Root biomechanical properties during establishment of woody perennials

Background and aims: Soil bio-engineering using vegetation is an environmentally friendly solution to stabilise soil slopes. This study investigates tensile strength, Young’s modulus, and root diameter relationships for establishing woody perennials.Methods: Specimens of ten woody European shrubs and small trees were transplanted into sandy loam soil to establish for six months. Root tensile strength and Young’s modulus were measured as well as the root length-diameter distribution. The effect of root water status on root diameter was evaluated for Scotch Broom.Results: More than half of the root length for all species was thinner than 0.5 mm diameter. Typical tensile strengths were <40 MPa, with Young’s modulus <600 MPa. Negative power relationships between root strength and root diameter existed only for Gorse and Spindle, whilst Blackthorn, European Box and Holly showed slight increase in tensile strength with diameter. Hawthorn, Hazel and Privet showed rapid initial increase in strength with diameter followed by strength decrease with diameter, post-peak. Young’s modulus was linearly related to tensile strength for all ten species (P<0.001; R2 values 17% to 64%). Root diameter, investigated for Scotch Broom, depended strongly on root water potential and root water content by mass). Root water content could influence considerably the calculations of tensile strength.Discussion and conclusion: Root strength-diameter relationships often do not follow a negative power law, and depends strongly on taxa. Young’s modulus was strongly related to tensile strength of roots for certain species. Water status of roots strongly influences root diameter and hence strength and Young’s modulus properties, and must be controlled carefully in experiments.