Forest edges, tree diversity and tree identity change leaf miner diversity in a temperate forest

In forests, besides tree diversity, tree identity can determine herbivore species diversity. Herbivore species diversity can also depend on spatial factors, such as edge effects; however, empirical evidence for this remains scarce. Furthermore, patterns in herbivore diversity may differ between forest stand level and responses at individual tree species. It is therefore important to disentangle stand-level patterns from associational responses specific to certain host species. We studied the effects of edge distance, tree diversity and tree species composition on leaf miner abundance, richness and diversity in temperate forests. We disentangled leaf miners' responses at stand level from those of miners associated with each of three individual tree species: Quercus robur L., Quercus rubra L. and Fagus sylvatica L. We found that tree diversity increased stand-level leaf miner richness and diversity. Fagus sylvatica and stand-level leaf miner abundance increased closer to edges. This was suppressed at stand level in more diverse mixtures. Underlying tree diversity effects, stand-level leaf miner metrics are strongly associated with tree species composition, due to many unique species found on F. sylvatica and Q. robur. Additionally, F. sylvatica experienced associational susceptibility to abundance in mixtures with Q. robur. Quercus robur experienced association susceptibility to miner richness in the mixture with Q. rubra. Studying the herbivore community at different spatial scales is a first step towards better understanding tree identity effects underlying tree diversity effects. Our findings emphasise context dependency of positive diversity effects on herbivores in terms of edge effects and tree species composition.