More diverse temperate forests are more resistant against non‐native insect herbivores

Abstract In general, trees suffer less damage by insect herbivores when growing in forest mixtures than in tree monocultures. Yet, most current knowledge is based on responses of native herbivores to tree diversity. Since introduced insect herbivores differ from native ones in their biotic interactions, their sensitivity to tree diversity is uncertain. We measured the damage caused by 11 non‐native herbivorous insects in monospecific and mixed forest stands in Europe. We merged these data with the results of published studies on native insects in temperate forests and applied a meta‐analytic approach to compare the effects of tree diversity on native vs. non‐native insect herbivores. We found that the damage by non‐native pest insects was reduced in mixed forest stands, that is associational resistance. The magnitude of this resistance was comparable to that measured for native herbivores. Associational resistance increased with increasing proportion of non‐host trees in the mixed forest. These results suggest that promoting mixed forests could be an effective strategy to attenuate the impact of invasion by non‐native forest pests.