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Wildlife
Fire has different effects on the many species
of animals in a burned area.
Those that do not survive a fire, either from direct contact
with the flames or due to smoke inhalation, will become fresh carrion
for the carnivorous animals. The herbivores and omnivores will soon
find new grasses growing from which they can feed.
The 1988 fires were responsible for the deaths
of fewer than one percent of the mammals in Yellowstone National
Park (YNP). Of these, most probably died as a result
of smoke inhalation and not by direct contact with the flames (Singer
1989). However, the
amount of burned forest and meadowland had a considerable effect
on those that survived.
Foraging
| Fire causes both shrubs and grasses to burn to
the ground. The
shrubs are not able to grow again until new seedlings have sprouted.
While the shrubs are waiting for seeds to sprout, grasses
are able to grow quickly in the burned areas, providing food
for elk and bison. A
burned area can thus provide ungulates with increased quantities
of foraging grasses for approximately three to four years following
a fire. This can be particularly helpful in harsh
winter seasons (Pearson et al. 1995). According to one plant ecologist, for the first three years
following the 1988 fires, there was fifty percent more forage
available than before the fire (Robbins 1998). |
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Elk
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Elk may benefit in many ways from fire.
For example, seed production in Northern Yellowstone
National Park grasses was found to be enhanced due to burning
in one study on elk herbivory.
Elk returned to the grasslands soon after the fires,
but they did not return to the burned forests for about three
years. This was
likely due to the lack of a forest canopy, thus deeper snow
on the forest floor, and less efficient foraging for elk (Singer and Harter 1996).
The winter directly following the 1988 fires
was particularly harsh and was responsible for the deaths
of 38%-43% of the northern range elk.
Approximately 14%-16% were harvested by humans and
24%-27% died of natural causes. This was a dramatic increase compared
to the 1987-1988 winter in which the elk mortality was less
than 5% (Singer and Harter 1996).
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Lodgepole pine (Pinus contorta) is usually a less preferred choice of food for elk because they are
not able to digest the bark very well.
After the fires, however, studies showed that more elk were
consuming the bark from these trees.
One study found burned bark to be more than twice as digestible
as live bark for elk, primarily in the winter ranges (Jakubas et
al. 1994).
In the following years, the elk have made a healthy
comeback. Depending
on the season, there may be anywhere from 15,000 to 30,000 elk in
Yellowstone (National Park Service).
For more information, please see our elk
pages.
Moose
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Moose and elk may share foraging areas and
thus may compete for food following a fire.
Both animals feed on aspen and willow trees, both of
which are likely to burn to the ground in a fire.
The most successful moose during and after
the 1988 fires in YNP were those that focused on unburned
or lightly burned mature conifer stands at high elevations.
Moose that shared winter ranges with elk were successful
if they moved to mature conifer stands with deeper snow, for
such areas were not favorable to elk (Tyers and Irby, 1995).
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Although the YNP moose population suffered a loss
of habitat to some degree due to the fires, the first five years
after the fires brought abundant summer foraging for moose in certain
areas (Knight 1994). The winter ranges, however, could take
up to 200 years to recover, for the forest canopies that catch a
lot of snow in the winter (allowing for better foraging areas) were
burned in the fires.
Moose will often forage on saplings and seedlings
that grow in the forest understory.
The 1988 fires wiped out a large portion of this food source. Up to 50% of the moose population in YNP has died as a result
of starvation; some have moved to other habitats (Robbins 1998).
Bison
| Studies have shown that fires can improve bison
foraging habitats and that bison may actually prefer to forage
on recently burned sites. In the winter after the 1988 fires,
almost all of the 900 YNP bison moved to the edges of the park
or left the park in search of food.
As a result, more than 500 bison were shot as game (Schullery
1997). Over the
years, as the bison have returned to the open grasslands and
meadows, the Yellowstone bison population has recovered (USDA
Forest Service). A 1998 estimate
places the bison population at approximately 2200 (National
Park Service). Please see our bison
pages for more information. |
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Grizzly
Bears
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Fire suppression threatens the future of
whitebark pines. Whitebark
pine nuts are a common food for YNP grizzlies, especially
in the summer and fall, before hibernation (Robbins 1998).
White pine blister rust is a pathogen that is threatening
the pines.
Whitebark pine has been found to grow again
on burned areas, but only after about 100 years are they truly
successful. These issues not only threaten the whitebark
pine; they in turn threaten the grizzly population of YNP
by wiping out one of their primary food sources (Pease and
Mattson, 1999).
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Ants
are also an important food for grizzlies and can thrive with all
of the burned trees falling to the ground, providing more places
for ants to live (Robbins 1998).
For more information, please see our grizzly
pages.
Cougars
| Due to their agility and speed, cougars are likely
to escape from a fire with little difficulty.
Research has shown that the effect of fire on a cougar
population depends on the size of the fire.
One study was completed in a variety of burned habitats:
chaparral, oak woodlands, coastal scrub, and conifer forests.
Three cougars were included in the study and were found
to avoid the burned area for only 2-6 weeks (Beier and Barrett,
1993). In a second
study, two cougars were observed in a conifer forest that had
undergone a catastrophic fire, one that burned the canopy and
the understory. The
study found that a conifer stand greater than three square kilometers
suffering a catastrophic fire may reduce cougar habitat quality
until the vegetation grows back and the prey returns (Williams
1995). |
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Coyotes
| Coyotes can survive in a wide variety of habitats
and can escape from most fires without suffering any harm directly
from the flames. In fact, fires
studies have shown that fires may be beneficial to coyote
habitats. Because fires create a mosaic of burned
versus unburned areas, coyotes may find more carrion to feed
on and more places to hide while hunting or being hunted (USDA
Forest Service). |
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Mule Deer
| Mule deer, like coyotes, are often able to escape
from fires. Research
has shown that fire may also improve mule deer habitats, for
mule deer feed mostly on grasses and forbs.
When fires burn the old vegetation, new plants grow which
are often more nutritious.
However, some favored shrubs take longer to recover,
which could have a detrimental effect on the mule deer population
or cause them to search for another habitat (USDA Forest Service). |
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Bighorn
Sheep
| Fire is an important factor for healthy bighorn
sheep habitats. Fire
suppression can allow conifers to take over grassland areas,
effectively wiping out the bighorn sheep’s feeding area. If fire occurs at a time when forage quality is poor, such
as during a drought, then it may take longer for new grasses
to grow, and the sheep population may suffer (USDA Forest Service). Today, there are approximately 150 – 225 bighorn sheep
on Yellowstone’s northern range (National Park Service). |
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