カラマツ造林木から得られた丸太の未成熟材率

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九州大学北海道演習林内のカラマツ材を対象に，人工造林木の未成熟材率に関する研究を行った．その結果，つぎのことが明らかになった．1）同一林分内における材積未成熟材率について，平均値と変動係数値を得た．すなわち，41年生のとき，未成熟材率ほ，全幹材で46％，元玉で34％，2番玉で舶％であった．しかし，そのバラツキは同山林分内の結果にもかかわらず大きかった．なお，1玉の長さは4mである．2）樹齢15年生から41年生までのとき，樹齢の増加にともなう未成熟材率およびそのパラツキの変化を示す図を得た．その結果，未成熟材率には伐期齢の関与が大きいことを認めた．3）立木の胸高直径だけで未成熟材率を推定することは，難しいことがわかった．4）樹幹のどの部位からの丸太であっても，丸太末口に含まれる年輪数で未成熟材率が推定できることが明らかとなり，推定のための実験式が得られた．5）カラマツ材の未成熟材率は，生育地，間伐強さおよび間伐時の樹齢，伐期齢によって，大きな影響をうけることが明らかになった．Karamatsu (Larix Leptolepis) is one of the principal planting species in Japan and has a welldeserved reputation for rapid growth. However karamatsu trees have a high content of juvenile wood like other first-grown softwoods. The purpose of this study is to clarify the variation in juvenile wood percentages in logs from karamatsu planted trees. The results of this study are summarized as follows ; 1) As shown in Table 1, juvenile wood percentage values of whole tree stem, butt logs and second logs within a 41-year-old stand were 46%, 34% and 44%, respectively. The coefficients of variation in each were 14%, 16% and 15%, respectively. The variability in juvenile wood percentage among logs was very large. 2) As shown in Fig. 2, the proportion of juvenile wood in whole tree stems, butt logs and second logs decreased with tree age. A significant relationship was found between cutting age and juvenile wood percentages in logs. 3) It is difficult to estimate the juvenile wood percentage at breast height diameter, as shown in Fig. 3. 4) There were no significant differences among the averaged percentages of juvenile wood area at various height levels, except 0.3m height level above ground (Fig. 4). A regression equation was obtained to predict the juvenile wood percentage from growth ring number from pith. 5) The variation among logs within a stand is smaller than among stands. It became clear that the site difference and thinning greatly affected juvenile wood percentage of karamatsu logs as shown in Fig. 5 and Fig. 6. Further studies concerning the effect of silvicultural practices, cutting age and site on log quality are necessary.
九州大学の論文

カラマツ造林木から得られた丸太の未成熟材率

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