Regeneration of Woodland Vegetation after Deer Browsing in Sharon Woods Metro Park, Franklin County, Ohio

Overbrowsing by deer can decrease plant abundance and change plant species composition, especially in isolated forest fragments. Sharon Woods Metro Park, Franklin County, OH is a 308 ha suburban woodland preserve that had a deer population of 347 individuals in 1992 (112 deer/km), which was subsequently reduced to the currently maintained level of ~40 individuals (14 deer/km). Deer exclosures (~0.4 ha) established in 1990 in three habitats were used to compare vegetation that recovered under complete protection with that which had sustained continued browsing. Tree seedlings, herbaceous and shrub species richness, diversity, and floristic quality were quantified in browsed and fenced treatments as indicators of plant diversity. Percent ground cover was assayed as a measure of plant biomass. Total percent ground cover was significantly lower in browsed treatments in two of the three habitats. Species richness and floristic quality of forest floor species were consistently, though not significantly, lowered in browsed treatments where the more disturbance-tolerant native species increased in frequency and abundance. Reduced deer browsing has allowed some plant species to regenerate but not others. For example, pawpaw (Asimina triloba), American beech (Fagus grandifolia), and jewelweed (Impatiens capensis) are disturbance tolerant and/or unpalatable species that may inhibit regeneration of more sensitive species under browsing pressure. A further reduction in deer density to ~4 deer/km and continued vegetation monitoring are recommended next steps for vegetation management at Sharon Woods. OHIO J SCI 106 (3):86-92, 2006 Manuscript received 15 April 2004 and in revised form 10 June 2005 (#04-12). Corresponding Author: Department of Evolution, Ecology, and Organismal Biology, 1465 Mt. Vernon Avenue, The Ohio State University, Marion, OH 43302. Voice: 740-389-6786, Fax: 614-292-5817, Email: [email protected] INTRODUCTION The white-tailed deer (Odocoileus virginianus) is now acting as a keystone herbivore in the eastern United States. Pre-European settlement white-tailed deer densities were estimated to be ~4 deer/km (Alverson and others 1988; Rooney and Dress 1997). Most of this region now contains areas where densities substantially exceed this value (Anderson 1994). Deer populations often reach particularly high densities in parks and preserves, with significant consequences for the plant communities within them (Augustine and Jordan 1998). In Northern Wisconsin’s Flambeau River State Forest, for example, Anderson and Katz (1993) estimated the deer density at 50-100 deer/km, and in northeast Ohio’s Cuyahoga Valley National Park, the population has been estimated at 17-35 deer/km (Dengg 2002). Since deer are selective feeders, damage to plant species occurs differentially and herbivory is often not noticed until many species are impacted, sometimes resulting in a distinct browse line (Augustine and Frelich 1998; Webster and others 2001). The impacts of deer browsing in several areas of the eastern US have been well studied. In northwestern Pennsylvania, Tilghman (1989) conducted a five-year study of the impact of browsing on tree seedlings, woody shrubs, and herbs in Allegheny Forest, and Rooney and Dress (1997) examined plant species loss after sixty-six years of elevated deer density in the Heart’s Content forest. Balgooyen and Waller (1995) studied historic and recent deer effects on woody and herbaceous plant frequency and cover as well as overall plant species diversity in northern Wisconsin and its surrounding islands. All of these studies have resulted in management recommendations for their particular areas. These include the use of indicator species to gauge browsing impacts on vegetation as a whole, the construction of deer exclosures, reduction of the deer herd to appropriate levels, and the removal of undesirable browsetolerant plant species that have become dominant. Since population trends for white-tailed deer in Ohio are similar to other areas of the eastern US (Shafer-Nolan 1997), these studies are useful as a general guide for deer management. However, because habitat, browse species, and management concern vary among regions, local studies are necessary to solve specific vegetation management issues related to deer browsing (Strole and Anderson 1992; Balgooyen and Waller 1995; Augustine and Jordan 1998). We studied the regeneration of woodland vegetation following intense deer browsing in Sharon Woods, a central Ohio metropolitan park (Franklin County). This site was of interest because it typifies a suburban park, consisting of forested land bordered sharply by development (major highways on two of its four sides, and commercial/residential streets on the other two). The primary outcome of this study was the assessment of long term intense browsing (>10 yrs). This included measuring its effects on species diversity and determining whether browsing has favored certain plant species, thereby altering plant community composition. The deer population has recently been lowered at Sharon Woods, thus a secondary goal was to determine whether further OHIO JOURNAL OF SCIENCE 87 K. M. ASNANI AND OTHERS reductions in deer density are necessary. MATERIALS AND METHODS