The dense ombrophilous forest, also known as terra firme forest in the Amazon is characterized by the high diversity of tree species with a low number of individuals and that arouse scientific interest due to ecological, environmental and business standards and processes regarding the timber potential. This research aimed to analyze the floristic composition and structure of the tree community in a stretch of terra firme forest in the National Forest (FLONA) of Caxiuanã. Six plots of 1 hectare (100m x 100m) were installed, 100 m to 500 m apart, divided into 25 subplots of 20 m x 20 m where, for the floristic composition, all tree species with DBH≥ 10 cm were sampled and identified at the level of family, genera, species, characterized the similar species and exclusive species and calculated the índices of of Sorenson Similarity (S’), Shannon-Wiener Diversity (H’) and Equability (J’). For analysis of the horizontal structure, the phytosociological parameters of Relative Density, Relative Frequency, Relative Dominance, Coverage Value Index and Importance Value Index were calculated.The results showed in the floristic composition that Fabaceae and Sapotaceae and Chrysobalanaceae dominated in number of species; Eschweilera coriacea and Rinorea guianensis in number of individuals; from a total of 135 recorded species, twenty-two species were similar while 113 were exclusive (24, 13, 16, 14, 23 and 23) distributed in each plot and the mean value for the Sorenson similarity index was 5.73. Eschweilera coriacea, E. grandiflora, Licania membranacea, L.octandra, L.canescens, Lecythis idatimon, Rinorea guianensis, Tetragastris panamensis and Protium tenuifolium were representative in the importance value. It is concluded that the Caxiuanã terra firme forest corresponds to the floristic and structural patterns with high diversity and species richness concentrated in some families, with low similarity and high species exclusivity when compared to other terra firme forests, demonstrating a good stage of conservation. and adaptation of species in different environmental conditions.
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