The effects of natural enemies on herb diversity in a temperate forest depend on species traits and neighbouring tree composition

Abstract There is mounting evidence that top‐down control by natural enemies helps maintain plant diversity in ecosystems. Previous work has concentrated on either forest trees or grassland herbs. Our knowledge of how affect herb forests limited. We used fungicides and insecticide to experimentally examine the effects fungi insects abundance at community‐wide scale within groups species with certain traits. also assessed assemblages were modified neighbouring tree composition an old‐growth temperate forest. found increased overall 7% while decreasing 5%. This effect both weakened increase diversity. Insecticide did not noticeably, except areas dominated deciduous where application reduced Fungicides decreased relatively less defended (i.e. thin‐leaved non‐clonal) but had no herbs stronger defensive traits thick‐leaved clonal). non‐mycorrhizal (NM) arbuscular‐mycorrhizal (AM) species, although was unrelated species' mycorrhizal association. NM than AM species. Synthesis . conclude insect herbivores are critical regulating this forest, their dependent composition. results highlight importance understory communities forests, advancing our understanding processes shaping