森林における大型土壌動物の落葉粉砕と土壌耕耘に関する研究 : 1. 個体数・現存量と環境要因

Abstract

大型土壌動物をほぼ体長1mm以上になる動物とし, 線虫, ヒメミミズ, トビムシ, ダニ類はすべて除外し, 大型土壌動物の範囲を定め, 各種の森林および草地においてHand sorting法により50cm×50cmのクォドラートを数ヵ所設定し, 深さ30 - 80cmまで堀りとって, 大型土壌動物の種類組成・個体数・現存量を調べた。森林における土壌動物の役割を落葉・落枝の摂食・粉砕と土壌中を移動することによっての土壌と有機物の混合, 土壌の耕耘に大別し, それによっての土壌の性質の変化 (土壌に与える影響), 土壌の性質の変化にともなう動・植物への影響にまとめることができた。森林の土壌動物として出現してくる主要なものはミミズ, ヤスデ, イシムカデ, ジムカデ, クモ, コムカデ, アリ類で, この他ハネカクシ, コガネムシ, コメツキムシ, 双翅類なども共通して出現する。また, ヒメハマトビムシ, ダンゴムシ, ワラジムシ, ヒメフナムシ, カニムシ, ゴキブリ, シロアリ, セミ類などは温帯落葉広葉樹林や暖帯常緑広葉樹林では優占種であった。個体数・現存量は亜寒帯針葉樹林, 温帯落葉広葉樹林, 暖帯常緑広葉樹林の順に大きくなり, シイ・ツバキ林では個体数144 - 1432/m_2, 現存量49. 6 - 145. 0g/m_2の大きな値を示した。この個体数・現存量と温量指数との関係をみると, 温量指数に比例して大きな値を示し, マクロなスケールでみた場合, 土壌動物の個体数・現存量を支配する最も大きな環境要因は温度条件であると考えられる。しかし, 同一温度条件下でも最大値と最小値の較差は大きい。これをミクロな要因, 地域的な要因としてとらえてみると, 動物の季節的変動よりも, 地形のちがい, 地形のちがいに基づく植生, 土壌, とくに水分条件の影響が大きいと認められた。各種の森林においてA_o層量およびその平均分解率と現存量との関係をみると, 現存量の大きいところほど, 落葉の分解率の大きいことを示し, ミミズ類を主とする大型土壌動物の落葉分解への関与を間接に示した。

The faunistic composition, individual numbers and biomasses of soil macro animals exceeding 1 mm in body length excluding nematodes, enchytraeds, springtails and mites were investigated in various types of forests and grasslands in different environmental conditions. The collections of macro animals were carried out by hand sorting method. The important components encountered were mainly earthworms, millipedes, contipedes, spiders, symphyllas and ants. Further, staphylinids, maybeetles, wireworms, dipteran larvae were common in the all soils of the investigated forest vegetations. In deciduous borad leaved forests in warm temperate zone and in evergreen broad leaved forests in warm temperate zone, Orchestia platensis, Armadillidium vulgare, Porcellio scaber, Ligidium japonicum, false scorpions, termites and cicadas were dominant. On the other hand, they were found scarcely in coniferous forests in subarctic zone. The numbers and biomasses were the smallest in the subarctic coniferous forests and the largest in the warm evergreen borad leaved forests and the values in the deciduous broad leaved forests were between them. The largest value was recorded in the mixed forest of Castanopsis cuspidata and Cameria japonica, and it amounted to 144-1432 individuals /m2 and 49.6-145.0g/m2. They were composed mainly of earthworms. Because of the fact that the numbers and the biomasses increased in parallel with the index of warmth, the temperature seemed to be the most important factor effecting the values of the numbers and biomasses. Under the same temperature condition, the number and the biomass were larger at the bottom or lower part of slopes than at the upper part. Because the vegetations, properties of soil, water condition in soil etc. were closely related to the slopes or the topography, the number and the biomass of soil animals seemed to be affected by their conditions. As the numbers and biomasses of macro animals became larger in proportion to the average decomposition rate of leaf litter, the macro soil animals seemed to play an important role in breakdown of leaf litter.