The northern Brazilian Amazon has ecological transition ecosystems with high diversity and endemism of tree species and few botanical collections. We evaluated the phytosociology between Dense Ombrophilous Forest (Ds) and Forested Campinarana (Ld) within the Anauá National Forest (Flona) in Roraima, Brazil. A total of 14,730 trees with a DBH > 10 cm were inventoried across 30 hectares (ha), distributed among 55 botanical families, 183 genera, 386 species, and 123 undetermined trees. Ten hyperdominant tree families accounted for 69% of the sampled trees and 65% of the stored forest carbon (102.9 ± 5.0 Mg ha-1), like Arecaceae (2,555), Fabaceae (1,738) and Sapotaceae (1,311). Ten hyperdominant species accounted for 32% of the sampled individuals and 32% of the stored forest carbon (46.3 ± 3.8 Mg ha-1), like Euterpe precatoria (1,151), Pouteria macrophylla (561) and Inga alba (574). The Anauá National Forest has great potential for sustainable multiple-use forest management through forest concessions; however, tree mortality due to natural causes and anthropogenic actions (deforestation, illegal selective logging, and forest fires) was considered high (7%) for tropical forests in the Amazon. We recommend further studies to broaden the understanding of tree diversity and forest structure present in ecological transition ecosystems in the Brazilian Amazon.