Root Strength in Some Populus and Salix Clones

The tensile strength of the roots of six Populus and Salix clones, and its relation to their anatomy and chemical composition, was investigated to assist selection of improved varieties for soil conservation planting. The amount of stele in the roots and its specific gravity were the most important factors determining tensile strength. Variation in specific gravity accounted for 79% of the intra‐clonal variation in the tensile strength of the stele, and was also correlated with inter‐clonal and seasonal variation. Fibre wall strength and specific tensile strength were correlated with S 2 microfibril angle intra‐clonally, cellulose content inter‐clonally, and the lignin/cellulose ratio seasonally. The load required to break the roots did not increase linearly with the diameter of the roots. The results show that, in future, tensile testing is not essential in the selection of clones with the strongest roots, because these can be identified from the amount of stele in their roots and its specific gravity.