentley, J. R.; M. W. Talbot. 1951. Efficient use of
annual plants on cattle ranges in the California foothills. Circular 870. Washington, DC: U. S. Department
of Agriculture. 52 p.
Blaisdell, J.P. 1953. Ecological effects of planned burning
of sagebrush-grass range on the upper Snake River
Plains. Tech. Bull. 1075. Washington, DC: U.S. Department of Agriculture. 39 p.
Bunting, S. C.; Kilgore, B. M.; Bushey, C. L. 1987. Guidelines for prescribed burning sagebrush -grass rangelands in the northern Great Basin. Gen. Tech. Rep.
INT-231. Ogden, UT: U.S. Department of Agriculture,
Forest Service, Intermountain Research Station. 33 p.
Carpenter, L. H. 1976. Nitrogen-herbicide effects on
sagebrush deer range. Fort Collins, CO: Colorado
State University. 159 p. Dissertation.
Dasmann, W. P.; Blaisdell, J. A. 1954. Deer and forage
relationships on the Lassen-Washoe interstate winter
deer range. California Fish and Game. 40(3): 215-234.
Evans, R. A.; Young, J. A. 1978. Effectiveness of rehabilitation practices following wildfire in a degraded big
sagebrush-downy brome community. Journal of Range
Management. 31(3): 185-188.
Fowler, G. S.; Kahre, K. S.; Conrad, K. R. 1985. The Doyle
deer herd management plan. California Department of
Fish and Game. 79 p.
Hobbs, N. T. 1989. Linking energy balance to survival in
mule deer: development and test of a simulation model.
Wildlife Monograph 101.
Holmgren, R. C. 1956. Competition between annuals and
young bitterbrush in Idaho. Ecology. 37(2): 370-377.
Hormay, A. L. 1943. Bitterbrush in California. Res. Note
34. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 13 p.
Hubbard, R. L.; Sanderson, H. R. 1961. Grass reduces
bitterbrush production. California Fish and Game.
47(4): 391-398.
Kufeld, R. C.; Wallmo, 0. C.; Feddema, C. 1973. Foods
of the Rocky Mountain mule deer. Gen. Tech. Rep.
RM-111. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and
Range Experiment Station. 31 p.
Lassen, R. W.; Ferrel, C. M.; Leach, H. 1952. Food habits,
productivity and condition of the Doyle mule deer herd.
California Fish and Game. 38(3): 211-224.
Leach, H. R. 1956. Food habits of the Great Basin deer
herd of California. California Fish and Game. 42(3):
243-308.
Leach, H. R. 1988. Food items eaten by 16 Rocky Mountain mule deer, Buffalo Creek area, Washoe Co.,
Nevada. California Department of Fish and Game. 1 p.
Leckenby, D. A.; Sheehy, D. P.; Nellis, C. H.; [and others].
1982. Wildlife habitats in managed rangelands-The
Great Basin of southeastern Oregon. Gen. Tech. Rep.
PNW-139. Portland, OR: U.S. Department of Agriculture, Pacific Northwest Forest and Range Experiment
Station. 40 p.
Longhurst, W. M.; Lesperance, A. L.; Morse, M.;
[and others]. 1977. Livestock and wild ungulates.
(b) Consider the impact of prescribed fire on deer
and the plant community. In light of the devastating
wildfires, we view summer prescribed fires that reduce
shrub abundance to be detrimental to Great Basin deer
winter ranges. Options exist for burning degraded sagebrush ranges at cooler seasons of the year to maximize
bitterbrush and sagebrush survival and regeneration
(Bunting and others 1987).
(c) Give higher priority and faster response time to
fires on these winter ranges. Simultaneous fires in other
areas may take priority over deer winter range fires because timber and developments may be in danger of
burning. Also, some view fires in the sagebrush range
as a good range livestock practice because they will convert brush to grass. We agree that burning anywhere
that cheatgrass is a component risks the perpetuation
of the remaining native plant community (B. L. Kay,
pers. commun.; Young and others 1987). The remaining
high-quality winter ranges are becoming fewer.
(d) Consider rehabilitation of range for wildlife with
seeding ofbitterbrush (Shaw and Monsen 1986) and
other browse species, such as sagebrush (Welch and
others 1986), in addition to seeding grass species.
(e) Control livestock and wildlife browsing/grazing pressure during the recovery phase by limiting stocking rate
and by liberalizing deer harvest to take more antlerless
deer.
To achieve these objectives will require cooperation
among the agencies involved and probably some concessions by each. A great deal of work on bitterbrush ecology
in the area was done in the 1950's by range and wildlife
researchers. It has successfully been seeded and transplanted into deer and cattle exclosures on recently burned
range in an intensive effort, but no reasonable method of
establishing bitterbrush on a large scale in the wild has
been found.
Finding a solution on a large scale should be addressed.
Can we establish bitterbrush without protection from
herbivory and can it become established given the presence of cheatgrass as a competitor?
There is consolation in knowing that good deer wintering habitat in this study area usually provides desirable
summer shrub and herbaceous forage for livestock as well
(Hormay 1943). The difficulty has been avoiding overuse
of such habitats at either season of the year.
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R. B.; Baker, D. L. 1977. Evaluation of deer habitat
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Welch, B. L.; McArthur, E. D. 1979. Variation in winter
levels of crude protein among Artemisia tridentata
subspecies grown in a uniform garden. Journal of
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J. C.; Davis, J. N. 1986. 'Hobble Creek'-A superior
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to burning than needle-and-thread. Journal of Range
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46