Structural convergence and floristic heterogeneity in restinga high forests of the south-eastern Brazilian coast

Context Restinga forests are threatened coastal ecosystems developed on Quaternary deposits where variation in sediment origin, drainage, soil and edaphic conditions may shape plant communities. However, it remains unclear whether structurally similar Restinga High Forests on different Quaternary units also converge floristically. Aims We evaluated whether forest structure, species richness, diversity and floristic composition differ among three Restinga High Forest sites established on distinct Quaternary units within a protected area in south-eastern Brazil. Methods Thirty 100-m2 plots were sampled. All trees and arborescent palms with circumference at breast height of ≥10 cm were measured and identified. Forest structure was analyzed using principal component analysis, incorporating tree density, mean height, forest stratification, basal area and stem size. Richness and diversity were compared with ANOVA or Kruskal–Wallis tests. Floristic composition was analyzed using abundance and presence–absence-based dissimilarity matrices. Key results Structural attributes did not differ significantly among Quaternary units, indicating structural convergence within the same physiognomy. In contrast, species richness, Shannon diversity and Simpson dominance differed mainly between the paleolagoon-influenced forest and the mixed fluvial–colluvial forest. Floristic composition differed among all units for both abundance and presence–absence data, with no overlap among the main species contributing to within-unit similarity. Conclusions Restinga High Forests may reach similar structural states while maintaining distinct floristic assemblages shaped by geomorphological history, drainage and edaphic filters. Implications Conservation strategies should treat Quaternary units as complementary ecological compartments that are essential for maintaining floristic heterogeneity across coastal landscapes.