Trees provide many ecosystem services in our urban environments. However, city trees are often stressed by pests and hot urban temperatures. Our research evaluates the mechanisms driving both pests and their natural enemies on city trees and explores how identifying these mechanisms may be used to inform landscape design and improve urban tree health. This research will test a well-known ecological concept, the enemies hypothesis, in a space that has not be thoroughly explored - the city. To test our hypothesis that the urban habitat can be locally manipulated to decrease pests on urban trees, we have collected data on 33 crape myrtle trees in Raleigh, NC. Over the course of two years, we have measured vegetation complexity around study trees, quantified impervious surface cover among other urban habitat elements, and collected pests and natural enemies on trees.
Results/Conclusions
We have found in keeping with previous urban ecology studies that impervious surface is a strong driver of crape myrtle aphid pest abundance. With an increase in impervious surface cover within 100m of crape myrtle trees, aphid abundance increases. Encouragingly, however, we have also found that local vegetation elements around crape myrtles in the landscape have some effect on natural enemy abundance. Community multivariate analysis has also shown that some species of natural enemies respond differentially to various urban habitat variables. Together these findings suggest that although the impervious nature of our cities is favorable to pests, local landscapes around trees may be manipulated to attract certain species of natural enemies and help regulate tree pest populations. Results from this study could be used to help inform landscape design for city landscape practitioners, reduce pests on urban trees, and improve city tree health.