Spatio-temporal evolution and optimization strategy of ecological security pattern in the Middle Reaches of the Yellow River of China

The Yellow River Basin is geographically critical to protect the ecological environment in China. But there is a large demand for agriculture, rapid economy as well as ecological and environmental pressure in the Yellow River Basin, especially in the Middle Reaches of the Yellow River (MRYR) at present. An ecological security pattern (ESP) is also very urgent to clarify the ecological bottom line and areas for restoration, in order to maintain a green ecological protection barrier. Taking MRYR as the study area, this study aims to construct a scientific ESP for the restoration and protection of the ecological environment. Firstly, the core area was calculated using morphological spatial pattern analysis. The national nature reserve was also superimposed to screen the ecological sources. Secondly, a comprehensive system was constructed for the resistance surface indicator. Then the circuit theory model was used to identify the ecological corridors, ecological pinch points, and barrier areas. The ESP of MRYR was constructed to obtain the dynamic trends and features of ESP from 2000 to 2020. Finally, some strategies were proposed to optimize the ESP for ecological and environmental protection, according to specific ecological conditions. The results showed that the number and area of ecological sources remained basically stable. The eastern basin and mountains were distributed densely, while the western plateau was distributed more sparsely. The number of ecological corridors evolved from 96 in 2000 to 103 in 2020. There was a dense distribution in the eastern part of the country, where the mountains were widespread. While in the western part of the country, the ecological corridors were sparse and spanned longer distances. The area of ecological pinch points remained stable. A slight decreasing trend was observed in the area of barrier areas. The pinch points and barrier areas were most densely distributed in the connecting area of the source and the corridor and in the middle of the corridor. The ESP presented a dense spatial pattern in the southeast, while the sparse spatial pattern in the northwest. Pinch-point protection areas were changed frequently in the sparse western corridors. The barrier restoration areas were concentrated in the basins or plains with high human activity intensities. The sparse source-protected areas required stable "staging areas" to maintain corridor connectivity over long distances. The number and length of corridors showed an increasing trend. The ESP shared the promising potential during this time. The spatial difference in the ESN between the eastern and western parts of the MRYR was attributed to the combination of high-intensity human activities and ecologically sound mountainous areas concentrated in the eastern part of the region, and fragile ecological environments and irrational development activities in the western part of the region. According to the specific ESP and the actual ecological situation in the region, some measures were proposed to restore and protect the ecological sources, and corridor elements. The finding can provide a strong reference to optimize the ESP in MRYR, particularly for the high-quality development of the ecological environment.