Assessing spatial changes of roots tensile strength of Salix purpurea L. in riparian zone of Karun (Case study: Susan plain in Khuzestan province)

Vegetation in riparian areas, including trees with various hydrological and mechanical effects has an essential role in soil reinforcement. This is accomplished by increasing soil shear strength and inhibiting the higher layer of soil into the lower layers and reducing erosion by roots. The aim of this study was to evaluate the tensile strength changes of Salix purpurea L. trees in different trunk distances and soil depths. Therefore, five trees were randomly selected for root system sampling, which was done by using the soil core technique. Sampling was taken in three different depths, tree horizontal distances and in four directions of the trees. Finally, 97 successful tensile tests were performed on root samples. The relations between tensile force- diameter and tensile strength-diameter were analyzed and compered. The results showed the average of tensile strength of 57.91, 46.96 and 46.27 Mpa for depths 0-10, 10-20 and 20-30 cm, respectively. Furthermore, the average of tensile strength was 29.18, 76.81 and 28.78 Mpa for 0.5, 0.75 and 1 m distances, respectively. Root diameter and tensile force fallowed positive power and exponential trends. However, the association between root diameter and tensile strength followed a negative power trend. Results of Wald test showed no significant difference between tensile strength of three soil depths and three horizontal distances, though root diameter as a covariate parameter with a significant effect on tensile strength.