Does Bark-Decortication for <i>Hiwada</i> Production Change Mechanical Properties of Xylem in <i>Chamaecyparis obtusa</i>?

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  • 檜皮採取によりヒノキ材の木部性質は変わるか
  • ヒワダ サイシュ ニ ヨリ ヒノキザイ ノ モクブ セイシツ ワ カワル カ

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Taking Hiwada bark for roof plates from Japanese cypress, (Hinoki, Chamaecyparis obtusa), is sustainable because the cambium zone is carefully left without damage by traditional technicians (Motokawa-shi). This study aimed to clarify whether bark decortication for Hiwada changes the mechanical properties of the wood of the decorticated tree, focusing on changes in Young's modulus and cellulose microfibril angle (MFA) in the secondary cell wall of tracheids. Several pairs of Japanese cypress trees, planted in similar environmental conditions and aged > 69 years, were carefully selected. One tree of each pair was decorticated, and the other (control) was left without any treatment. In order to remove the variability at each cell level, serial sections having the same mother cells were collected by sampling along the radial direction. The Young's modulus and MFA of the specimens were tested and the measured values were averaged for each annual ring. Then, five to nine annual rings each before and after decortication, and their changes over time were compared to the control, and the impact of decortication itself was discussed and investigated. In order to remove individual variability, we suggested the value of v=(Xn-Xn-1)/Σ|(Xn-Xn-1)|, where Xn and Xn-1 are the measured values of current and previous years, respectively. The value Xn-Xn-1 represents the level of change in the year. Individual variability was removed by dividing by Σ|(Xn-Xn-1)|. The difference in v of the decorticated and untreated trees was plotted for each annual ring, but a conspicuous change was absent for both Young's modulus and MFA. These findings indicate that the xylem part was not affected by Hiwada decortication any more than by the usual climate impact. The Hiwada decortication by master technicians therefore does not affect the wood properties.

Journal

  • Mokuzai Gakkaishi

    Mokuzai Gakkaishi 61 (1), 25-32, 2015

    The Japan Wood Research Society

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