Chemically mediated plant–enemy interactions promote positive biodiversity effects on young tree growth

Abstract The tree diversity–productivity relationship is key to effective forest restoration and management; however, it remains unclear what role foliar chemical diversity and interactions between trees and their enemies play in driving this relationship. Trees produce chemical metabolites in their leaves that impact herbivory and pathogen infection. If trees alter the diversity of metabolites they produce when grown in more diverse communities, this could impact interactions with herbivores and pathogens. Ultimately, these tropic interactions with plant enemies, mediated by chemical diversity, could be important drivers of diversity–productivity relationships. Using a large‐scale tree diversity experiment, we used a focal tree sampling design from 14 species across a gradient of tree species richness to assess the role of foliar chemicals and trophic interactions in the diversity–productivity relationship. We used untargeted metabolomics to measure foliar phytochemical diversity, monitored tree–enemy interactions, including f