Fragmented tropical forests can maintain tree diversity and function, but not under high deforestation

Habitat loss threatens biodiversity, yet the independent effects of habitat fragmentation remain debated. Resolving this debate is critical for managing biodiversity in tropical forests undergoing rapid land-use change, but it requires a sampling design difficult to implement empirically. We developed a virtual framework by extending a spatially explicit, trait- and individual-based model to simulate tropical forest landscapes and disentangle the impacts of forest loss, fragmentation, and patch size on tree diversity and function. Deforestation reduced species richness, evenness, and biomass at patch and landscape scales. Smaller patch size and fragmentation further exacerbated these declines—except for neutral to positive fragmentation effects on landscape-scale species richness—but only in landscapes with less than 30% forest cover. Trait-mediated species turnover underpinned these changes, leading to increased dominance by fast-growing, high-dispersal species. These results suggest that conservation efforts should prevent further fragmentation and prioritize the restoration of large patches in highly deforested regions.