Abstract:Reinforcement by tree roots is the most effective mechanical process effecting soil stability and slope protection in shelter-forests. In mountainous areas particularly, traction of lateral roots plays an important role in this regard. The importance of this effect rises positively with the roots’tensile strength. This study developed a mechanical model of the relationship between the tensile strength and the traction effect of roots. The model was tested in a Pinus-Cyclobalanopsis forest. The results show that the tensile strength of the Pinus and Cyclobalanopsis roots were 30-5 MPa and 40-10 MPa respectively, and increased negatively with root diameter. In the 0-60 cm layer, the density of lateral roots of the two tree species was relatively high and the roots are able to increase the tensile strength of the rooted soil by 6.85-12.41 kPa, through their traction effect. Though the strength of the pine’s roots and its role in increasing strength of the rooted soil are significant, the root strength of the Pinus is lower than that of Cyclobalanopsis and other broad leaved trees.