This work presents results of the analysis made in four 1-hectare plots of floristic inventory in the flooded forests located in the delta and lower basin of the Amazon river. The flooded forests, so called "várzea" forests, harbor a relatively low species richness in relation to other areas such as "terra firme" forests. However the structure in size is considerable, with trees attaining high plant biomass. Probably that is due to the constant contribution of nutrients through the sediments that travel thousands of kilometers from the watersheds of the Andes to the delta of the Amazon river. The flooded forests of "várzea" are dominated by very few species (oligarchic forests), some they with so many individuals such us the açaí (Euterpe oleracea) and the muru-muru (Astrocaryum murumuru) palms, another with very big trees like the pitaíca (Swartzia polyphylla), pracuúba (Mora paraensis) and the seringueira (Hevea brasiliensis). The ucuúba (Virola surinamensis), a species whose populations are threatened by the timber logging, it has both large trees and great abundance. The delta flooded forests have low similarity when compared to each other, probably due to the immense variation of the environment in rivers, channels, islands and lakes. Local effects such as topographic gradient, flood height, salinity, velocity of the water can strongly affect the diversity, abundance and distribution of plants. Strategies of selection of várzea areas for conservation should take into account the environmental variation, the degree of human interference and both local and the diversity between habitats.
flooded forests; varzeas; estuary; phytossociological analysis; Amazonia forest diversity