Land characteristics of the hills and the man-induced change of their natural potential

Abstract

Since the 1960's, large-scale residential developments have concentrated on suburban hills covered mostly with secondary forests which, consisting ofQuercus serrata and other deciduous and evergreen trees, had been used as coppice until the so-called fuel revolution of the 1950's.
Land characteristics of the hills and their modification history was outlined in this paper. Field study was carried out in the selected hills in Sendai, Tokyo and Osaka in order to measure the natural potential of conserved lands and developed lands which were made by cut and fill operations. Cut depth and fill thickness exceed 20m in parts of every develeped lands. The tree vitality of conserved and plantedQuercus serrata was used as a biological index of natural potential and its change caused by land transformation. Here low tree vitality point shows good tree growth and suggests high land potentiality, while high point shows poor tree growth and low potentiality. The range of point is between 1.00 and 5.00.
Followings are the main results obtained from the field study;
1) Mean tree vitality points are low in conserved lands. The lowest-point area is in the Tomiya Hills in Sendai, probably because the hills are located near the distribution center ofQuercus serrataforests and the soil condition of the hills is rather good particularly in physical property. On the other hand, the Senboku Hills in Osaka show relatively high points, which suggest the poorness of inherent natural land potentiality of the hills.
2) Mean tree vitality points and variances remarkably increase in developed lands in every surveyed hills, suggesting the lowering of land potentiality through land transformation. However, uneven distribution of points can be observed according to the differences of site characteristics. For example, in the Tama Hills in Tokyo, tree vitality points on artificial fill are higher than those on cut which was made through the compaction of weathered volcanic ash by heavy machinery and provides worse plant growing condition.