Effects of Deforestation and Fragmentation on Tree Beta Diversity and Endemism Across Landscapes in the Atlantic Forest Biodiversity Hotspot

ABSTRACT Biodiversity is highly heterogeneous across space, shaped by factors such as climate, geographical distance, and human activities. However, as we enter the Anthropocene, the impacts of habitat loss and fragmentation on biodiversity are becoming increasingly severe and insufficiently disentangled. Here we assess how habitat amount, habitat fragmentation, regional climate, and geographical distance influence beta diversity and endemism levels in tree communities across 95 landscapes in the Brazilian Atlantic Forest. We generated landscapes of 100 km 2 around forest inventory data extracted from the Neotropical Tree Communities database (TreeCo). Each landscape was characterized in terms of habitat amount, fragmentation (number of patches, mean patch size, and mean distance to the nearest neighbor), mean spatial distance (geographical distance among forest inventories), and climate across the region. The landscape variables (habitat amount and fragmentation) and the mean spatial distance were stronger predictors of beta diversity and endemism level when compared to regional climate. Beta diversity declined with increasing fragmentation, suggesting biotic homogenization in highly fragmented landscapes. On the other hand, spatial distance promoted increases in beta diversity, with more dissimilar communities as the distance increased. Moreover, endemism increased with habitat amount, with higher endemism levels in landscapes with more habitat. We highlight that our study contributes to the ongoing debate on the effects of fragmentation on biodiversity, reporting negative effects of habitat fragmentation on beta diversity within landscapes across the entire Atlantic Forest. Our findings successfully separate the effects of habitat fragmentation, habitat amount, and spatial distance on biodiversity, providing a better understanding of the processes that determine biodiversity change at the landscape scale. We advocate for conservation strategies that simultaneously protect both large and smaller habitat patches to sustain tree beta diversity and endemism across human‐modified landscapes.