The present study was undertaken with the aim of to characterize, according to physiognomic point of view, the vegetation communities in the UMA forest and to evaluate the influence of physico-chemical and pedo-morphological parameters in the spatial organization of floristic diversity in the UMA forest. Five vegetation communities were identified in the UMA forest which sharing many common species. The restriction of certain species of plots belonging to the diameter class ≥ 50 cm show a variation even on the level of arborescent layers in this forest. The floristic variability is mainly explained by the soil humidity in the Limbali mono-dominant vegetation communities in the western part. In the easten part, it is explained by the pH, the conductivity and the soil depth in the heterogeneous vegetation communities. However, in the transition forest, it is explained by the retention of the soil phosphorus. The UMA forest is classified among the semi-deciduous dense heterogeneous forests. The identified vegetation communities are inserted in the alliances Gilbertiodendrion Devred 1958 and Oxystigmo-Scorodophleion Lebrun & Gilbert 1954 in the class of Strombosio-Parinarietea Lebrun & Gilbert 1954. The Guinean-Congolese element represents more than 82% of listed species, of which the endemic species of the center of Guinean-Congolese endemism accounts for at least 90% of species. The presence of Afro-American elements (2%) shows stochastic transgression. The sedentary species are abundant in the plant communities of the Western part, while the pioneers and cicatricial species are abundant in the plant communities of the Eastern part.

The present study was conducted with the aim of analyzing the physiognomy and structure of major forest types found at UMA. To achieve this study, 40 floristic inventories plots (of 0.25 ha each) were considered and all individuals with dbh ≥10 cm were identified. A total of 3882 trees were identified: 696 (348 trees/ha) for trees stand at Limbali on white sand, 657 (325.5 trees/ha) for trees stand at Limbali on ground hydromorphe, 731(365.5 trees/ha) for monodominant settlement of transition on sandy soil, 887 (443.5 trees/ha) for the heterogeneous population disturbed on clay soil and 991 (455.5 trees/ha) for the heterogeneous population on soil shallow and rocky. They represent a basal area of 32.85 m²/ha, 25.08 m²/ha, 25.56 m²/ha, 30.86 m²/ha and 31.67 m²/ha respectively. The difference in density and basal area was significant between tree stands in all compartments. Statistical analysis indicated a significant difference between populations for species diversity, and Shannon index (stratum A2), Simpson index, Fisher index (Alpha) and equitability (strata E+A1 and A2) but there was not any difference in (E + A1) stratum according to these biodiversity indices. There was floristic similarity between monodominant and heterogeneous stands transitions but no floristic similarity between heterogeneous tree stands and disturbed stands monodominant trees. So these two stands of trees are different. The heterogeneous transition stands is therefore only monodominant forest Julbernardia seretii the interior of what Gilbertiodendron dewevrei (Fabaceae) came to replace Julbernardia seretii (Fabaceae) in the stratum (E + A1).