Beech bark disease: Assessing the potential impacts of an exotic forest pest complex on native small mammal communities in the Upper Peninsula of Michigan

Among the issues facing forest managers is the problem of exotic species. When an organism is introduced into a novel habitat and is able to establish itself, there is potential for significant ecological damage. Often, that organism's natural enemies are absent from the new habitat, and host species are not coevolved with that organism. There is also potential for exotic organisms to have indirect effects on native fauna that result from effects on the exotic species' plant host. This dissertation seeks to better understand the indirect effects of an exotic forest pest complex, Chapter one is introductory and provides the theoretical background for the chapters that follow. The second chapter examines the extent to which the indirect effects of exotic species on native fauna have been reported in the existing primary literature. The third chapter demonstrates the importance of American beech in structuring certain forest communities. Chapter four suggests that granivorous small mammal communities in the Upper Peninsula of Michigan preferentially choose European beech seed over sugar maple seed, regardless of whether or not American beech is a component of the study site. Finally, chapter five reports that beech bark disease is not producing a measurable impact on small mammal populations. However, their body condition and population size do appear to be affected to different degrees by the presence or absence of American beech and previous autumn's seed crop. Additionally, seed production of American beech in healthy stands appeared to fluctuate annually, while seed production trees in forests afflicted with beech bark disease declined throughout the three years of the study. These five chapters compare native fauna in forests already infected by an exotic forest pest complex, forests that have not yet been infected but will likely be so in the near future, and forests that are predicted to resemble currently infected forests after the epidemic has passed. Similar research efforts may allow us to predict and ideally mitigate the effects of future incursions of exotic species into novel systems.