Assessing drivers of insect biodiversity change in urban green spaces

Urban forests provide critical ecosystem services by capturing carbon, mitigating pollution, reducing energy costs, improving human health, and providing habitat for wildlife. However, urbanization increases heat and pollution, fragments natural habitats, and alters the composition of the urban biota through the introduction of exotic species. Such stressors threaten the services urban forests provide and may alter the ability of these green spaces to support biodiversity. In this study, we use review and meta-analysis to synthesize the literature on the effects of urbanization on urban forest arthropods. We identify key patterns of altered urban forest structure, including changes to the density, diversity, and geographic origin of trees and the ubiquity of the urban heat island effect. We tie these changes to arthropod demographic parameters, abundance, diversity, and rates of interaction. For the studies reporting comparable quantitative data, increasing urban pressures (such as higher impervious surface cover, lower vegetation cover, and small patch sizes) generally lead to declines in arthropod species richness, though effects on abundance are more variable and depend on the taxon and taxonomic resolution reported. Similarly, the increased proportion of exotic species in cities has led to a variety of outcomes, including reduced tree health, outbreaks of herbivores, loss of arthropod diversity, or no discernable effects. Our study highlights the major trends in the study of arthropod responses to urbanization, quantifies the relationships between particular urban environmental variables and arthropod responses, and points to the need for targeted future studies and the preservation of biodiversity in urban green spaces.