<p>Assessing carbon stocks in forest ecosystems is key to developing effective climate change mitigation strategies. However, the role of plant traits, particularly bark, sapwood, and heartwood, in biomass accumulation remains poorly understood. Clarifying these relationships can improve predictions of tropical forest carbon storage and management strategies. This study investigated the contributions of these stem layers to aboveground biomass in four vegetation types in Benin: semi-deciduous forest, gallery forest, swamp forest, and woodland. Data were collected using a non-destructive method; 470 trees across 25 species with diameters ranging from 5 to 77 cm were sampled from 111 plots. Multiple linear regressions and analysis of variance were performed to determine the contribution of each stem layer to aboveground biomass. The findings revealed significant variations in bark, sapwood, and heartwood characteristics across different vegetation types and among species. Woodland species presented the thickest bark (1.38 cm), whereas semi-deciduous forest species at seasonally flooded sites had the thinnest bark (0.80 cm). Bark and sapwood thickness were identified as key predictors of biomass accumulation (p &lt; 0.000 and adj R² between 53.04 and 76.39%). Lower bark mass density was generally observed in semi-deciduous forest, gallery forest, and woodland species than in sapwood and heartwood. Notably, <i>Daniellia oliveri</i> in woodland revealed an atypical pattern, with the bark mass density exceeding that of the inner wood layers. A consistent increase in wood mass density from the bark to the pith was observed in the swamp forest. These findings highlight the importance of incorporating bark and sapwood traits into tropical biomass models to enhance carbon stock estimates and guide more effective, ecosystem-specific forest management for climate change mitigation.</p>