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Deer exclosures

Vanessa Fox, Kristen Frederick, Ryan Kelly, and Emily Meadows
Independent Research, BIO 490, Biology Department, DePauw University
Spring semester 2012

Deer-induced changes in forest vegetation have been well documented.  At high population levels, deer overbrowse vegetation and cause shifts in the composition of understory plant communities.  The goal of our research was to assess the potential effects of abundant deer on forest understory vegetation in the DePauw Nature Park. 

We set up eight exclosures and eight adjacent control sites at two forested sites in the park.  Each exclosure was 5 x 5 meters in size and was surrounded by 2.5-m tall mesh fencing.  Each control plot was 5 x 5 meters in size and located within 5 m of each exclosure.  We monitored vegetation within four subplots in each exclosure and control plot.  Each subplot was 1 x 1 meter in size.  Within each subplot, we counted the number of plants by species and estimated percent cover of vegetation during spring and fall for four years from 2008 to 2011.  We set up infrared digital game cameras to estimate the number of deer in the park.  We identified individual bucks based on antler configurations to estimate the buck population.  We calculated the doe to buck ratio, estimated the doe population, and estimated the total deer population.  

We observed a total of 32 understory plant species.  Snakeroot (Sanicula canadensis)was the most abundant plant species.  There was no significant effect of exclosures on total number of plants or percent cover of vegetation.  Abundance of jewelweed (Impatiens capensis) increased in exclosures and remained low in control plots.  Abundance of garlic mustard (Alliaria petiolate) was low in the exclosures and varied in abundance among years in the control plots.  Based on the camera surveys, the estimated number of deer in the park during fall was 97 to 138. Given the size of the park (2.1 km2), these estimates are equivalent to 46 to 66 deer per km2.

We observed few differences in forest understory vegetation between the controls and exclosures during the four year period.  Our data suggest that deer are not overbrowsing the forest understory vegetation in the park.  However, our camera surveys showed very high population levels of deer in the park.  We believe that deer often move in and out of the park, feeding in surrounding agricultural fields and returning to the park for shelter.  Effects of a large population of deer may be mediated by movement of deer in and out of the park as well as hunting pressure outside the park.