Structure and species richness of low-diversity floodplain forest on the Rio Tapajos, Eastern Amazonia, Brazil

Abstract

Rivers in the Amazonian region have annual water level fluctuations varying from 6 to 20 m, and the flooding period ranges from 50 to 270 days between the rising and falling phases. Along the rivers there are many different types of vegetation which are annually flooded. In order to study the variation of the species composition and structure of a forest that is seasonally flooded by a clear water river in Brazilian Amazonia 20 km SW of Santarem, Para State, Brazil, we surveyed three hectares, each divided in ten randomly placed rectangular quadrats (10 x 50m). The number of species per hectare ranged from 21 to 30. The number of trees varied from 242 to 741. Total basal area ranged from 0.70 to 10.9 m2. Leguminosae was the most abundant and dominant family in the three hectares sampled. Couepia paraensis (Chrysobalanaceae), Campsiandra laurifolia (Leguminosae) and Leopoldinia pulchra (Palmae) were the most abundant species in the hectares sampled. Similarity indexes at species level varied from 46 to 60% between the three hectares sampled. The hectares studied have the lowest species richness observed in igapo floodplain forest of the Brazilian Amazonia. This may be correlated with the water type, soil condition and proximity of savanna.