Associational Interactions Between Native and Non-Native Urban Trees: Do Plant Neighbors Matter?

As urban and suburban regions expand throughout the United States, a variety of non-native plant species are becoming more and more prevalent.  Most non-native plants produce a smaller abundance and fewer species of herbivores, especially caterpillars, and suburban landscapes are often planted with a mixture of natives and non-natives.  This begs the question: can the associations between native and non-native plants influence the abundance of herbivorous insects in suburban landscapes?  Associational Resistance (AR) and Associational Susceptibility (AS) are widely cited concepts in ecology and are used to better understand the relationship between an herbivore and its host plant in various plant community contexts.  This study investigates the roles that AR and AS play in mediating caterpillar abundance on native red maples (Acer rubrum), when either native or non-native neighbor plants are present.  In a two year field experiment, we are assessing caterpillar abundance and feeding on native plants when provided neighboring plants that vary in origin (native vs. non-native) and relatedness (congener vs. non-congener).  In addition, we are also monitoring natural enemy abundance and diversity on these plots.