Moose browsing alters tree diversity effects on birch growth and insect herbivory

Producer diversity is known to affect a wide range of ecosystem processes including plant growth and insect pest resistance. Consumers such as mammalian herbivores too have been shown to modify plant growth and insect herbivory by triggering changes in host plants. However, few studies have investigated whether consumer effects interact with plant species diversity effects on a focal plant. To unravel consumer-diversity interactions, we recorded both the presence and intensity of winter browsing by moose (Alces alces) on silver birch (Betula pendula) in a long-term forest diversity experiment in Finland and measured birch tree growth as well as insect chewing damage during the following growing season. Although browsing on birch by moose was not affected by tree species richness, the intensity of moose damage altered tree diversity effects on birch tree growth. At minor browsing intensity, tree height, trunk diameter and canopy projections showed positively-humped relationships with tre...