“…Wu (1976) and Wu et al (1979) pioneered a model that was applied in numerous studies for the assessment of how roots contribute to soil shear reinforcement. The impact of root reinforcement on soil is generally expressed as an increase in soil cohesion (Borroughs and Thomas, 1977;Wu et al, 1979;Wu, 1984a, b;Sidle et al, 1985;Sidle, 1992;Wu and Sidle, 1995;Abernethy and Rutherford, 2001;Stokes et al, 2008. A number of factors influence the tensile strength test: species, season, age, soil compaction, deformation of roots, soil and root moisture, root preservation, field or lab test, type and size of testing equipment, root clamping procedure, test speed, and rate of elongation (Rienstenberg, 1994;Cofie and Koolen, 2001;Fan and Su, 2008).…”