Climate–land-use interactions and canopy cover shape soil organic carbon dynamics in African agroforestry landscapes

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Résumé

Climate change, land-use intensification, and agroforestry management are key drivers of soil organic carbon (SOC) dynamics in Sub-Saharan Africa, yet their combined effects remain poorly understood. Using a hierarchical space-for-time substitution approach, we analysed 1,440 soil samples from protected areas, fallows, and croplands across four climatic zones spanning a humid-to-semi-arid gradient in Ghana and Burkina Faso. We also assessed the role of tree canopy cover on SOC stocks and soil properties. Climate was the dominant driver of SOC dynamics, explaining 26.3% of the variation in topsoil SOC, while the interaction between climate and land-use accounted for 34% of the variation in total SOC stocks. The effects of land-use intensification increased along the aridity gradient, causing substantial SOC depletion in croplands within dry sub-humid and semi-arid zones, likely due to reduced organic matter inputs and limited biomass production, which exacerbate cultivation-induced carbon losses. Across all climatic zones and land-use systems, SOC stocks were positively influenced by canopy cover, highlighting the contribution of agroforestry parklands to carbon storage. Random Forest analyses identified total nitrogen as the strongest predictor of SOC stocks across climatic zones, while clay content and rainfall were important predictors of total SOC stocks. Although significant climate×land-use interactions were also observed for soil physical properties, these patterns likely reflect, at least in part, non-random land selection across pedologically heterogeneous landscapes rather than direct manage ment effects. Our findings emphasise the importance of geographically tailored soil conservation and carbon management strategies adapted to specific climatic and edaphic contexts.

Mots-clés

Land use intensification, carbon stocks, land management; aridity gradient, space-for-time substitution, agroforestry, West Africa