This research has taken place in four of 100 x 100 m in São José do Aracy, in the municipallity of Santa Bárbara do Pará, State of Pará, Brazil. Each part was divided in five transects of 20 x 10 m.The arboreal woody species with DBH³ 10cm and palms with CBH 10cm were evaluated and the height was estimated. This collected botanical material was identified in family, genera and species, and was incorporated in the João Murça Pires Herbarium, at Museu Paraense Emílio Goeldi (MPEG). For phytosociology analysis were calculated Relative Density (DR), Relative Frequency (FR), Relative Dominance (DOMR), Index Value of Importance (IVI), Index of Value of Coberture (IVC) and this Index of similarity of Sorenson (S'), Index of Diversity of Shannon (H') and Equability (E'). These results showed 29 families, 58 genera and 70 species. These families with major diversity were Caesalpiniaceae, Mimosaceae and Papilionaceae, with nine, eight and seven species respectively. Arecaceae and Papilionaceae obtained major density (27.75% and 25.84%); thirteen families were frequently with 4.88%; Papilionaceae obtained major dominance and Index value of importance (37.50% and 68.21%); Euterpe oleracea Mart. presented major relative density while Pterocarpus officinalis Jacq. presented major relative dominance, major Index of value of importance and coberture. This Index of diversity of 2.63 was considered low, with equability of 0.63 and similarity of 0.60. The floodplain forest presented low diversity in the species.
Açaí palm; floodplain; floristic composition; structure; diversity
