The Dual-Edged Role of Vegetation in Evaluating Landslide Susceptibility: Evidence from Watershed-Scale and Site-Specific Analyses

Vegetation is widely recognized for its beneficial role in landslide mitigation. However, shallow landslides frequently occur even in densely vegetated regions, suggesting that the influence of vegetation on gravity-driven erosion hazards remains incompletely understood. This study investigates the interactive effects of vegetation and key environmental factors—including rainfall, lithology, wind speed, and slope gradient—on landslide susceptibility in an area with substantial vegetation cover (≥65.5 %). At the watershed scale, we employed structural equation modeling and geographic detectors to assess the primary drivers of landslide susceptibility under high vegetation conditions. At the point scale, we calculated the stability coefficient of a representative landslide, accounting for both vegetation self-weight and artificial waste sediment. Our findings reveal that the combination of vegetation, rainfall, and wind speed significantly increases landslide susceptibility, as evidenced by a 21.3 % rise in high and very high susceptibility zones and a 42.7 % reduction in low and very low susceptibility zones. Interactions among multiple factors exerted a stronger influence than individual factors, with the most pronounced interaction observed between slope gradient and rainfall (Geodetector q = 0.81), followed by rainfall and lithology (q = 0.79). Under saturated conditions, the stabilizing effect of root systems was outweighed by the self-weight of tree vegetation, leading to a marked decrease in slope stability compared to scenarios without additional loading. These results offer new insights into the complex role of vegetation in landslide control and highlight the importance of considering interactive environmental effects at multiple spatial scales.