Effects of the duration of flooding on species richness and floristic composition in three hectares in the Jau National Park in floodplain forests in central Amazonia

Rivers in Central Amazonia show annual water level fluctuations of up to 14 m; the flooding period ranges from 50 to 270 days between the rising and falling phases. Differences in duration and type of flood in Amazonian floodplain forests result in a mosaic of habitats which include lakes, grasslands, forests, streams etc. To study the floristic composition, structure, variation on number of species and diversity in a forest that is seasonally flooded by a black-water river in Brazilian Amazonia, 200 km NE of Manaus, I surveyed three hectares in habitats which included lake, river margin, and stream. The number of species per hectare ranged from 44 to 137. The number of trees varied from 796 to 1130. Total basal area ranged from 22.3 m(2) to 41.8 m(2). Leguminosae was the most abundant and dominant family in the river margin and stream plot, while Euphorbiaceae and Leguminosae were, respectively the most abundant and dominant families in the lake plot. The most dominant species in the river margin and stream plots was Aldina latifolia (Leguminosae), while Amanoa oblongifolia (Euphorbiaceae) was the most abundant and dominant species in the lake plot. Mean water level and flooding period decreased significantly from lake to the river margin to the stream. The mean number of species and the Shannon diversity increase significantly from the lake to the river margin to the stream habitats plots. Similarity indexes varied from 0.3 to 0.55% between the three plots sampled in this study.