壮齢のヒノキ人工林のリターフォール量におよぼす地位と施肥の影響について

Abstract

50年生のヒノキ人工林で地位と施肥の影響によるリターフォール量の変化を調べた。調査は地位のよい所に隣接してA, B区を, 地位の劣る所に隣接してC, D区を設けた。試験当初の1年間は全区とも施肥は行なわず, 2年目に入った時にこのうちのA, C区に施肥した。計11年間にわたってリターフォール量を調べた結果, 全リターの年間落下量はA, B区で3. 31 - 5. 53 t ha_-1y_-1, C, D区で2. 83 - 4. 85 t ha_-1y_-1, 4調査区を通じては2. 83 - 5. 53 t ha_-1y_-1の間にあった。このうちヒノキの葉リターはおよそ全体の60 - 75％を占め, A, B区で2. 33 - 3. 69 t ha_-1y_-1, C, D区で1. 70 - 3. 20 t ha_-1y_-1, 4調査区を通じては1. 70 - 3. 69 t ha_-1y_-1の間にあった。このように地位の劣るC, D区は地位のよいA, B区に比べて明らかに少ないことが認められた。また施肥したA, C区は無施肥のB, D区に比べて, 施肥後1 - 2年間はヒノキの葉リター量への施肥の影響はみられなかったが, 施肥後3年目位から無施肥区に対して増加しているのが認められた。この傾向は施肥後10年目までもある程度続いていたが, この両区の差が最も大きかったのは施肥後4 - 6年位であった。

The changes of the rates of litterfall in relation with site quality and fertilization were studied in about fifty years old stands of Chamaecyparis obtusa at Tokuyama Experimental Forest Station of Kyoto University, located in Tokuyama City, Yamaguchi Prefecture. Four plots were set up in the studied stand (Oct. 21 1974) : Two plots (A, B) were on good site and the other two plots (C, D) were on poor site. Fertilizer was applied for A and C plots on the second and third year, and the litterfall was measured for 11 years. Fertilization was carried out four times, from Nov. 1975 to March 1977. The amount of nutrient elements for each fertilization plot was as follows: 100kg/ha for N, 44kg/ha for P and 52kg/ha for K respectively. 1)The annual rate of litterfall varried from year to year. The ratios of the highest rate to the lowest for all the plots were as follows: 2.0 for total litterfall, 2.2 for leaf litterfall of Chamaecyparis obtusa, 3.3 for branch and twig litterfall, 11 for corn and seed litterfall, 5.5 for bark litterfall, and 11 for insect feces litterfall respectively. The yearly variation was wide for corn and seed litterfall, for insect feces litterfall, and for insect body litterfall. 2)There was no definite difference in the trend of the yearly change of the annual rate of leaf litterfall among four plots (Fig. 1). 3)The monthly rate of leaf litterfall was highest in autumn season, though the rate in autumn season varried from year to year. However, there was no definite difference in the trend of the seasonal change of leaf litterfall among four plots for each year (Fig. 8). 4)The annual rate of total litterfall for the four plots ranged from 2.83 to 5.53 t ha-1 y-1 (Table 1). There is no clear difference in the rate of litterfall as compared to the rates of litterfall in various Chamaecyparis obtusa stands which have heen reported so far. While, the rate was lower than that of the Machilus thunbergii stands (5.78~7.79 t ha-1 y-1) growing in the same study area of Tokuyama Experimental Forest Station. The rate of leaf litterfall ranged from 1.70~3.69 t ha-1 y-1, that covered 60~75% of the total litterfall (Table 1 and Fig. 1). 5)The rate of leaf litterfall changed depending on the site condition. The rate of litterfall for B plot (good site, control) was higher than that for D plot (poor, control). And the rate for A plot (good site, fertilized) was high as compared to that for C plot (poor, fertilized). This indicates that the rate of litterfall is high for good site and low for poor site (Fig. 1 and Table 2). 6)There was no effect of ferilization for two years after fertilized. However, the rate of litterfall, particularly the leaf litterfall increased from the third year after fertilized to the tenth for A plot and C plot as compared to B and D plots respectively (Fig. 1 and Table 3). And this increase of the rate of litterfall would be attributable to the fertilization.