Forests, fungi, and small mammals: The impact of fire and thinning on a tri-trophic mutualism

A fundamental question of forest management in North America is whether selective timber harvest mimics the effects of a natural fire regime. Understanding such effects on forest structure, ecological interactions, and wildlife within forest ecosystems is crucial to effective forest management. In Chapters 1 and 2, I identify significant habitat features of the northern flying squirrel (Glaucomys sabrinus), the primary prey of the California Spotted Owl (Strix occidentalis occidentalis), in a mixed-conifer and red fir forest of the southern Sierra Nevada. In Chapters 3 and 4, I report on the short-term effects of mechanical thinning (light, heavy, and none) and prescribed burning (burned vs. unburned) on the interaction between truffle-producing mycorrhizal fungi and truffle-consuming lodgepole chipmunks (Tamias speciosus).; Northern flying squirrels were strongly associated with perennial creeks. This association could be partly explained by the greater availability of truffles, the main food resource of flying squirrels, adjacent to creeks (Chapter 1). Flying squirrels selected nest trees that were larger in diameter, taller, and closer to riparian habitat than random or large neighboring trees. Flying squirrels also showed a preference for snags over live trees and selected red fir (Abies magnifica) but avoided incense cedar ( Calocedrus decurrens, Chapter 2). Forest management practices that remove these preferred habitat elements could impact this important prey species of the California Spotted Owl.; Prescribed burning and mechanical thinning had very different effects on forest structure (e.g. canopy cover, large tree density, shrub and herbaceous plant cover, soil depth), but both treatments had similar impacts on truffle production (no significant impact) and consumption of truffles by lodgepole chipmunks (both significantly reduced consumption). In addition, neither treatment had a significant effect on the densities or demographic parameters of T. speciosus (Chapter 4). Different intensities of thinning also had similar impacts on T. speciosus densities and demographic parameters. These results suggest that burning and thinning have similar short-term effects on T. speciosus. However, longer-term data are needed to thoroughly evaluate the relative impacts of prescribed burning versus mechanical thinning on forest wildlife and their interactions.