Abstract
Riparian forests are vital for biodiversity at local and regional scales, but dam construction for hydroelectric power alters these ecosystems, causing habitat loss and changing river dynamics. We investigate dam impacts on tree diversity in the southern Brazilian Atlantic Forest, sampling trees along riverbanks and uplands across 15 fragments affected by dams. We analyse the relationship between habitat loss, elevation difference, fragment size, and dam implementation time with alpha and beta diversity using mixed models and redundancy analyses. Habitat loss had a more significant impact on beta diversity than on alpha diversity, resulting in varied implications across spatial scales for riparian forests. The loss of local habitats led to a shift in the species composition of communities. As the intensity, spatial extent, and temporal scale of the impact intensified, communities exhibited diminished uniqueness. Meanwhile, alpha diversity displayed an increase solely in response to the local elevation differences between uplands and riverbanks. We propose that our sampling design is transferable to inadequately monitored systems to inform about beta diversity, a component of diversity which is still often neglected either on licensing stages or during mitigation of dam-related impacts. Furthermore, our findings indicate a transient local heterogenisation, which subsequently transitioned into biotic regional homogenisation, attributed to dam-induced habitat loss in the Brazilian Atlantic riparian forests.