Multiscale geospatial transitions and sustainable strategies for mountainous urban agglomerations: From the perspective of social–ecological systems

The sustainability of mountains, among Earth's most dynamic and fragile ecosystems, is pivotal for global SDGs. A core challenge, however, is the profound overlap between human actions and natural systems, which dissolves the conventional boundaries between natural and urban systems. We synthesize research on classic ecotones and propose a novel coupling index of social–ecological systems as a unified metric for identifying multiple transition types. Applied to a Chinese mountainous urban agglomeration, our framework successfully delineates urban-rural, agropastoral, and terrain transition zones. This study identifies a complex coupling ecosystem (CCE) at the grid scale, a critical transition area where socio-economic and natural systems intensely interact, covering 17.28 % of the study area. It is the transition zone from the basin-periphery mountainous area (The average elevation of the western mountainous region exceeds 3000 m, with the highest peak reaching 7500 m) to the plain area. It concentrates the drastic transitions of multiple elements, including topography, climate, economy, and land use. The CCE-type areas exhibit a profound spatial conjunction between ecological sensitivity and socio-economic vulnerability, evidenced by nine out of the 10 counties/districts with the most CCE-type areas in Sichuan Basin being previously considered poverty-stricken counties in China at the national level. With a relatively large population and scarce high-quality land resources, this area is the core region facing the trade-off dilemma between economic development and ecological conservation. These findings contribute to our understanding of the mutual feedback within mountainous urban agglomeration systems, thus supporting sustainable land management and government policies.