Zachary Steel, Alissa Fogg, Ryan Burnett, L. Jay Roberts, Hugh Safford

Aim:

Modern wildfires increasingly create large high-severity patches with interior areas far from less disturbed habitats. We evaluated how these trends impact montane bird communities by investigating the effect of internal distance to lower severity areas, high-severity patch size, and years since fire on avian alpha and beta diversity.

Location:

Sierra Nevada Mountains, California, USA

Methods:

Bird occurrence data were collected during 2009-2017 within high-severity patches of 27 wildfires representing 1-30 years since disturbance. A two-step multispecies occupancy method was used to account for imperfect detection of 94 species and estimate effects of high-severity patch characteristics on community richness and dissimilarity as well as richness of nesting guilds.

Results:

Community richness decreased with distance from patch edge and with high-severity patch size. Richness increased with years since fire, but this pattern was mediated by distance to edge with higher peak richness (23 species) on the patch edges than interiors (18 species). Community dissimilarity was not explained by distance from edge or patch area indicating that interiors of large high-severity patches contain a subset of rather than a complement to the edge community. Guild richness of tree and primary cavity nesters was negatively associated with distance and patch size. Richness of ground and shrub nesters was insensitive to these metrics but due to declines among other species, the groups made up a greater percentage of the avian community within patch interiors.

Main conclusions:

As fire activity increases due to accumulating forest fuels and accelerating climate change, high-severity patches and their resulting early-seral habitats are becoming more extensive with less edge and more interior area. Such changes are likely to decrease avian diversity locally and shift community composition away from forest-associated species. Management actions that promote the full range of fire effects but limit the size of high-severity patches may best conserve bird diversity within fire-adapted ecosystems.