Fire Effects on Communities

Many animal-fire studies depict a “reorganization” of animal communities resulting from fire, with increases in some species accompanied by decreases in others. In the following sections, we use the literature about fire and birds to search for response patterns in the relationship between fire regime and changes in bird community composition. The literature does not at this time provide enough studies of mammal communities to complete a similar analysis.

Analysis of the literature using the framework explained below shows that fire effects on bird communities are related to the amount of structural change in vegetation. In burned grasslands, bird communities tend to return to prefire structure and composition by postfire year 3. Postfire shrub communities are generally in flux until the shrub canopy is reestablished, often 20 years or more after fire. In forests, understory fire usually disrupts the bird community for 1 year or less. Stand-replacing fire generally alters bird communities for 30 years or more. However, variation is great. Many bird communities conform only loosely to this pattern.

The following sections explain these patterns in more detail, reviewing bird community responses to fire according to understory, stand-replacement, and mixed-severity fire regimes (for definitions, see Fire Regimes):

• Bird community responses to understory fire regimes (forest cover types only)
• Bird community responses to stand-replacement fire regimes in
  • grassland and shrub-grasslands
  • shrublands
  • forest
• Bird community responses to mixed severity fire regimes (limited to forest types that leave at least 40% cover of large trees)

Framework used to organize bird community responses to fire

Each animal species in a community is likely to respond differently to fire and subsequent habitat changes. To synthesize information about these responses, we modified Rowe’s (1983) classification of plant responses to fit animal responses to fire. Rowe’s approach was to assign to each plant species an adaptation category based on reproduction and regeneration attributes in the context of fire. Using similar categories in our evaluation of the animal-fire literature, we classified species’ responses (not species themselves) for a given study location using observed changes in animal abundance. Mean changes in species abundance before and the first few years after fire, or in burned versus unburned areas, can be classified into one of six categories (Table: Bird species response to fire). Possible community response patterns using these six categories include:

1. Increasers predominate: A high proportion of invader and/or exploiter responses. This pattern represents an upward shift in abundance, especially for opportunistic species.
2. Decreasers predominate: A high proportion of avoider and/or endurer responses. This pattern represents a downward shift in abundance and unsuitable or poor habitat conditions for species established prior to the burn.
3. Most populations change: An equitably high proportion of invader and/or exploiter responses and of avoider and/or endurer responses. This pattern represents a small change in total abundance but large shift in abundance of many individual species.
4. Few populations change: A high proportion of resister responses and a low proportion of other responses. This pattern represents little change in species composition and relatively minor fire effects on the animal community.
5. Intermediate change: A high proportion of resister, endurer, and exploiter responses; low proportion of invader and avoider responses.

Interpreting changes in species diversity

Many studies of fire effects on bird communities report species richness or other indices of diversity. Conserving all species is obviously essential for sustaining ecosystem patterns and processes, but maximizing diversity in a given location does not necessarily sustain the ecosystem (Telfer 1993). Bird responses to fire in Southeastern scrub communities provide an example. Many bird species (for instance, the Carolina wren and northern cardinal) are negatively affected by regimes of frequent fire in these scrub communities. Increasing fire frequency may reduce these species, thus reducing species richness. But the populations reduced by frequent fire represent forest edge species common in Eastern North America. In contrast, increasing fire frequency favors the threatened Florida scrub-jay and other scrub specialists, which have a narrow geographic range and are the species that make Florida scrub habitat unique (Breininger and others, in press). Their habitat is declining because fire frequencies have declined, and these changes have long-lasting effects on habitat structure even when fires later return to the system (Duncan and others 1999).