あて材を考慮した樹枝モデルの力学応答

抄録

Trees in nature have many branches so that the leaves growing at the ends of the branches can receive a sufficient amount of sunlight. Furthermore, it is presumed that the tree branch autonomously forms a mechanically optimal structure in order to distribute stress almost uniformly over the branch. Reaction wood is one of the primary organs that seems to contribute to the realization of such a mechanically optimal structure. It is abnormal woody portion that develops at the base of the branches in response to gravity and the growth environment inducing mechanical stresses in the tree. The position where the reaction wood is formed depends on the tree species. In general, conifers have compression wood just below the base of the branches, and the broad-leaf trees have tension wood right above the base. To obtain a better understanding of the tree’s structural optimization mechanism, we have theoretically scrutinized the correlation between the spatial distribution of reaction-wood-related material parameters (mass density, Young’s modulus, etc.) and the mechanical response (bending stress, deflection curve, etc.) of the branches. In particular, we have explored the effect of the positional difference in the formation of reaction wood on the loading condition that suffices to realize uniform stress distribution.