Estimation of unrealized forest carbon potential in China using time-varying Boruta-SHAP-random forest model and climate vegetation productivity index

Forest carbon storage is the net result of carbon gained through photosynthesis and carbon lost through respiration, mortality, and disturbances. It plays a crucial role in mitigating climate change as a key component of the global carbon cycle. To understand the "realized" (actual carbon stored in the forest) and "unrealized" (the difference between the maximum potential carbon storage under current climate conditions and actual stored) potential carbon storage of forests in China, as well as their spatial distribution, is crucial for developing effective forest management strategies to enhance carbon sinks and reduce emissions. To estimate the forest realized potential carbon density/storage (RPCD/RPCS) in China, this study used a Time-varying Boruta-SHAP-Random Forest Model (TBS-RF), while the Paterson's Climate Vegetation Productivity (CVP) index was employed to determine the forest potential carbon density/storage (PCD/PCS) in China. The results reveal several key insights: (1) The average RPCD of Chinese forests is 56.12 Mg C/ha, with a total forest RPCS of 7.96 Pg C, indicating that China's forests play a significant role in carbon sequestration. (2) The Alpine Subtropical region exhibits the highest forest RPCD (96.89 Mg C/ha), attributed to its high precipitation and rich biodiversity, while the Mid-subtropical region shows the highest forest RPCS (1.92 Pg C), highlighting its significant contribution to national carbon storage. (3) The average productivity potential of Chinese forests is 10.00 m3 ha-1.a-1. (4) The Alpine Subtropical region shows the highest forest unrealized potential carbon density (UPCD) at 202.91 Mg C/ ha, emphasizing the region's latent capacity for increased carbon sequestration, while its forest unrealized potential carbon storage (UPCS) reaches 0.85 Pg C. This underscores the region's vast untapped capacity for contributing to carbon sink strategies, reflecting the considerable gap between current and potential carbon sequestration in many forested areas across China.