Relationships between soil properties and environmental factors along elevational gradients in the University of Tokyo Chichibu Forest

森林土壌の生態系機能を維持管理する上で，土壌特性と環境要因の関係を理解することは重要 である。急峻な地形を有する秩父演習林では，その土壌特性が植生のみならず，標高や傾斜度，曲率などの地形によって規定されると考えられる。そこで，本研究では，深度別の土壌特性（pH，全炭素量，全窒素量，CN 比）と，植生（樹木の種多様性，針葉樹率）および地形（標高，傾斜度および斜面方位，曲率，累積流量）の関係を報告し，土壌特性に対する各環境要因の相対的重要性を調べた。土壌pH は土壌が深くなるにつれ上昇し，標高と樹木の種多様性は有意な負の関係を示していた。土壌特性と各環境要因の関係を線形混合モデルにより解析した結果，表層土壌のpH については標高と植生が最も重要な変数であった。一方で，深度10-20 cm と20-30 cmの全窒素量においては，南側で流速が小さい場所で多くなる傾向が示され，地形が標高や植生より土壌特性に強い影響を及ぼし得ることが明らかとなった。これらの結果から，森林の土壌特性に対する局所的な地形や標高に沿った植生変化の重要性が示唆された。It is important to understand the relationship between environmental factors and soil properties in managing the ecosystem functions of forest soils. In the University of Tokyo Chichibu Forest (UTCF), located in a steep mountainous region, soil properties are prescribed by topographic factors such as elevation, slope, and curvature as well as vegetation. In this study, we investigated soil properties (pH, total carbon contents, total nitrogen contents and CN ratio) for each depth, and vegetation (tree diversity and the proportion of coniferous trees) and topography (elevation, slope, aspect, curvature and flow accumulation) in UTCF, and examined the relative importance of environmental factors to soil properties. Soil pH increased with depth and tree diversity showed a significant negative correlation with elevation. In topsoil layers (0-5 cm and 5-10 cm), elevation was the most important variable in explaining soil pH, based on analyses of linear mixed models. On the other hand, total nitrogen content in the 10-20 cm and 20-30 cm depths increased toward sites with south facing slopes and low flow rate, where these topographic variables have stronger influences than elevation and vegetation. These results suggested the importance of local topographic factors and vegetation changes to soil properties along elevational gradients