The habitat changes caused by fire influence animal populations and communities much more profoundly than fire itself. Animals’ immediate responses to fire are influenced by season, intensity, severity, rate of spread, uniformity, and size of the fire.
Long-term faunal response to fire is determined by habitat change, which influences feeding, movement, reproduction, and availability of shelter. The immediate and short-term effects of fire on terrestrial birds and mammals include injury, mortality, emigration, and immigration.
Most fires have the potential to injure or kill fauna and large intense fires are certainly dangerous to animals caught in their path. Fires generally kill and injure a relatively small proportion of animal populations because many vertebrate species flee or seek refuge during fires.
Animals with limited mobility living above ground appear to be the most vulnerable to fire-caused injury and mortality, but occasionally even large mammals are killed by fire. Nestlings and juveniles of birds and small mammals are vulnerable to fire-caused mortality.
While non-burrowing mammals and most birds leave their habitat while it is burning, many return within hours or days. Others emigrate because the food and cover they require are not available in the burn. The length of time before these species return depends on how much fire altered their habitat structure and food supply.
Many insects, birds, and mammals are attracted to fire, smoke, and recently burned areas. Most birds and mammals that immigrate in response to fire are attracted by more abundant or more exposed food resources. Intense activity by insects after a fire attracts insect-feeding birds.
The effects of fire on fish and aquatic macroinvertebrates are mostly indirect in nature. Fire typically improves habitat conditions for aquatic species over the long-term. However, fires that result in longer-term changes in stream temperature, ash-laden slurry flows, increases in flood peak flows, and sedimentation due to increased soil erosion can have negative impacts on aquatic organisms.
Chemical, biological, and physical properties of soil are all altered from heat and oxidation of fuels. Effects of fire on soil come primarily from high temperatures that affect surface as well as deeper soils (Neary et al. 2005). Low- and moderate-temperature fires generally have long-term benefits for ecosystems that evolved with fire (DeBano et al. 1998).
Fires affect water quality and water cycle processes to a greater or lesser extent depending on fire severity. When a fire occurs, changes in water quality are primarily the result of soil erosion and deposition of soil materials into water (Neary et al. 2005). Fires may cause suspended sediment, elevated streamflow temperatures, increased pH values, and changed chemical concentrations and aquatic organism populations.
Severe wildfire can produce substantial effects on the streamflow regime of small streams and rivers (Neary et al. 2005). The effects of low severity fires on water resources are generally minimal and short-lived.
- Fire can change plant community composition.Fire can promote plant species that are well adapted to fire and suppress plant species that are poorly adapted to fire. As a result, fire can cause dramatic and immediate changes in species composition and diversity (Duchesne 1994).
- Fire can alter plant community structure.Fire consumes dead and living plant material, resulting in changed horizontal and vertical distribution of plants within a community. Stand-replacement fires that occur in forests, woodlands, shrublands, and grasslands kill above ground parts of the dominant vegetation, changing the above ground structure substantially (Brown 2000).
- Fire can change vegetation patterns.Fires can create more structurally diverse landscapes that include patches that differ in vegetation composition and stand structure (Turner and Romme 1994).
Fire can maintain ecological processes. Fire (along with insects and pathogens) is responsible for the decomposition of dead organic matter and the recycling of nutrients (Olson 1963, Stoszek 1988). Without fire, plant debris can accumulate and nutrients are tied up in dead vegetation.
In some ecosystems, plant debris accumulation can suppress living vegetation, increase likelihood of plant mortality from insects and disease, and lead to higher intensity fires (Brown 2000). For some plant species, fire is an important catalyst for reproduction, regeneration, and germination.