スギ高齢林における広葉樹による樹幹への傷被害

概要

論文の詳細を見る
We examined stem wounds of sugi(Cryptomeria/aρoηlca) trees induced by understory broad-leaved trees in an 100-year-old stand in Soo-city, Kagoshima Prefecture.The investigation was conducted in four plots with different thinning in-tensity in the past (i.e.,heavy-, moderate-,light-thinned and unthinned). The objectives of our study are to examine thedamage ratio of sugi stem(i.e., ratio of wounded stems to total stems)and the pattern of wounds (height, length), and to examine size characteristics of broad-leaved species that damaged sugi stem. Stem wounds were caused by contact of branch and trunk of under storybroad-leaved trees with sugi stem. The damage ratio differed by the four plots and was affected by stem density of broad-leaved species. We found high damageratio in moderate-thinned(damage ratio was 13.6%) and Iight-thinned (11.6%)plots, compared to heavy-thinned (7.0%) and unthinned (5.3%) plots. The height above the ground of wounded part ranged from 2m to 16m. The average length of wound was 65cm, which was larger than the diameters of branch and trunk of broad-leaved trees, indicating that strong wind blowing in the stand might enlarge wound length. We found six broad-leaved species damaging sugi stem,for example, Ficuserecta, Machilusjaponica, Cinnamomum tenuifolium. The size of damage-inducing tree was more than 6cm in dbh and more than 7m in height. Our results indicated that the past thinning in old-agedstands, which might introduce and develop broad-leaved trees, would induce stem wounds of planted tree. From the viewpoint of timber production, our results also suggested that big broad-leavedtrees (i.e., more than 6cm in dbh and more than 7m in height) should be removed from the forest floor to avoid damage of stem wounds in old-aged plantation, especially in strong wind area.鈴木寿仁・竹内郁雄・寺岡行雄・吉田茂二郎,スギ高齢林における広葉樹による樹幹への傷被害鹿児島県曽於市財部町にある高齢スギ人工林(102年生)で,下層広葉樹の幹や枝と接触することにより生じたスギ樹幹の傷被害を調査した。調査林分は,過去の間伐強度が異なる無間伐,弱度,中度,強度区の4つに設定されている。傷被害は,樹皮が剥がれ,木質部が露出しているものと定義した。受傷したスギの本数被害率は無間伐,弱度,中度,強度区の順で5.3,13.6,11.6,7.0%であった。下層広葉樹の密度が高いと本数被害率が増加する傾向がみられた。下層広葉樹全29種のうち,加害した広葉樹はイヌビワ,ホソバタブ,ヤブニッケイなど6樹種で,胸高直径の最小値は6.2cm,樹高の最小値は6.9mであった。傷の地上高を示す傷高は2から16mで,傷の垂直方向の長さを示す傷長の平均値は65cmと,接触している広葉樹の幹や枝の直径より大きかった。強風により幹や枝が上下に擦れて断続的に接触し,傷が広がったと考えられた。台風や季節風などの強風にさらされる地形条件のスギ高齢林内で広葉樹を混交させる場合は,高齢林から生産される大径材が傷被害により経済的価値を損ねないためにも,広葉樹の生育を直径6～7cm,樹高を7m以下にすることが必要であることが示唆された。
2010-03-01

スギ高齢林における広葉樹による樹幹への傷被害

スポンサーリンク

概要

著者

関連論文

スポンサーリンク