Changes in host basal area explain associational resistance of mixed forests to primary pests

Tree species diversity generally has positive effects on forest primary productivity and resistance to natural perturbations, but diversity-function relationships can vary with site conditions. Recently, studies in experiments have shown that tree local climate, particular drought intensity, interactively affect insect herbivory. On the other hand, many focused response of forests terms growth without analysing concomitant susceptibility pests. It is interest understand combined host tree, since resource concentration a determining factor pest’s choice. We used experiment where conditions were both manipulated evaluate their interactive maritime pine (Pinus pinaster Aït.) two pests (i.e. infesting healthy trees): stem borer (PSB) Dioryctria sylvestrella, processionary moth (PPM; leaf chewer), Thaumetopoea pityocampa. Using structural equation models, we investigated direct indirect mediated by resources) presence birch total number attacks PPM PSB, same plots year. showed pine-birch more resistant PSB than monocultures. Furthermore, found this associational pattern was due trees attacks, possibly related disrupting non-host volatiles (NHVs), also indirect, resource-mediated whereby reduced amount resources available Drought modulated only for attacks. Overall, our work improves understanding diversity-herbivory helps explain how climate might modulate such relationships.