Abstract
Biodiversity is a multidimensional concept, and capturing its various facets simultaneously offers a more robust framework for predicting vegetation responses to anthropogenic disturbance. Yet, multifaceted studies exploring forest understory regeneration remain scarce. We investigate taxonomic (TD), functional (FD), and phylogenetic (PD) diversity in the understory plant communities of 38 hop-hornbeam forest stands in the Central Apennines (Italy), which differ in time since last coppice event, i.e., 20–25 years (younger stands) and 40–45 years (older stands). We tested differences in TD, and standardized effect sizes (SES) of FD and PD between younger and older stands using two-tailed t-tests. Further, we evaluated the presence of a random or non-random mechanism by checking the distribution of the SES-FD and SES-PD. Our results revealed no significant change in TD between the two forest age classes. However, SES-FD and SES-PD changed significantly. SES-FD shifted from convergence in younger forests to divergence in older ones, aligning with expectations that greater environmental heterogeneity in mature forests supports functionally distinct species. In contrast, SES-PD exhibited increasing convergence over time, suggesting that the forest understory becomes increasingly dominated by closely related species as regeneration progresses. This growing phylogenetic convergence may reflect long-term landuse impacts and a limited regional species pool, pointing to a gradual loss of evolutionary diversity. Overall, our findings emphasize that different facets of biodiversity shape the dynamics of forest regeneration, and that an integrated, multidimensional approach is essential to fully understand and predict these complex ecological processes.