Abstract: Carbon sequestration rates (CSRs) in forest ecosystems can be accurately predicted at different spatial and temporal scales. However, the variation of CSRs among different ecosystem components and the correlation with socioeconomic development remain unclear, although they are important to know to ensure that high CSRs are achieved on schedule in the long run. We aimed to develop a novel four-dimensional forest carbon sink (4-D carbon sink) framework considering spatial, temporal, component, and socioeconomic factors. The Forest Carbon Sequestration Model (FCS) was applied under three climate scenarios (SSP119, SSP245, and SSP585) to assess the 4-D carbon sinks in the forest ecosystems of the Heilongjiang Province from 2020 to 2060, across two periods (2020–2030 and 2030–2060). The average CSR in Heilongjiang’s forests was 23.25 ± 1.14 Tg C yr^–1, with Daxing’anling, Heihe, Yichun and Mudanjiang accounting 75% of the provincial total. Temporally, CSRs should reach a maximum in 2035–2040. Vegetation and soil consistently accounted for most CSRs, whereas litter exerted minimal influence across spatial and temporal contexts. Notably, northern Heilongjiang displayed markedly higher CSR per unit GDP (> 80% of the provincial total) than eastern areas. Overall, carbon sinks in Heilongjiang varied greatly across spatial, temporal, component, and socioeconomic scales, and the strong heterogeneity and clear imbalances among different regions, time periods, forest components, and socioeconomic conditions should be emphasized in the future. Our results offer new insights and guidance for strengthening carbon sequestration and regional economic development under China’s 2060 carbon neutrality goal.

Key words: Forests, Carbon cycle, Carbon sequestration, Imbalance, Carbon neutrality, Carbon trading