Associations between stand spatial structures and carbon sequestration on natural Larix gmelinii forests in Northeast China

• Effects of stand spatial- and nonspatial structure on carbon sequestration were quantified. • Larix forests were characterized with 0.29 mixing, 0.50 dominance and 0.70 competition. • Optimizing mingling, dominance and competition can increase carbon sequestration. Forest structure is a fundamental component of the forest ecosystem and significantly impacts carbon sequestration. Previous studies mainly focused on optimizing forest non-spatial attributes for restoring carbon, but the significance of stand spatial structure characteristics to carbon sequestration remains unclear. To understand the relationship between stand spatial structure (SSS) [i.e., Mingling index (M), Dominance index (D), Uniform angle index (W), Crowdedness index (C), and Hegyi competition index (Hy)] on carbon sequestration (Cs), this study was carried out based on four 50m×50 m plots of natural Larix gmelinii plots at Cuigang Forest Farm, located in the Daxing'an Mountains of Heilongjiang province, northeast China. The results revealed that the SSS of the forest exhibited minor instabilities, characterized by constant species mixing and moderate unpredictability in species dominance over 10 years (2012–2022). At the plot level, carbon stock increased significantly with an annual increment carbon (Aic) (i.e., 0.9–1.38 t ha⁻¹ per year) and relative increment carbon (Ric) significantly fluctuated (i.e., 4.48–5.84 %). A significant positive correlation was observed between SSS and Cs, particularly with M, D, and Hy, while a negative correlation was found with W and C. Hence, our findings demonstrate that SSS is crucial in regulating carbon sequestration, with dense and competitive structure contributing to maximized carbon sequestration capacity and mitigating the impact of climate change, offering critical insights for sustainable forest management.