Deer exclosures impacts on bee communities in northeastern temperate forests

Background/Question/Methods:

White-tailed deer (Odocoileus virginianus) are increasingly overabundant in northeastern temperate forests. They have a large impact on plant communities. As herbivores they feed on early spring annuals as well as on young woody plants.  Large deer populations modify the plant community creating trophic cascades on other organisms.  We hypothesize that deer are negatively impacting bees by removing their floral resources.   To test this hypothesis we are using deer exclosures as our experimental treatment. Deer exclosures have been built in many parks throughout the northeastern temperate region as a means of restoring forests and as a part of research efforts to understand deer herbivory impacts. We predicted that bee communities would be both more diverse and more abundant near deer exclosures and that both bee richness and bee abundance would decline with distance from deer exclosures. Throughout Spring 2012 we sampled 10 pairs of exclosures and control sites at Morristown National Historical Park, using pan traps known as “bee bowls.”  At each exclosure we sampled for bees adjacent to deer exclosures and at increasing distances (5m and 10m) from the exclosure.

Results/Conclusions:

 Preliminary results from our first year of sampling indicate that deer exclosures are highly variable in floral resources and do not consistently contain more flowering plants than control sites.   As a result, we did not observe statistically significant differences in richness or abundance of bees between sites near deer exclosures and sites further away.  However, there is a non-significant trend that both bee abundance and bee richness are highest adjacent to deer exclosures but bee communities at sites 5 m and 10 m from exclosures do not differ from control sites in richness or abundance.  These trends suggest that despite the variability among deer exclosures there may be a benefit of deer exclosures to bee communities.  However, any benefit of deer exclusion may only persist at a small spatial scale.  Our future work includes sampling at a wider array of deer exclosures and more fine-scale plant community measures.  We expect that these improvements will elucidate the mechanisms of how deer exclosures impact bee communities.