Graduate Program
Biological Sciences
Degree Name
Master of Science (MS)
Semester of Degree Completion
2006
Thesis Director
Scott Meiners
Thesis Committee Member
Thomas Nelson
Thesis Committee Member
Andrew Methven
Abstract
High population densities of white-tailed deer are changing woodland plant communities in the eastern United States. Deer populations subjectively characterized as overabundant are widely perceived as a threat to forest succession and conservation of rare plant species. I conducted a survey of 11 deer exclosures located at 7 sites through the state of Illinois in order to 1) determine the broad effects of deer at various densities on community attributes and 2) attempt to quantify the population density at which deer are overabundant, i.e., have negative effects on a) community attributes such as richness and diversity and b) survival of rare plant species. The entire area of each exclosure and an identically sized, adjacent control plot were subjected to a nested species-area sampling regime, along with visual cover estimates for five 1-m² subplots. Surveys were sent to site managers to collect information on deer densities, site history, exclosure age, and other factors. Differences various ecological attributes between exclosure and control plots were correlated with deer densities and other site factors to determine the effects of deer on species richness, diversity, cover by functional group, exotic species invasions, rank abundance curve attributes, and survival of plants in the Liliaceae and Orchidaceae.
There was a positive correlation between winter deer density and higher plant cover, shrub cover, species-area intercepts, species richness, and diversity in exclosure plots when compared to controls. There were no changes in evenness or species-area curve slopes associated with deer density. Levels of deer density above approximately 16 deer km² were associated with reduced species richness, species-area curve intercepts, and diversity in control plots, while sites with lower densities tended to have higher richness and diversity in controls than exclosures. This equilibrium level is likely inflated due to pre-exclosure deer impacts. No relationship was found between deer density and exotic species invasions or abundance of members of the Liliaceae and Orchidaceae. Site factors such as exclosure age or site history were related only to Jaccard similarity between exclosures and control plots. Illinois Nature Preserves had significantly higher similarity between exclosures and controls compared to non-preserve sites.
Higher richness in control plots at sites with low deer densities suggests that deer may increase richness at some sites. This effect is likely due to dispersal of propagules via endozoochory and limitation of competitively dominant species by deer herbivory.
Although the threshold level of 16 deer km² indicated by my data provides a useful quantitative benchmark for overabundance of white-tailed deer, effects of deer on plant communities are dependent upon the richness and abundance of plants already present within the community and landscape context. Therefore sites with rare plants of high conservation concern should maintain much lower deer densities, while highly disturbed or early successional sites may benefit from higher population densities through dispersal of novel species into the community.
Recommended Citation
Wachholder, Brent E., "Quantifying impacts of white-tailed deer on woodland plant communities" (2006). Masters Theses. 743.
https://thekeep.eiu.edu/theses/743
