Changes in soil organic carbon stocks of forestlands and grasslands on the Loess Plateau, 1980–2015

Soil organic carbon stocks (SOCS) are critical for both maintaining many ecosystem functions and regulating global climate. To address the serious soil erosion and land degradation problems on the Loess Plateau (LP), the Chinese government launched the famous “Grain for Green Program” (GGP) in 1999. However, how the SOCS change under the impacts of both GGP and climate change remains unclear. Here, we investigated the impacts of climate change and the GGP on SOCS of the top 1 m soil on the LP during 1980–2015, using a data-driven model and a multi-period land use/cover dataset. Our SOCS estimates showed that SOCS of grasslands and forestlands on the LP ranged from approximately 1400 ± 75 to 1700 ± 77 Tg C during 1980–2015. The SOCS of grasslands ranged from approximately 1000 ± 56 to 1200 ± 58 Tg C, which were roughly twice those of forestlands. Our analyses suggested that SOCS of grasslands and forestlands on the LP varied in the years before the GGP was launched in 1999, due to the continued warming and frequent drought. Unexpectedly, the SOCS did not significantly enhance after the GGP was implemented. Compared to 1995, the SOCS of grasslands and forestlands on the LP only increased on average by approximately 3.7% during 2000–2015, due mainly the adverse impact of climate change, as well as the limited effect of vegetation restoration on SOC at the early stage of the vegetation restoration programs. The study highlights the noticeably adverse effects of climate change on SOCS in the LP, providing valuable scientific support for the implementation of large-scale ecological restoration initiatives in the region.