Generation of radial growth stresses in the big rays of konara oak trees

In previous models the distribution of radial tensile stresses in the tree trunk has been explained as a response to the mechanisms of growth stress generation in the longitudinal and tangential directions. We investigated the contribution of ray tissue to growth stress generation in the tree trunk by the origin of the radial stresses during differentiation of parenchyma cells. Measurements on three konara oak trees (Quercus serrata Thunb.) were carried out comparing the radial residual strain of big oak rays with the radial residual strain of the axial tissues (containing only uniseriate rays). The results indicated that the ray tissue generated tensile growth stress in the radial direction of the trunk (the axial direction of the parenchyma cells). In contrast to previous assumptions, the growth stresses seem to be variable in relation to the individual tissue types. The mechanical advantage of a radially prestraining effect of the rays is discussed for the living tree.