Exploring the role of deer browsing preference in plant invasion

Background/Question/Methods

Abundant deer can cause a reduction in or elimination of palatable plant species and an increase in unpalatable species. Consequently, selective deer browsing could act as a strong community assembly filter of introduced invasive plants. Our research objective was to understand the effects of white-tailed deer Odocoileus virginianus browsing on plant invasion in the Mid-Atlantic Region of the United States. Previous field research shows that deer affect invasive plants on a species- or trait-specific basis, causing decreased abundance of some plant species and increased abundance of others. We hypothesized that palatability to deer is the underlying mechanism accounting for this pattern. We tested deer preferences for a suite of 15 invasive-introduced and native plant species commonly found throughout the region. We expected half of the native and half of the introduced species to be preferred. At the Penn State Deer Research Center, we conducted 24 cafeteria-style (multiple choice) preference trials across spring, summer, and fall seasons. For each 1-day, 1-night trial, two deer were moved into a paddock where freshly collected shoot material of each species was offered. We determined the percentage of biomass consumed for each plant species and used a motion sensor trail camera to quantify browsing behavior.

Results/Conclusions

Several invasive plants were largely avoided (< 20% biomass consumed) in the preference trials, including Japanese barberry Berberis thunbergii, Japanese stiltgrass Microstegium vimineum, and garlic mustard Alliaria petiolata. The lack of deer browsing on these species, along with release from competition with palatable species, has potential to explain why they have become invasive in areas with abundant deer. Oriental bittersweet Celastrus orbiculatus, Morrow’s honeysuckle Lonicera morrowii, and European privet Ligustrum vulgare were the most preferred (> 80% biomass consumed) invasive species, raising the question about why these species are considered invasive in areas where deer are abundant. Interestingly, deer behaviors correlated strongly with introduced, but not native, plant consumption. In general, deer browsing could facilitate the invasion of less preferred invasive species, while potentially decreasing the invasion of palatable fleshy-fruited invasive species. We conclude that selective deer browsing plays a prominent role in the community assembly of introduced plant species.