This study makes an analysis of the floristic variations in an equatorial "terra-firrne" forest near Manaus, using the Floristic Expansion Index. The index was taken trough the natural regeneration rate, within the average of the relative abundance of species. As a conclusion was detected the existence of a 54 species group which expanded its representativity at the floristic composition occupying free spaces left by other group of 51 species that had a narrow floristical represetativity. The two groups firstly cited showed to be responsible for the floristic variations at the study area. Another group of 123 species representing 30% of individuals and more than 50% of species is responsible for keeping the fisionomical structure of the forest.