Urbanization decreases the extent and variety of leaf herbivory for native canopy tree species Quercus rubra, Quercus alba, and Acer saccharum

The extent to which urban trees can support associated biodiversity and provide ecosystem services depends on how urbanization affects the relationship between plants and the herbivorous arthropods that feed on them. Previous studies suggest that urbanization tends to increase the abundance, but decrease the diversity of herbivorous arthropods, but also reveal that this pattern may be an artifact of a narrow focus on pests and ornamental plants. We aimed to assess the effect of urbanization on whole leaf herbivore communities of three native canopy trees, red oak (Quercus rubra), white oak (Quercus alba), and sugar maple (Acer saccharum). For each species we compared the extent of herbivory (assessed as percent leaf loss) and diversity of herbivores (using the number of identifiable damage types as a proxy for feeding guild diversity) between sites in southeast Michigan that were more forested vs. more urbanized (with lower tree density and canopy coverage and higher percent hardscape and turf). We found that across all three species and sites compared, both the percent leaf area lost to herbivory and the number of different types of herbivory were consistently and significantly higher in forested than urbanized sites. While future studies are needed to confirm the mechanisms responsible, we conclude that at least for native canopy tree species, trees in more urbanized sites do not appear to experience higher herbivory, and instead support diminished herbivore communities compared to the same trees in a more forested setting.