The relative densities of tree species in virgin bottomland forests of Louisiana are reported for eight types of sites ranging from well-drained second bottoms to almost permanently flooded swamps. The second bottom terraces and the swamps had distinct species associations, but the intermediate first bottoms were characterized by a continuum of over 15 species gradually changing in abundance from the best to the most poorly drained sites. The distribution of each species appears to be determined by its tolerance to flooding and saturated soils. These forests contained a wide range of size classes and many young trees, indicating a continual replacement of older by younger trees.