Unveiling the impacts of forest loss on taxonomic and phylogenetic beta diversity of juvenile and adult tropical trees

Changes caused by anthropogenic disturbances are a major driver of local diversity, but their effects on the species replacement across space (beta-diversity), remain poorly understood, particularly with respect to different life-stages and ecological groups. We investigated these effects by examining juvenile and adult assemblages of shade-tolerant and intolerant tree species in 20 Brazilian Atlantic Forest fragments. We quantified taxonomic and phylogenetic beta-diversity among forest fragments and assess landscape predictors that might explain species turnover. Additionally, we assessed the turnover between juvenile and adult assemblages within forest fragments. Our results show that taxonomic beta-diversity among forest fragments was higher in adults than juvenile assemblages, mainly to shade-intolerant species, indicating a time lag between life-stages. In contrast, phylogenetic beta-diversity among forest fragments was consistently low and similar between life-stages and ecological groups (shade-tolerant and intolerant species). Forest cover and geographic distance were the main drivers of taxonomic beta-diversity, while edge amount was not an important predictor. Within each forest fragment, we reveal a high taxonomic turnover among life-stages, characterized by a broad shift between juvenile and adult assemblages, irrespective of forest cover. Conversely, phylogenetic turnover was influenced by forest cover, exhibiting a greater dissimilarity among life-stages in deforested landscapes. These findings underscore the importance of considering different life-stages to capture temporal responses between juveniles and adults, as well as to anticipate future community dynamics. Forest loss appears to drive taxonomic homogenization, by influencing changes in species composition. This results in a future juvenile community that is more similar among fragments than the current community. Additionally, forest loss induces phylogenetic changes within fragments, ultimately leading to future communities with different composition and evolutionary heritage compared to natural forested landscapes.