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oslfire Rodent Succession
Following
scribed Fire In
Southern
Chaparral1
Abstract.-This paper describes species
composition and density changes in rodent
populations during postfire succession following
prescribedfire in the chaparral community of the
San Gabriel Mountains. Conclusions are drawn from
a 4-year, live-trap, mark and release study of postfire
succession in two watersheds receiving "hot" burns
and two receiving "normal" burns.
William 0.
Wirtz, II,?David H o e k r n ~ nJohn
,~
R. M ~ h r na,n~d Sherrie L. Souza5
The chaparral community of southern California is associated with
nearly two million years of fire history (Hanes 1971). In recent centuries
major fires have occurred at intervals
of 20 to 40 years (Byrne et al. 1977;
Philpot 1977).Postfire plant succession (Fatric and Hanes 1964, Hanes
and Jones 1967, Hanes 1971)and the
fire itself have varying short term
effects on the birds and small mammals found in the chaparral (Lawrence 1966, Quinn 1979, Wirtz 1977,
1979).Wirtz (1977) summarized the
work of earlier authors concerning
conditions in small vertebrate microhabita ts during fire, vertebrate behavior during fire, and survival of
small vertebrates exposed to fire.
Both Lawrence (1966)and Quinn
(1979) studied rodent populations
before and after a burn, in addition
to documenting microhabitat conditions during the fire. Wirtz (1977,
'Paper presented at symposium, Managemen t of Amphibians, Reptiles, and
Small Mammals in North America. (Flagstaff, AZ,July 19-2 1, 1988.)
William 0. Wirlz, I1 is Professor of Biology,
Department of Biology, Pomona College,
Claremont, CA 9 17 1 1.
3David Hoekrnan is a research assistant,
Department of Biology, Pomona College,
Claremont, CA 9 1 7 1 1.
4JohnR. Muhm is a research assistant,
Department of Biology, Pomona College,
Claremont, CA 9 17 1 1.
?SherrieI. Souza is a research assistant,
Departmen t of Siology, Pomona College,
Claremont, CA 9171 1.
1982,1984) presents preliminary
analyses of data collected on postfire
rodent succession following wildfire
in the chaparral community of southern California.
Because of the recently recognized
significance of the use of prescribed
fire in the management of chaparral
ecosystems, the Pacific Southwest
Forest and Range Experiment Station, USDA Forest Service, began formulating plans in 1983 for a series of
prescribed fires in the San Dimas Experimental Forest, located in the San
Gabriel Mountains of southern California, that might be utilized for long
range studies of the effects of prescribed fire in chaparral. In October,
1984, the Forest Service burned four
chaparral watersheds of approximately 40 ha each in the San Dimas
Experimental Forest. This paper describes the changes in rodent community structure for the 4-year period following prescribed burning.
Methods
In October, 1984, four chaparral watersheds of approximately 40 ha each
were subjected to prescribed burns in
the San Dimas Experimental Forest.
The vegetation of the two of these
watersheds (874 and 775) had been
hand cut in the spring of 1984 to produce the dried fuel for an exceptionally hot fire. Two adjacent watersheds (804 and 776) burned normally
for climatic conditions at the time. A
fifth watershed (803), which has been
extensively studied since 1976 (see
Wirtz 1977,1979,1982,1984), serves
as a control for studies on the prescribed burn areas.
Rodent live-trap, mark and release, studies were conducted on all
experimental areas prior to the burns
to document the size and species
composition of the prefire rodent
community on all watersheds, and
175 individuals were permanently
marked by toe-clipping to provide a
prefire pool of marked rodents from
which to determine survival rates
following the burn. Following the fire
grids of 50 stations at 15 m intervals
were established in each of the four
watersheds on the sites of the prefire
censusing, and a live-trap, mark and
release, program was initiated to determine fire survival and postfire rodent succession patterns.
For this paper, population estimates were done by the Hayne (1949)
equation. Area sampled, for each
species, for each month, was estimated by determining the mean distance traveled for each species between captures, for each month, and
then adding a zone equal to the mean
distance travelled to the perimeter of
the grid. Biomass was determined by
the product of the estimated population times the mean weight for each
species for the month, and these values are then summed for all species
taken on the grid for the month.
Results
Postfire trapping was initiated in
February 1985, and both experimental and control plots were sampled
bi-monthly. Hayne equation population estimates for rodent populations
on each study plot are presented in
figures 1-5. The absence of data
points from February through April
or May means that no rodents were
trapped, except for watershed 803 in
which trapping was not begun until
June 1985.
Mice of the genus Peromyscus
(deer mouse, P. rnaniculatus; brush
mouse, P. boylii; California mouse, P.
californicus), and California pocket
mice, Perognafhus californicus, constitute the bulk of the postfire rodent
population. Pacific kangaroo rat, Dipodomys agilis, dusky-footed wood
rat, Neotoma fuscipes, and California
vole, Microtus californicus, are present
in low numbers, and a few Botta's
pocket gopher, Thomomys bottae, and
Figure 2.-Hayne equation estimates of
population size of rodent species in Bell
804, normal prescribed burn. Note that
points at 0 on the x-axis against the y-axis
are populations estimates prefire.
1985
Figure 1 .-Hayne equation estimates of
population size of rodent species in Bell
803, the 28-year-oldchaparral control plot.
.
1986
-
1987
Figure 4.-Hayne equation estimates of
populationsize of rodent species in San
Dimas 776, normal prescribed burn. Note
that points at 0 on the x-axis against the yaxis are populations estimates prefire.
1988
Figure 3.-Hayne equation estimates of
populations size of rodent species in Bell
874, hot prescribed burn. Note that points at
0 on the x-axis against the y-axis are populations estimates prefire.
Figure 5.-Hayne equation estimates of
population size of rodent species in San
Dimas 775, hot prescribed bum. Note that
points at 0 on the x-axis against the y-axis
are populations estimates prefire.
western harvest mouse, Reithrodontomys megalotis, have also been taken.
Larger mammals observed in burned
watersheds, for which no quantitative data are available, included
Beechey ground squirrel, Spermophilus beecheyi, Audubonfs cottontail,
Sylvilagusauduboni, brush rabbit, S.
bachmani, coyote, Canis la trans, black
bear, Ursus americanus, badger, Taxidea taxus, and mule deer, Odocoileus
hemionus.
Fire Survival
No marked wood rats survived the
fires. Nine (12.5%)Peromyscus survived normal fires, and one (1.4%)
survived hot fires. Tow (12.5%)
Pocket mice survived normal fires,
and two (12.5%)Survived hot fires.
These data support the currently
held opinion that some rodents do
survive fires, and help provide the
nucleus, along with immigration
from unburned areas, for rodent
postfire succession.
Larger mammals seen in the
burned watersheds in the first month
postfire included coyote, black bear,
badger, and mule deer.
Early Postfire Succession
Pocket mice and all three Peromyscus
species were present on one hot burn
(874) by April 1985, six months
postfire, but no rodents were present
on the other hot burn (775). Pocket
mice moved into this hot burn (775)
by May, and two Peromyscus species,
(P. californicus, P. maniculatus) were
present by July.
Pacific kangaroo rats appeared on
some burned areas by June or July
1985 (they are rare in mature chaparral). Woodrats appeared on one normal bum (804) by June 1985, and another (776) by September 1985, and
on one hot burn (874)by August
1985. Single pocket gophers and harvest mice have been taken on one hot
burn (775).
Demography
Sampling was not begun on the control plot (803) until June 1985. The
rodent population on this plot consists chiefly of wood rats, California
mice, and pocket mice (fig. 1). The
California mouse population peaked
during the fall, winter, and spring of
1985-86, and again in the winter and
spring of 1986-1987. Pocket mice
were rare on the control until the fall
of 1986 and remained common until
the summer of 1987 (fig. 1).The
wood rat population has peaked in
each summer studied to date.
The prefire rodent population on
the normal bum in Be11 (804) was
composed primarily of woodrats,
with smaller numbers of other species (fig. 2) (note that symbols at 0 on
the x-axis against the y-axis represent
prefire density estimates). The
postfire rodent population on this
grid has been composed primarily of
brush mice and pocket mice, with
population peaks of the latter in each
winter (1985,1986, and 1987).Wood
rat populations did not show significant increases on this grid until the
spring of 1987, about 30 months after
the burn, and they have yet (June
1988) to reach prefire densities (fig.
2). Pacific kangaroo rats have occurred on this burned area in numbers above prefire densities since the
summer of 1985. Brush and California mouse populations have occurred in numbers above prefire densities since the winter of 1985-86 (fig.
2).
The prefire rodent population on
the hot burn in Bell (874) was composed largely of wood rats, California mice, and pocket mice (fig. 3). All
species, except kangaroo rats, were
present again on this grid by August
1985, 10 months postfire. The postfire
rodent community on this hot burn
has been dominated by brush mice
and pocket mice (fig. 31, with both
species reaching, or exceeding, prefire densities by the winter of 1985,
approximately a year after the burn.
California mouse and wood rat
populations have yet (June 1988) to
reach prefire densities (fig. 3).
The prefire rodent population on
the normal burn in San Dimas (776)
was composed primarily of California mice and wood rats, with smaller
numbers of pocket mice and no
brush mice (fig. 4). The postfire rodent community has been dominated
by California mice and pocket mice,
with both species exceeding prefire
densities by the winter of 1985, approximately one year postfire. Wood
rats have yet (June 1988) to reach
prefire densities, brush mice have not
appeared on this grid, and California
voles were common in the summer
of 1987 and the spring of 1988 (fig. 4).
The prefire rodent population on
the hot burn in San Dimas (775) was
very similar to that on the normal
burn here (fig. 5). And, like the normal bum, the postfire comnaunity
has been dominated by California
mice and pocket mice, with pocket
mice exceeding prefire densities by
the summer of 1985 and California
mice exceeding prefire densities by
the fall of 1986 (fig. 5). Pacific kangaroo rats also exceeded prefire densities within one year postfire on this
grid.
Comment should be made about
the presence of deer mice (P. maniculatus) and California voles (Microtus)
on these grids. Neither species was
present on any grid prefire, and neither has been taken on the control
(figs. 1-5).P. maniculatus has been
taken on all burned grids, with peaks
of abundance by the second year
postfire and declining abundance by
the fourth year postfire (figs. 4 and
5).
Effects of Hot and Normal Fires
The effects of hot and normal fires on
rodent demography were examined
by (1) comparing pre and post fire
populations in areas exposed to these
two fire regimes (figs. 6 and 7), (2)
comparing the number of captures of
each species postfire under each fire
regime (fig. 81, and (3) comparing
total postfire biomass on areas exposed to different fire regimes (fig. 9)
(note again that points at 0 on the xaxis against the y-axis are prefire
populations estimates). Only species
with relatively high abundances are
considered in this paper.
Prefire populations of brush mice
were essentially the same on both
areas to be burned in Bell, while densities of pocket mice and California
mice were greater on the area to receive the hot burn, and deer mice
were not present on either grid (fig.
6). All prefire populations were severely impacted by fire, dropping in
most instances to near zero for several months postfire. Pocket mice increased to twice their prefire density
on the hot bum and 25 times prefire
density on the normal burn (fig. 6).
Brush mice increased to 14 times
their prefire density on the hot burn
and six times prefire density on the
normal bum (fig. 6). California mice
returned to prefire density by one
year postfire on the normal burn, and
numbers have remained relatively
constant since then. Deer mice were
present on both burned areas
postfire, but have been more abundant on the hot burn (fig. 6).
Prefire populations of California
mice and pocket mice were similar
on both areas to be burned in San
Dimas (fig. 7). Some individuals survived the normal burn. Pocket mouse
populations exceeded prefire densities on both normal and hot burns by
eight months postfire (fig. 7). California mouse populations exceeded prefire densities by one year postfire on
the normal burn, but took two years
to reach prefire densities on the hot
bum (fig. 7). Two species not present
prefire, Pacific kangaroo rats and
deer mice, colonized both burned
areas by eight months postfire; kangaroo rats have remained numerous
on the hot burn, and deer mice are
more numerous on the hot bum than
on the normal burn (fig. 9).
Captures of California mice
postfire are greater on normal burns
than on hot burns, and exceed captures on the control on one normal
burn (776) (fig. 8). Captures of brush
mice postfire are greater on both hot
bums and one normal burn than on
the control, and captures on hot
bums are greater than on normal
burns for each pair of watersheds
burned (fig. 8). Deer mice have not
been captured on the control; captures are greater postfire on hot
burns than on normal burns for each
pair of watersheds burned (fig. 8).
Captures of wood rats are less on all
burned areas than on the control, and
they are less on hot bums than on
normal burns for each pair of watersheds burned (fig. 8).
California voles have not been
taken postfire on the control nor on
one normal burn, and are greater on
the other normal burn than on either
hot bum (fig. 8). Captures of Pacific
kangaroo rats postfire are greater on
both normal and one hot burn than
on the control, while captures of
pocket mice postfire are greater on
all burned areas than on the control
(fig.8).
Total biomass on the control, not
28 years old, has fluctuated during
the period of study, but shows a
slight increasing trend (fig. 9). Total
biomass on both burned plots in Bell,
the location of the control, has also
fluctuated, with a slight increasing
trend, in a fashion similar to that of
the control (fig. 9). Total biomass on
the burned plots in San Dimas has
also fluctuated, with slight increasing
trend, but with two dramatic biomass increases, one in the Spring of
1987 and the other in the spring of
1988 (fig. 9). The pattern of fluctuation, and increase, on the normal
burn in San Dimas is similar to that
observed for the control, and the pattern of fluctuation, and increase, if
Figure 6.-Comparison of rodent postfire
population growth on normal (804) and hot
(874 prescribed fire plots in Bell. Note that
points at 0 on the x-axis against the y-axis
are populations estimates prefire.
Figure 7.-Comparison of rodent postfire
population growth on normal (776) and hot
(775) prescribed fire plots in San Dirnas.
Note that points at 0 on the x-axis against
the two sharp peaks are not considered, is also similar to the control
(fig. 9).
Discussion
General patterns of rodent postfire
succession following these prescribed
burns are similar to those reported
by Wirtz (1977,1982,1984) for succession following wildfire in the
chaparral of the San Gabriel Mountains, but lack the dramatic increases
in density, and therefore biomass,
observed in these earlier studies. He
notes (1984) that rodent succession
following wildfire takes about four
years before populations stabilize at
essentially prefire conditions found
in older chaparral stands. The response of species to these prescribed
fires varied, with some species reaching prefire densities in less than four
years and others having not yet
reached prefire densities at essentially four years postfire.
Only slight differences are noted
between rodent postfire succession
on normal and hot bums, and these
may probably be attributed to differences in the biology of individual
species. In Bell, both normal and hot
burns were dominated postfire by
pocket mice and brush mice, though
pocket mice had the highest density
on the normal burn (804) and brush
mice had the highest density on the
hot burn (874) (fig. 6). California
mice recovered to prefire density on
the normal bum, but have not yet
(June 1988) recovered on the hot
burn, and wood rats have not recovered to prefire densities on either
burned area (fig. 6). Deer mice have
been more prevalent on the hot burn
than on the normal burn during the
period of the study. By the second
year postfire, populations of all species, except wood rats, exceeded prefire densities on the normal burn (fig.
2), and populations of brush mice
and pocket mice had exceeded prefire densities on the hot bum (fig. 3).
In San Dimas, where considerable
brush was left alive on the normal
burn (776), both normal and hot
bums were dominated postfire by
-
CONTROL
m
NORMAL
0
HOT
l o 0 U n ,
CNHNH
Perom~scua
caltlornicus
Pmrwnyscur
boylii
0 0
,-,-
pocket mice and California mice (fig.
7). Both of these species recovered to
prefire densities on the normal burn
by one year postfire (fig. 41, as did
pocket mice on the hot bum (fig. 5),
but California mice did not reach
prefire densities on the hot burn until
the second year postfire (fig. 5). For
reasons not immediately apparent,
but probably because of the presence
of some grass prefire, California
voles were found only in these two
watersheds postfire. The greater relative abundance of Pacific kangaroo
rats on the hot burn is most likely
due to the fact that more open space,
necessary for kangaroo rat saltitorial
locomotion, was left by the hot fire
here.
Pocket mice increase rapidly on
burned areas, there being essentially
no difference between normal and
hot burns (figs. 6 and 7). Brush mice,
if present prefire, recover more rapidly postfire than California mice,
and the latter recover more rapidly
on normal burns than on hot burns
(figs. 6 and 7). Deer mice, virtually
nonexistent in mature chaparral,
colonize both normal and hot burns,
and increase more rapidly on hot
burns (figs. 6 and 7).
Data on captures (fig. 8) indicate
that increase of deer mice on hot
burns. The species is known to colonize disturbed areas, whether they be
caused by fire, logging, or over-
CNHNH
Peromyrcur
maniculrlu8
Figure 8.-Comparison of postfire captures of all rodent species on control and prescribed
burn plots.
Figure 9.-Total postfire biomass (grams) for
control and burned plots.
gazing (Williams 1955). These data
also illustrate the decline of California mice on hot burns and its increase in normal burns, and the increase of brush mice, where present
prefire, on both normal and hot
bums. Burning favors density increases of pocket mice, with essentially no difference between normal
and hot burns. Kangaroo rats exhibit
variable increases in response to fire,
and wood rats are severely impacted
by fire.
Biomass increases in response to
fire are variable, and in this study,
were similar in variability to those
occurring on the control (fig. 9). The
sharp peaks in biomass observed on
one hot burn (775) are due to large
density increases in pocket mice during these periods.
It is important to note, when comparing data for normal and hot
bums, that in one normal burn (776)
a lot of unburned brush remained,
perhaps more accurately simulating
an "island" in a burn rather than a
burn per se. So, for this study, the
data for 776 are somewhat atypical,
and 804 represents more accurately
the situation following a normal
bum. But it is also important to note
that "islands" of unburned vegetation are frequently left by wildfire,
providing refugia for both plants and
animals from fire.
Several general conclusions may
be drawn from the rodent data: (1)
fire may impact rodent species severely, probably chiefly through loss
of habitat resources, especially shelter and food; (2) some individuals
survive fire; (3) colonization from
adjacent habitats may be rapid; (4)
postfire succession is somewhat dependent on prefire species composition of the area; (5) in southern California chaparral, at least two species,
deer mouse and California vole, are
fire specialists, entering the system
only for relatively short periods of
the postfire succession; (6) species
requiring brush for cover and/or
food, like wood rats and California
mice, are most severely impacted by
fire, and require the longest time to
recover to prefire densities; (7) there
is no clear-cut difference in rodent
postfire succession following normal
and hot fires; (8) rodent postfire succession is characterized by increases
in successionally-adapted species,
with declines in those species for
which essential habitat features are
lacking; and (9) recovery of the rodent community to its prefire condition probably takes four to six years,
with the exact pattern of recovery
being dependent on prefire species
composition and features of the prefire plan community and postfire
plant succession that have not been
delineated.
Acknowledgments
This research was supported by
USDA Forest Service, Pacific Southwest Forest and Range Experiment
Station Grant Number PSW-850004CA to WOW and a summer research assistantship from Pomona
College to JRM.
We are indebted to Susan Conard,
Project Leader, Pacific Southwest
Forest and Range Experiment Station, Forest Fire Laboratory, Riverside, CA, for her support and cooperation during this study. Many biology students at Pomona College have
assisted with field work. The senior
author wants to acknowledge 5 years
of field work by Sherrie Souza and
David Hoekman, all computer programming by David Hoekman, and
all data analysis by John R. Muhm.
We are grateful to Helen Wirtz for
our figures. Preparation of this paper
was greatly assisted by a summer
research assistantship to JRM.
Literature Cited
Byrne, Roger, Joel Michaelsen and
Andrew Soutar. 1977. Fossil charcoal as measure of wildfire frequency in southern California: A
preliminary analysis. p. 361-367. In
Harold A. Mooney, Eugene C.
Conrad, eds. Proceedings of the
Symposium on the Environmental
Consequences of Fire and Fuel
Management in Mediterranean
Ecosystems. USDA Forest Service,
General Technical Report WO-3.
Hanes, Ted L. 1971. Succession after
fire in the chaparral of southern
California. Ecological Monographs
41(1):27-52.
Hanes, Ted L. and Harold W. Jones.
1967. Postfire chaparral succession
in Southern California. Ecology
48:259-263.
Hayne, Don W. 1949. Two methods
of estimating population from
trapping records. Journal of Mammalogy 30(4):399-411.
Lawrence, George E. 1966. Ecology
of vertebrate animals in relation to
chaparral fire in the Sierra Nevada
foothills. Ecology 47(2):278-291.
Patric, James H. and Ted L. Hanes.
1964. Chaparral succession in a
San Gabriel Mountain Area of
California. Ecology 45:353-360.
Philpot, Charles W. 1977. Vegetative
features as determinants of fire
frequency and intensity. p. 12-14.
In Harold A. Mooney, Eugene C.
Conrad, eds. Proceedings of the
Symposium on the Environmental
Consequences of Fire and Fuel
Management in Mediterranean
Ecosystems. USDA Forest Service,
General Technical Report WO-3.
Quinn, Ronald D. 1979. Effects of fire
on small mammals in the chaparral. Cal-Neva Wildlife Transactions, 125-133.
Williams, Olwen. 1955. Distribution
of mice and shrews in a Colorado
montane forest. Journal of Mammalogy 36(2):221-231.
Wirtz, William O., 11. 1977. Vertebrate postfire succession. p. 46-57.
In Harold A. Mooney, Eugene C.
Conrad, eds., Proceedings of the
Symposium on the Environmental
Consequences of Fire and Fuel
Management in Mediterranean
Ecosystems. USDA Forest Service,
General Technical Report WO-3,
Washington, D.C., 498 p.
Wirtz, William O., 11. 1979. Effects of
fire on birds in chaparral. CalNeva Wildlife Transactions, 114124.
Wirtz, William O., 11. 1982. Postfire
community structure of birds and
rodents in southern California
chaparral. p. 241-246. In Eugene C.
Conrad, Walter C. Oechel, technical coordinators. Proceedings of
the Symposium on Dynamics and
Management of Mediterraneantype Ecosystems. USDA Forest
Service, General Technical Report
PSW-58.
Wirtz, William O., 11. 1984. Postfire
rodent and bird communities in
the chaparral of southern California. p. 167-168. In MEDECOS IV.
Proceedings of the 4th International Conference on Mediterranean Ecosystems. University of
Western Australia, Perth, Western
Australia.