Meta-analysis of wildlife responses to fire severity, time since fire, and fire surrogates in North American fire-prone forests

Background/Question/Methods

Management in fire-prone ecosystems increasingly relies upon application of prescribed fire and/or fire-surrogate (e.g. forest thinning) treatments to restore biodiversity and ecosystem function.  Recently, published literature examining wildlife response to fire and fire management has increased rapidly.  However none of this literature has been synthesised quantitatively precluding assessment of patterns of wildlife response among treatment types, particularly the efficacy of fire-surrogates and their capacity to emulate wildland fire of varying severities. We meta-analysed the scientific literature on vertebrate demographic responses to burn severity (low/moderate, high), time since fire (0-4, 5-9 and ≥10 yrs) and fire surrogates (forest thinning) in the most extensively studied fire-prone, forested biome (dry forests of the United States).  Effect sizes and their 95% confidence limits were estimated for each species by treatment combination.

Results/Conclusions

We found 52 studies of 124 bird, 17 small mammal, 1 reptile, and 4 amphibian species which examined short-term responses to thinning, prescribed low-severity fire, thinning + prescribed fire, and high-severity fire.  Longer term data (>4 yrs) were available only for avian response to high-severity fire.  At the stand scale (< 50 ha), thinning and prescribed fire demonstrated similar response patterns.  Combined thinning + prescribed fire produced a higher proportion of positive responses.  Response patterns between low- and high-severity fire were distinct.  Contrary to the paradigm that high-severity fire produces primarily negative responses, positive and neutral responses were larger at all time scales considered.  In the short term and at fine spatial scales, fire surrogate forest thinning treatments appear to effectively mimic low-severity fire whereas low-severity fire is not a substitute for high-severity fire. The varied response of taxa to each of the six conditions studied makes it clear that the full range of fire-based disturbances (or their surrogates) is necessary to maintain a full complement of vertebrate species.  This is especially true for high-severity fire where positive responses from many avian taxa over all timescales suggest this disturbance (either as wildfire or prescribed fire) be included in management plans where maintenance of sub-regional to regional vertebrate biodiversity is a goal.