Management and impacts of oak wilt in Lake States forests.

Abstract

Oaks, one of the most ecologically important genera of trees in North America, are experiencing widespread declines. Oak wilt, caused by the fungus Bretziella fagacearum, is a major threat to oak ecosystems in the United States. My dissertation uses applied and theoretical approaches to understand how we can control oak wilt outbreaks while also examining how the disease and its management will shape the future of oak forests. In my first chapter, I describe the successful implementation of an oak wilt management technique (“root rupture” method) using data collected over ten years of operational disease control efforts in the Chequamegon-Nicolet National Forest and Menominee Forest in Wisconsin. Here, we found that the root rupture method achieved a high level of disease control and that the opportunity for successful control is highest when disease infection centers are small, providing forest managers with insights on how to prioritize disease management activities. The second chapter is an exploration of the long-term efficacy of oak wilt treatments and evaluates the longevity of B. fagacearum in root systems of diseased trees. Results from this study indicate that the pathogen and root systems may stay alive for longer periods of time (at least five years) than previously thought, putting remaining mature oaks and regenerating trees at risk for future infection. Finally, the third chapter explores how oak wilt alters forest resource availability, plant community composition, and plant diversity, with implications for long-term oak regeneration. Overall, we found that plant communities in oak wilt-affected sites shifted in composition and had higher diversity; yet, regenerating species in oak-wilt affected sites shifted away from dominance by oaks and towards shade tolerant tree species or nuisance species such as buckthorn. Taken together, the chapters of my dissertation illustrate that, while oak wilt can be successfully managed on the landscape, there may be substantial ecological implications of management that focuses on disease suppression without accounting for long-term regeneration.