The implementation of the Grain for Green Program - one of the largest ecological restoration projects in China - has had significant positive impacts on the country’s soil organic carbon levels, a study published in Scientific Reports shows. The research provides a comprehensive, quantitative understanding of the potential role of the program in carbon sequestration for terrestrial ecosystems and in climate change mitigation.

China’s Grain for Green Program (GGP), which launched in 1999, involves the conversion of steep-sloped and degraded cropland and barren land into forest and grassland with the aim of reducing soil erosion and enhancing biodiversity. By 2012, the GGP had converted 9.06 million hectares of cropland to forest and 0.64 million hectares of cropland to grassland. Afforestation has been proposed as an effective means of mitigating climate change, but the impacts of the GGP on soil organic carbon (SOC) levels have remained poorly understood.

Xinzhang Song and colleagues conducted a metanalysis to examine the effects of the GGP on SOC levels in China. They show that carbon accumulation has increased significantly since the GGP’s introduction, with a greater effect in the top 20 cm of soil than in deeper soil layers. The findings also reveal that conversion of cropland to forest - especially woodland, rather than shrubland or orchard - was associated with a greater increase in SOC accumulation than conversion of cropland to grassland. The results suggest that GGP implementation increased SOC levels and that there is the potential for further carbon accumulation in the soil, which could help to mitigate the effects of climate change.