Seeing the Forests through the Deer: A Regional Assessment of White-tailed Deer Browsing Preferences and the Impact on Forest Regeneration

Abstract

As the widest ranging and most populous mammalian herbivore in North America, white-tailed deer (Odocoileus virginianus; hereafter deer) and their browsing impacts have been of interest to natural resources professionals for nearly a century. Despite the myriad of research projects devoted specifically to deer browsing on forests, most of these studies are spatially and temporally limited. Any landscape-level impacts tend to be inferred from syntheses of many localized studies that often represent a snapshot in time of browsing. The spatial and temporal limitations of such collections of local studies represents a real management challenge because they fail to adequately capture the inherent heterogeneity and interdependence in forest understory plant communities and deer densities within and among forest stands and types.  In Wisconsin, a unique empirical dataset is being built that spans the entire forested area of the state (46%; ca. 6,500,000 ha) and will continue to grow in the long-term as sample sites are re-visited and new sites are added to the program. The Forest Regeneration Metric (FRM) is a monitoring tool used to quickly assess seedling and sapling regeneration and browsing severity on a three-year rotation from post-harvest until stems exceed the reach of deer. Additionally, the Big Data Mapping & Analytics Platform (BIGMAP) is a new tool developed by the US Forest Service Forest Inventory & Analysis (FIA)program, which combines remotely sensed data and ancillary ecological attributes with field-measured plot data to produce wall-to-wall, fine scale maps of woody understory composition and abundance. For our study, we are integrating preference data (i.e., FRM) with BIGMAP seedling and sapling data layers to develop a regional-scale map of deer browsing preferences for Wisconsin. Our goal is to map tree species risk by ecological landscape according to their preference values to get a better understanding of the spatial variability of browsing pressure. Preliminary results from this ongoing study indicate a high degree of variability among preferred species and ecological landscapes. The most preferred tree species in northern hardwoods forests of Wisconsin was different across all ecological landscapes. For example, deer preferred bigtooth aspen (Populus grandidentata) in the Northern Highlands and yellow birch (Betula alleghaniensus) in the Western Coulees and Ridges, while in the Northeast Sands and North Central Forest ecological landscapes deer most preferred white oak (Quercus alba) and swamp white oak (Quercus bicolor), respectively. As one example of our proposed risk assessment we also found that the white oak species listed above are thus at highest risk of over-browsing by deer across 24% of those two ecological landscapes and ca. 4% of the entire forested landscape of Wisconsin. 

Contributors: 1Amanda M. McGraw, 2Deahn DonnerWright, 3Alex Royo, 4Emilie Champagne, 2John Hak, 1Teresa Pearson, 1Meg Sanders 

1 Wisconsin Dept. of Natural Resources, Division of Forestry, Rhinelander, WI 

2 US Forest Service, Northern Research Station, Rhinelander, WI  

3 US Forest Service, Northern Research Station, Irvine, PA 

4 Direction de la recherche forestière, Ministère des Ressources naturelles et des Forêts, Québec, Qc, Canada