ヒノキ人工林とタブ天然生林のリターフォールについて

Abstract

約50年生のヒノキ人工林で地位と施肥によるリターフォール量の変化をしらべた。2ヵ年のリターフォール量は地位のよいA, B区で年, haあたり4. 66 - 5. 26ton, 地位の劣るC, D区で3. 83 - 4. 70tonであった。このうち, ヒノキの葉リターはおよそl/2ないしそれ以上を占め, A, B区で2. 50 - 3. 26ton, C, D区で1. 90 - 2. 46tonで, 地位のよい区で多かった。しかし, ヒノキ林のリターフォールは年によって変化があるから, もう少し, 測定を継続する必要がある。ヒノキの落葉は秋季に集中するが, 第1年次は12月に集中し, 第2年次は11月から1月に分散しており, 秋季の落葉のおこり方にも年変化がうかがえる。施肥のリターフォール量への効果は, 本測定期間では明らかでなかった。天然生タブ林の中で生長の劣るT-1区と生長のよいT-2区のリターフォール量は2ヵ年の平均で, 年, haあたりT-1区で7. 78ton, T-2区で6. 32tonで, ヒノキ林より多かったが, 地位との関係は明らかでなかった。落葉は秋季のほかに春季にもピークがみられ, 第1年次は9月にも台風による落葉のピークがあった。葉リターは全リターの65 - 73％を占めたから, リターフォールの季節変化はヒノキ林とやや異なって, 秋季への集中の傾向が弱められているようである。

The change of the amount of dry matter of litterfall with site quality and fertilization was studied in Forestry experimental station of Kyoto University at Tokuyama. The studied stands were about fifty years old Chamaecyparis obtusa forest and natural ever green broad leaved forest in which Machilus thunbergii is dominant. Four plots were set up in Chamaecyparis obtusa forest. Two of them were located on lower slope (A and B) and another two were on upper slope (C and D). The site quality was higher in the former two plots (A, B) than the latter two (C, D). The measurement of litterfall had started on Nov. 1974 and it carried out over two years. Fertilization were performed on A and C plot after one year had past. The effect of fertilization to litterfall was indistinct. This may due to shortage of period after fertilization. The amounts of litterfall of Chamaecyparis obtusa stands were 4.66 ~ 5.26 ton/ha･yr in A and B plot, and 3.83 ~ 4.70 ton/ha･yr in C and D plot. The amounts of leaf litter of Chamaecyparis obtusa which took about half or more of total litter, were accounted to 2.50 ~ 3.26 ton/ha･yr in A and B plot and 1.90 ~ 2.46 ton/ha･yr in C and D plot. The present result implies that the amount of litterfall was higher in good site than in poor site, however, it should be continued the measurement to be able to make mention of the relationship between litterfall and site quality, because considerably wide range of yearly variation of litterfall was reported in Chamaecyparis obtusa forest. The peak of leaf-litterfall was on autumn, from Oct. to Dec. In the first year, the amount of leaf-litter in Nov. was conspicuously higher than the other months, while in the second year, the peak of leaf-litterall extended over three months, from Oct. to Dec.. There would be yearly variation in the seasonal change of leaf-litterfall. Two plots were set up in Machilus thunbergii forest. T-1 plot was located on upper slope and T-2 plot was on lower slope. Tree hight was higher in T-2 than T-1, while density and basal area were lower in T-2 than T-1. The amounts of litterfall were 7.78 and 6.32 ton/ha･yr for T-1 and T-2, respectively, and there was no significant correlation between site quality and the amount of litterfall in these two plots. Two peaks of leaf-litterfall were observed; one was in late spring, Apr. and May, and another was in late autumn, from Sep. to Nov.. In the first year there was another one more peak in Aug. due to typhoon. The litterfall in Machilus thunbergii forest was not concentrated in late autumn as compared with Chamaecyparis obtusa forest, and it extended over growing season, though there was some monthly fluctuation.