Slope instability along forest roads exacerbates soil erosion and ecosystem degradation, presenting a persistent challenge for sustainable forest management and ecological restoration. This study provides a quantitative assessment of an integrated bio-structural stabilization system composed of terracing, brushwood beams, and soil reinforcement by roots using black alder ( Alnus glutinosa (L.) Gaertn.) seedlings. The evaluation combines field measurements with numerical modeling based on the Limit Equilibrium Method (LEM). Results demonstrate a clear, stepwise improvement in stability conditions: the untreated slope exhibited marginal stability with a Factor of Safety of 1.12, which increased to 1.54 with terracing, to 1.76 with brushwood beams, and to 1.89 with soil reinforcement by roots alone. The fully integrated system achieved the highest stability (Factor of Safety of 2.14), indicating strong synergistic interactions among its structural and biological components. Sensitivity analysis identified soil cohesion as the dominant factor governing stability, while geometric and reinforcement-related parameters produced secondary but meaningful effects. Geometric assessments emphasized the critical influence of terrace configuration, showing that lower terrace heights (0.35–0.42 m) significantly enhanced the mechanical performance of brushwood beams. Soil reinforcement by roots increased soil cohesion within the upper soil layer by 1.91–4.63 kPa. In the integrated system, the depth of the critical slip surface was reduced from 4.1 m to 2.1 m, effectively shifting the failure mechanism from a deep-seated to a shallow slip mode. Correlation analyses further confirmed that narrower terraces combined with optimized riser heights maximized overall reinforcement efficiency. Collectively, the findings establish a validated and transferable framework for designing sustainable, bioengineered slope stabilization systems. Machine-learning forecasts indicate a critical transition period of four to five years, during which timely maintenance is essential to bridge the gap between brushwood-beam decay and root-system maturation, thereby ensuring long-term slope stability. • Terracing, brushwood, and roots significantly enhance slope stability along forest roads. • Terrace geometry influences brushwood mechanical behavior and biological reinforcement effectiveness. • The combined stabilization measures alter the dominant failure mechanism from deep-seated to shallow slip surfaces, resulting in enhanced controllability and safety. • Machine learning reveals a critical 4–5 year stability transition due to brushwood decay and root growth.
Nasiri et al. (Mon,) studied this question.
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