An integrated evaluation framework for multiscale ecological protection and restoration based on multi-scenario trade-offs of ecosystem services: Case study of Nanjing City, China

Ecological protection and restoration is an important bridge to adjust the contradiction between ecological protection and economic development, and it is essential for ecological security and sustainable development. An integrated evaluation framework for multiscale ecological protection and restoration based on multi-scenario trade-offs of ecosystem services was proposed in this study, and the city of Nanjing was taken as an example to identify key areas and land strategies for ecological protection and restoration. In our framework, carbon storage, habitat quality, nitrogen retention, and water conservation services were quantified by InVEST model, and recreational service was quantified as the total areas of green spaces within ecological land accessibility. The ordered weighted averaging model was used to simulate the priority areas of ecological protection under 11 scenarios of trade-offs of ecosystem services, and ecological sources, ecological corridors, ecological pinch points and ecological barriers at the Nanjing city scale and the main urban scale were identified based on circuit theory. We also nested the ecological conservation and restoration patterns at two scales and analyzed the coincidence degree between two scales. Our results showed that the S7 scenario had the highest average conservation efficiency among the 11 scenarios. The priority areas for ecological protection in this scenario had an area of 1582 km2 and are mainly distributed in the central and southern parts of Nanjing. In our study, 50 ecological sources (with an area of 1153.36 km2), 77 ecological corridors (with a length of 443.04 km), 25 key nodes for ecological protection and 31 key nodes for ecological restoration were identified in Nanjing. By nesting the ecological protection and restoration patterns of two scales, we found that the overlap of ecological sources and ecological pinch points at two scales is 100%, and the overlap of ecological corridors and ecological barriers is 45.28% and 57.14%, respectively, which means that the ecological protection and restoration patterns at the two scales in Nanjing were well connected, but the ecological network at the large scale cannot fully reflect the real ecological problems and needs at the small scale. We suggest regarding the ecological protection and restoration pattern at large scale as the basis and the pattern at small scale as the supplement. We also propose that priority should be given to the protection and restoration of key areas where the two scales overlap, and strictly control their land development to promote sustainable development. This framework and these strategies are applicable to other rapidly urbanizing regions of the world.