Construction and optimization of ecological security pattern in the source regions of the Yangtze River and the Yellow River in northwestern Sichuan

Taking biodiversity protection as the starting point, the northwestern Sichuan region with fragile ecological environment and frequent earthquakes was focused on, to realize the construction and optimization of the ecological safety network in Aba Tibetan and Qiang Autonomous Prefecture (Aba Prefecture in short). Elevation, slope, land cover, vegetation coverage, susceptibility to geological disasters, distance from water system, and distance from construction land were selected as resistance surface factors, and weighted superposition was used to construct a comprehensive resistance surface. Based on circuit theory and using Linkage Mapper tool, the ecological corridors of Aba Prefecture were built, ecological nodes were identified, and then the ecological security pattern of Aba Prefecture was optimized. The results showed that 18 ecological sources were identified, with an area of 28553.83 km², showing the characteristics of concentrated distribution in the south and north, and sporadic distribution pattern in the east and west. 39 ecological corridors were constructed, and 61 ecological nodes were identified. There were 35 pinch points and 26 obstacle points, showing a spatial pattern of long corridors in the central and western regions and short corridors in the east. 8 core ecological sources, 4 central ecological sources, and 6 general ecological sources were planned, with 9 first-level ecological corridors, 22 second-level ecological corridors, and 8 third-level ecological corridors, and with 17 first-level ecological nodes and 44 second-level ecological nodes. The ecological sources and ecological corridors were scientifically graded, and the pattern optimization system of "two districts, two belts, and three corridors" was proposed. Some suggestions were also provided, including developing high-quality tourism, improving species migration channels, and connecting river corridors, so as to effectively maintain the ecological security pattern of the source regions of the Yellow River in northwest Sichuan.