The Grain for Green project eliminated the effect of soil erosion on organic carbon on China’s Loess Plateau between 1980 and 2008

Abstract Erosion and vegetation change intertwine in affecting soil organic carbon (SOC), yet their separate effects have not been explicitly disentangled, precluding a precise assessment of terrestrial carbon cycling and reliable application of Earth system models. Herein, we assessed the changes in the SOC, normalized difference vegetation index (NDVI) and soil erosion between 1980 and 2008 on China’s Loess Plateau, a region that suffered severe soil erosion, prompting the implementation of the Grain for Green project in 1999 to reduce soil erosion and rehabilitate degraded land. We established structural equation model and conducted Sobol sensitivity analysis to evaluate how soil erosion and the Grain for Green project-induced vegetation change altered the temporal patterns of SOC at the regional scale. We showed that SOC was not significantly changed, while the NDVI increased and the soil erosion decreased between 1980 and 2008. The Grain for Green project contributed 67% and 100% to the changes in the NDVI and soil loss, respectively. Additionally, changes in the NDVI and soil loss were negatively correlated and showed significant spatial variation. The change in SOC was negatively affected by soil erosion before the Grain for Green project but positively affected by the increased vegetation after the Grain for Green project. The positive effect of the Grain for Green project on SOC after 1999 offset the negative effect of erosion between 1980 and 1999. Additionally, the SOC change and its response to vegetation and erosion were closely affected by climate and clay content. These results suggest that the Grain for Green project eliminated the negative effect of soil erosion on SOC on China’s Loess Plateau.