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

Authors: ZHU, JINQI - Nanchang University; WANG, YUJIE - Beijing Forestry University; ZHENG, BOFU - Nanchang University; Langendoen, Eddy; WANG, YUNQI - Beijing Forestry University

Submitted to: Journal of Plant Nutrition and Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2024
Publication Date: 4/30/2024
Citation: Zhu, J., Wang, Y., Zheng, B., Langendoen, E.J., Wang, Y. 2024. How revegetation reinforces soil at early stage of restoration: A 6-year field study in southwest China. Journal of Plant Nutrition and Soil Science. 187: 274-286. https://onlinelibrary.wiley.com/doi/full/10.1002/jpln.202300236.

Interpretive Summary: Vegetation is an environment-friendly method to stabilize hill slopes by providing additional soil strength through its root system. However, limited information is available how the growth of vegetation following restoration with different species affects soil strength. Scientists at the USDA, ARS, National Sedimentation Laboratory in collaboration with researchers at Beijing Forestry University, China have investigated the change in root strength and soil reinforcement of trees (Symplocos setchuensis Brand), shrubs (Buxus megistophylla), and grasses (Cynodon dactylon) that are species used for afforestation in southwest China. In the early stages of plant growth, the grasses provided a stronger mechanical soil stabilization effect to shallow soil layers more quickly than the trees and shrubs. However, the consistent root growth of the trees and shrubs provided a stronger and deeper mechanical soil stabilization effect over time. The findings can be used by hydraulic and agricultural engineers when evaluating bio-engineered slope stability measures.

Technical Abstract: Background and aims: Restoring vegetation on hillslopes has been found to increase soil strength, thereby reducing the risk for 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 six-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 horizons (0 to 20 cm and 20 to 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, while S. setchuensis exhibited a consistent increase in soil reinforcement during the study period and provided more deep roots which could reinforce subsoil. Conclusion: Chemical and mechanical effects almost equally contributed to soil reinforcement. While 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.