Positive interactions between herbivores and plant diversity shape forest regeneration

Abstract

The effects of herbivores and diversity on plant communities have been studied separately but rarely in combination. We conducted two concurrent experiments over 3 years to examine how tree seedling diversity, density and herbivory affected forest regeneration. One experiment factorially manipulated plant diversity (one versus 15 species) and the presence/absence of deer (Odocoileus virginianus). We found that mixtures outperformed monocultures only in the presence of deer. Selective browsing on competitive dominants and associational protection from less palatable species appear responsible for this herbivore-driven diversity effect. The other experiment manipulated monospecific plant density and found little evidence for negative density dependence. Combined, these experiments suggest that the higher performance in mixture was owing to the acquisition of positive interspecific interactions rather than the loss of negative intraspecific interactions. Overall, we emphasize that realistic predictions about the consequences of changing biodiversity will require a deeper understanding of the interaction between plant diversity and higher trophic levels. If we had manipulated only plant diversity, we would have missed an important positive interaction across trophic levels: diverse seedling communities better resist herbivores, and herbivores help to maintain seedling diversity.

When anthropogenic‐related disturbances overwhelm demographic persistence mechanisms

“…). Here, the effects on diversity were highly selective, as has been reported elsewhere for deer (Cook‐Patton, LaForgia & Parker ). Many species, other than oak and small subset of native forbs, show little or no evidence of browsing including the exotic dominant grasses and non‐savanna tree species (MacDougall et al .…”

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

“…We observed that intensity of moose browsing not only altered the shape of the relationship between tree growth and tree species richness but also reversed the effects of tree species richness on insect herbivores. Interestingly, the only two previous studies exploring interactions between effects of mammalian herbivores and plant diversity have shown that browsing effects enhance rather than counter the positive effects of plant species (Cook‐Patton, Laforgia & Parker ) and genetic diversity (Parker, Salminen & Agrawal ) on the performance of tree seedlings or herbaceous plants, respectively. Both Parker, Salminen & Agrawal () and Cook‐Patton, Laforgia & Parker () cite browsing selectivity and associational protection as the main mechanisms through which browsing shifted polyculture output to less palatable but high‐performing species or genotypes.…”

Microbial interactions and community assembly at microscales

“…Similarly, in ecology, there is significant evidence that local, microscopic interactions between and within populations affect properties such as resistance to perturbations, efficiency of resource utilization, rates and yields of biomass production, etc. [2–4]. All these are macroscopic properties that depend on how the microscopic building blocks (genes, genotypes, and cells) are assembled.…”