Fire drives landscape pattern and wildlife community composition in many of the world’s ecosystems. Historically, California dry forests experienced frequent fires dominated by low-moderate burn severity, which maintained heterogeneous landscapes composed of a mix of habitat types and successional stages. However, following a century of fire exclusion and accelerating climate change, the prevalence of extreme fire events has risen, resulting in increasingly large patches of stand-replacing fire surrounded by largely homogenous and uncharacteristically dense unburned forests.
At the same time, large gaps remain in our understanding of how fire patterns affect the ecology of these forests. Forest bat species have been particularly difficult to study in the past, and the influence of fire on bat habitat quality is largely unknown. To address this knowledge gap, we used automated recording units and classification software to survey forest bat species in and around three large wildfires in the Sierra Nevada Mountains during 2014-2017. To test whether bat species occupancy and community composition varied across a gradient of burn severity, we utilized a hierarchical modeling framework that accounts for imperfect detection.
Results/Conclusions
For many of the 17 bat species found in the Sierra Nevada, rates of occupancy were highest at moderate levels of burn severity, consistent with the intermediate disturbance hypothesis. Furthermore, bat community richness was higher on average within burned areas than areas that had not experienced fire in many decades. Fire directly alters forest structure and indirectly influences foraging, and roosting habitat quality. The magnitude of this effect varies by species and is likely dependent on bat life-history characteristics, such as their ability to forage within dense forest environments. The findings presented here provide evidence that diversity of the Sierra Nevada bat community may benefit from fire in the aggregate, especially where the disturbance increases habitat heterogeneity on the landscape; a concept known as pyrodiversity. Thus, a mix of fire effects such as those found in a natural fire regime may be necessary to maintain the range of habitats utilized by the various species observed. In contrast, if fire patterns continue along a trajectory of increasingly large and severe wildfires burning within a matrix of dense, fire-excluded forests, we are likely to see shifts in the regional composition and configuration of habitats utilized by the forest bat community.