Plant growth form modulates the effects of trait and environment on global leaf insect herbivory

Abstract

Plant-herbivore interactions play a critical role in shaping plant performance and community dynamics. The strength of herbivory is expected to be associated with plant functional traits and environmental conditions. However, it remains unclear how these relationships differ between plant growth forms, particularly woody and herbaceous species at the global scale. By collecting global plant leaf herbivory data from 1,651 sites, including 2,594 species belonging to 1,060 genera and 204 families, we analyzed the variation in leaf herbivory and its relationships with plant functional traits and environments for woody and herbaceous species. We found that most variation of herbivory occurred among species and across ecoregion. The relationships between herbivory and plant traits and soil differed for woody and herbaceous plants: conservative leaf traits were associated with higher herbivory in woody plants but lower herbivory in herbaceous plants, while sandier soils increased herbivory in herbaceous plants but had weaker effects on woody species. In woody species, higher temperatures and infertile soils enhance herbivory both directly and indirectly through increased plant height. Conversely, in herbaceous species, while higher temperatures and sandier soils directly promote herbivory, higher temperatures and infertile soils indirectly suppress it via increased leaf dry matter content. These findings suggest distinct ecological processes control the variation of herbivory in woody versus herbaceous plants. We highlight the importance of integrating plant growth form to understand the trait-environment-herbivory relationships across terrestrial ecosystems.