Balancing disturbance: How moderate grazing sustains functional diversity along secondary succession in the Brazilian dry forest

Goat grazing is an increasing disturbance in seasonally dry tropical forests, yet its effects on plant functional diversity remain poorly understood. This study examines how grazing intensity and successional stage jointly influence inter- and intraspecific functional trait variation in the Brazilian Caatinga, the largest tropical dry forest in South America. Using a split-plot design, we evaluated three grazing intensities (low, medium, high) across early and late successional fallows and measured key functional traits of tree species. Functional composition shifted significantly due to the interaction between grazing and succession, revealing clear trait syndromes along the disturbance gradient. Moderate grazing enhanced interspecific functional diversity by allowing the coexistence of conservative and acquisitive strategies. In early successional fallows, intermediate grazing reduced dominance by stress-tolerant species, promoting more functionally heterogeneous communities. In contrast, high grazing intensity reduced functional diversity, favoring acquisitive, thorny species with thin, nitrogen-rich leaves and lowering both inter- and intraspecific trait variability. At the intraspecific level, strong grazing-mediated plasticity was observed. Trait variability increased along the successional gradient, particularly under moderate grazing, as later stages provided greater resources and structural complexity. Variance partitioning showed that grazing mainly drove intraspecific trait adjustments, while successional effects were largely explained by species turnover. Overall, moderate grazing sustains higher functional diversity, whereas intense grazing narrows functional strategies and may compromise ecosystem resilience, offering valuable implications for sustainable grazing management in dry forests.