How revegetation reinforces soil at early stage of restoration: A 6-year field study in southwest China

Background and aims: Restoring vegetation on hillslopes has been found to increase soil strength, thereby reducing the risk of soil erosion and shallow landslides. However, limited information is available on the temporal changes in root biomechanical traits and increased soil shear strength related to vegetation growth following restoration with different species. Methods: In 2012, Symplocos setchuensis, Buxus megistophylla, and Cynodon dactylon were replanted in a forest gap in Jinyun Mountain, Beibei District, China, and studied over a 6-year period. We measured root traits (root tensile strength, Young's modulus, cellulose content, and root density) and soil traits (cohesion and internal friction angle) at two soil depths (0-20 and 20-40 cm) for undisturbed and reconstituted samples. Results: S. setchuensis was found to have the highest tensile strength and resistance to failure for root diameters <2 mm. With elapsed time, tensile strength and cellulose content decreased. Cohesion and root mechanical reinforcement of topsoil generally increased with time (+10% per year). Root chemical and mechanical effects contributed approximately 50% to soil reinforcement. C. dactylon had the fastest growth rate and reinforced the topsoil soil rapidly, whereas S. setchuensis exhibited a consistent increase in soil reinforcement during the study period and provided more deep roots that could reinforce subsoil. Conclusion: Chemical and mechanical effects almost equally contributed to soil reinforcement. Although the relative contributions varied for different species, the variation in each contribution sheds new light on the sustainable use of vegetation for mitigating shallow landslides in mountainous areas.