Spatiotemporal Evolution of Land Use, Coupled Ecological Responses, and Multi-Scenario Trade-Off Simulation: A Case Study of the Danjiangkou Reservoir Area

As the core water source area of the Middle Route of the South-to-North Water Diversion Project, the Danjiangkou Reservoir Area plays a critical role in regional ecological security and water resource security. Its land use transitions and associated ecosystem service dynamics are examined. Based on land use, ecological sensitivity, and ecosystem service value data from 2000 to 2020, this study employed the FLUS model to simulate four scenarios—natural development, cropland protection, ecological protection, and ecological–cropland synergy—for 2050, systematically revealing the characteristics of land use transition, the coupled evolution of ecological sensitivity and ecosystem service value, and the trade-off mechanisms between ecological security and food security under multiple scenarios. The results show that: (1) From 2000 to 2020, land use in the reservoir area exhibited an ecological transition characterized by “two expansions and three contractions”: forestland and water bodies increased by 764.16 km2 and 324.36 km2, respectively, while cropland and grassland decreased by 664.33 km2 and 547.08 km2, the comprehensive index of land use degree declined by approximately 1.0%, indicating continuously weakening development intensity. (2) The overall hierarchical structure of ecological sensitivity improved, with the area of highly sensitive zones decreasing from 5201.60 km2 to 3729.91 km2; however, the concentration risk of highly sensitive forestland and the unexpected increase in extremely sensitive cropland persisted. (3) Total ecosystem service value increased from CNY 51.92 billion to CNY 58.35 billion (+12.38%), with hydrological regulation contributing 79.83% of the total increment; regulating services remained the core functional type. Sensitivity analysis indicated that the coefficient of sensitivity (CS) values were below 1, confirming the robustness of the findings. (4) Multi-scenario simulations revealed a rigid ecological–food security trade-off: under natural development, ESV increased by 15.44% but cropland loss reached 1033.29 km2; under cropland protection, ESV decreased by 1.50%, the only scenario with negative ecological outcomes; under ecological protection, ESV increased by 16.59% but with the most severe cropland loss (−1072.98 km2); under ecological–cropland synergy, water bodies expanded the most substantially (+562.75 km2) while cropland loss was the most severe (−1118.19 km2), indicating that the synergy goal was not achieved, as gains in regulating services came at the cost of further provisioning services losses. The study confirms the positive effects of ecological land use transition in the reservoir area, while also highlighting the intensifying conflict between ecological protection and food security against the backdrop of ecological improvement.