Abstract: Abstract Aims Investigating the relationship between individual tree size and carbon sequestration rate in temperate forest communities provides a scientific basis for understanding the nature of tree growth and enhancing the carbon sink capacity of these ecosystems. Methods Based on the fixed monitoring data of 125,000 standing trees in temperate coniferous and broad-leaved mixed forests in different regions of Northeast China, the relationship between tree carbon sequestration rate and tree size was analyzed, and the tree species in each region were divided into four tree species groups according to their life forms and regeneration modes: (1) Understory tree species with L-shaped diameter distribution(UNL); (2) L-shaped subcanopy species (SUL); (3) bell-shaped subcanopy species (SUB); (4) Canopy species (CAB) with bell-shaped diameter distribution. Partial correlation analysis was used to quantify the effects of tree size, neighborhood competition, and species diversity on the carbon sequestration rate of individual trees. Important findings Carbon sequestration rate continuously increased with tree size. The trend of carbon sequestration rate with tree size is similar in different tree species groups, but there are differences in growth rate, with the fastest growth rate in the CAB group and the slowest growth rate in the UNL group. Tree size is the main factor affecting carbon sequestration rate and is significantly positively correlated with carbon sequestration rate (p < 0.001). The effects of neighborhood competition and species diversity on carbon sequestration rate vary among tree species groups, usually showing a significant negative correlation (p < 0.001). Conclusion This study reveals the factors influencing carbon sequestration rates of trees in temperate mixed coniferous and broad-leaved forests, highlighting the significant carbon sequestration role of large-diameter individuals. Our findings provide further insights into the nature of tree carbon sequestration rates and offer a theoretical foundation for sustainable forest management and the restoration of carbon sink functions.

Key words: Key words carbon sequestration rate, tree size, tree classification, neighborhood competition, species diversity