Root anchorage of Vitex negundo L. on rocky slopes under different weathering degrees

In southwestern China, Vitex negundo L. has been widely applied on rocky slopes for slope eco-engineering (SEE). This work studied the anchorage mechanism of root system of 8-year-old V. negundo L. plants on severely, moderately, or weakly weathered rocky slopes through a pullout experiment with winch. On severely and moderately weathered rocky slopes, more secondary laterals embedded in the rock cracks enabled higher anchorage resistance of plants than that on weakly weathered rocky slope. On the weakly weathered rocky slopes, however, the less embedded roots led to poorer anchorage function of plants. On severely and moderately weathered rocky slopes, the secondary laterals embedded in the rock cracks contributed mostly to anchorage. At failure of anchorage, the upslope secondary laterals in the cracks were broken while the downslope ones kept intact. It was concluded that the anchorage resistance had a close relationship to the weathering degree of rock mass and the distribution of secondary laterals.