DISTRIBUTION PATTERN OF MOUNTAIN SOIL IN THE SOUTHERN ALPS, CENTRAL JAPAN

Abstract

Soil is thought to be a natural body which is formed and transformed as a result of complicated interaction of soil making factors such as climate, living organism, landform, parent material and time. So we can expect that soil is distributed corresponding to the difference of the combination of soil making factors. Standing on this view point, this paper aims to get the law of soil distribution, especially vertical distribution, connected with environmental factors, taking the mountain area of the Southern Alps as an example field, and to make an assumed soil map by using air photographs as an application of the law. Soil types distributing in the Southern Alps are Brown Forest Soil and Podsol. Brown Forest Soil is distributed in the montane and lower subalpine zones governed mainly by topographic factors such as landform type and the gradient of the ground. Brown Forest Soil is subdivided into six types BA_??_BF. BA and BB (dry type) are situated at summit, ridge and other convex slope. BC and BD (semi dry and moderately wet type) are distributed on both convex and concave slopes of mountainside. BE and BF (wet type) are tonally located on tales, river terrace and other sedimental landform along the valley. The distribution of each soil type has particular relations with environmental factors such as altitude, landform type, the mode of deposition, the gradient of the ground, the direction of the slope, vegetation and surface temperature. The distribution of Podsol is closely connected with surface temperature (=altitude and landform) and vegetation. The lower boundary of Podsol is found where the surface temperature is around 4.0°C. It is also affected by topographic factors. At gentle ridge the height of the boundary is lower (higher in surface temperature) and on steep concave slope higher. Comparing 10 degrees of convex slope with 40 degrees of concave slope, the difference is about 1.5°C in temperature and about 300 meters in height. It also varies with the direction of the slope. On the south slope of 20 degrees the height of the boundary is about 2100 meters, while on the north slope about 1700 meters. In granite areas the height of the boundary seems to be lower. Podsol area coincides with subalpine coniferous forest such as Abies veitchii, Abies nariesii, and Tsuga diversifolia. Vertically from the river bed to the summit, soil types are distriluted in the order of BE—BD, BC (—BA)—BB—PD. The patterns of vertical soil distribution vary with landform type, gradient and direction of the slope. They are diagrammatically shown in Figs. 6, 7, 8, and 9.