Human Disturbance Modifies Sexual Expression and Floral Traits in a Tropical dry Forest Tree

Anthropogenic disturbances, including selective logging, grazing, canopy opening, and extraction of non-timber forest products, can modify habitat conditions and influence plant reproductive traits. In seasonally dry tropical forests (SDTFs), these effects may be especially important for species with complex sexual systems. Bursera linanoe, an ecologically and economically important tropical tree, exhibits a mixed sexual system. We evaluated whether anthropogenic disturbance is associated with variation in sex ratio, sexual expression, and floral morphometry. Two natural populations under contrasting disturbance conditions were compared. We sampled 100 reproductive individuals (50 per site). A composite disturbance index was developed using Principal Components Analysis (PCA). Sex ratio differences were evaluated using chi-square tests and multinomial logistic regression. Floral traits were analyzed using generalized linear mixed models and linear mixed-effects models that included a three-way interaction among site, branch orientation, and sexual category. Disturbance was significantly greater at the disturbed site (Welch's t = 4.20, p = 0.024), primarily due to grazing, logging, and land-use change. Sex ratio did not differ between sites (χ² = 4.22, p = 0.121), and disturbance had no detectable effect on sexual expression (p > 0.99). In contrast, reproductive traits responded in a context-dependent manner. Significant three-way interactions among site, branch orientation, and sexual category were detected in three of the four reproductive traits examined (p < 0.05). Anthropogenic disturbance did not alter population-level sex ratios but modified key floral traits. These responses were driven by the interaction among disturbance, branch orientation, and sexual category, suggesting context-dependent expression of reproductive traits. Although sexual structure remained stable, changes in floral morphology and reproductive output indicate that disturbance may affect reproductive performance before demographic shifts become evident. Maintaining habitat quality while limiting intensive extractive practices may therefore help preserve reproductive performance in Bursera linanoe populations.