The tree growth–herbivory relationship depends on functional traits across forest biodiversity experiments

While studies have demonstrated that higher tree species richness can increase forest productivity, the relationships between tree species richness, tree growth and herbivore damage remain insufficiently explored. Here we investigate these linkages using data from 8,790 trees across 80 species in 9 biodiversity experiments, spanning temperate and subtropical biomes. Despite considerable geographic variation, we reveal an overall positive relationship between tree species richness and insect herbivory, as well as between tree growth and herbivory, at individual, species and community levels. The tree growth-herbivory relationship is further influenced by leaf functional traits. In particular, we show that tree species with a higher carbon to nitrogen ratio and, to a lesser extent, tougher leaves, experienced higher herbivory when their growth rate increased. The associations between tree growth and herbivory are further modulated by climatic and soil variation among the sites. Our study highlights the role of functional traits in shaping the relationship between tree growth and herbivory, supporting the resource availability and plant vigour hypotheses.