Long-term and large-scale ecological restoration projects shaped the spatial heterogeneity in new forests

The implementation of long-term ecological restoration projects and policies over the past two decades has played a crucial role in advancing the achievement of Sustainable Development Goal 15. However, the resulting dynamics of new forests remain unclear. In this study, we initially examined the distribution and sources of new forests and subsequently investigated the gross primary productivity (GPP) variations within these forested regions. We discovered that new forests are mainly converted from previously cultivated land, which is primarily due to the Grain for Green Project. The new forests are mainly distributed in mid-low altitude areas and gentle slope regions, indicating that accessible areas are prone to damage but also easy to recover. Over approximately two decades of ecological restoration projects, the GPP of new forests has significantly increased trends and the growth rates of new forests vary significantly in different climatic zones. Moreover, the GPP and growth rates of new forests displayed spatial heterogeneity. Specifically, the GPP in the new forests was highest in the eastern region, followed by the central south region, while the northwest region had the lowest GPP. Meanwhile, the southwest region shows the highest GPP growth rate among new forests, while the northwest region has the slowest growth rate. Furthermore, the average GPP of new forests is lower than stable forests, but new forests in China grow faster (3.735 vs. 2.587), highlighting their substantial carbon potential. These findings indicate that it's crucial to account for variations in stand and forest change rates when modeling forest carbon sequestration potential.