Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 25, 2025 - November 29, 2025
Bark is a tissue that transports and stores assimilated substances, provides ventilation, and protects the tree body. It is formed by cell division in the cork cambium and peels off at the surface accompanied by cracks. However, how the bark cracks and peels off varies depending on the tree species, resulting in characteristic patterns such as vertical cracks, horizontal cracks, and delamination. Therefore, bark patterns are also used to identify tree species as important visual information.
However, the mechanism that produces bark patterns is not understood. For example, vertical cracks, which are the most typical bark pattern seen in Japanese cedars, are known to be formed when dead tissues, such as the outer bark and cork tissue, are pulled in the tangential direction by the thickening growth of the trunk and break in the axial direction. On the other hand, although previous studies have been conducted, there have been few studies on the mechanism of bark pattern formation other than vertical cracks, and they remain largely unexplored.
In this study, to explain the mechanism of various bark pattern formation, a physical model was constructed. The deformation of bark in a cross-section and the mechanical properties and mechanical state of bark tissue were considered. As a result, it became clear that bark patterns are determined by the competition between three characteristic parameters: (i) trunk growth, (ii) change in natural length of the bark, and (iii) change in spontaneous curvature of the bark.
This study demonstrated the possibility of a unified explanation of the mechanism by which diverse bark patterns are formed in terms of the competition between several parameters. Furthermore, it is expected that the findings of this study can be utilized to reproduce the changes in bark patterns throughout a tree's life, from young trees to aged trees.
