Abstract:
How does fire affect the plant and animal community
of the boreal forest? This study attempted to examine the
changes in plant composition and productivity, and small
mammal demography brought about by fire in the northern
boreal environment at Chick Lake, N.W.T. (65053fN, 128°14,W).
Two 5*6 ha plots measuring 375m x 150m were selected
for study during the summers of 1973 and 197^. One had been
unburned for 120 years, the other was part of a fire which
burned in the spring of 1969. Grids of 15m x 15m were established
in each plot and meter square quadrats taken at each of the
250 grid intersections in order to determine plant composition
and density. Aerial primary production was assessed by
clipping and drying 80 samples of terminal new production
for each species under investigation. Small mammal populations
were sampled by placing a Sherman live trap at each grid
intersection for ten days in every month.
The two plots were similar in plant species composition
which suggested that most regrowth in the burned area was
from rootstocks which survived the fire. The plant data
were submitted to a cluster analysis that revealed nine
separate species associations, six of which occured in the
burned area and eight of which occured in the control. These
were subsequently treated as habitats for purposes of comparison
with small mammal distributions. The burned area showed a greater
productivity in flowers and fruits although total productivity
in the control area was higher due to a large contribution
from the non-vascular component. Maximum aerial productivity
as dry wieght was measured at 157.1 g/m and 207.8 g/m for
the burn and control respectively. Microtus pennsylvanicus
and Clethrionomys rutilus were the two most common small
mammals encountered; Microtus xanthognathus, Synaptomys
borealis, and Phenacomys intermedius also occured in the area.
Populations of M. pennsylvanicus and C. rutilus were high
during the summer of 1973; however, M. pennsylvanicus
was rare on the control but abundant on the burn, while
C. rutilus was rare on the burn but abundant in the control.
During the summer of 197^ populations declined, with the
result that few voles of any species were caught in the burn
while equal numbers of the two species were caught in the
control.
During the summer of 1973 M. pennsylvanicus showed a
positive association to the most productive habitat type in
the burn which was avoided by C. rutilus. In the control
£• rutilus showed a similar positive association to the most
productive habitat type which was avoided by M. pennsylvanicus.
In all cases for the high population year of 1973# the two
species never overlapped in habitat preference. When populations
declined in 197^f "both species showed a strong association
for the most productive habitat in the control. This would
suggest that during a high population year, an abundant species
can exclude competitors from a chosen habitat, but that this
dominance decreases as population levels decrease. It is
possible that M. pennsylvanicus is a more efficient
competitor in a recently burned environment, while C. rutilus
assumes this role once non-vascular regrowth becomes extensive.
