Deer herbivory as an important driver of divergence of ground vegetation communities in temperate forests

Ungulate herbivory can fundamentally affect terrestrial vegetation at the landscape and regional levels, but its impact has never been analyzed from meta-community perspectives. Here, we study a meta-community of forest ground-layer plants in a warm-temperate region along a clear gradient of deer density interplaying with gradients of other environmental factors (forest type, sky openness and topographic wetness). Canonical corresponding analysis showed that deer density was the most important determinant of species distributions. These distributions conformed to a two-directional filtering model, which selects for competitive species at low deer density but favours herbivory-tolerant plants at high deer density, with these two directions counterbalancing each other when herbivory is intermediary. This resulted in a bi-directionally nested meta-community, in which local species richness was highest at intermediate levels of deer density, conforming also to the intermediate disturbance hypothesis. Our results suggest that herbivory can be the most important driver of meta-community structure in mesic systems; this contrasts with the results of earlier studies conducted in harsh environments, where species sorting by abiotic factors at early life stages reduced the role of biotic interactions, including herbivory.