Where does the boundary of high-efficiency urban ecological corridors lie? A functional connectivity efficiency perspective

High-density urban areas face acute shortages of ecological space and severe landscape fragmentation. Establishing high-efficiency urban ecological corridors (UECs) to enhance connectivity among isolated habitat patches is critical for maintaining urban ecosystem stability. However, optimal spatial boundaries for maximizing corridor connectivity remain undefined, representing a fundamental challenge in urban conservation. This study develops an integrated framework to identify high-efficiency UEC boundaries in Nanjing's historic urban core, addressing the complexity of the urban matrix and land constraints. We first optimize ecological source identification through Morphological Spatial Pattern Analysis, treating interconnected core areas and bridging zones as unified functional units. Using least-cost path (LCP) modeling and circuit theory, we simulate 145 LCPs between 94 ecological sources and generate 2900 corridor variants under graduated cost-weighted distance widths. Building upon the integration of functional connectivity and the spatial area of UECs, we innovatively propose the concept of functional connectivity efficiency (FCE) to quantitatively assess corridor performance. Specifically, “static FCE” enables direct efficiency comparisons between different design schemes, facilitating rapid screening among multiple options. “Dynamic FCE” varies with the width of UECs, thus, we identify its efficiency inflection point—a threshold marking the optimal spatial value for enhancing connectivity. Three distinct patterns emerged: 85% of corridor groups exhibited clear efficiency inflection points with initial increases followed by declines; 6% showed stable efficiency across widths; and 9% demonstrated delayed efficiency improvements. Targeted strategies to enhance connectivity based on each type's characteristics are then proposed. These findings offer both methodological foundations and practical guidelines for delineating high-efficiency UEC boundaries, providing scientific support for UEC conservation and sustainable urban development through spatially optimized ecological infrastructure.