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この研究は，同一施業条件下で生育したスギ品種内の木材性質のバラツキを明らかにすることを目的とした．すなわち，アヤスギ，クモトオシ，メアサ，ヤブクグリのスギ4品種を対象に，樹幹胸高部において，髄から5年輪間隔で5年輪にまたがる容積密度数，髄から5年輪目と10年輪目の晩材仮道管長，および樹幹を四つ割りにした試験片の縦圧縮強さの測定を行い，それらの品種内バラツキを検討した．容積密度数は品種および樹幹半径...方向の部位によって異なるが，そのバラツキの程度はどの品種においても横断面内の部位間に大差はない．なお，胸高部位において髄から最外年輪にまたがる容積密度数の変動係数は，3．3～8．8％の範囲に分布し，さらに容積密度数のバラツキは各品種とも晩材率に大きな影響を受けていた．同一品種の同山年輪における晩材仮道管長の変動係数は，品種間と年輪間とに大きな違いはなく，4．6～9．2％の範囲にあり，品種内の晩材仮道管長のバラツキは小さいと推定された．縦圧縮強さは品種によって異なり，その変動係数は品種間に著しい違いが認められなかった．なお，縦圧縮強さのバラツキには，容積密度数のバラツキが大きく影響していた．生育地が異なるとき，容積密度数や縦圧縮強さに生育地間の違いが認められる品種と，ほとんど差異が認められない品種とが存在した．縦圧縮強さと胸高直径との間に，負の相関関係が認められる品種と認められない品種があった．つまり，同一樹齢の林木において，胸高直径を肥大生長の速さの指標とするとき，肥大生長の速さが縦圧縮強さのバラツキに影響を及ぼす品種と，ほとんど影響を及ぼさない品種とが存在する可能性を示唆している．
The purpose of this study is to clarify the variation of the morphological and mechanical properties of sugi (Cytptomeria japonica) cultivars. The sample trees analized were collected in six stands located in six different distincts, which were established for growth test and managed in same way. The data on sample trees were shown in Table 1. The results of this study were summarized as follows ; 1) The basic density of sugi cultivar was inherent chararcteristics. The basic density in all cultivars decreased outward from the pith at a given stem level. The basic density variation within a cultivar were no large differences among cultivars and in the radial direction of the tree stem. The coefficients of variation within a cultivar were 3.3 to 8.8% at a given stem level and the variation was mainly affected by the differences of latewood percentage among trees. 2) The latewood-tracheid lengths at the 5th and 10th annual ring from the pith were inherent characteristics, respectively. No remarkable differences in the latewood-tracheid length variation were found among cultivars and between the 5th and 10th annual ring from the pith. The coefficients of variation within a cultivar ranged from 4.6 to 9.2% at the 5th and 10th annual ring from pith. 3) The compressive strengths parallel to the grain depended on cultivars, and the coefficients of variation within a cultivar were about 10% or less. The variation was mainly affected by the differences of basic density among trees. 4) There were the significant differences among six stands in the basic density and compressive strength properties of cv. Measa. 5) The growth rate of cultivars was correlated negatively with compressive strength except for cv. Kumotooshi and cv. Measa. 6) The basic density and compressive strength variations which were obtained from whole stands were slightly larger than those of a stand.続きを見る
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