Characteristics and Influencing Factors of Soil Shear Strength in Gully Erosion at Different Developmental Segments of Subalpine Meadows

ABSTRACT

Subalpine meadows play important roles in biodiversity conservation and soil carbon sequestration, but gully erosion poses a serious threat to their ecological stability. Soil shear strength ( τ ) is a key mechanical parameter for evaluating gully stability and soil resistance to failure. However, the spatial variation in soil shear strength and its controlling factors in subalpine meadow gullies remain insufficiently understood. In this study, three typical subalpine meadow gullies in Gaobenshan, Yunnan Province, China, were selected and divided into head, middle, and outlet segments. Soil samples were collected from the gully edge, wall, and floor of each segment. Soil shear strength and physicochemical and mineralogical properties were measured. Their relationships were then analyzed. The results showed that soil shear strength was lowest in the gully head segment of this subalpine meadow gully system. Compared with the gully head segment, soil shear strength in the gully wall and floor of the middle segment increased significantly by 10%–50% and 4%–47%, respectively. In the outlet segment, soil shear strength reached its maximum at the gully edge and floor, whereas soil shear strength in the gully wall decreased by 4%–37% compared with that in the middle segment. Correlation analysis indicated that soil physicochemical properties and mineral composition were significantly correlated with soil shear strength ( p  < 0.05). Structural equation modeling (SEM) further showed that, at the investigated sites, increased soil water content reduced cohesion, whereas improved aggregate stability, increased soil organic matter, and decreased soil bulk density enhanced the internal friction angle, suggesting potential pathways by which soil physicochemical properties affect soil shear strength. This may indicate that soil‐structure improvement driven by the combined effects of soil physicochemical properties enhances soil shear strength. This study preliminarily revealed the linkage between gully development and soil mechanical properties in the investigated subalpine meadow gullies and identified the main factors associated with soil shear strength in gully soils. Monitoring changes in these factors may help evaluate gully stability and provide a scientific basis for gully‐erosion control in subalpine meadow ecosystems.