Mixed-severity wildfire and salvage logging affect the populations of a forest-dependent carnivoran and a competitor

Effects of historical fire suppression in forested ecosystems, combined with increasingly frequent and prolonged periods of drought due to a changing climate, are predicted to drive increases in the extent and intensity of wildfires in western North America and elsewhere. Understanding the effects of wildfires on forest-dependent species and interactions among species is important for conservation and management decisions. We used data collected from a long-term carnivore monitoring program in northern California and southern Oregon, USA to investigate the effects of three mixed-severity wildfires and salvage logging on a population of fishers (Pekania pennanti), forest-dependent carnivoran of conservation concern, and a co-occurring population of gray foxes (Urocyon cinereoargenteus), a competitor of similar body size. We developed a spatial capture-recapture population model to estimate the short-term effects of the wildfires and salvage logging on fisher and gray fox abundances, distributions, apparent survival and recruitment, and species interactions using non-invasive genetic data collected three years prior to and three years following wildfires. Fisher abundance decreased significantly in areas of low-, medium-, and high-severity wildfire. Gray fox abundance decreased in the years before the wildfires, but rebounded in subsequent years. Medium-severity wildfire had a negative effect on gray fox density, but high-severity wildfire and fisher density had positive effects on gray fox density. Salvage logging had negative effects on both fisher and gray fox density. Our results suggest that increased severity, extent, and frequency of wildfires in the western USA will affect fisher populations negatively and alter the composition of mesocarnivoran communities.