ストローブマツ林の12年間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上賀茂試験地で育てられているストローブマツ (P. srobus L.) 林のリターフォールを1978年から1989年 (林齢16年から27年) の12年間に亘って調査した結果, 以下のことが明らかになった。ストローブマツ林の平均年落葉量は4. 92ton/ha・y (3. 78 - 5. 87ton/ha・y) で, その50 - 70%が10月と11月に落葉している。葉鞘量の年変動はすくなく, 268. 4kg/ha・y (238. 0 - 297. 7kg/ha・y) で, 針葉の伸長が終了した8月以後に落下し, 8月と9月で, 年間量の71 - 89%が, 10月を加えると88 - 98%の量が落下している。落枝量は105. 1 - 785. 6kg/ha・yで, 年々増加の傾向にある。雄花, 雌花, 球果, 種子の生殖器官は17. 2 - 482. 1kg/ha・yで, 樹齢にともなう球果の結実量の増加が落下量に反映し, 年々増加の傾向にある。食葉性昆虫類の虫糞量は70. 5 - 272. 8kg/ha・y, 平均して137. 6kg/ha・yで, 大きな年変動はみられなかった。昆虫類の死体は1. 3 - 5. 2kg/ha・yで, 非常にすくなかった。総リターフォール量は6. 13ton/ha・y (5. 19 - 7. 02ton/ha・y) であった。虫糞量から推定された食葉性昆虫類の食害量の130 - 500kg/ha・yは, 落葉量の3 - 10%で, 昆虫類による被害量は微々たるものであった。

The annual and seasonal fluctuations of litter fall and the grazing loss of leaves by the herbivorous insects were investigated in an eastern white pine, Pinus strobus L., stand at Kamigamo Experiment Station of Kyoto University Forest, Kyoto City. The study site was an artificial experimental stand of eastern white pine which was planted at about 2, 500 trees per hectare in 1962. Five traps, each haveing surface of one fourth square meter (50cm×50cm), were set up about ninety centimeter above the ground of the pine stand. Fallen litters in the traps were collected twelve times for a year of one month interval from January in 1978 to December in 1989. Colected litters were divided into the components by hand sorting, i.e. leaves, leaf sheath, branches and sexual organs of eastern white pine, feces of herbivorous insects, dead bodies or residues of insects and others. Annual leaf litter were collected from 3.78ton/ha to 5.87ton/ha, and leaf-falls was 4.92±0.59ton/ha･y in arerage. The leaf falls in October and November were accounted for 50~70% to its total annual leaf litter. Annual branch-falls ranged from 105.1~785.6kg/ha･y and sexual organs collected were 17.2~482.1kg/ha･y. The both falls of branch and sexual organ tend to increase with the growth of eastern white pine. The feces of the herbivorous insects collected were 70.5 ~272.8kg/ha･y, 137.6±52.2kg/ha･y in average. These feces were much a little than the feces obtained in various healthy forest. But these values were seemed to be ordinary level in the pine stands. The annual fall of insect residues weighed were 1.3~5.2kg/ha･y. Total litter fall collected by the traps were summed up 5.19 ~7.02ton/ha･y, 6.13ton/ha･y in average. The amount of annual feeding leaves by the herbivorous insects was estimated at about 120~460kg/ha･y and damaged leaves was estimated at bout 130 ~500kg/ha･y. The grazing losses were equivalent to 3 ~10% of annual leaf-falls and were negligible to the growth of eastern white pine.