生育開始前の全摘葉がアカマツの生育におよぼす影響

Abstract

アカマツがマツカレハに食害された場合の生育におよぼす影響を知るために, 今までに数多くの試験が, アカマツの生育期に摘葉し, 実施されたが, 生育開始前の摘葉試験はみあたらない。本報告は, 京都大学農学部附属演習林本部苗畑に植えられていた満5年生アカマツを材料として, その生育開始前および生育初期に全摘葉を行ない, その後の生育にどのような影響をあたえるかを調査し, とりまとめたものである。試験を1963年より始め, 3月15日 (試験I) および4月18日 (試験II) に摘葉し, 前者は, 葉鞘もろとも手でむしり取る"むしり"と葉鞘の部分を残してハサミで切断する"切断"の2方法を用い, 後者は"むしり"のみの処理をした。さらに1964年1月18日に"むしり"の処理を実施した (試験III)。摘葉強度はいずれの試験も100%摘葉であった。測定は1965年に, 最終的に地上部について行ない, 樹幹解析により摘葉後の生育経過を調べた。調査の結果をまとめると次のようになる。1) 生育開始前の1月下旬よりその初期の4月中旬までに, アカマツは全摘葉されても, 枯れることはまれのようである。すなわち, 試験Iでは2摘葉方法とも, 供試木19本中, 枯死は1本, 試験IIIでは25本中2本枯死した。試験IIは15本全部が生育を続けた。2) 摘葉の影響は, 直径, 樹高, 林積生長ともに, 処理した年に最も大きくあらわれた。摘葉した年には処理木は, 直径生長は無摘葉木の1/10も生長していない (試験I, III)。生育初期の摘葉 (試験II) では, 生長量は25％であつた。樹高生長は, 直径生長がうけたほど大きな影響をうけず, 無摘葉木の生長量に比べ, 約40% (試験I), 約75％ (試験II), 26％ (試験III) であった。すなわち, 早い時期に摘葉されたものほど, その影響は大きかった。材積生長は, 試験Iで無摘葉木の約8％, 試験IIで約29％, 試験IIIで約8％であった。3) 1965年12月の皮なし材積を比較すると, 無摘葉木は2046cm_3で, 試験Iの"切断"で723cm_3, "むしり"で732cm_3, 試験IIで992cm_3, 試験IIIで661cm_3と大きな差があらわれた。4) 摘葉後2年目以後は, 摘葉木は樹勢を比較的早く回復したようである。すなわち, 生長量は無摘葉木に比べてすくなかった (皮なし材積で2年目は, 試験I : 33％ (切断), 34％ (むしり), 試験II : 48％, 試験III : 26％, 3年目は, 試験I : 36％ (切断), 33％ (むしり), 試験II : 46％) が, 生長率の回復を樹勢の回復と考えるならば, 試験IIでは, 2年目ですでに回復し, 3年目では試験Iも回復していた。すなわち, 生育最盛期の摘葉に比べて, 本試験のように, 生育の旺盛な若いアカマツを生育開始前およびその初期に, たとえ100％摘葉しても, 影響は2年目までのようである。5) アカマツ針葉の平均純同化率, 非同化器官の平均呼吸率は, それぞれ a = 2.829 - 1.594g/g・year, R = 0.055g/g・year となり, 以前に苗畑に生育した幼令アカマツで推定したそれらの値と一致した。

It is well-known that leaves of forest trees have a great influence upon the growth of trees. There are many reports on the investigation into the effects of artificial defoliation in a growing period upon the growth of Japanese red pine (Pinus densiflora S. et Z.), but we can not find the studies on artificial defoliation before growing period. In this report, the author investigated the effects of artificial defoliation before growing period upon the growth of Japanese red pine. These investigations were carried out in the nursery of Kyoto University Forest from 1963 to 1965. The treatments of artificial defoliation were practiced on Mar. 15 (Ex. I) and on Apr. 18 (Ex. II) in 1963, and on Jan. 28 in 1964 (Ex. III). These treatments were 100%-defoliation by picking the leaves in each case, and in Ex. I leaf-cutting with scissors leaving the part of leaf-sheath (6 ~ 7mm) was added. In December, 1965, five non-defoliated red pine and twenty-six defoliated trees (leaf-cutting in Ex. I, seven, picking, four, in Ex. II, seven, in Ex. III, eight) were cut on ground level. Each part of stem, branch and leaf was measured in fresh weight in gr. and materials for stem analysis and dry weight were gathered. The results obtained from these investigations were as follows: 1. The number of the withering of these defoliated trees was only one among nineteen in each case of the two techniques of defoliation in Ex. I, and two among twenty-five in Ex. III. In Ex. II, any of fifteen defoliated trees did not wither. Namely, it seems that many Japanese red pine will continue to grow without withering, in case of 100%-defoliation performed between the end of January and the beginning of April. 2. These artificial defoliations had the greatest influences upon the growth (of diameter, height and volume) of Japanese red pine in the treated year. That is, as to the diameter growth, the defoliated trees in Ex. I and Ex. III had grown less than 10% of the normal growth, and growth in Ex. II was about 25% as compared with the normal in the year. The height growth of defoliated trees sufferred smaller influence than the diameter growth. These were about 40% (Ex. I) or the normal, about 75% (Ex. II) and about 26% (Ex. III) in the year. Namely, it seems that the earlier the defoliated period is, the less the height growth in the year becomes. Similarly, on the growth of stem volume, these were about 8% (Ex. I), about 29% (Ex. II) and about 8% (Ex. III). In December, 1965, the stem volume without bark was 2046 cm3 at non-defoliated tree, 723cm3 (leaf-cutting in Ex. I), 732cm3 (picking in Ex. I), 992cm3 (Ex. II) and 661cm3 (Ex. III). The above number shows the considerable difference between the stem of defoliated tree and the normal. 3. The growth of stem volume of defoliated trees measured either two or three years after the defoliation was less than the normal (two years after treatment, about 33% in Ex. I-leaf-cutting, about 34% in picking, Ex. II: 48% and Ex. III: 26%, and three years after, 36%: Ex. I-leaf-cutting, 33%: picking and 46%: Ex. II), but growth percentage of defoliated trees was almost the same as the normal two years after in Ex. II and three years after in Ex. I. Namely, it seems that even if 100%-defoliation is practiced before growing period, its effects will continue for only two years. 4. In case of these investigated red pines, mean net-assimilation rate of leaves was 2.829~1.594 g/g･year and mean respiration rate of non-assimilation parts was 0.055 g/g･year. And these were the same values that the author, in the past, estimated with saplings of red pine in the nursery.