Monitoring planted forest expansion from 1990–2020 in China

Abstract. China has undertaken extensive afforestation efforts in recent decades. However, the effectiveness of these plantings varies with different environmental conditions. Whether China's forest expansion is primarily due to intentional planting or natural reforestation remains uncertain. Thus, assessing the growth of planted forests (PF) is crucial for monitoring forest quality and supporting China’s commitment to carbon neutrality. In this study, using 30 m Landsat time-series, we proposed a Continuous Change Detection and Classification (CCDC)-based PF expansion monitoring (C-PFM) method. Based on the C-PFM, 30 m annual maps for PF and natural forests (NF) across China from 1990 and 2020 were produced. The resulting PF map in 2020 achieved a F1-score of 79.2 % for PF and an overall accuracy of 90.8 % when validated against visually interpreted reference data. The PF maps for the years 1998, 2003, 2008, 2013, and 2018 were evaluated using data from the 5th, 6th, 7th, 8th, and 9th National Forest Inventory (NFI) data across 34 provinces and autonomous regions of China. The results demonstrated that all Pearson’s product-moment correlations were larger than 0.86. According to the C-PFM results, we found 8.06 million ha (Mha) of net forest gains across China from 1990 to 2020, with 16.15 Mha net gains of PF and 8.09 Mha net loss of NF. In eight forestry ecological engineering areas, we observed that the upper and middle reaches of Yangtze river Shelterbelt Program and Pearl River Shelterbelt Program experienced the most significant PF expansion. The resulting dataset can serve as valuable scientific data for policymakers, researchers, and forest managers, guiding appropriate planting, environment enhancement, and carbon sequestration efforts. The produced 30 m annual maps for PF and NF in China are publicly available at https://doi.org/10.5281/zenodo.15559086 (Xiao, 2025).