Importance of plant diversity and structure for urban garden pest resistance

Abstract

Urbanization is occurring at a dramatic rate, driving numerous unfavorable environmental effects. Urban designed ecosystems have been used to mitigate these impacts through the provisioning of ecosystem services. These services may be enhanced by manipulating the plant community composition and structure of designed ecosystems. Here we test this possibility by determining the degree to which plant diversity and structure in ornamental gardens are related to the ecosystem service of pest resistance, as inferred by the taxonomic richness (at the family level) and abundance of arthropod pests that harm plants and arthropod natural enemies that feed on pests. To do so, we quantified plant diversity and structure and collected arthropod pests and natural enemies in the winter and summer from 13 ornamental gardens nested within four residential communities in north-central Florida, United States. Pest abundance decreased exponentially as vegetation clumping and volume increased, but only in winter when pests were most abundant. Natural enemy abundance and family richness increased with the number of plant species present and spatial variability in plant species composition, again in the winter, but not summer. These relationships were likely driven by the direct effects of vegetation on arthropod habitat and not its indirect effects on temperature. Our results demonstrate the potential to enhance pest resistance in ornamental gardens by manipulating vegetation and reveal the need to expand these investigations into other designer ecosystems to enhance the ecosystem services they provide in urban landscapes.