クロマツの生育におよぼす摘葉の影響

Abstract

林木の生育におよぼす食葉性害虫の影響を知るために, 各種の摘葉試験, 被害林 (木) の調査が数多く行なわれ, アカマツの生育とその異常な葉量減少との関係はほとんど明らかにされた。しかし, クロマツでは, その関係は推定の域をでていなかった。本報告は, クロマツの苗木を用いて, 1965年に時期別の摘葉試験を行ない, 摘葉後3年間の生育状況を調査し, アカマツでの結果と比較したものである。試験は京都大学農学部附属演習林本部苗畑で行なわれ, 試験開始時の供試クロマツの平均地際直径は15. 1mm, 平均苗高は46. 7cmで, 4月から10月まで各月下旬につぎの3摘葉処理を行なった。1. 旧葉摘葉 2. 新葉摘葉 3. 全葉摘葉 処理は葉鞘の部分を残してハサミで針葉を切断した。1968年2月に地上部の幹, 枝, 葉の重量と樹幹解析により幹生長経過を求めた。結果をまとめるとつぎのようになる。1) 8, 9, 10月の全葉摘葉木は, 全個体とも枯れた。これはアカマツと全く同じである。2) 旧葉摘葉は, 4月下旬の処理で, その年に摘葉の影響があらわれたほか, 摘葉はとくに生長に影響をおよぼさなかった。3) 樹高生長には, 摘葉の影響は処理の翌年に激しくあらわれ, 摘葉時期がおくれるほどその影響が大きかった。7月全葉摘葉で無摘葉木の生長率の28％, 新葉摘葉で56％と生長減退は大きい。4) 直径生長には, 摘葉後すぐにその影響があらわれ, 2年目もつづいて影響が強くあらわれた。全葉摘葉で, 5月処理のもの76％, 6月処理のもの50％, 7月処理のもの26％となった。5) クロマツは6月以後, 新葉が, 全部一度でもなくなれば, 3年後でも, なおその影響が残っている。また, 摘葉後3年間の生長率を無摘葉木のそれと比較すると, 生育期に新葉を摘むと45 - 80％と, 摘葉の時期に応じた生長減退をあらわした。6) 本調査クロマツの針葉の平均純同化率 (a), 非同化器官の平均呼吸率 (R) は a=2. 097 - 1. 257g/g・year R=0. 055g/g・yearと推定された。7) クロマツが摘葉によりうける影響は, アカマツの場合と非常によく一致し, クロマツが食葉性害虫の被害をうけた場合も, アカマツと同様な被害解析の方法を用いることが可能となった。

In order to know the effects of leaf-eating insects upon the growth of forest trees, many defoliation tests and damage-analysis of defoliated forest trees have been carried out, and consequently, as for Japanese red pine (Pinus densiflora), the relation between its growth and unusual decrease of needles has been almost explained. But the growth of Japanese black pine (Pinus thunbergii) infested with defoliator has not been explained. In this report, the author investigated the effects of artificial defoliation upon the growth of Japanese black pine on the nursery of Kyoto University Forest and compared its results with Japanese red pine. In April, 1965, Japanese black pine was 15.1 mm in diameter at the base and 46.7 cm in height in average. Four groups of five trees every month from April to October were subjected to various artificial defoliation tests. The needles were removed from the test trees with scissors in each group as follows: 1. removal of old needles only; 2. removal of new needles of the current year only; 3. removal of both the new needles of the current year and the old needles; and 4. removal of no needles on check trees. The test trees were cut down at the base in February, 1968. And the fresh weight of stem, branch and needle was measured respectively and the materials for stem analysis and for determination of dry-fresh weight ratio were sampled. The results obtained from this investigation were as follows: 1) All test trees defoliated new and old needles from August to October were withering like Japanese red pine. 2) The artificial defoliation of old needles only late in April had the influence upon the growth (diameter, height and volume) of Japanese black pine. That is, the growth rate was about 70% to that of check trees in diameter, height and stem volume respectively. In the next year of defoliation, the growth rate was similar to the normal. 3) The height growth of defoliated trees suffered less than the diameter growth in the treated year. In the next year, defoliation had the greatest influence upon the growth. 4) The artificial defoliation had the greatest influence upon the diameter growth both in the treated year and in the next. It seems that the later the defoliated month is, the less the growth becomes, namely, parallel growth rate in the next year was 76% (defoliation in May), 50% (June) and 26% (July) on defoliation of all needles respectively. 5) The growth of Japanese black pine which defoliated all new needles from June to October was smaller than that of non-defoliated trees in the third year after defoliation. 6) Parallel growth rate of Japanese black pine which defoliated new needles was 45 ~ 80% as compared with the normal growth rate for three years. 7) In case of this investigated Japanese black pine, it was estimated that mean net-assimilation rate of needles was 2.097 ~ 1.257 g/g･year and mean respiration rate of non-assimilation parts was 0.055 g/g･year. 8) Japanese black pine is quite like Japanese red pine on effects of artificial defoliation upon its growth. It seems that the damage-analysis can be applied to the investigation of Japanese black pine infested with leaf-eating insects just as in the case of Japanese red pine.