Description of the subject. In tropical Africa, relations between biomass, diversity and floristic composition are poorly understood and rarely addressed in studies of forest ecology. Objectives. The aim of this study carried out in the forest of Isangi (latitudes 00 °30’ 00’’N and 01°05’00’’N and longitudes 23°40’00’’E and 24°30’00’’E) was to test the floristic, structural (density, basal area, diameter structure) variability and carbon stocks between the different forest types of the area and to analyze the relationship between biomass and species richness and species composition. Methods. Data were recorded on trees with dbh ≥ 10 cm in 145 plots of 50 x 50 m² installed in different land use classes (fallow of different ages, secondary forest, mixed forest on dry land, mixed primary forest on hydromorphic soils and monodominant forest with G. dewevrei). Non-symmetric correspondence analysis (NSCA) allowed discriminating the floristic composition in different groups. Results. This study showed the presence of floristic and structural variability and the difference in total biomass between the four forest types studied. There was also positive correlation between biomass and standardized species richness, density and basal area. Conclusion. This study shows the importance of the upper stratum (dbh ≥ 30 cm) in the accumulation of biomass (about 85% of storage).