Beavers as water bioengineers: effects on the bank roughness in the early years of new settlement in Tuscany

The Eurasian beaver (Castor fiber L.) is widely considered as a key ecosystem engineer due to its ability to modify riparian habitats by felling trees for food and constructing dams and lodges. This study investigates the effects of beaver activities on riparian vegetation structure and bank hydraulic roughness during the early years following their recolonization along rivers in Tuscany, central Italy. Field surveys conducted between 2022 and 2024 across the riparian buffers of three watercourses, i.e. Ombrone, Merse and Tevere (Tiber), assessed changes in tree stand characteristics induced by beaver activity. Results indicate that recently established rodents have selectively reduced tree density and altered the diameter distribution of riparian trees, showing a preference for stems between 2 and 8 cm. Riverbanks roughness and composite roughness at the cross-sectional scale have both slightly decreased. Consequently, the presence of beavers does not appear to increase hydraulic risk in the studied areas. This research enhances understanding of the hydraulic effects of beavers on riparian buffers, supporting their integration into nature-based river management and risk mitigation strategies.