A distribution dependence study on the impacts of land urbanization on terrestrial vegetation carbon sequestration in China using Quantile-on-Quantile method

China's "Dual Carbon" strategy faces severe challenges from rapid land urbanization, and the resulting erosion effect on terrestrial vegetation carbon sequestration requires precise quantification. Based on panel data from 288 Chinese cities, this study empirically tests the distributional dependence of land urbanization's impact on terrestrial vegetation carbon sequestration using the Quantile-on-Quantile regression (QQR). The results show that: (1) The effect of land urbanization on terrestrial vegetation carbon sequestration exhibits an inverted U-shaped relationship, with the average inflection point occurring at a land urbanization level of 19.7%. (2) This relationship demonstrates significant distributional heterogeneity: the more favorable the ecological baseline conditions, the later the negative inflection point of land urbanization's impact on vegetation carbon sequestration appears, indicating that a stronger ecological baseline enhances resilience to land urbanization pressures. However, once the inflection point is exceeded, the decline in vegetation carbon sequestration accelerates more rapidly in regions with superior ecological conditions. (3) Compared to traditional linear regression and quantile regression, the QQR provides results with higher precision and captures the nonlinear influences under varying levels of land urbanization and carbon sequestration conditions. (4) Based on these findings, land management and ecological conservation policies should establish a differentiated governance system tailored to urban development stages and ecological endowment characteristics. Specifically, three typical models can be identified: eco-optimization, resource-dependent, and high-density expansion, to enhance the targeting and effectiveness of policy implementation.