Coupled species-ecosystem-landscape diversity index for assessing biodiversity: An approach for ecological security patterns construction in the Three Parallel Rivers region

Rapid urbanization has led to the fragmentation of regional ecosystems and reduced landscape connectivity, thereby threatening biodiversity conservation and habitat sustainability. Identifying critical biodiversity areas and establishing an ecological security pattern (ESP) are effective strategies for addressing these challenges. Using the Three Parallel Rivers (TPR) region as a case study, we developed a multi-tiered framework that integrates species, ecosystem, and landscape diversity to identify critical biodiversity areas. We combined Morphological Spatial Pattern Analysis (MSPA) with landscape connectivity assessment and incorporated the core zones of existing protected areas to jointly identify ecological sources. Circuit theory was then applied to construct an ESP for the TPR region, and corresponding strategies were proposed to enhance biodiversity conservation. The results showed that: (1) overall biodiversity in the TPR region remained relatively high, with medium-high and high biodiversity areas accounting for 33.78% of the total study area; (2) 56 ecological sources were identified, covering 19500.83 km² and accounting for 41.62% of the study area, with a spatial pattern characterized by higher density in the south and lower density in the north; (3) 304 ecological corridors were delineated, with a total length of 1723.97 km and a primary concentration in the northeastern part of the study area. In addition, 2180 ecological pinch points and 256 ecological barrier points were identified, mainly along the corridors and their surrounding areas; and (4) a biodiversity conservation framework was developed based on ecological resistance and the spatial distribution of corridor nodes, characterized by "one shield, three axes, four cores, and multiple zones." Within this framework, targeted strategies for biodiversity conservation and ecological restoration were proposed. This study provides an integrated approach for identifying biodiversity priority areas, supports the development of regional ESP, and contributes to regional biodiversity conservation.