Fire drives landscape pattern and wildlife community composition in many of the world’s ecosystems. Historically, California dry forests experienced frequent low-moderate severity fires, which maintained open forests dominated by large fire-resistant trees. Following a century of fire exclusion, density and the proportion of fire-intolerant species has risen, contributing to increasing fire size and severity, and the prevalence of large homogenous patches of high-severity fire.
Increasing fire severity directly affects regional habitat composition, but shifts in the size and configuration of high-severity patches also influence ecological process. Quantifying the effect of landscape context within high-severity patches is necessary for understanding how shifting fire regimes reshape wildlife communities. For example, we hypothesize that habitat quality differs between edges and core areas of large high-severity patches. Furthermore, as time since fire increases, successional trajectories diverge between areas near living conifers and those far from seed sources, possibly leading to divergent wildlife community composition.
To test the effect of landscape context on the wildlife community within high-severity patches, we conducted avian surveys during 2009-2016 in eight large Sierra Nevada fires. Using an occupancy-modeling framework, we evaluated species and community associations with distance to patch edge (i.e. moderate/low severity areas).
Our models show a significant decline in species richness in high-severity areas with increasing distance from moderate/low severity fire. This negative relationship was largely consistent regardless of time since fire (1-12 years). However, the composition of the local bird community changed with succession as shrub cover increased, and shrub-associated bird species were observed more often.
High-severity areas are increasing in size and core areas of high-severity patches are becoming increasingly isolated from surviving forests. Our results indicate that in the short- to medium-term this may reduce local species richness. In the long-term, if isolated areas remain shrub-dominated rather than returning to a forested state, we are likely to see corresponding shifts regionally; to the benefit of shrub-associated species and the detriment of mature forest-associated species.
Post-fire management commonly strives to actively reforest high-severity areas. However, due to limited resources and negative impacts to some wildlife species, reforestation activities (including salvage logging, shrub abatement and conifer plantings) are not universally practical and desirable. By improving our understanding of where faunal diversity is highest within these seemingly homogenous burned areas, managers can target interventions to both facilitate regrowth of forests and maintain valuable habitat created by wildfire.