Different facets of diversity are driving browsing intensity of tree saplings on plot and individual level

Browsing of tree saplings by deer hampers forest regeneration in mixed forests across Europe and North America. It is well known that tree species are differentially affected by deer browsing, but little is known about how different facets of diversity, such as species richness, identity and abundance, affect browsing intensity on the plot and individual sapling level. Based on forest inventory data from the Hainich National Park, a mixed deciduous forest in central Germany, we examined drivers of browsing intensity of saplings. In a hierarchical approach, we first modelled between-plot selectivity, i.e. the probability of a plot being browsed by roe deer. In a second step, we modelled within-plot selectivity, i.e. the species specific proportion of saplings being browsed within a plot. We found that species-rich plots were more likely to be browsed, however, within species-rich plots, a lower proportion of saplings per species was browsed, presumably because browsing pressure on single individuals of each species is diluted by the presence of co-occurring species. Between plots, the abundance of Fagus sylvatica
, as well as forest stand parameters and disturbance, further influenced the browsing probability of a plot. Within plots, species identity was the most important factor for predicting the proportion of saplings browsed per
species, providing a “palatability ranking” of the 11 tree species under study. By showing the effects that various facets of diversity, as well as environmental parameters, exert on browsing selectivity at the plot and individual level, our study advances the understanding of mammalian herbivore – plant interactions across scales.