Herbivory after calamity – Patterns and drivers of roe deer browsing on bark beetle induced disturbance sites

Cascading forest disturbances, such as drought and bark beetle outbreaks, likely as consequences of climate change, lead with increasing frequency to large-scale forest calamities. To reduce their impact, forest managers aim to increase forest resilience by increasing tree species richness. However, large herbivores, such as roe deer, can counteract these efforts through selective browsing and biotic filtering among young trees. The extent of tree browsing on calamity sites by roe deer, is largely unknown. In general, roe deer habitat selection is strongly affected by calamities; for example, freshly salvaged logged sites offer very high forage availability and transient edges but initially little hiding cover. In this study, we assess the spatial browsing patterns of roe deer on calamity sites and adjacent intact forest stands, investigating how local forage, anthropogenic disturbance, and hiding cover influence roe deer browsing on specific plant species. We conducted a large-scale browsing survey covering 1370 survey plots on and around 137 calamity sites in the southern Black Forest, Germany. Overall, we found higher roe deer browsing on calamity sites compared to intact forests, specifically close to the forest edge. Locally, attractive forage plants in the surroundings reduced browsing pressure on individual woody plants, likely distracting the roe deer’s forage selection away from young trees. Conversely, browsing on young trees increased with high proportions of unattractive plants like grasses. We found no strong effects of anthropogenic disturbance or the availability of hiding cover on browsing on calamity sites, though browsing was lower in proximity to forest roads on forest sites. Although the natural succession was not completely hindered by roe deer in our study, as indicated by moderate apical browsing, we demonstrate that young trees in open areas are disproportionately affected by roe deer browsing. In areas with higher deer densities, afforestation measures may require browsing protection, especially close to the forest edge and in areas without high availability of alternative attractive forage plants. • We found higher roe deer browsing on calamity sites compared to intact forest stands. • Browsing on young trees is highest close to transient forest-edges. • Availability of attractive forage reduces browsing pressure on woody vegetation.