Assessment of carbon storage in China's National key Ecological Function Zones: Historical evolution, driving forces, and future projections

Terrestrial ecosystems play a critical role in climate change mitigation through carbon storage (CS). However, the long-term dynamics, driving mechanisms, and future trajectories of CS remain insufficiently understood across China's National Key Ecological Function Zones (NKEFZs). By combining the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model, an improved integrated patch-based land-use simulation (int-PLUS) model, Extreme Gradient Boosting with SHapley Additive exPlanations (XGBoost–SHAP), and partial least squares structural equation modeling (PLS-SEM), this study explored the dynamics, drivers, and future projections of CS in China's NKEFZs. Results show that the total CS across NKEFZs exhibited a decline–recovery trajectory from 1990 to 2020, decreasing from 5.29 × 10 10 Mg C to 5.20 × 10 10 Mg C and then rebounding to 5.24 × 10 10 Mg C, closely linked to land-use transitions. The Integrated Water Conservation and Biodiversity Conservation Zone (IWBCZ) consistently accounted for the largest share of the total CS across NKEFZs, while the Biodiversity Conservation Zone (BCZ) exhibited the most pronounced decline. Climatic factors outweighed socioeconomic influences, with precipitation (PRE) playing the dominant role. Climatic effects on CS were mainly mediated through normalized difference vegetation index (NDVI)-driven climate–vegetation–carbon pathways, particularly the PRE–NDVI–CS pathway and the temperature (TEMP)–NDVI–CS pathway. Future projections indicate divergent trends: compared with the 2020 baseline, CS showed a slight decrease under the Natural Development Scenario (NDS, −0.47%), whereas it showed positive growth under both the Cultivated Land Protection Scenario (CLPS, +1.37%) and the Ecological Protection Scenario (EPS, +1.49%), with EPS producing the largest improvement. Overall, this study highlights the critical role of climate–vegetation interactions in shaping CS and demonstrates that ecological protection strategies can enhance carbon sequestration and support sustainable land management.