Wolves, tree logs and tree regeneration: Combined effects of downed wood and wolves on the regeneration of palatable and less palatable tree species

The objective was to study via both descriptive studies and experiments how regenerating saplings can profit from the interplay between wolves and downed wood. We studied this in the Białowieża Primeval Forest, Poland, where wolves and deer co-occur for more than 100 years, and where downed wood covers the forest floor. Previous studies have shown that deer become more vigilant on sites they perceive as risky, such as in the core of a wolf territory and near downed wood that block view and escape possibilities. I was interested to see whether this change in deer behavior let to different browsing patterns and what this would mean for the regeneration of different tree species.
We found that obstacles, like downed wood, enhance successful tree regeneration by physically obstructing access for deer, and because deer avoid such obstacles. Moreover, deer visit areas with a higher perceived predation risk less often, however this is attenuated on more productive sites. Therefore saplings have the highest chance to outgrow the 2 meter browsing line (after which their top shoot is safe for browsing) when surrounded by downed wood, or when associated with downed wood in areas actively used by wolves. Especially preferred tree species (Acer platanoides, Tilia cordata) profit from the reduction in browsing on risky places leading to a more diverse forest in the long-term. Therefore the presence of downed wood and a complete assemblage of ungulates and carnivores leads to a spatial, structural and compositional heterogeneous forest.