Stiffness of wood in fast-grown plantation softwoods: the influence of microfibril angle.

In fast-grown softwoods, there are very large changes in the longitudinnal Young's modulus of wood going outward from the pith. Typically, stiffness increases by a factor of 3 to 5 during the first 30 years of growth. A change in the microfibril angle of the S2 layer of the tracheid wall is the only mechanism that has been proposed that can account for this. There appear to be sufficient variations in microfibril angle between trees to justify selection of clones to yield stiffer timber