Cameroon’s ecosystem is rich in biodiversity, although its forests are under significant anthropogenic pressure, which contributes to climate change; this is particularly relevant given that little is known about their biomass and carbon sequestration potential, particularly in community forests. This study assesses the floristic biodiversity and estimates the above-ground carbon stock in the Mvangan community forest. The floristic inventory scheme comprised 24 plots covering 6 ha. Data collection involved surveying and identifying all tree species in two size categories: DBH ≤ 10 cm and DBH ≥ 10 cm. In total, 788 individuals were recorded, comprising 182 individuals with DHP ≤ 10 cm and 606 individuals with DHP ≥ 10 cm, corresponding to a density of 197.75 stems/ha. These individuals belonged to 118 species, 40 families and 16 genera. The Caesalpiniaceae (123 stems) was the most abundant family, and Gilbertiodendron dewevrei (94 stems) was the most abundant species. The diversity indices are as follows: Shannon: 4.02 bits; Simpson: 0.96 bits; and Piélou: 0.84 bits. The total above-ground biomass and above-ground carbon are 6,734,713.018 kg and 3,165.28 tonnes of carbon, respectively. The species that stores the greatest amount of biomass and carbon is Erythrophloeum ivorense, 25,216.06 kg of biomass and 11.85 tC of carbon, respectively. Communal forests require a well-developed management plan and participatory management that considers the uses and interests of local communities. Integrated management will help to increase the carbon sequestration capacity of biomass in communal forests in the Congo Basin.