The alteration of trophic interactions due to climate change will be one of the most influential factors in determining future ecosystem health. Climate change is expected to allow insects to expand outside their historic ranges and milder winters will allow pests to proliferate which may reshape the relationship between plants, insect herbivores, and their predators. Without sufficient controls on populations, insect pest outbreaks can cause widespread damage and mortality in forested ecosystems. The enemies hypothesis proposes that more diverse plant communities may be naturally protected against excess herbivore pest damage due to top-down controls by predators such as arthropods, birds, and mammals. In this study, we examined the effects of tree species diversity on predation rates of insect herbivores using artificial caterpillars in an existing forest diversity experiment in Edgewater, Maryland. Artificial caterpillars were installed on selected trees within plots containing one, four, and twelve tree species and checked regularly for signs of predator damage.
Plot-level tree diversity did not have an effect on caterpillar predation rates. Instead, species-specific impacts were seen as caterpillars on sycamores (Platanus occidentalis) were attacked more frequently. Additionally, caterpillars on taller trees had a higher attack rate, likely because greater canopy cover provided better foraging habitat for predators. Our findings suggest that, after three years of restoration, forest diversity is not the most important driver of predation on insect herbivores. Rather, faster growing trees that more quickly establish canopy cover, attract more predators and should therefore be utilized in forest restoration.