Deer Facilitate Invasive Plant Success in a Pennsylvania Forest Understory
Tiffany M. Knight
Jessica L. Dunn
Lisa A. Smith
JoAnn Davis
Susan Kalisz
Invasive species impose severe biological and economic costs worldwide. In forested ecosystems, invasive species supplant native species, resulting in decreased biodiversity. Furthermore, human-mediated disturbances may stress native forest species and benefit invasive species that thrive in disturbed habitats. Anthropogenic changes to the landscape have caused unprecedented increases in white-tailed deer (Odocoileus virginianus) numbers, which has resulted in the degradation of understory native plant communities. We suggest that deer-mediated disturbance to understory communities facilitates the success of invaders in forests. Many North American forests experience both exotic plant invasion and deer overabundance, but the two problems have never been empirically linked. In this paper, we quantify deer effects on native and exotic understory herbs in a western Pennsylvania forest. We show that the percentage of bare ground and the relative abundances of the invasive herbs, Alliaria petiolata and Microstegium vimineum are significantly greater, while native plants are significantly smaller with a lower proportion flowering in deer access vs. deer exclusion plots. Our data support the idea that invader success is due in part to both preferential foraging by deer on native herbs that reduces their size and flowering status and the creation of open patches when deer are present. We conclude that deer overabundance facilitates the success of invasive species in forested ecosystems and that management will benefit by considering these factors jointly.
Improving the Design of Amphibian Surveys Using Soil Data: a Case Study in Two Wilderness Areas
Kenneth D. Bowen
Erik A. Beever
Ulf B. Gafvert
Amphibian populations are known, or thought to be, declining worldwide. Although protected natural areas may act as reservoirs of biological integrity and serve as benchmarks for comparison with unprotected areas, they are not immune from population declines and extinctions and should be monitored. Unfortunately, identifying survey sites and performing long-term fieldwork within such (often remote) areas involves a special set of problems. We used the USDA Natural Resource Conservation Service Soil Survey Geographic (SSURGO) Database to identify, a priori,potential habitat for aquatic-breeding amphibians on North and South Manitou Islands, Sleeping Bear Dunes National Lakeshore, Michigan, and compared the results to those obtained using National Wetland Inventory (NWI) data alone. The SSURGO approach identified more target sites for surveys than the NWI approach, and it identified more small and ephemeral wetlands. Field surveys used a combination of daytime call surveys, nighttime call surveys, and perimeter surveys. We found that sites that would not have been identified with NWI data often contained amphibians and, in one case, contained wetland-breeding species that would not have been found using NWI data. Our technique allows for easy a prioriidentification of numerous survey sites that might not be identified using other sources of spatial information. We recognize, however, that the most effective site-identification and survey techniques will likely use a combination of methods in addition to those described here.