Functional organization of woody plant assemblages along precipitation and human disturbance gradients in a seasonally dry tropical forest

Chronic anthropogenic disturbances (CAD) and rainfall are important drivers of plant community assembly, but little is known about the role played by inter- and intraspecific trait variation as communities respond to these pervasive forces. Here, we examined the hypothesis that lower precipitation and higher CAD reduce both intra- and interspecific trait variation in Caatinga dry forests. We sampled woody plants across 15 plots along precipitation and CAD gradients and measured resource-use traits. The effects of precipitation and CAD on RaoQ functional diversity were decomposed into species turnover and intraspecific variability. We used "T-statistics" to assess the trait sorting from the regional pool to local communities (i.e., external filtering), and within-community forces leading to low trait overlap (i.e., internal filtering) at individual and species levels. Intraspecific variability explained at least one-third of the total trait variation and 46% of variation in multitrait diversity across communities. Increasing disturbance reduced multitrait diversity, while precipitation affected some particular traits, such as wood density. Overall, precipitation determined species sorting across communities, while disturbance relaxed internal filters, leading to higher trait overlap within communities due to higher intraspecific variability. Our results suggest that the woody Caatinga flora contains a substantial amount of both inter- and intraspecific trait variation. This variation is not randomly distributed within and across communities, but varies according to rainfall conditions and disturbance intensity. These findings reinforce the emerging idea that human disturbances can reorganize plant communities at multiple scales and highlight trait variability as a key biological asset for the resilience of dry forests.