Achieving Win-Win Ecosystem Restoration and Grain Production: Multi-Period Causal Effects, Mechanisms, and Heterogeneity Analysis Based on China's Three-North Shelterbelt Program

Balancing ecological restoration and grain production is a central challenge in sustainable land management, particularly in arid and semi-arid regions. Large-scale ecological engineering programs are often perceived as potentially limiting agricultural output due to land-use competition; however, causal evidence regarding their long-term impacts and underlying mechanisms remains limited. This study examines whether and how China’s Three-North Shelter Forest Program (TNSFP) influences grain production. Guided by the social–ecological systems framework and ecosystem-services theory, we hypothesize that ecological restoration enhances agricultural output through improvements in ecosystem services rather than by crowding out cropland. Using county-level panel data from 2000 to 2022, we employ a difference-in-differences (DID) model, parallel trend test, placebo test, and multiple robustness checks to estimate causal effects. Mechanism analysis integrates grain production data with satellite-derived vegetation indices, air quality indicators, and ecosystem quality measures. Our results indicate that the TNSFP significantly increases county-level grain production, with effects robust to controls for agricultural inputs, climate, and socioeconomic conditions. Mechanism analyses reveal that enhanced vegetation cover, improved air quality, and overall ecosystem quality jointly promote grain production. Significant regional heterogeneity is observed: the policy effect is stronger in Northeast and North China, positively moderated by cropland area and negatively moderated by the relief degree of land surface. These findings provide new causal evidence that ecological restoration can achieve synergistic gains in land restoration and food production, offering practical implications for sustainable land management in dryland regions.