Methodological Investigation of Boundary Thresholds for Delineating Ecologically Important Source Areas: A Case Study of Lhasa

Abstract

The delineation of ecological protection red lines is crucial for environmental conservation in critical ecological zones, particularly on the Tibetan Plateau, a key ecological highland in China. Accurately defining the scale and boundaries of ecological sources (ES) in such unique habitats presents a significant challenge due to the complex interplay between ecosystem service functions and spatial patch structures. Existing research often overlooks the uncertainties involved in determining the thresholds necessary to optimize ecological functions within reserves. This study aims to address these gaps by developing an integrated system for analyzing ES through evaluations of function, attributes, structure, and morphology. Combining assessments of ES functions, landscape patterns, spatial correlations, and fractal theory, we comprehensively analyze Lhasa’s ecological landscape. Five key factors—habitat capacity, habitat quality, water conservation, habitat connectivity, and habitat shape index—are employed to identify ES patches. The results indicate that a minimum patch area threshold of 20 km² is essential, with the total ES in Lhasa estimated at approximately 14,284.05 km². Landscape pattern analysis reveals that the contagion index (CONTAG) is a critical measure for evaluating landscape connectivity. When CONTAG values ranges between 85% and 98.26%, all five ecological function indicators perform optimally. Spatial autocorrelation analysis further refines the identification of potential ecological source areas. Fractal dimension analysis highlights patches with low stability, suggesting that glacier lands should expand outward and sparse woodlands and low-coverage grasslands should contract inward to enhance boundary complexity and internal stability. These adjustments result in a defined ES for Lhasa with a maximum scale threshold of approximately 15,342.52 km². This research provides a valuable framework for optimizing ecological protection red lines in Lhasa and offers methodological insights into defining ES thresholds in ecologically sensitive regions.

Keywords: Lhasa, Ecological source, Threshold study, Landscape pattern, Fractal dimension