ヒノキ人工林のリターフォールによる養分の還元について : 施肥と地位との影響

Abstract

約50年生のヒノキ林で, 地位の良否と施肥によるリターフォール量の変化を3年間にわたって調べた。またこのリターに含まれてそれぞれの林床へ還元された, チッ素, リン, カリウム, カルシウム, マグネシウムの5養分元素の量を測定した。その結果, 1) 各区のリターフォール量は3. 83 - 5. 26ton/ha・yrで, このうちヒノキの葉リターは約半分かそれ以上を占め, 1. 90 - 3. 27ton/ha・yrであった。2) このリターに含まれてそれぞれの林床へ還元された養分元素の量は, チッ素は27. 3 - 44. 5kg/ha・yr, リンは3. 0 - 5.0kg/ha・yr, カリウムは7. 0 - 15. 1kg/ha・yr, カルシウムは23. 7 - 35. 0kg/ha・yr, マグネシウムは3. 9 - 5. 6kg/ha・yrであった。3) ヒノキの落葉は11月にその大部分が集中した。このため各養分元素の還元もこの時期に集中したことになる。しかしこの時のヒノキの葉リター中のチッ素, リン, カリウムの含有率は比較的低い時期にあたるのに対し, カルシウム, マグネシウムはむしろ比較的高い時期にあたっていた。4) 還元された各養分元素を, リターの組成別にみると, どの養分元素もヒノキの葉がもっとも多く, 次いで枝, 球果とタネ, ヒノキ以外の樹種の葉, 樹皮, 虫のふん, 虫の遺体の順であった。5) リターフォール量とそれにともなう養分の還元量は, ヒノキ林に由来するリターだけでみると明らかに地位の良い調査区で多かった。6) 施肥の影響についてはまだ試験を始めてからの年数が浅いので, 現時点でははっきりとはわからなかった。しかし施肥によってヒノキの葉リター中のチッ素の含有率はやや増加しているように思われた。この問題については今後もこの試験を継続することによって明らかにしていきたい。

The amounts of litterfall and their contents of nutrient elements have been measured in about fifty years old Chamaecyparis obtusa stands at Tokuyama Experimental Forest Station of Kyoto University, located in Tokuyama city, Yamaguchi Pref. Four plots were set up in the studied stand at the end of Oct. 1974. Two of them were settled at the lower area of slope (A and B; good site) and the other two were at the upper area (C and D; poor site). After one year measurement of litterfall without fertilizer, the fertilizations to A and C plots were executed for four times on Nov. 1975, Mar. 1976, Oct. 1976 and Mar. 1977. Litterfall was assorted to leaves, branches, barks, cones and seeds, leaves of the other trees, insects, feces and the others. And the concentration of N, P, K, Ca and Mg were analyzed for every components. The results obtained throughout three years measurements are follows. 1) The annual amount of total litterfall for three years ranged from 3.83 to 5.26 ton/ha･yr, and that of leaf litter of Chamaecyparis obtusa ranged from 1.90 to 3.27ton/ha･yr. This accounts for about a half or more of total litters (Table 1 and 2). 2) The annual amounts of nutrient elements, contained in total litter were 27.3~44.5 kg/ha･yr for N, 3.0~5.0 kg/ha･yr for P, 7.0~15.1 kg/ha･yr for K, 23.7~35.0 kg/ha･yr for Ca and 3.9~5.6 kg/ha･yr for Mg respectively (Table 4). 3) The distinct peak of leaf litterfall was on late autumn, from Nov. to Jan. Consequently, the amount of each nutrient element was remarkably high into this season. The seasonal variation of each element concentration of litter was not so distinct except of N. The concentration of N was gradually increased from winter to summer and clearly decreased in autumn, when the leaf litterfall being peak (Fig. 1, 2 and 3). 4) The leaf litter of Chamaecyparis obtusa was the major parts of litter in the amount of dry matter and of nutrient element contents (Table 4). 5) The annual amounts of litterfall and the amounts of nutrients contained in litterfall were consistently higher in A and B plots than C and D plots throughout three years. However, there was no definite difference in the concentration of nutrient element between good site and poor site (Table 1, 2, 3 and 4). 6) The effect of fertilization on the amount of litterfall and the concentration of nutrient could not be detected. The concentration of N in the leaf litter of Chamaecyparis obtusa, however, seemed to be slightly increased in the 3rd year (Table 1, 2, 3 and 4). The effect will be clarified with the continuation of this experiment hereafter.