Avifaunal responses to fire in southwestern montane forests along a burn severity gradient

U.S. Geological Survey, Fort Collins, Colorado 80526, USA.
Ecological Applications (Impact Factor: 4.13). 04/2007; 17(2):491-507. DOI: 10.1890/06-0253
Source: PubMed

ABSTRACT The effects of burn severity on avian communities are poorly understood, yet this information is crucial to fire management programs. To quantify avian response patterns along a burn severity gradient, we sampled 49 random plots (2001-2002) at the 17351-ha Cerro Grande Fire (2000) in New Mexico, USA. Additionally, pre-fire avian surveys (1986-1988, 1990) created a unique opportunity to quantify avifaunal changes in 13 pre-fire transects (resampled in 2002) and to compare two designs for analyzing the effects of unplanned disturbances: after-only analysis and before-after comparisons. Distance analysis was used to calculate densities. We analyzed after-only densities for 21 species using gradient analysis, which detected a broad range of responses to increasing burn severity: (I) large significant declines, (II) weak, but significant declines, (III) no significant density changes, (IV) peak densities in low- or moderate-severity patches, (V) weak, but significant increases, and (VI) large significant increases. Overall, 71% of the species included in the after-only gradient analysis exhibited either positive or neutral density responses to fire effects across all or portions of the severity gradient (responses III-VI). We used pre/post pairs analysis to quantify density changes for 15 species using before-after comparisons; spatiotemporal variation in densities was large and confounded fire effects for most species. Only four species demonstrated significant effects of burn severity, and their densities were all higher in burned compared to unburned forests. Pre- and post-fire community similarity was high except in high-severity areas. Species richness was similar pre- and post-fire across all burn severities. Thus, ecosystem restoration programs based on the assumption that recent severe fires in Southwestern ponderosa pine forests have overriding negative ecological effects are not supported by our study of post-fire avian communities. This study illustrates the importance of quantifying burn severity and controlling confounding sources of spatiotemporal variation in studies of fire effects. After-only gradient analysis can be an efficient tool for quantifying fire effects. This analysis can also augment historical data sets that have small samples sizes coupled with high non-process variation, which limits the power of before-after comparisons.

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Available from: Natasha B Carr, May 29, 2014
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    • "High-severity fires—also called stand-replacement or crown fires—cause widespread mortality of existing vegetation and result in a forest structure no longer dominated by live trees but by herbs, shrubs, and dead trees (Swanson et al. 2011). Only high-severity fires burn intensely enough to initiate ecological succession and restore essential habitat for a variety of fire-dependent and early-seral-stage species (Smucker et al. 2005, Kotliar et al. 2007, Hutto 2008, Fontaine et al. 2009), but data are scarce regarding the specific effects of this type of fire on wildlife characteristically associated with older forests, such as the Spotted Owl. Furthermore, high-severity burned forest is frequently logged—often called 'salvage logging'—which has additional effects on wildlife (Lindenmayer et al. 2004). "
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    • "Efforts to introduce low severity surface fires in lower montane landscapes will not be sufficient to create the habitat required by bird species that associate with stand-replacement burns or the variety of wildlife species that require undisturbed forest habitats. Therefore, a diversity of management approaches, including high-severity wildfire, may be necessary to create habitat for the full suite of avian and mammalian biodiversity (Hutto, 1995; Kotliar et al., 2007; Zwolak and Foresman, 2007). The upper montane zone would be a prime area for implementing treatments designed to create landscape heterogeneity since a mixture of stand structures historically characterized the forests there. "
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