The Influence of Local and Landscape Characteristics on Deer Browsing, and Subsequently The Composition and Structure of Forest Understories, in Indiana

Richard D Sample, Purdue University

Abstract

White-tailed deer (Odocoileus virginianus; hereafter deer) are a keystone herbivore within forest ecosystems. While deer rely on plant species for growth, reproduction, and survival, multiple external factors can dictate browsing behavior. These factors ultimately drive browsing selection, browsing intensity, and diet composition, which in turn can shape the influence deer have on forest ecosystems. To better understand the complex relationship between deer populations, their habitat, and public perception of deer, the Indiana Department of Natural Resources partnered with Purdue University to initiate the Integrated Deer Management Project (IDMP). As part of the IDMP, this dissertation evaluated the ecological condition of deer habitat to assess the influence deer have on woody and herbaceous plant species within Indiana forests.Our study aimed to i) rank woody species according to their selection by deer and evaluate how the ranking of individual species varies across the state (Chapter 2); ii) evaluate variables and spatial extents associated with differences in browsing intensity, and evaluate different indices used to assess differences in browsing intensity (Chapter 3); iii) quantify winter deer diet composition using DNA barcoding to evaluate how diets vary across a gradient of deer densities, browsing intensities, non-native plant densities, and landscape characteristics (Chapter 4); and iv) evaluate the interactive effects of deer, non-native plant species, and landscape characteristics on the herbaceous layer of forests, while further evaluating the spatial extent at which landscape characteristics are most strongly related to herbaceous-layer composition and diversity (Chapter 5). To do this, I sampled 152 woodlots over three years across three regions of Indiana, collecting data on the browsing selection of individual woody species, the browsing intensities on all woody species, and the composition of vegetation communities (Chapters 2, 3, and 5, respectively). To address diet composition (Chapter 4), we collected deer pellet groups to analyzed diet components.We ranked a total of 63 woody species regarding their browsing selection by deer. While most of these remained consistent from region to region, 16 varied greatly in selection, as deer often showed increased selection for a given species when it resided in an area that provided greater browsing opportunities. Browsing intensity was most associated with food availability, however, it was also influenced by deer density in the region with the lowest forest cover. The twig age index of browsing intensity showed promise as the most efficient and effective index for use in Indiana woodlots. Although diet composition did not differ across regions of Indiana, we found that deer consumed several uncommon taxa when the greater landscape exhibited homogenous patch composition. Similarly, deer consumed different native taxa in forested landscapes with greater deer densities in comparison to agricultural landscapes with lower deer densities. Lastly, though browsing varied within and across regions landscape characteristic, and not deer, were the most influential suite of variables. Additionally, the spatial extent at which these variables exhibited their best fit varied depending on the dependent variable being evaluated and the region of analysis.Together, our results highlight that variables ranging from the woodlot to the landscape-scale influence browsing behavior. This showcases that deer respond to variables at varying scales when browsing and in general, browse more in areas that offer the greatest benefit, whether these areas offer greater food availability or quality, or offer lower risks associated with anthropogenic development.

Degree

Ph.D.

Advisors

Jenkins, Purdue University.

Subject Area

Wildlife Management|Agriculture|Wildlife Conservation|Behavioral Sciences|Botany|Ecology|Environmental Health|Forestry|Natural Resource Management

COinS