Phytosociology of a dense ombrophilous forest in the northern Amazon, Roraima, Brazil

This study was carried out to characterize species composition and phytosociology of a native forest located at Caracarai, Roraima, Brazil. All trees with breast diameter (DBH) above 10 cm in nine 1-ha-permanent plots (100 x 100 m each) were inventoried. We observed 4,724 individuals (525 trees per hectare) distributed in 42 families, 111 genera and 165 species. The families with greater number of individuals were Fabaceae (1883), Lecythidaceae (609) and Sapotaceae (434), comprising 52% of the total. The higher densities of individuals were observed in the pioneer (219 trees ha(-1)), followed by secondary (193 trees ha(-1)) and climax species (113 trees ha(-1)). However, species of secondary group had the highest species richness (95), followed by the climax (44) and the pioneer (26). The Shannon diversity index (H' = 3.27) and the value of Pielou equability (J = 0.64) were lower than those obtained in other floristic inventories in the Amazon, because of the high occurrence of Pentaclethra macroloba. The importance values (VI) were higher for Pentaclethra macroloba (52.1), Eschweilera bracteosa (23.7) and Pouteria caimito (8.1). The importance values of these three species alone accounted for 28% of the total VI across species. Most of the individuals (71.3% = 374 trees ha(-1)) were recorded in the middle stratum (12.4 m <= height < 26.5 m) of forest. The forest community can be considered well-structured, mature and diverse, and so it is in good state of conservation.