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材質を表わす指標として幹材容積密度,晩材率および年輪内の容積密度分布パターンなどの年輪構造について,スギ在来品種や精英樹クローン間の変異を調べた.供試木は,同一条件で植栽,管理されている六演習林共同スギ品種試験地の中から3演習林で採取した在来の6品種,および6演習林に植栽された25の精英樹クローンで,いずれも供試木は,植栽後12～13年生で若い.年輪構造の解析は,軟X線･デンシトメータ法によりおこ...なった.まず,品種をもちいて容積密度の樹幹内の高さ,髄からの年輪数ないし距離の違いによる変動を調べた結果,髄周囲の年輪内の密度は大きく樹皮側に向かい減少し不安定であったが,外周の数年輪はかなり安定した値を示し,また,胸高部位の測定値のみで,幹全体の容積密度の傾向が把握できることが明らかとなった.品種においては,平均密度,晩材率ともにアヤスギおよびヤブクグリが大きく.オビアカは小さい値を示した.両者の特性値とも年輪幅の増加にともなって減少する傾向がみられた.これは品種のもつ生長特性(年輪幅)の違いの反映に過ぎないと考えられるが,共分散分析によって年輪幅の影響を除外した修正平均値においても有意な差がみられた.年輪内の容積密度の変化には,品種固有の特徴があり,アヤスギ,ヤブクグリは,早材形成初期から次第に密度が増加するが,オビアカなどの品種は,最低密度を持続し,急に晩材化する傾向がみられた.この変化パターンをべき乗式に当てはめ,その係数bの値でくらべる方法を提案し,品種間で比較した結果, 品種間で有意な差がみられた.精英樹25クローンについても同様であったが,同一の在来品種に同定されているクローン間の年輪構造の違いは小さくその他のクローンと区別でき,品種で調べたことと矛盾しないことが明らかとなった.
In order to investigate the wood quality variation of Cryptomeria japonica, bulk density, late wood ratio, and the distribution pattern of bulk density within annual ring were determined using the soft X-ray and densitometric method for 6 native cultivars and 25 clones of plus trees selected in Kyushu, The test trees were obtained from the experimental areas of C. japonica cultivars, which had been established 6 different location in Kyushu in a same experimental design and had been treated homogeneously. Although the ages of trees were young (12 or 13 years after plantation), it is considered to be able to compare the clonal difference using those several outer annual rings at breast height which showed rather stable variation of wood density and the mean was representative of the whole trunk. Cultivars Ayasugi and Yabukuguri showed the greatest bulk density and latewood ratio among the native cultivars, while Obiaka showed the smallest. The values of the both characteristics were decreased accompanied with an increase of ring width. Although the clonal difference of the characteristics seemingly resulted form the clonal difference of the annual ring growth, it was clarified that even after an exclusion of the dependence on annual ring width using the covariance analysis, the corrected mean of bulk density and latewood ratio were still significantly different among some cultivars. The distribution pattern of bulk density within an annual ring was specific to the cultivar, that is, Obiaka and Ayasugi increased the bulk density in the beginning of the early wood formation, whereas Obiaka maintained the lower density as same as the minimum density within early wood and increased drastically to latewood. To compare the pattern obtained from all annual density among cultivars, a simple model was suggested to express the curve of the pattern and the coefficiant b of power function could indicate the pattern difference. The b values were significantly different among some cultivars, Almost same results were obtained for the 25 clones of plus trees. 15 out of 25 clones were reportedly identified as equivalent to each of 7 native cultivars, and their tendencies of bulk density and latewood ratio were similar to the identified cultivars, It is suggested that the tree breeding for faster radial growth and higher wood density at the same time might be possible for C. japonica.続きを見る
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