Unified Regulatory Framework for NPP-Based Ecosystem Carbon Absorption Capacity and Its Application in China

Terrestrial ecosystem carbon absorption capacity has become an important component of China’s strategy to enhance nature-based climate mitigation. However, existing studies on China’s terrestrial ecosystem carbon dynamics are still insufficient to support source-oriented control and unified supervision by national-level government departments, particularly in terms of temporal consistency, spatial completeness, and cross-ecosystem comparability. Here, we present a systematic assessment framework for NPP-based ecosystem carbon absorption capacity (NPP-based CAC) designed to support unified ecological and environmental supervision. In this study, NPP-based CAC is defined as the annual vegetation production-based carbon fixation capacity derived from net primary productivity. It represents carbon retained by vegetation after plant autotrophic respiration has been accounted for in the NPP estimation, and it should not be interpreted as gross ecosystem carbon uptake, NEP, NBP, net land–atmosphere carbon exchange, or a carbon sink for carbon neutrality accounting. The framework adopts year as the temporal unit and a 500 m × 500 m grid as the spatial unit, and integrates four core components: temporal series analysis, spatial distribution mapping, protection effectiveness evaluation, and enhancement potential estimation. Applying this framework to China from 2000 to 2022, we found that national NPP-based CAC increased from 0.673 Pg C yr−1 in 2000 to 0.868 Pg C yr−1 in 2022, with carbon absorption intensity rising from 98.47 to 121.37 t C km−2 yr−1. High-value areas covered 3,009,571 km2, accounting for 40.90% of the national area with NPP-based CAC, whereas areas showing degradation signals covered 2,075,286 km2, accounting for 29.01%. The national historical reference gap, termed enhancement potential in this framework, was estimated at 152.63 Tg C yr−1, equivalent to 17.6% of the 2022 national total; this value represents the difference between current NPP-based CAC and grid-level historical maxima, rather than a directly attainable restoration target. Because no formal attribution analysis was conducted, the observed temporal and spatial patterns are interpreted as diagnostic changes in NPP-based CAC rather than as direct evidence of policy effects or ecosystem degradation. This framework enables integrated assessment across temporal, spatial, and ecosystem-type dimensions and provides an operational diagnostic basis for national-level ecological supervision, spatial prioritization, and follow-up attribution or field verification.