Impacts of urbanization on pathogens and pests of wild and cultivated plants

Understanding how urbanization affects plant interactions with pathogens and herbivores is important for clarifying how changes in land use, climate and biodiversity affect ecological and evolutionary processes, and for managing urban plants to maximize ecosystem services. We performed a systematic literature review of relationships between urbanization and pathogens or pests of wild and cultivated plants. We identified k = 171 relationships from n = 54 studies in which pathogen or pest abundance was quantified in both urban and non-urban areas and summarized their distribution across taxa, geographic regions and directions and mechanisms of effects proposed by the authors. Most studies featured tree hosts and their arthropod pests or fungal pathogens. Grasses and forbs were the next most commonly studied hosts, followed by crops and shrubs. We then performed a meta-analysis limited to trees, which had the most studies with sufficient statistical information (k = 55 relationships, n = 14 studies). In that meta-analysis, we found no overall effect of urbanization on tree pest or pathogen abundance. However, there was a significant effect of pest/pathogen, with arthropod pests trending towards lower abundance in urban areas and fungal pathogens trending towards higher abundance. Drawing on literature from the broader fields of urban ecology, disease ecology and plant pathology, we synthesize our findings and offer insights into mechanisms by which urbanization influences disease and herbivory in wild and cultivated plants. We conclude by identifying research gaps, with the goal of informing management strategies that prioritize food security, environmental health and global biodiversity. This article is part of the theme issue 'Wild plant pathosystems'.