Finding floral and faunal species richness optima among active fire regimes

Changing fire regimes have important implications for biodiversity and challenge traditional conservation approaches that rely on historical conditions as proxies for ecological integrity. This historical-centric approach becomes increasingly tenuous under climate change, necessitating direct tests of environmental impacts on biodiversity. At the same time, widespread departures from historical fire regimes have limited the ability to sample diverse fire histories. We examined 2 areas in California's Sierra Nevada (USA) with active fire regimes to study the responses of bird, plant, and bat communities to a broad spectrum of temporal, spatial, and severity patterns of fire. Bird and plant species richness peaked in the first decade following fire. Species richness was highest with moderate burn severity for birds and with low burn severity for plants. Bat richness increased with longer mean fire-return intervals and was greatest in landscapes that included predominantly unburned areas or moderate to high burn severity patches. All taxa responded positively to pyrodiversity, with effect sizes varying with the metric used to assess variation in fire patterns. Our results suggest that restoring historical fire regimes would benefit biodiversity relative to most contemporary dry forests in California, but that total species richness would be highest under somewhat more frequent and varied severity fires than historical targets would indicate. Given the variable optima among taxa, managing for a range of complementary conditions that create local and landscape heterogeneity would best accommodate diverse flora and fauna and other forest conservation objectives.