林木の枝量とその生長量 (I)

Abstract

スギの林内被圧木 (サンプルNo. 1), 林内優勢木 (サンプルNo. 2), 孤立木 (サンプルNo. 3) の枝量とその材積生長量を, 主として個々の枝のもつ特性という観点から考察をこころみた。試料はいずれも京都大学農学部附属芦生演習林からえたもので, サワ谷試験林でNo. 1, No. 2を, 宮の森でNo. 3を1966年9月に伐倒した。樹冠内平均枝密度はNo. 1, No. 2, No. 3についてそれぞれ15. 9, 16. 4, 17. 9本/mであった。幹からの分枝位置と各枝の幹重は梢端から樹冠の下部へむかって増加するが, その増加は林内木にくらべ孤立木でいちぢるしい。葉重は林内木では樹冠の上部ですでに頭うちに達してしまう。F/Cはいずれも樹冠上部で4. 0に達する。3者にF/Cの分布にいちぢるしいちがいは, 特にない (図3)。葉重は枝重に対し実験式として拡張相対生長式であらわされる関係をもつことがみとめられるが, 上限値は試料木ごとにことなる (図4)。枝の基部直径と長さは, その直径の最小値, および長さの上限値の存在をおもわせるような関係がみとめられ, 長さの上限値がNo. 1, No. 2, No. 3について2. 0, 2. 2, 2. 9mとそれぞれ試算された (図5)。Specific Pipe Lengthは林内木, 孤立木について157, 211cmであった (図8)。皮なし枝材積の最近1年間の生長量は, 枝の材積に対し試料木ごとにことなった関係をしめした (図9)。枝の総材積生長量はNo. 1, No. 2, No. 3について, それぞれ365, 1918, 5849cm_3であり, 生長率は0. 23, 0. 21, 0. 22であった。

Three sample trees (suppressed, dominant, and open-grown) of Cryptomeria japonica D. Don were taken at Ashiu School Forest of Kyoto University, in September 1966, to investigate their branch dimensions and volume increments. Average branch density within the crown is estimated at 15.9, 16.4, and 17.9 per meter along the main stem, for suppressed, dominant, and open-grown trees, respectively. Branch wood dry weight (wBi) and branch bearing leaf-dry weight (wLi) increases as the distance to its branching point from the apex (H--HB) becomes longer, the increase is more remarkable in the open-grown tree than in the trees in the stand. Branch bearing leaf-dry weight (wLi) reaches its maximum value at the upper half of the crown. The ratio of the assimilating organ to the non-assimlating organ (F/C) attained its maximum of 4.0 in the upper part of the crown, and its distribution in the crown reveals no clear difference among the samples. The relations of branch bearing leaf-dry weight (wLi) to branch wood dry weight (wBi) are expressed by the extended allometric relationship (fig.4), each sample having an intrinsic asymptote. Branch length (LBi) and its diameter at the base just above butt (DBi) can also be expressed by a similar equation, having asymptotes of 2.0, 2.2, and 2.9 m for suppressed, dominant, and open-grown trees, respectively. Sample trees taken from the stand show a common specific pipe length of 157cm, while the open-grown sample is found to have a longer specific pipe length of 211cm (fig.8). Annual branch volumes without bark increments (△VBi) are plotted against the branch volume without bark (VBi) representing a characteristic trend among the samples (fig. 9). Total annual branch volume without bark increment of each tree is calculated at 365, 1918, 5849 cm3/yr. for suppressed, dominant, and open-grown trees, respectively, for which the rate of increment is 0.23, 0.21, and 0.22, these latter values could be considered to be of little significance.