Effects of river level fluctuation on plant species richness, diversity, and distribution in a floodplain forest in Central Amazonia

River levels in Central Amazonia fluctuate up to 14 m annually, with the fl ooding period ranging from 50 to 270 days between the rising and falling ph ases. Vast areas of forest along the rivers contain plant species that are well adapted to annual flooding. We studied the effect of flooding level on tree species richness, diversity, density, and composition in lake, river, and stream habitats in Ja ir National Park, Brazil. 3051 trees >10 cm diam eter (at 1.3 m diameter at breast height, dbh) were measured and identified in 25 10 m x 40 m randomly selected plots in each habitat. Ordination meth ods and analysis of variance results sheared that forested areas near lakes had significantly lower species richness of trees than riverine and stream side habitats. Plot. species richness and diversity were strongly negativel y correlated with, the water level and duration of flooding. The drier (str eam) habitat had more total species (54 species of trees) and more unique s pecies of trees (6 tree species) than the riverine (52 tree species; 3 uniq ue species) and lake (33 tree species; 3 unique species) habitats. Species composition overlap among habitats was surprisingly high (42.6-60.6% overla p), almost one-third of the species were found in all three habitat types, and few species were unique to each habitat. We conclude that: (1) duration of flooding has a strong impact on species richness, diversity and plant d istribution patterns; (2) most species are adapted to a wide range of habit ats and flood durations; and (3) while flood duration may decrease local di versity, it also creates and maintains high landscape-scale diversity by in creasing landscape heterogeneity.