Interactions Between Fire Severity and Forest Biota in the Central Sierra Nevada: Formation and Impact of Small-Scale Fire Refugia and the Effect of Fire on Forest Structure Predictive of Fisher (\u3ci\u3ePekania pennanti\u3c/i\u3e) Den Habitat

Fire is a natural and essential component of forests in western North America. Fire maintains biodiversity through the creation of different habitat types, and regular fire rotations reduce the accumulation of woody fuels and thick understory plant densities that give rise to catastrophic fire. The practice of fire exclusion has altered western forests and increased the risk of widespread change under rising temperatures projected for the 21st century. To manage for the reintroduction of fire it is critical that we understand the interactions between fire and forest biota in recently fire-suppressed forests. In Chapter 2, I studied the formation and impact of small-scale fire refugia. Fire refugia are areas within burned forest that experienced relatively little change, and are recognized as important places that offer protection for forest biota (vegetation, wildlife) during and after the fire. Very few studies, however, have examined small-scale fire refugia despite their importance to many organisms (e.g., small mammals, understory plants). In a long-term forest monitoring plot in Yosemite National Park, I mapped all unburned areas ≥ 1 m2 the first year after fire. I found small fire refugia were abundant, somewhat predictable, and fostered increased survival and diversity of nearby plant life. My results suggest that small fire refugia are an important component of burned forests that should be included in management considerations. In Chapter 3, I examined possible fisher habitat in burned areas. Fishers are forest carnivores of high conservation concern due to widespread declines since European settlement and the risk of habitat loss due to fire. An isolated population remains in the Sierra National Forest, where managers are weighing the need to reintroduce fire against possible detrimental impacts to current habitat. My research examined the forest structural characteristics (vegetative cover, heights of different forest layers) surrounding fisher dens. I found suitable thresholds of these structural characteristics in recently burned areas in Yosemite, particularly after low-severity fire. My results suggest that burned areas may offer suitable denning habitat for fishers, though more research is needed to determine if this conclusion holds for all fisher activities (e.g., foraging, resting) and scales of selection