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.

城市化正在以惊人的速度发生，带来了许多不利的环境影响。城市设计的生态系统已被用于通过提供生态系统服务来减轻这些影响。可以通过操纵设计生态系统的植物群落组成和结构来增强这些服务。在这里，我们通过确定观赏花园中的植物多样性和结构与害虫抗性的生态系统服务相关的程度来测试这种可能性，这是由危害植物和节肢动物的节肢动物害虫的分类丰富度（在家庭水平）和丰度推断的以害虫为食的天敌。为此，我们量化了植物多样性和结构，并从位于美国佛罗里达州中北部四个住宅社区内的 13 个观赏花园收集了冬季和夏季的节肢动物害虫和天敌。随着植被丛生和体积增加，害虫丰度呈指数下降，但仅在害虫最猖獗的冬季。天敌丰度和科丰富度随着存在的植物物种数量和植物物种组成的空间变异性而增加，同样在冬季，但不是夏季。这些关系可能是由植被对节肢动物栖息地的直接影响而不是对温度的间接影响驱动的。