テーダマツ幼－壮齢林のリターフオールについて

Abstract

京都大学農学部附属演習林白浜試験地で, 植栽密度を3段階に変えて育てられているテーダマツ林 (P. taeda L.) のリターフォールを, 1968年5月から1981年4月 (林齢8年から20年) の13年間 (低密度 (A林分), 中密度 (B林分)) および1985年5月までの17年間 (高密度 (C林分)) にわたって調査した結果, 以下のことが明らかになった。テーダマツ林の年落葉量は, 3. 00-6. 47ton/ha・yr (A林分), 3, 23-7. 13ton/ha・yr (B林分), 3. 76-7. 95ton/ha・yr (C林分) で, うっ閉初期と思われる調査初期の落葉量がとくに多かった。落葉量は次第に減少し, 各林分とも, 1977年に最小となり, 以後, 再び増加の傾向を示している。落技量は, 217. 1-1, 239. 0kg/ha・yr (A林分), 292. 3-1, 838. 0kg/ha・yr (B林分), 367. 5-1, 404. 0kg/ha・yr (C林分) で, 林分の生育とともに増加している。とくに, 台風の通過で多量の落枝がみられた。雄花, 雌花, 球果, 種子の生殖器官は, 1973年まではみられなく, 以後, 次第に増加しているが, 多いC林分でも20kg/ha・yr前後で, 調査したテーダマツ林の結実は多くない。食葉性昆虫類の虫糞は, 27. 0-69. 0kg/ha・yr (A林分), 22. 7-64. 4kg/ha・yr (B林分), 24. 2-59. 5kg/ha・yr (C林分) で, 各林分とも似たような虫糞量を示し, 大きな年変動はみられない。隔年に発生するスジコガネの糞が年間量の50%に達した年もあった。昆虫類の死体は, 3林分とも大きな違いはなく, 0. 4-2. 6kg/ha・yrで非常にすくなかった。総リターフオールは, A林分は3. 90-6. 83ton/ha・yr (5. 28±0. 77ton/ha・yr), B林分は4. 44-7. 69ton/ha・yr (5. 82±1. 00ton/ha・yr), C林分は4. 53-8. 48ton/ha・yr (6. 44±0. 98ton/ha・yr) 高密度林分ほど総リターフオールは多かった。虫糞量から推定された食葉性昆虫類による被食量の49. 9-239. 7kg/ha・yrは, 落葉量の1-8%に相当し, 調査例の多くは3%以下で, 昆虫類の食害量は無視し得る量であった。

The annual and seasonal fluctuations of litter fall and the grazing loss of leaves by the herbivorous insects were investigated in three Loblolly pine, Pinus taeda L., stands at Sirahama Experiment Station of Kyoto University Forest, Wakayama prefecture. The study sites were three experimental stands of Loblolly pine which planted at 2, 500 (A stand), 5, 000 (B stand) and 10, 000 (C stand) trees per hectare in March, 1961. Mixed fertilizer which contains nitrogen (15), phosphorus (8) and potassium (8) had been manured 100 grams per a tree in each stand for three years after planting annually. Four traps (from April in 1968 to April in 1975), each having surface of one square meter (1.0 m×1.0 m) and five traps (from April in 1975 to April in 1985), each having surface of one fourth square meter (50 cm × 50 cm), were set up in each pine stand. Fallen litters in each trap were collected twelve times for a year of one month interval from April 21 in 1968 to April 20 in 1985. Collected litters were divided into the components by hand sorting, i.e. leaves, branches including bark and sexual organs of Loblolly pine, feces of herbivorous insects, dead bodies or residues of insects and others. Annual leaf litter were collected from 3.00 ton/ha･yr to 6.47 ton/ha･yr (A stand), 3.23-7.13 ton/ha･yr (B stand) and 3.76-7.95 ton/ha･yr (C stand), and in the early years of investigation, there were a great deal of leaf litter particularly. The amount of leaf litter was on the decrease yearly, and the minimum leaf litter was weighed in 1977 each stand. Annual branch litter were collected 217.1-1, 239.0 kg/ha･yr (A stand), 92.3-1, 838.0kg/ha･yr (B stand) and 367.5-1, 404.0 kg/ha･yr (C stand), branch fall tend to increase with the growth of Loblolly pine in each stand. Sexual organs collected were a little in each stand. The feces of the herbivorous insects were collected 27.0-69.0 kg/ha･yr (A stand), 22.7-64.4 kg/ha･yr (B stand) and 24.2-59.5 kg/ha･yr (C stand), the range of these annual fluctuations were narrow in each stand. The feces of the striated chafer occurred in every other year were sometimes equivalent to 50% of annual feces. Total litter falls were collected 3.90-6.83 ton/ha･yr (A stand, 5.28±0.77 ton/ha･yr in average), 4.44-7.69 ton/ha･yr (B stand, 5.82±1.00 ton/ha･yr) and 4.53-8.48 ton/ha･yr (C stand, 6.44±0.98 ton/ha･yr), total litter in C stand consisted of high density were large compared with A and B stand. The annual loss of canopies by grazing of the herbivorous insects were estimated 49.9-239.7 kg/ha･yr. These grazing losses were equivalent to 1-8% of annual leaf falls and were negligible to the growth of Loblolly pine stands. [Table omitted]