Exploring Phylogenetic Diversity and Floristic Shifts Along an Elevational Gradient in a Northeast Brazilian Alpine Ecosystem

This study examines plant diversity along an elevational gradient in the Serra de Itabaiana National Park, northeastern Brazil, focusing on species richness, phylogenetic diversity, and beta diversity. We identified 108 plant species across five elevation bands, with species richness declining linearly with increasing elevation. Precipitation and temperature positively influenced richness, but no significant relationship was observed for phylogenetic diversity metrics. Notably, phylogenetic diversity peaked at mid-elevations, exhibiting a hump-shaped pattern, while higher elevations hosted phylogenetically clustered communities, reflecting environmental filtering. Beta diversity analysis revealed turnover as the dominant driver of species and phylogenetic dissimilarity between elevation belts, emphasizing the role of species replacement over nestedness. These findings underscore the influence of climatic variables and environmental constraints on community composition, with distinct patterns of species adaptation across elevations. Contrary to expectations, phanerophytes dominated across the gradient, challenging the predicted prevalence of hemicryptophytes at higher elevations. Our study highlights the importance of integrating phylogenetic data to understand biodiversity dynamics in understudied regions like northeastern Brazil. Conservation efforts in Serra de Itabaiana should prioritize maintaining beta diversity to capture species turnover and ensure ecosystem resilience. These findings contribute valuable insights into the interplay of ecological and evolutionary processes shaping plant communities in low-elevation mountain systems.