The Eurasian beaver (Castor fiber Linnaeus, 1758) can be considered a hydrological ecosystem engineer as it shapes environmental characteristics through its building activities and feeding behaviour. Even if several studies have so far reported beaver impact on multi-taxon biodiversity and forest regeneration, there is a lack of research on forest stand structure evolution following beaver direct activity on trees. This represents a pivotal topic for predicting restoration outcomes and reccommending sound silvicultural and management practices to maintain specific forest conditions. Specifically, the study aims at investigating forest stand structure and tree species diversity changes considering river variability, distance from the riverbank and beaver's gnawing activity intensity. The Eurasian beaver is only recently recolonising the three analysed Mediterranean rivers, but stand structure seems to be already significantly impacted by the species. The number of trees was reduced, increasing mean diameter at breast height at stand level, as most of the youngest and/or smaller trees are entirely cut down. Strongest structural variations can be detected in intensively impacted stands and in the forest portions closer to the riverbank. The absence of a significant effect on most of the diversity indices is likely due to the initially homogeneous composition of the tree layer in each stand and to the limited variety of beaver's diet within the sites. Future resprouting of secondary tree shoots, as well as beaver gnawing activity changes in intensity over time and space, can further produce variations in structural parameters and woody species diversity in the medium- and long-term period. Therefore, it will be crucial to further monitor the long-term effects, as structural shifts can produce significant effects on riparian ecosystem functions.

Forest biodiversity studies conducted across Europe use a multitude of forestry terms, often inconsistently. This hinders the comparability across studies and makes the assessment of the impacts of forest management on biodiversity highly context-dependent. Recent attempts to standardize forestry and stand description terminology mostly used a top-down approach that did not account for the perspectives and approaches of forest biodiversity experts. This work aims to establish common standards for silvicultural and vegetation definitions, creating a shared conceptual framework for a consistent study on the effects of forest management on biodiversity. We have identified both strengths and weaknesses of the silvicultural and vegetation information provided in forest biodiversity studies. While quantitative data on forest biomass and dominant tree species are frequently included, information on silvicultural activities and vegetation composition is often lacking, shallow, or based on broad and heterogeneous classifications. We discuss the existing classifications and their use in European forest biodiversity studies through a novel bottom-up and top-driven review process, and ultimately propose a common framework. This will enhance the comparability of forest biodiversity studies in Europe, and puts the basis for effective implementation and monitoring of sustainable forest management policies. The standards here proposed are potentially adaptable and applicable to other geographical areas and could be extended to other forest interventions.