Soil reinforcement of tree roots is the main mechanical effect of shelter-forest on soil stability and slope protection, and the traction effect of lateral roots plays an important role in this concern in mountainous areas. The magnetite of this role rises positively with the tensile strength of the roots in the soil. This study developed a mechanical model of relationship between the tensile strength of roots and the traction effect used in pine forests. The results showed that the tensile strength of the pines mostly lays in a range of 5～25MPa, and decreased with diameter of the roots. In the depth interval of 0～60cm, the density of lateral roots of the three pines is relatively high, and the roots are able to increase the tensile strength of the rooted soil by 6 85～9 50 kPa, through traction effect. Though the strength of the pine roots and its role in increasing strength of the rooted soil are significant, the strength of the pines is lower than those of some broad leaved trees. This means that the pines have certain limitation on their role of shallow slope stability.
