Abstract
The major rivers of the Amazon River basin and their biota are threatened by the planned construction of large hydroelectric dams that are expected to have strong impacts on floodplain plant communities. The present study presents forest inventories from three floodplain sites colonized by alluvial riparian vegetation in the Tapajós, Xingu and Tocantins River basins in eastern Amazonian. Results indicate that tree species of the highly specialized alluvial riparian vegetation are clearly distinct among the three river basins, although they are not very distinct from each other and environmental constraints are very similar. With only 6 of 74 species occurring in all three inventories, most tree and shrub species are restricted to only one of the rivers, indicating a high degree of local distribution. Different species occupy similar environmental niches, making these fragile riparian formations highly valuable. Conservation plans must consider species complementarily when decisions are made on where to place floodplain forest conservation units to avoid the irreversible loss of unique alluvial riparian vegetation biodiversity.
Highlights
In the Brazilian Amazon River basin, two huge hydroelectric dams are currently in operation: Balbina, in Amazonas state, and Tucuruí, Pará state
The objective of this study is to assess the and compare species richness, alpha and beta diversity, density and composition of the riparian plant vegetation of the Tapajós, Xingu and Tocantins River basins in areas that will be heavily influenced by projected hydroelectric dams in Pará state in the Brazilian Amazon, as well as to suggest mitigatory measures for environmental compensation
A total of 4,823 individuals of shrubs and trees were sampled, belonging to 39 species on the Tapajós River, 42 species on the Xingu River, and 25 species on the Tocantins River. These were clear differences in species richness and diversity among the three sites, these being significantly higher in plots on the Xingu River compared to those on the Tapajós and Tocantins Rivers which were not significantly different from one another (Figure 4)
Summary
In the Brazilian Amazon River basin, two huge hydroelectric dams are currently in operation: Balbina, in Amazonas state, and Tucuruí, Pará state. Their construction caused the flooding of thousands of square kilometers of forested area (Fearnside 1995). The hydroelectric dams planned for the Xingu, Tapajós and Jamanxim Rivers are the focus of an intensive controversy due to the vast areas they will flood and the magnitude of their expected impacts. In their natural state, large tracts of floodplain forests along these rivers are subject to periodic.
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