A Guide to 23 Global Syntheses of Plant Diversity Effects: Unpacking Consensus and Incongruence across Trophic Levels

Plant diversity drives the trophic ecology of arthropod communities, and is the focus of thousands of studies and a growing field of meta-analysis. Although syntheses of plant diversity studies have yielded valuable insights, their sheer number and complexity limits broader interpretation. Here we scrutinize 23 syntheses published over three decades to identify common themes and contrasting results. We find that plant diversity consistently attracts more abundant and diverse communities of predators. Herbivore diversity tends to increase in response to plant diversity treatments, while herbivore abundance and plant damage generally decrease. Yet, these net effects often mask nuanced responses to plant diversity that depend on ecosystem, scale, and specialization. For instance, specialist herbivores often respond negatively to plant diversity, while generalists more often mount positive or neutral responses. Studies conducted at greater spatial scales show a dilution of effects on herbivores, but reveal conflicting effects on predators. Despite complexity in outcomes, syntheses show that diversifying plant communities holds great promise for enhancing the resilience of managed ecosystems. A closer examination of how insect diet breadth, spatial scale, and plant arrangement interactively determine the strength of trophic cascades will improve reliability and precision in how we leverage biodiversity for conservation and biocontrol.