| 概要 |
九州大学粕屋地方演習林における六演習林スギ品種試験地第Ⅰ試験他に植栽されているスギ6品種について，1991年台風19号による被害を報告するとともに，台風被害に対する抵抗性と感受性について分析し，これによる品種間の比較が行われた．試験地の総被害率は46．1％で，3タイプに区分された被害形態のうち，「曲がり・傾き」が最も高い割合を示していた．品種別に見ると，クモトオシ，ヤブクグリが60％以上，オビアカ...，ヤイチが40～50％，メアサ，アヤスギが30％以下の被害率であった．クモトオシでは「幹折れ」の割合が高く，「曲がり・傾き」の割合が高かった他の品種とは異なっていた．他のスギ林における品種別被害率と被害形態についての比較を行ったところ，クモトオシが「幹折れ」しやすいこと，メアサの被害率が比較的低いことが共通した傾向として認められた．しかし，他の品種については明かな傾向は認められなかった．樹木サイズと被害率の関係については，平均胸高直径が大きい品種ほど被害率が嵩まる傾向が見られた．また胸高直径階別の被害率は，品種により異なった傾向が認められた．品種の台風害に対する抵抗性を比較するために，間接環境傾度による立地環境および台風強度の評価がなされた．間接環境傾度は各区画の被害率をもとに算出され，6品種の平均的な抵抗性を持つ仮想の品種を，本試験地全面に植栽した場合の推定被害率を意味していた．この間接環境傾度と実際の被害率の関係を各品種ごとに一次の回帰式で示すことによって，品種の持つ台風害感受性が回帰式の傾きによって評価された．感受性は品種によって異なり，ヤイチで最も高く，クモトオシで最も低い感受性を示した．メアサとオビアカ，ヤブクグリとアヤスギの感受性は類似しており，これらについては回帰式の切片の大小によって抵抗性を評価することができた．しかし，感受性の異なる品種間において，環境の変化を考慮せずに，実際の被害率のみにより抵抗性を比較することは不可能であることが示された．以上の結果から，異なる林分で被害率による品種の序列を比較した場合，共通した傾向を抽出し難いのは，林分によって台風強度や立地環境の差異が存在することと，品種による感受性の違いが影響している可能性が示唆された．
We investigated wind damage to Sugi (Cryptomeria japonica D. Don) cultivars at the experimental stite No. 1 in the Kasuya forest of Kyushu University. Many trees at this site were damaged by Typhoon 19 in 1991. We analyzed and discussed the resistivity and sensitivity of six cultivars to wind damage caused by typhoons. Damage rate was 46.1% to all trees at this site, and the rate of bent or slanted trees was higher than for other kinds of damage. Six cultivars were divided into three groups on the basis of damage rate. Kumotooshi and Yabukuguri suffered more than 60% damage, Measa and Ayasugi less than 30% and the other two culivars, Obiaka and Yaichi, from 40 to 50%. Concerning the percentage of damage categories, trunk-breakage was prominant in Kumotooshi, and the rate of bent and slanted trees was highest in the other five cultivars. In comparison with the percentage of various damage categories in other Sugi stands damaged by the same typhoon, there were only two common tendencies - trunks of Kumotooshi were broken easily, and the damage rate in Measa was lower. However, other cultivars showed different resistivity at each stand. In relation to tree size, the damage rate of each cultivar tended to increase as mean DBH increased. The distribution of damage rate in the DBH class showed different patterns for each cultivar. To compare the resistivity of each cultivar to wind damage, environmental factors at this site were measured using indirect gradient. The value of indirect gradient at the division on the intersection at the i-th line and the j-th row was calculated as the square root of the product of mean damage rate at the i-th line and the j-th row. These values indicate the assumptive damage rate, if one hypothetical cultivar with the mean resistivity of six cultivars was grown over whole site. Therefore this value indirectly expresses the difference in environmental conditions between each division. The slope of regression line between indirect gradient and actual damage rate indicates the sensitivity of each cultivar. The sensitivity of each cultivar was different. Yaich was most sensitive, but Kumotooshi was not sensitive. Measa had a similar sensitivity to Obiaka, and Yabukuguri to Ayasugi. Therefore, resistivity to wind damage could be compared between Measa and Obiaka, and between Yabukuguri and Ayasugi. But it was impossible to compare Yaichi and Kumotooshi with other cultivars. In many Sugi stands, it was difficult to identify a common tendency in resistivity, not only due to the environmental conditions of stands but also because there were differences in the sensitivity of the cultivars.続きを見る
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