Fire regimes-that is, patterns of fire occurrence, size,
uniformity, and severity-have been a major force shaping landscape
patterns and influencing productivity throughout North America for
thousands of years. Faunal communities have evolved in the context
of particular fire regimes and show patterns of response to fire
itself and to the changes in vegetation composition and structure
that follow fire. Animals' immediate responses to fire are
influenced by fire season, intensity, severity, rate of spread,
uniformity, and size. Responses may include injury, mortality,
immigration, or emigration. Animals with limited mobility, such as
young, are more vulnerable to injury and mortality than mature
animals. The habitat changes caused by fire influence faunal
populations and communities much more profoundly than fire itself.
Fires often cause a short-term increase in productivity,
availability, or nutrient content of forage and browse. Fires
generally favor raptors by reducing hiding cover and exposing prey.
Small carnivores respond to fire effects on small mammal
populations (either positive or negative). Large carnivores and
omnivores are opportunistic species with large home ranges. Their
populations change little in response to fire, but they tend to
thrive in areas where their preferred prey is most plentiful-often
in recent burns. In forests and woodlands, understory fires
generally alter habitat structure less than mixed severity and
stand-replacement fires, and their effects on animal populations
are correspondingly less dramatic. Stand-replacing fires reduce
habitat quality for species that require dense cover and improve it
for species that prefer open sites. Population explosions of
wood-boring insects, an important food source for insect predators
and insect-eating birds, can be associated with fire-killed trees.
Woodpecker populations generally increase after mixed-severity and
stand-replacement fire if snags are available for nesting.
Secondary cavity nesters, both birds and mammals, take advantage of
the nest sites prepared by primary excavators. Many animal-fire
studies depict a reorganization of animal communities in response
to fire, with increases in some species accompanied by decreases in
others. Like fire effects on populations, fire effects on
communities are related to the amount of structural change in
vegetation. Bird abundance and diversity are likely to be greatest
early in succession. When shrub or tree canopy closure occurs,
species that prefer open sites and habitat edges decline and
species that prefer mature structures increase. Major changes to
fire regimes alter landscape patterns, processes, and functional
linkages. These changes can affect animal habitat and often produce
major changes in the composition of faunal communities. In many
Western ecosystems, landscape changes due to fire exclusion have
changed fuel quantities and arrangement, increasing the likelihood
of large or severe fires, or both. Where fire exclusion has changed
species composition and fuel arrays over large areas, subsequent
fires without prior fuel modification are unlikely to restore
presettlement vegetation and habitat. In many desert and semi
desert habitats where fire historically burned infrequently because
of sparse fuels, invasion of weedy species has changed the
vegetation so that burns occur much more frequently. Many animals
in these ecosystems are poorly adapted to avoid fire or use
resources in postfire communities. Collaboration among managers,
researchers, and the public is needed to address tradeoffs in fire
management, and fire management must be better integrated with
overall land management objectives to address the potential
interactions of fire with other disturbances such as grazing,
flood, wind throw, and insect and fungus infestations.
General
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