European bison debarking is species-specific and influenced by bark chemistry

Megaherbivores can significantly influence the structure and functioning of ecosystems. Most of our knowledge on the ecological role of these animals is based on grassland ecosystems; much less is known about forest-dwelling megaherbivores and knowledge is particularly lacking regarding their role in forest disturbance potentially altering gap dynamics. Here, we investigate the bison-induced forest disturbance regime by recording debarking activities in a young nature conservation project in southern Germany. Across141 plots, we quantified feeding preferences for tree genus identity, diameter at breast height and various variables related to forest stand characteristics. In addition, we measured chemical bark traits to examine if they could be linked to the bison’s foraging behavior. We show that the bison strongly favored specific tree genera over others. Debarking frequency and severity were highest in Salix , Tilia and Sorbus and lowest in Pinus , Carpinus , Larix and Betula . These feeding preferences corresponded to gradients in bark chemistry traits. Tree species with high debarking rates had low bark CN ratios, high pH values and high potassium and phosphorus concentrations. On a stand level, bison debarking activity was significantly linked to species richness, cover of the shrub layer, and distance to the feeding site. Our data suggest that bison debarking behavior contributes to the structural diversity of forest ecosystems, supported by the fact that the animals prefer tree species and forest stands at the beginning of forest succession. Existing forest gaps are preserved or even expanded by these animals, thereby increasing environmental heterogeneity and biodiversity in forest ecosystems. ● European bison show clear debarking preferences. ● Deciduous trees are preferred over conifers. ● Debarking preferences are linked to chemical bark composition. ● Debarking activity is linked to stand level tree species richness. ● Bison activity boosts alters gap dynamics by preserving and enlarging gaps.