Diversity and structure of tree and regenerating strata in fragments at different successional stages in the Atlantic Forest of Brazil

The Atlantic Forest is one of the most biodiverse Brazilian biomes and has also been the most impacted by anthropogenic activities, leading to fragmentation of its remnants in different stages of succession. Therefore, this study aimed to evaluate the floristic and structural composition of the tree and regenerating strata in three different Atlantic Forest remnants located in the state of Espirito Santo. All living tree individuals with diameter at breast height (DBH at 1.30 m) >= 5 cm were sampled, and phytosociological, entropy and evenness parameters were obtained. In the regenerating stratum, 45 sample units with dimensions of 5 x 5 m were established. Inclusion criteria were a minimum height of 50 cm and DBH< 5 cm. Phytosociological parameters, Shannon diversity index, Pielou's evenness, as well as structure and floristic composition similarities among fragments, were obtained for both strata. Indicator Species Analysis (ISA) was performed to identify indicator species, and cluster analysis was conducted among sample units, along with NMDS to assess the homogeneity of groups. In both the tree and regenerating strata, disturbed fragments (F1 and F2) exhibited lower species richness and diversity, with a predominance of early secondary species. The older stand (F3) showed a predominance of late successional species, indicating more advanced vegetation conditions compared to the other two evaluated fragments. The families Fabaceae and Myrtaceae were more abundant and species-rich in both strata. Regarding the ISA for each fragment in the studied strata, there were observed changes in species composition in the regenerating stratum, suggesting a possible future shift in stand composition. Additionally, it was concluded that regeneration played a significant role in indicating possible successional advances and forest recovery.