台風被害木の被害形態別モメ発生分布

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1991年の台風17，19号による30～41年生スギおよぴヒノキ人工林における被害木について，モメ発生分布を被害形態別に調査した．剥皮丸太の外周面に見られるモメは，湾曲木および折損木で著しく，地際付近から樹高の80％のところ付近まで，広い範囲に分布していた．モメの発生は，倒伏木と直立木では，湾曲木や折損木ほど顕著ではないが，やはり地際付近から樹高の60％のところ付近まで，広い範囲に分布していた．丸太横断面内のモメは，湾曲木と折損木の風下側を中心に，三日月状に分布していたが，倒伏木と直立木には殆ど見られなかった．したがって，挽板面におけるモメは，湾曲木，折損木の，特に風下側からの挽板に多く見られたが，倒伏木，直立木からの板面には殆ど見られなかった．また，簡易な計算式を用い，風圧により生じる樹幹高さ方向の応力分布を求め，林木の被害状況との対応を調査した．その結果，折損木の折損位置と応力分布のピーク位置がほぼ一致し，また，モメ発生分布との対応も確認された．これによって，モメの集中，ひいては折損が生じ易い位置推定の可能性が示唆された．In September 1991, the middle and northern districts of Kyushu Islaild were struck by typhoons, 9117 and 9119. Then, numerous sugi- and hinoki-planted stands had been damaged by the great wind. In the damaged trees from these forests, many partial compression failures(momes) in these stems were noticed, In this paper, the distribution of mome in the stem of each type of damaged trees, which ages were distributed from 30 to 41 years old, was investigated. On the surface of peeled log, many and severe momes in the logs cut from the bending and breaking trees were observed to be ranged widely on the stem from nearly base to about 80% of the height of the tree. Momes on the logs cut from the overturning and outwardly normal trees (upright trees) did not appear so terrible as these from bending and breaking trees. In the cross section, momes on the logs cut from the bending and breaking trees were distributed on the leeward of stem such as the crescent in shape, but these on the logs cut from the overturning and outwardly normal trees did not almost appear. On the same way, momes on the lumber cut from the bending and breaking trees appeared in a large amount, but these cut from the overturning and outwardly normal trees did not almost appear. The distributions of the bending stresses in the direction of the height of the stem were calculated by a simplified equation. And the relationships between these distributions of stress and damage condition of trees were investigated. In this result, the peak of stress in the stems of the breaking trees was nearly located at the same position as breaking points of the stems. In the same way, the distributions of momes in the stems of the damaged trees were similar to these of stresses in the stems. Therefore, it was suggested that the position of concentration of momes i, e. breaking point in the stem could be estimated.
九州大学の論文

台風被害木の被害形態別モメ発生分布

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