Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Forest Science (PhD)

Administrative Home Department

School of Forest Resources and Environmental Science

Advisor 1

Christopher R. Webster

Advisor 2

John A. Vucetich

Committee Member 1

Joseph K. Bump

Committee Member 2

John J. Durocher

Abstract

Winter in the northern Great Lakes presents a suite of challenging conditions for animals, in terms of limited food availability and increased energetic cost of locomotion and thermoregulation. Variable winter severity is liable to cause interannual fluctuations in habitat viability and use by animals, in addition to modulating physiological responses in animals to conserve energy. For example, white-tailed deer (Odocoileus virginianus) congregate at high densities under eastern hemlock (Tsuga canadensis) or northern white-cedar (Thuja occidentalis) stands, which provide forage, thermal cover, reduced snow depth, and enhanced vigilance. However, a suite of climatic, edaphic, and management changes, in addition to novel deer densities, have compromised regeneration of eastern hemlock in recent years, while facilitating the propagation of hardwoods. For this research, I monitored 39 randomly selected eastern hemlock stands across the western Upper Peninsula. I selected a subset of 15 of these stands to survey for forest community composition and assess changes between 2006 and 2015, and found evidence of a transition to hardwoods such as maple (Acer rubrum and A. saccharum). This change in forest composition will have significant implications for migratory white-tailed deer, particularly when coupled with more extreme winter conditions predicted to occur with climate change. I monitored local deer use in all 39 stands from winter 2014-15 to 2017-2018, building on a dataset extending back to winter 2005-2006, by counting fecal pellet groups in each stand, and found evidence of reduced use following recent severe winters, as well as a spatial shift in intensity of use. I assessed diet composition by collecting fecal samples during spring pellet surveys, and found evidence of spatial variability in the diet, likely due to spatiotemporal variation in winter severity. To further understand the physiological implications of winter severity and winter diet, I assessed physiological stress response (via non-invasive fecal glucocorticoids) and found evidence of endocrine down-regulation in animals with a poor diet and in extreme conditions. My findings underscore the importance of maintaining a mesic conifer component in northern forests to provide winter habitat for regional migratory deer populations.

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