Earth Observation of Ecological Restoration Effectiveness and Ecosystem Functional Recovery in the South China Karst: From Greenness Monitoring to Functional Verification

Long-term Earth observation has reliably documented vegetation greening, biomass increases, and the mitigation of rocky desertification across the South China karst. However, “greening” alone neither demonstrates an incremental effect of ecological restoration interventions nor substitutes for the verification of functional recovery in hydrology, soils, carbon, biodiversity, and ecosystem resilience. Based on structured searches completed on 10 August 2026 in the Web of Science Core Collection, Scopus, and China National Knowledge Infrastructure (CNKI), which yielded 837 records in total, this review is organized around three evidence chains: the identification of state changes, the attribution of intervention effects, and the verification of ecological functions. The available evidence indicates that (1) optical, microwave, LiDAR, thermal infrared, and UAV observations have clear advantages for monitoring vegetation cover, canopy structure, aboveground biomass, evapotranspiration, and landscape patterns; (2) key functional variables, including soil thickness, soil physicochemical properties, groundwater processes, soil and dissolved carbon, and species composition, can generally only be constrained indirectly and must be jointly validated using field plots, sensor observations, laboratory analyses, and process models; and (3) existing quasi-experimental studies in karst regions show that, where project boundaries, implementation timing, and comparable controls are available, methods such as difference-in-differences can strengthen the credibility of intervention-effect identification, although such evidence remains limited. Future research should prioritize function-oriented multi-source Earth observation products, independent validation across years and catchments, the explicit representation of uncertainty, and testable designs such as BACI and DID, thereby advancing remote sensing from merely documenting surface greening to providing verifiable evidence for judging ecosystem functional recovery.