母竹の皆伐が新竹の発生、成長および地下茎の成長におよぼす影響

Abstract

本試験は母竹の役割を明らかにするため, 京都大学上賀茂育種試験地のマダケ (Phyllostachys reticulata C. Koch) 林において, 6月下旬のタケノコの伸長中, および2月, 8月, 11月の三期に母竹 (全生立竹) を皆伐して, その後の影響を調査した｡ その結果を要約すれば次のとおりである｡ I. タケノコの伸長中における母竹の皆伐試験の結果母竹を皆伐したのは6月下旬であるが, その当時に発生伸長中のものと, その後に発生したものとの新竹の全竹稈生重量は, 皆伐前年1カ年の発生竹に対して51.2%減少し, 本数においては20%の減少が認められた｡ しかし, このうち, 皆伐当時にすでに伸長中であつたタケノコは, 母竹の皆伐によつて一時的に成長が低下したが, やがて正常な成長経過を示して, 母竹の皆伐によるいちぢるしい影響をうけないが, 皆伐後に発生したタケノコは, 伸長をつづけながらも萎縮状態となつて, ササのような極端に細小なものとなつた｡ 母竹の皆伐を行つた翌年に発生した新竹は, 本数においては皆伐前年の発生竹に対して約1.3倍に増加し, 全竹稈生重量でも39%の増加を示した｡ しかし, その稈の直径についてみると, 皆伐前年の発生竹よりも20%以下に細り, いちぢるしい低下を示し, 母竹の皆伐による影響をつよくうけていた｡ 母竹を皆伐した当年に成長した地下茎の伸長量は, 皆伐前年の伸長量に対して62%減少し, 皆伐翌年の伸長量においてはやや伸長量を増しているが, なお20%の減少が認められた｡ II. 新竹の成長完成後における時期別皆伐試験の結果母竹の皆伐当年に発生した新竹と, 皆伐時に立竹していた母竹とを比較すると, 8月の皆伐が最も大きい影響をうけ, 2月および11月の皆伐はその影響が比較的に少なかつた｡ その内容をみると, 本数については, 2月と11月皆伐区では約1.1倍に増え, 8月皆伐区では1.3倍にも増えていたが, 稈の大きさはいちぢるしく細小となつていた｡ すなわち, 直径 (根元), 竹稈長などは2月と11月皆伐区では約40%低下し, 8月皆伐区は約50%低下していた｡ したがつて, 竹稈1本当りの生重量については, 皆伐後に発生した新竹は皆伐前の生立竹 (母竹) に比べて, 2月および11月皆伐区では約70%も低下し, さらに8月皆伐区にあつては, その影響を最もつよくうけて82%にも低下していた｡ 母竹の皆伐後に伸長した新らしい地下茎についても, 8月皆伐区が他の2区に比べて, 最もつよく影響をうけていた｡ すなわち, 8月皆伐区においては, 新らしく伸長した地下茎が地表に向つて伸長し, さらに地上にあらわれて細小な実竹となつたものが多数みられた｡ しかも, 地下茎の伸長量についても8月皆伐区が最も劣り, 皆伐前年の伸長量に比べて, わずかに9%であつた｡ しかし, 11月と2月の皆伐区に比べるとやや良好な伸長を示していたが, それでもなお, 皆伐前年の伸長量に比べて約半減していた｡ この地下茎の伸長低下は, やがて新竹の発生にもわるい影響があらわれるものと思われる｡

In order to make clear the function and the action of mature culms, the whole standing culms of the groves of Phllostachys reticulata C. Koch were cut in the elongating season of sprouts at the end of June and besides in the three seasons of February, August and November in Kamigamo Breeding Experimental Forest Station of Kyoto University and it has been investigated the influences after clear cutting. The results are as follows: I. Results on the experiment of clear cutting of mature culms except the growing shoots in the elongating season of sprouts. The mature culms were wholly cut at the end of June. It was found that the total fresh weight of new culms developed in the same year of clear cutting decreased 51.2%, and also the numbers of new culms decreased 20% for the culms developed in one year before clear cutting. The daily elongation was lowered temporarily in 2-3 days after clear cutting, but shortly recovered its normal growth. It was supposed that the clear cutting of all mature culms had no affect on the elongating sprouts. But the new culms developed after clear cutting showed withering state in the elongation and matured in very slender culms as Sasa. The numbers of new culms developed in the next year after clear cutting, showed the increment of about 1.3 times, and the total fresh weight of them increased 39%, but the diameter of them decreased 20% lower than that of the culms before clear cutting. These decline of new culms was caused by the influence of clear cutting of mature culms. The elongation amounts of new rhizomes grown in the same year of clear cutting, decreased 62% compared with the amounts of rhizomes before the cutting, and also the growth amounts of new rhizomes of next year after the clear cutting decreased 20% in comparison with that bofore the clear cutting. II. Results on the experiment of seasonal clear cutting after complete growth of the new culms. Seasons of the clear cutting of all culms were three times of February, August and November. New culms developed in one growth season after clear cutting, were mostly affected in the August plot as compared with the February and the November plots. Numbers of the new culms increased about 1.1 times in the February and the November plots and about 1.3 times in the August plot for the numbers of mature culms before clear cuting. However the new culms of every plots grew remarkably slender, Namely both of the diameter and the length of new culms showed the declines of 40% in the February and the November plots and 50% in the August plot. Therefore the fresh weight of one new culm developed after clear cutting of the February and the November plots, decreased 70% as compared with that of a culm before clear cutting, especially that of the August plot showed the reduction of 82% by the mighty influence of clear cutting. The growth of the new rhizomes after clear cutting of all culms, was mostly affected in the August plot compared with other plots. In the August plot, it was numerously found that new rhizomes grew up the ground and became into slender culms (Jitchiku; solid culm, ) and also the elongation amounts of new rhizomes in the August plot were most inferior among these plots. Namely, it has shown only 9% in comparison with the amounts of one year before the clear cutting, and the growth of new rhizomes in the February and the November plots showed a little better results than the August plot, but they were reduced by half of that before clear cutting. It is inevitable that the growth reductions of the new rhizomes should give bad affects to develop the new culms in the several years.