Woody plant biodiversity explains arthropod pest management interventions in residential landscapes

The woody plant communities found on residential properties constitute an integral component of cities’ green infrastructure and serve as a nexus between urban residents and the natural world. Despite this importance, residential landscapes are infrequently designed with principles of sustainability in mind, resulting in the extensive use of pesticides to suppress a diverse array of plant pests. In this study, we ask whether ecological theory can inform the sustainable design and management of woody plant communities on urban residential properties. The associational resistance and dilution effect hypotheses are analogous hypotheses, which posit that increasing biodiversity can inhibit the abundance of herbivores and pathogens, respectively. Importantly, theory suggests that it might not just be diversity that matters, but the right kind of diversity (i.e., community composition). Previous studies have demonstrated that herbivore abundance can be greater on native plants compared to exotic plants in residential landscapes. However, little is known regarding whether this translates into greater numbers of interventions to reduce damage associated with plant pests on native plants. To test these hypotheses, we utilized a multi-year, commercial plant health care program dataset. We examined, at the residential property scale, the relationships between woody plant diversity, the percentage of plants that were native, and pest management interventions. We found that the number of pest management interventions targeting phytophagous arthropods, but not plant pathogens, was negatively related to woody plant biodiversity. The percentage of native plants on a property had no relationship with the number of pest management interventions that occurred. Consequently, efforts to increase woody plant biodiversity in residential landscapes could result in increased phytophagous arthropod pest suppression, thereby reducing the need for pesticide applications and their associated adverse effects.