Dynamics and Drivers of Soil Organic Carbon Sequestration by Cropland Afforestation: A Global Meta‐Analysis

ABSTRACT Cropland afforestation is a key strategy for enhancing soil organic carbon (SOC) sequestration and mitigating climate change, yet its global patterns and drivers remain unclear. Here, we conducted a meta‐analysis of 1691 observations to quantify the impact of cropland afforestation on SOC and identify key influencing factors across climatic zones, forest types and soil depths. Results revealed that cropland afforestation significantly increased SOC by 44% on average, with natural forests (+81%) exhibiting superior SOC sequestration compared to plantation forests (+36%). In addition, afforestation on wheat cropland resulted in greater increases in SOC relative to beans, maize and rape croplands. These findings indicated that the SOC response largely depended on the types of the prior cultivated crop and forest. The positive response of SOC peaked in temperate climates (+61%) and arid regions (+45%). Soil properties were the most significant predictors of SOC response upon cropland afforestation, followed by climate factors and management factors, collectively explaining 56% of the variation. Furthermore, changes in topsoil SOC after cropland afforestation were mainly driven by initial SOC, while soil pH was the dominant factor regulating SOC changes in subsoil. The response of SOC accumulation showed nonlinear relationships with soil depth and afforestation duration, peaking in topsoil and after more than 36‐year afforestation. These results highlight that converting cropland to mixed‐species forests can markedly enhance the accumulation of SOC in temperate and arid regions, amplifying the ecological benefits of cropland afforestation. This study emphasizes the ecological necessity of site‐specific afforestation strategies to maximize long‐term soil carbon stabilization and ecosystem carbon persistence.