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

The effects of burn severity on avian communities are poorly understood, yet this information is crucial to. re 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-. re avian surveys ( 1986 1988, 1990) created a unique opportunity to quantify avifaunal changes in 13 pre-. re 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 signi. cant declines, (III) no signi. cant density changes, (IV) peak densities in low- or moderate- severity patches, (V) weak, but signi. cant increases, and (VI) large signi. cant increases. Overall, 71% of the species included in the after- only gradient analysis exhibited either positive or neutral density responses to. re 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. re effects for most species. Only four species demonstrated signi. cant effects of burn severity, and their densities were all higher in burned compared to unburned forests. Pre- and post-. re community similarity was high except in high- severity areas. Species richness was similar pre- and post-. re across all burn severities. Thus, ecosystem restoration programs based on the assumption that recent severe. res in Southwestern ponderosa pine forests have overriding negative ecological effects are not supported by our study of post-. re avian communities. This study illustrates the importance of quantifying burn severity and controlling confounding sources of spatiotemporal variation in studies of. re effects. After- only gradient analysis can be an efficient tool for quantifying. re 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.