Three Bets

Sandra Steingraber ’81 writes about the inescapable links between our environmental and personal health

Film version of Living Downstream brings Steingraber’s message to a new audience

Alum\u27s second edition includes a film version of her story

Deer browsing, plant competition, and succession in a red pine forest, Itasca State Park, Minnesota.

In this study I investigate the impact of whitetail deer (Odocoileus virginianus) on the replacement of white pines by deciduous species in the understory of a red pine forest. A literature review of exclosure studies and experiments show that mammalian herbivory can alter competitive relationships and vegetative composition in plant communities and influence community structure. The effect of deer on pine regeneration in Itasca State Park is a long-standing question. I examine the interactive relationship between ecological research and management decision-making in Itasca and conclude that management policies such as hunting and herbicide use have dictated the direction of ecological research and determined its economic and political context. The Mary Lake deer exclosure, erected in 1937, is considered one of the best long-term experiments. However, historical records reveal that pine reproduction was artificially encouraged through disking and planting, although I found few appreciable effects of this treatment in 1988. Comparisons inside and outside the exclosure in 1984 indicate that hazel shrubs (Corylus cornuta) have replaced red and white pine saplings as the dominant understory constituent in the presence of browsing. Hazel stems are 2.9 times more dense outside than inside. The density of white pine seedlings is similar inside and outside; however, no individuals taller than 0.5m were found outside the fence due to stunting by browsing, while inside, white pines are succeeding into the understory and overstory. I conducted clipping and planting experiments to elucidate the mechanisms behind these trends and to test whether browsing stimulated hazel productivity. Hazel growth was decreased by both moderate (50%) and heavy (100%) clipping although the number of new sprouts produced by severely clipped shrubs and unclipped controls were not significantly different. In contrast, white pine seedlings planted in and out of the exclosure lost vertical height over a four-year period unless they were both unshaded and protected from deer browsing. I conclude that hazel replaces white pine in the presence of browsing because white pine becomes stunted and cannot succeed into the understory and not because hazel productivity is directly stimulated by browsing.Ph.D.Biological SciencesBiologyEcologyEnvironmental scienceHealth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128393/2/9001717.pd