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風倒被害を軽減するトドマツ・カラマツ人工林の管理指針
浦田, 格;渋谷, 正人;鳥田, 宏行
Permalink : http://hdl.handle.net/2115/52011
KEYWORDS : 管理指針;形状比;風倒;林分密度管理図;management guideline;slenderness ratio;stand density-control diagram;windthrow
Abstract
北海道中央部の支笏湖周辺の平坦地に位置するトドマツ人工林とカラマツ人工林を対象に、林分の平均形状比を用いて、風倒被害を軽減するための林分管理指針を検討した。林分調査データと、各樹種の林分密度管理図を利用して、平均形状比－平均樹高関係を収量比数（Ry）ごとに求め、それらと調査林分の平均形状比を比較した。その結果、両樹種で、風倒被害林分と無被害林分でRy値に差があり、被害林分でRy値が大きかった。境界値はトドマツでRy=0.7で、カラマツでRy=0.4であった。この結果と林分密度管理図によって、風倒被害を軽減するための林分管理指針を、樹種ごとに検討した。その管理指針によれば、風倒被害を軽減するためには若齢時からの密度管理が重要であり、またトドマツ、カラマツ人工林の一般的な疎仕立て管理よりさらに低密度での管理が必要であることが明らかとなった。さらに調査対象地域は風害を受けやすい地域であるため、本研究で検討した管理指針は、北海道の他地域の平坦地にも適用可能であろうと考えられた。
We examined management guidelines for reducing windthrow damage in Abies sachalinensis and Larix kaempferi plantations located near Lake Shikotsuko in central Hokkaido, Japan, based on mean slenderness ratios of the plantations. The mean slenderness ratio-mean height relationships of the two species were determined from stand inventories and stand density-control diagrams, using the relative yield index (Ry), and the mean slenderness ratios of the plantations were compared to these relationships. For both species, differences in Ry were observed between windthrown and intact plantations, and the Ry of windthrown plantations was larger than that of intact plantations. The threshold of Ry between windthrown and intact plantations was 0.7 for A. sachalinensis and 0.4 for L. kaempferi. We prepared management guidelines for reducing windthrow damage for both species based on the thresholds, using stand density-control diagrams. Density control of young plantations is necessary to reduce windthrow damage, and stands must obviously be maintained at a lower density than the general guidelines for the sparse management of A. sachalinensis and L. kaempferi plantations. Because the plantations investigated were in a region that is vulnerable to windthrow damage, the management guidelines established in this study should be applicable to other regions of Hokkaido.
We examined management guidelines for reducing windthrow damage in Abies sachalinensis and Larix kaempferi plantations located near Lake Shikotsuko in central Hokkaido, Japan, based on mean slenderness ratios of the plantations. The mean slenderness ratio-mean height relationships of the two species were determined from stand inventories and stand density-control diagrams, using the relative yield index (Ry), and the mean slenderness ratios of the plantations were compared to these relationships. For both species, differences in Ry were observed between windthrown and intact plantations, and the Ry of windthrown plantations was larger than that of intact plantations. The threshold of Ry between windthrown and intact plantations was 0.7 for A. sachalinensis and 0.4 for L. kaempferi. We prepared management guidelines for reducing windthrow damage for both species based on the thresholds, using stand density-control diagrams. Density control of young plantations is necessary to reduce windthrow damage, and stands must obviously be maintained at a lower density than the general guidelines for the sparse management of A. sachalinensis and L. kaempferi plantations. Because the plantations investigated were in a region that is vulnerable to windthrow damage, the management guidelines established in this study should be applicable to other regions of Hokkaido.
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