Premise of research. The role of soil in shaping plant communities in forest ecosystems has long attracted scientific interest, and many studies have pointed out the importance of edaphic properties on species distributions within the tropics. There is still a need to investigate whether edaphic differentiation affects forest composition and structure and to assess which soil properties can be good predictors of potential differences in species diversity.

Methodology. We established 24 1-ha plots in nondisturbed semideciduous forests in the Central Congo Basin, following clear-cut edaphic heterogeneity between sandy soils and clayey substrates. All individual trees with ≥10-cm diameter at breast height were inventoried in order to account for the diametric structures of trees and patterns of their diversity.

Pivotal results. Sandy and clayey plots differed significantly in their soil physical and chemical properties. Soil clearly segregates tree species into sand community and clay community, with species abundances differently correlated with soil properties, driving clear cases of edaphic associations in tree species. This trend was confirmed when species data were constrained by edaphic variables through a redundancy analysis, for which statistical tests confirmed the significance of the canonical model and that of the canonical axes. The diametric structure of trees remains the same on clayey and sandy soils, as do their diversity patterns.

Conclusions. Edaphic differentiation did not affect the diameter of trees. It also did not have an impact on tree abundances, species richness, and the diversity of trees altogether. Soil pH is an important variable to consider to understand tree diversity patterns in these semideciduous forests, and maybe its effects can be much more evident on the other forest communities (i.e., shrub and herbaceous layers).