Variations of the mechanical properties of Acer saccharum roots

Longitudinal and transverse variations in the compressive strength sigma(c) and stiffness measured in bending and torsion (E and G, respectively) were determined for wood samples removed from three old lateral: roots of a lar ge sugar maple Acer saccharum L, whose canopy had been heavily pruned on on e side such that the three roots had loading conditions assumed to be domin ated by different stresses: tensile stresses along the axis of root I, comp ressive stresses along root III, and torsional shear stresses in root II. Values of sigma(c), E, and G tended to decrease from the base toward the ti p of each root, but maximized at approximately Im from the base (perhaps as a consequence of fibre fatigue near the base of the root system). Comparis ons between the mechanical properties of wood sampled from the upper and lo wer root surfaces showed that the wood along the lower surface of roots I a nd II was stiffer and stronger; the reverse was found for root III. Longitudinal variations in the geometry and size of root transections resul ted in a curvilinear pattern of root taper; maximum taper occurred at appro ximate to 1 m from each root base. These variations, which resulted in long itudinal changes in the second moment of area I and the polar second moment of area J, were sufficient to mask the effects of longitudinal variations in E and G on the flexural and torsional rigidity of roots (El and GJ, resp ectively) both of which decreased exponentially away from the base of the t ree. Based on the correlations observed between the stresses presumed to dominat e the loading conditions of each of the three roots and the mechanical prop erties of wood samples, it appears that the 'biomechanical plasticity' of w oody roots holds the potential to maximize the individual ability of roots to cope with the dominant stresses attending their growth and development.