In many ecological studies in tropical forests across the world, the role of substrate on the spatial organization of plant communities is increasingly recognized, and some studies have shown the impact of edaphic variables on the spatial distribution of species in the tropics. However, such studies were and remain rare in the forests around Kisangani, The forests of Yoko reserve, which arc the subject of this study are established on dissimilar substrates and contrasted topography (slope, lower slope and plateau). In this study, we assessed the impact of the microtopography offield on the diversity, the dominance and the structure of below arboreal stands (dominated trees stratum) of3 different toposequences in Yoko forest reserve. The method of diameter measurement was applied in an area of 0.9 ha, subdivided into 9 plots (20m x 20m) in which all the trees forming the lower tree stratum (Ad) were inventoried. This had generally led to the identification of 564 individuals belonging to 126 species, 96 genera and 33 families. At the end of the ordination analyzes (PCA and AFC), three stands were characterized: the shelf. the slope and the lowland stands. The alpha diversity index of Fisher and the species richness did not show a significant difference between the different stands but the species richness appears to be high for stands of slope.The study had contributed to the consideration of environmental factors in the characterization of forest vegetation.