Ecological Studies of Suzutake (Sasa borealis) (II)

前報では,1972年に殻蒐したスズタケの時期別刈払区の1975年までの結果について報告したが,さらに引続き個体生長･群落構成の調査をおこない,ほぼ12年間にわたる結果より次のようなことがわかった.i)成立稈数からみると,刈払処理後10年以上経過した段階でも,いずれの区も刈払前のレベルには回復せず,とくに7月刈払区は極端に低いレベルにあり,刈払とその時期は群落の回復に長期にわたって影響することがわかった.2)スズタケの群落を構成している稈のうち欠葉稈がかなりの割合を占め,その欠葉期間は比較的長いが再着葉することはなく,群落の再生産の面からはマイナスの存在である.3)稈の寿命を稈の本数変動より推定すると,最高寿命は発生後13年前後であり,群落を構成する稈の平均寿命は4～6年という値がえられた.4)稈高については,刈払処理区ではいずれも刈払前の稈高にくらべ極端に小さく,10～11生育期をすぎても刈払前の60～70%にも達せず,刈払効果が依然つづいていることを示している.また,根元直径では,刈払処理後発生数が比較的多い1月,4月刈払区が,無処理区にくらべかなり小さく,稈高,直径の面からみても刈払区の再生はまだ貧弱であるといえる.5)稈より直接分岐している一次枝は発生の当年か翌年に稈の先端5～6節のところに集中して分岐し,以後毎年1回前年枝より分岐するが,枝の分岐次数より稈齢を推定することは分岐次数が多くなるほど実績の稈齢との誤差が大きくなり不可能と思われる.6)稈の着葉数は,発生の翌年かそのつぎの年に最大に達する.着葉数は枝の分岐と密接に関連しており,枝の分岐が多くなると葉数もまた増加している.7)地下茎の伸長にも地上部の刈払処理が影響しており,とくに7･10月刈払区の地下茎の伸長は貧弱で,ばらばらに寸断された状態にあるのがみられ再生･回復はきわめて困難であることがうかがわれた.8)スズタケ自然群落は小集団をもつ集中分布を示すが,群落を構成する稈を発生年別にわけても,それぞれの集団は集中分布を示した.Cutting tests on Sasa borealis community have been carried out in 1972, and since then they are still under investigation; in the previous paper we dealt with the growth of Sasa community for four years from 1972 to 1975. In this paper we dealt with the results of the survey covering twelve years from 1972 to 1983. The summary of the results is as follows; 1) Ten years after cutting, culm density had not reached to its former level, especialy in July cutting plot. 2) Leafless culms took a part of Sasa community but they did not foliate any more, hence it is obvious that the existence of leafless culms is detrimental to Sasa community. 3) The culm life span estimated by culm number transition were 13 years at the maximum and 4-6 years on the average. 4) Culms in all cutting plots were shorter than non cutting plot. The average culm height of Sasa community after the lapse of ten or eleven growing seasons were 60-70％ of the height before the cutting. 5) Only once a year new branches of Sasa borealis bifurcates from the old branches, but the primary branches bifurcate directly from the upper part (5-6 nodes) of culm in the current or the next year of sprouting, and thereupon we investigated the relation between culm ages and branch bifurcation order. When it is young, culm age agreed approximately with branch bifurcation order but the discrepancy between culm age and branch bifucation order increased as it grew old. Accordingly we could conclude that it is quite difficult to estimate culm age by branch bifurcation order. 6) Leaves on one culm increase with bifurcation of branches and reach to the maximum in the next year or the year next after the sprouting. 7) In July and October cutting plots, the rhizome were underdeveloped and taken to pieces. As things stand, development of rhizome were seemed to be retarded. 8) It was observed that the distribution of culms by age group was identical to the community. From the above results, it becomes clear that the effect of cutting on Sasa borealis community stretches over a long period of time