In central Amazonian white-water floodplains (várzea), different forest types become established in relation to the flood-level gradient. The formations are characterized by typical patterns of species composition, and their architecture results in different light reflectance patterns, which can be detected by Landsat TM image data. Ground checking comprised a detailed forest inventory of 4 ha, with Digital Elevation Models (DEM) being generated for all sites. The results indicate that, at the average flood level of 3 m, species diversity and architecture of the forests changes, thus justifying the classification into the categories of low várzea (várzea baixa) and high várzea (várzea alta). In a first step to scale up, the study sites were observed by aerial photography. Tree heights, crown sizes, the projected crown area coverage and the gap frequencies provide information, which confirms a remotely sensed classification into three different forest types. The structure of low várzea depends on the successional stage, and species diversity increases with increasing age of the formations. In high várzea, only one successional stage was found and species diversity is higher than in all low-várzea formations. The more complex architecture of the high-várzea forest results in a more diffuse behaviour pattern in pixel distribution, when scanned by TM image data.

In the Central Amazonian floodplains, several hundred tree species grow in areas that are periodically flooded by nutrient-rich white-water rivers (várzea) and by nutrient poor black-water rivers (igapó). Seed masses of 31 species from várzea and 27 species from igapó were compared taking into consideration their taxonomic relatedness. Overall average seed mass was higher (mean = 7.08 g) in nutrient-poor igapó than in nutrient-rich várzea (mean = 1.16 g). In igapó, the species growing at high elevations on the flooding gradient had significantly higher seed masses than the species growing at low elevations. In várzea, no difference was found between species growing at high and low elevations. Four large-seeded species from igapó occurring at high elevations on the flooding gradient were responsible for most of the difference in average seed mass between forest types. These data suggest that at low positions in the flooding gradient in igapó, selection pressure on seed size is probably the same as in várzea. At sites with short periods of flooding in igapó forests, on high levels in the flooding gradient, the need for rapid height growth may have selected for species with larger seeds which enable seedlings to be less dependent on soil nutrients.