Insect herbivory on Acer rubrum varies across income and urbanization gradients in the D.C. metropolitan area

Abstract

Urbanization has increased wealth disparity within the United States, impacting the urban landscape and species interactions. In particular, the interactions between street trees and the arthropod communities that live among them may be modified by both human population densities across urban to suburban locations, as well as income levels within these areas. We examined the effect of land use type (urban vs suburban) and median household income on variation in leaf damage and arthropod abundance of red maples (Acer rubrum) in the District of Columbia metropolitan region. We compared these levels of leaf damage to rates observed in a nearby natural forest. We predicted leaf damage would be positively correlated with urbanization (forested < suburban < urban) and a negative relationship between leaf damage and neighborhood income level (low > medium > high). Instead, we observed higher levels of leaf damage on trees in the forest environment compared to the urban and suburban areas. Leaves from urban medium and high-income areas were less likely to exhibit herbivore damage than those from suburban areas. Of the leaves with any damage, those in urban high-income and suburban low-income areas exhibited the most leaf area missing. These trends may be related to specific factors associated with urbanization and income level, such as tree and impervious surface coverage and pesticide use. This study highlights differences in biotic interactions across individual neighborhoods and the importance of including socio-economic variables (e.g., household income) when examining species interactions in developed environments.