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Abstract

A floristic and structural analysis of a seasonal igapó forest at Rio Tarumã-Mirim, Central Amazonia, was performed. This floodplain vegetation is regularly inundated by nutrient-poor blackwater of the Rio Negro and its affluents, and it is distinct from nutrient-rich whitewater floodplains (várzea) and non-flooded uplands (terra firme). Trees with a circumference ≥10 cm were inventoried and measured in four 25 x 10 m plots, those with ≥100 cm in one 150 x 100 m plot. Family and species importance indices were calculated and compared with other forest stands in Amazonia. The four 25 x 10 m plots had a total of 162 trees, belonging to 44 species with 38 genera in 22 families (most common families: Mimosaceae, Rubiaceae, Lecythidaceae, Caesalpiniaceae, Clusiaceae). Four strata of height could be differentiated, each with typical representants. In the 150 x 100 m plot, there were 43 trees belonging to 10 species out of 10 genera and 5 families (most important family: Caesalpiniaceae). The species which dominated was the ochrospecies Aldina latifolia var. latifolia. All plots were distinct as related to number of trees, species, families, mean tree dbh, height, and dominating species. The results obtained with the two inventory methods complete each other to gain an insight into the vegetation composition and structure of the igapó. Thirty percent of the inventoried species are typical representants of igapó vegetation and can be considered endemic to the Rio Negro, other species have a wide distribution and also occur in várzea or terra firme vegetation.