Slope stability in vegetated hillslopes depends on groundwater, geometry, external loading, soil properties, and root reinforcement. This study evaluated a low-plasticity clayey silt (CL–ML) from Loja, Ecuador, under bare soil, Eucalyptus, Pine, Vetiver, and Kikuyu covers. Direct shear tests on root-containing specimens provided equivalent Mohr–Coulomb parameters for limit-equilibrium and PLAXIS 2D strength-reduction analyses considering three slope geometries and three loading conditions: elevated groundwater, groundwater plus an 8 kN m⁻² surcharge, and groundwater, surcharge, and pseudo-static loading. The resulting 90 factor-of-safety values were assessed using scenario-based factorial ANOVA and MANOVA. Geometry and loading explained 41.4% and 35.0% of total variance, respectively, whereas numerical method explained 1.1%. Limit-equilibrium factors of safety were 5.4% higher on average than PLAXIS 2D values. The vegetation-cover main effect was small and marginal (η² = 1.5%, p = 0.051), while significant cover–loading and cover–method interactions indicated a scenario- and method-dependent response. Under pseudo-static loading, Vetiver and Kikuyu showed the highest PLAXIS 2D factors of safety, whereas LEM results remained narrowly grouped, precluding a general ranking of vegetation effectiveness. These findings support scenario-specific evaluation of equivalent root reinforcement in slope-stabilization design.

Sustainable landslide hazard mitigation requires scenario-based assessment of nature-based solutions under realistic hydromechanical and multi-hazard conditions. This study evaluates the mechanical effect of Vetiver grass (Chrysopogon zizanioides) on slope stability in Loja, southern Ecuador, through an integrated framework combining geotechnical characterization, direct shear testing, finite element modelling, limit equilibrium analysis, and targeted statistical evaluation. Three fine-grained soils, classified as CH, MH, and ML, were analysed under baseline groundwater conditions, groundwater with an 8 kN/m² surcharge, and groundwater with surcharge plus pseudo-static seismic loading. Vetiver reinforcement increased apparent cohesion by 8.92–27.65% and internal friction angle by 6.90–17.43%, with the highest cohesion gain in ML soil. Numerical results showed that stabilization was controlled by soil type, slope geometry, loading condition, and interaction between the 2.0 m root-reinforced layer and the governing failure mechanism. Under surcharge loading, FS for ML at 0.5H:1V increased from 1.056 to 1.450. Under combined loading, FS increased from 0.217 to 1.440 for ML at 1H:1V and from 0.587 to 2.060 for CH at 1H:1V. Targeted ANOVA/MANOVA for MH soil confirmed the influence of geometry and combined loading. Therefore, Vetiver should be considered a complementary, site-specific, and risk-informed mitigation measure rather than a universal stabilization solution.