Construction of multi-level ecological security network in fragmented nature landscape using the three-dimensional framework of ecological adaptability

As the basis for constructing ecological security network, the ecological source has been broadly understood as larger patches that provide important ecosystem services and high comprehensive habitat quality. But the traditional methods for identifying ecological source (e.g. selecting natural vegetation patches and connectivity analysis) are not suitable for the Yanhe River Basin due to its fragmented patches and high vegetation cover. With the progress of research, the multidimensional evaluation framework is used to extract ecological source to mine more function and characteristic of ecosystem. Considering the fragmented nature of patches and the rapid recovery characteristics of vegetation in the Yanhe River Basin, a comprehensive evaluation model was developed based on the three-dimensional framework of ecological adaptability cycle (potential-resilience -connectivity) to extract ecological source. Additionally, due to the insufficient size of the extracted ecological source area to meet the increasing demand for ecosystem services in the future, the potential patches with high ecosystem services and large distribution were considered as secondary ecological source, and the patches with weak connectivity but high potential resilience were as considered tertiary ecological source. Finally, the ecological corridors were delineated based on the three ecological sources and the selected ecological resistance surface. The primary ecological sources were predominantly located in the central region, where grassland was the dominant land use type. The secondary ecological sources were mainly distributed in the southern woodland belt with the highest ecological services, but further enhancements to these services were unattainable. The tertiary ecological sources were mainly distributed in the western region and represented high-quality potential targets for future ecological source expansion. Therefore, it is recommended to give priority to the construction of a primary ecological corridors. The secondary ecological corridors exhibit the lowest comprehensive resistance, and can be constructed concurrently with the primary ecological corridors. Given its highest total comprehensive resistance, construction of tertiary ecological corridors should be contingent upon economic feasibility.