How does tree sapling diversity influence browsing intensity by deer across spatial scales?

Browsing of tree saplings by deer often hampers regeneration in mixed forests
across Europe and North America. It is well known that tree species are
differentially affected by deer browsing, but it is still unclear, whether foraging
selectivity of deer is also influenced by different facets of sapling diversity, such as species richness, species identity, and composition, and how their influence varies across spatial scales. We used forest inventory data from the Hainich National Park and applied a hierarchical model approach, mimicking browsing decisions across scales. We found that, at the regional scale, deer mainly selected patches according to species composition, whereas at the patch scale, the proportion of individual saplings browsed was largely determined by the species’ identity, providing a “palatability ranking” of the 11 species under study. Interestingly, species-rich patches were more often selected, but less saplings were browsed per patch, indicating that deer’s nutritional needs are satisfied faster with higher species richness. By indicating which regeneration patches and individual saplings are (least) prone to browsing, our study advances the understanding of mammalian herbivore - plant interactions across scales. It also shows the importance of different facets of diversity for the prediction and management of browsing intensity and regeneration dynamics.