Reconstructing Long‐Term Forest Age of China by Combining Forest Inventories, Satellite‐Based Forest Age and Forest Cover Data Sets

Forest age is one of the most important ecosystem characters for accurately estimating the magnitude and potential of carbon sink in forest ecosystems. During the past 40 years, national ecological restoration projects have led to the near doubling of the forest cover area in China, which has also substantially affected the dynamics of forest age. Therefore, there is an urgent need to generate long‐term forest age maps for China. This study reconstructed China forest age datasets (CFAD) from 1980 to 2015 at five year intervals at a 1 km spatial resolution by merging a satellite‐based forest age map in 2010 and forest cover dynamic maps from 1980 to 2015. The random forest method was used to reconstruct the forest age where forest age could not be inferred from the forest age base map in 2010 directly. CFAD showed a good agreement with the province‐level mean forest age derived from the several national forest inventories (R2 ranged from 0.66 to 0.86). In general, the younger forests are mainly distributed in southern and eastern China. The older forests are mainly distributed in the mountain areas of northeast, northwest and southwest China. The average age of China's forests increased from 18.2 to 44.0 years old from 1980 to 2015. Based on the current forest age and future afforestation planning, the average forest age in China is predicted to reach 71.6 years old in 2060. The CFAD provides an alternative data set to obtain improved estimates of local and national forest carbon sinks in China. Plain Language Summary Planting trees and protecting trees from timber harvest will help China to achieve the goal of carbon neutrality by 2060. The large scale national ecological restoration projects from the 1980s have substantially changed the structure of forest age in China. However, accurate long‐term forest age datasets for China are still unavailable. Therefore, we produced a new forest age data set for China from 1980 to 2015 by combining a reliable satellite‐based forest age base map in 2010 and high quality forest cover dynamic maps from 1980 to 2015. Using the latest four national forest inventories data set as independent observations, we found the new forest age map data set had a high validation accuracy. High quality and long‐term forest age maps are essential to better estimate the carbon dioxide absorption potential of trees and design of optimal forest management policies. Key Points We reconstructed long‐term China forest age datasets by combini