Forest-to-agriculture conversion drives collapse of regenerative and adult tropical tree communities

Understanding the effects of landscape-scale forest loss on the regenerative potential of tropical rainforests—measured through the abundance, species diversity, and composition of infant and juvenile trees—is essential for biodiversity conservation in human-modified landscapes. However, this topic remains poorly understood, particularly with regard to ecological thresholds, i.e., levels of forest cover below which regenerative potential may collapse. We sampled infant (<130 cm in height), juvenile (≥130 cm height and <10 cm DBH), and adult (≥10 cm DBH) trees across fourteen 1-km2 landscapes spanning a gradient of ∼0 to 100% forest cover in a biodiverse tropical rainforest region of southeastern Mexico. We assessed the impact of forest loss on tree density, species diversity, compositional integrity—defined as the proportion of species shared between fully forested and increasingly deforested landscapes—for each life stage, and compositional differences between them. All community attributes declined with forest loss across life stages, with more pronounced decreases in highly degraded landscapes. Our results indicate that maintaining more than 30% forest cover is critical to preserving the forest's regenerative potential. Below this threshold, assemblage density and species composition in regenerating communities sharply decline and begin to diverge from adult assemblages. These findings underscore the importance of incorporating forest cover thresholds into conservation strategies in human-modified tropical rainforest landscapes. • Assembly density decreases linearly with forest cover loss for all life stages. • Diversity and community integrity thresholds of regenerative trees ∼25 % forest cover • Regenerative density and diversity trends with forest cover mirror those of adults • Below 10 % forest cover, juvenile composition differs from that of other life stages. • Nearby reserve areas and low-intensity farming help forest regeneration.