Vegetation responses to natural and salvage logged fire edges in Douglas-fir/hardwood forests

Natural edges created by fire are a common component of forest ecosystems with moderate-severity fire regimes and will continue to be important as the frequency of extreme fire events increases due to historical fire suppression throughout North America. The effect of high-severity fires, with and without salvage logging, on adjacent intact forest patches has not been studied. Fourteen years after a wildfire, we examined the structure and composition of vegetation along the gradient from burned stands into the adjacent forest interior at three salvage logged edges and three unsalvaged edges in Douglas-fir/hardwood forests of northwestern California. Natural, unsalvaged edges were characterized by an increase of native, ruderal species, rather than a reduction of forest interior species. Only two forest interior species reacted negatively to the edge environment, both at salvaged edges. Old-growth community types, identified by two-way indicator species analysis (TWINSPAN), occurred 30 m closer to the edge at unsalvaged sites, compared to salvaged sites. Twenty commonly observed species (>10% frequency) demonstrated significant responses to the edge environment; 11 species had a larger depth of edge influence (DEI) at salvaged edges, three had a larger DEI at unsalvaged edges, and six had an equal DEI. Our results suggest that, compared to unsalvaged stands, the removal of snags and subsequent broadcast burning of salvaged logged stands significantly altered plant composition and structure of the edge environment. By increasing the patch contrast between burned and intact forest stands, salvage logging increased the depth of edge influence of fire-created edges by 15-30 m.