ABSTRACT
Aspen (Populus spp.) vegetation types are important throughout North America because of their economic importance to the pulp industry, as an energy resource, importance to wildlife, and for their contribution to biodiversity. Because of these factors, natural resources managers in Michigan have implemented management activities to intensify the production of aspen. High ungulate browsing intensity on the current annual growth of regenerating stands by white-tailed deer (Odocoileus virginianus) and elk (Cervus elaphus nelsoni) in Michigan, however, has influenced aspen regeneration, stand composition and structure, some nutritional qualities, and potentially natural successional patterns of forest habitat types. Forest and wildlife managers have attempted to use harvesting practices to mimic characteristics of natural disturbances that ultimately may aid in biodiversity conservation and meet other forest objectives while still regenerating aspen. Our objectives are to demonstrate (1) why aspen in various forest habitat types with different successional trajectories should be managed differently to conserve their unique natural vegetation types that spatially and temporally contribute to wildlife conservation, and (2) how ecological site potential of forest habitat types may influence the ability of managers to use forest management practices to mimic natural disturbances in aspen communities in the face of ungulate herbivory. White-tailed deer and/or elk herbivory on aspen age classes <20 years old can be problematic for managers when attempting to maintain the productive capacity of aspen and meet biodiversity objectives. These plant communities provide habitat for ungulates and numerous bird and small mammal species. Our results from investigating the biological contributions and effects of aspen anthropogenic disturbances and management practices on meeting long-term forestry and wildlife objectives in two landscapes in northern Michigan indicate that differences in vegetation composition and structure do occur among aspen age classes and habitat types. Ungulate herbivory may further complicate the multiple pathways of succession trajectories of habitat types and the resulting vegetation conditions for wildlife by altering habitat suitability across space and time. The influences of herbivory levels, site potential, and successional trajectories of aspen on various habitat types should be considered by managers when deciding when and how much aspen to harvest to help sustain the aspen resource and conserve biodiversity.
