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Loss Plateau of China is an area with long-term vegetation restoration while serious mass movements. Local vegetation does act as sediment reducing role while quantification of their effect on landslides is lacking. This work presents a first research work about the connection between landslides and vegetation by the example of July 25–26, 2013, extreme rainstorm. High-resolution sensing orthoimages, landside width, and simplified infinite slope theory were used to examine landslide distribution and the lateral apparent cohesion of roots. The results reveal that shallow landslides have a higher probability at the transitional slope area. The majority of them have a gradient of 20–25°, locate on south-facing slopes, and areas with sparse vegetation. Vegetation cover, represented by the Green-Red Vegetation Index (GRVI), is the controlling factor of landslide distribution and size. The estimated lateral apparent cohesion of plant roots is not positively related to GRVI, and increase when GRVI > 0.2. The relationship between landslide width and slope gradient indicates that strong root strength may result in larger landslide volume. This result of this work is a pioneering trial in correlating the lateral apparent cohesion from roots and forest crown, which is helpful for understanding the effect of vegetation on landslides. [ABSTRACT FROM AUTHOR]

Rainfall-induced shallow landslides and debris flows are one of the most common erosion process and primary channel initiation mechanisms in many steep landscapes. Their initiation conditions are physically controlled by the soil properties and topographically influenced by the competition between area- (A) and slope-dependent (S) sediment transport process. In this work, the A-S relationship of landslides in two forests was compared with respect to the physical properties of soil and plant roots. The results reveal that landslides in the Pinus tabuleaformis forest commonly have larger surface- and contributing area, deeper failure plane and gentler slope gradient than those in the Larix Kaemphferi forest. The saturated hydraulic conductivity in the Pinus tabuleaformis forest is higher and strongly correlates to plant root biomass. The effective cohesion and inner frictional angle of soil mass in the two forests are similar. Faster saturated hydraulic conductivity may lead to the higher upslope contributing area of landslides in the the Pinus tabuleaformis forest. A combination of finite-slope model and precipitation interception model reveals that landslides in the Pinus tabuleaformis forest require higher rainfall amount that those in the Larix Kaemphferi forest. Last but not least, this work provides a clue that strong root network and high saturated hydraulic conductivity may promote the A-S condition. [ABSTRACT FROM AUTHOR]

Plant roots positively and negatively contribute to hillslope stability by the perspective of soil strength and water flow infiltration improvement. To further examine the controversy, this work addresses the six root architecture types on the rainfall threshold for slope stability by tests of saturated conductivity and shear strength of the root-soil composite. An infinite slope model and a 1D flow model combine to obtain the rainfall intensity-duration threshold of slope failure. The results reveal that the saturated hydraulic conductivity of root-soil composite is 1 to 4.23 times of bare soil, which increases as the length density, volume density, and volume fractal dimension of plant roots. Furthermore, plant roots can enhance the cohesion and angle of internal friction by 35.19–81.79% and 12.92–42.36%, respectively. Finally, the R-type and V-type roots have the most effective root architecture for hillslope stability. In the process of afforestation, H-type may be suitable for areas with soft slope, while V-type and R-type may be suitable for steep slopes. The results of this work present an interesting study on the interaction of plant roots on slope stability, which is worthy of further study in the future. [ABSTRACT FROM AUTHOR]