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Carbon is a key element for the functioning and productivity of tropical soils. While the impact of organic inputs on carbon storage in these soils is known, little is known about the contribution of non-cultivated trees. In this study, we measured carbon content in non-cultivated trees (VC), soil organic carbon (SOC) and soil total nitrogen (TN) in different land uses in a West African forest – savanna transition zone. We used the Land Degradation Surveillance Framework for data collection and allometric equations to estimate the stocks of VC on a 10 km * 10 km landscape. Soil samples were taken in 160 sites at 0–20 cm, 20–50 cm, 50–80 cm and 80–110 cm depth in different land uses. We developed Partial Least Square regression models to predict SOC, TN and clay concentrations from mid-infrared soil spectra. We then considered soil bulk density to calculate the stocks of SOC and TN for each sampling depth and conducted a path analysis to identify the factors controlling these parameters. Our results showed that at landscape level, tree density and diversity explained most of VC stocks variability. SOC stock variability was mainly explained by clay content. The main drivers of TN stocks were clay and SOC stock. The VC and SOC stocks were not correlated with each other when considering all data. However, we found significant linear positive relationships between VC and SOC stocks for the land uses annual croplands, perennial croplands, grasslands and bushlands without soil depth restrictions until 110 cm. We concluded that in the forest-savanna transition zone, soil properties and topography determine land use, which in turn affects the stocks of SOC and TN and to some extent the VC stocks. Bushlands conservation and perennial trees cropping systems could be recommended for improved SOC storage.

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