The influence of site conditions and human activities on vegetation composition was studied in savannas of the Diambour Forest Reserve of southeastern Senegal. Vegetation inventories were carried out in areas of homogeneous vegetation in savanna woodland, tree-shrub savanna, grass savanna and gallery forest based on the Braun-Blanquet (1964) methodology. At each site, substrate data (soil types and moisture content), micro-topographic features and disturbance factors (cutting, fire and cattle grazing) were recorded. The vegetation of the Diambour Forest Reserve was classified into six communities, seven subcommunities and two other subunits. The drier savanna areas affected by fire tend to be richer in species than the wetter parts restricted to the riverside and depressions with tree cutting and cattle grazing. The communities on drier sites and affected by fire show higher values of Simpson's index of diversity and species richness. The lower diversity of wetter sites is caused by tree cutting, micro-topography and soil with a high content of laterite and other clays. Riverside communities are mostly composed of microphanerophytes, while the communities of drier sites show more diversified life-form spectra. This paper is the first phytosociological study of the Diambour Forest Reserve (DFR) in Senegal.