Characteristics of soil and soil macro-fauna in relation to slope directions in cool temperate natural forests and larch plantations of Ashoro Research Forest.

尾根から谷に至る斜面上の位置や斜面方位の違いは, 森林生態系の微気象要素に影響し, 土壌にも重要な影響を与えることが知られている。本研究は, 植生分布が詳しく調べられている九州大学北海道演習林内の天然落葉広葉樹林およびカラマツ人工林において, 斜面上の位置および斜面方位の違いが土壌層位と大型土壌動物の特徴に及ぼす影響を調査した。土壌は天然林, 人工林とも北向き斜面および谷部が湿潤, 南向き斜面が乾燥立地の特徴を示していた。すなわち, 北斜面および谷部では, 南斜面と比べて, 土壌表層の含水率が高く, C/N比が低く, A_0層の堆積量, 厚さが少なく, A層が厚かった。また, ミミズの個体数および現存量密度が北向き斜面で高く, 南向き斜面で低かった。大型土壌動物の群集構造は大きく北向き斜面および谷部と, 南向き斜面に分けられ, さらに北向き斜面および谷部の群集は人工林と天然林に分けられた。ミミズの個体密度と土壌のC/N比, またツリミミズの個体数密度とA_0層の深さおよび土壌のC/N比の間には有意な負の相関が見られた。土壌および土壌動物の特徴は, 斜面位置の違いよりも斜面方位の違いによる影響が大きいようであった。Slope positions and slope directions are important factors for micro-climates of forest ecosystems and should affect soil conditions. This study demonstrates characteristics of soil and soil-macrofauna communities in relation to slope positions and directions in natural cool-temperate deciduous broad leaved forests and in plantations of deciduous conifer, Japanese larch of ARF (Ashoro Research Forest) where vegetation patterns have been well surveyed. Soil characteristics of north-facing slopes and bottom valley were mesic with high water content and A depth, and low C/N ratio and A0 accumulation relative to those of southfacing slopes in both natural and plantation forests. Density and biomass of earthworms was higher in north-slopes and bottom of valley than south-slopes. Community structure of macro-fauna in northern-slopes and bottom of valley were different from that of southern-slopes. They were different between in plantation and in natural forests within north-slopes and bottom of valley. Population density of earthworms was negatively correlated with A0 thickness community were quite different between slope directions