Abstract: Enhancing the carbon sink of terrestrial ecosystems is an essential nature-based solution to mitigate global warming and achieve the target of carbon neutrality. Over recent decades, China has launched a series of long-running and large-scale ambitious forestation projects. However, there is still a lack of year-to-year evaluation on the effects of afforestation on carbon sequestration. Satellite remote sensing provides continuous observations of vegetation dynamics and land use and land cover change, is becoming a practical tool to evaluate the changes of vegetation productivity driven by afforestation. Here, a spatially-explicit analysis was conducted by combining Moderate Resolution Imaging Spectroradiometer (MODIS) land cover and three up-to-date remote sensing gross primary productivity (GPP) datasets of China. The results showed that the generated afforestation maps have similar spatial distribution with the national forest inventory data at the provincial level. The accumulative areas of afforestation were 3.02 × 10⁵ km² in China from 2002 to 2018, it was mainly distributed in Southwest (SW), South (Sou), Southeast (SE) and Northeast (NE) of China. Among them, SW possesses the largest afforestation sub-region, with an area of 9.38 × 10⁴ km², accounting for 31.06% of the total. There were divergent trends of afforestation area among different sub-regions. The southern sub-regions showed increasing trends, while the northern sub-regions showed decreasing trends. In keeping with these, the center of annual afforestation moved to the south after 2009. The southern sub-regions were the majority of the cumulative GPP, accounting for nearly 70% of the total. The GPP of new afforestation showed an increasing trend from 2002 to 2018, and the increasing rate was higher than existing forests. After afforestation, the GPP change of afforestation was higher than adjacent non-forest over the same period. Our work provides new evidence that afforestation of China has enhanced the carbon assimilation and will deepen our understanding of dynamics of carbon sequestration driven by afforestation.

Key words: Afforestation, Remote sensing, Gross primary production, Trend, Planted forests