DISTRIBUTION OF EVERGREEN BROAD-LEAVED FORESTS IN KANTO DISTRICT, JAPAN

Abstract

The writer intended to make clear the distribution area of evergreen broad-leaved forests in Kanto District, which are the climax forests of lowland vegetation. By surveying remnant forests in certain parts of mountain areas and the forests belonging to Shinto shrines and Buddhist temples, the latter are well conserved in the original condition, the inland limits of distribution were studied in relation to the climatic conditions. The species composition and structure of the forests were also dealt with in comparison with those in south-western Japan, the native ground of the forests. (1) Using the available data on the flora or the vegetational reports, the remnant stands of natural evergreen broad-leaved forest are plotted on a distribution map (Fig. 1). From the map the following facts must be noticed. The remnant stands appear on the coastal hilly terrain in Kanagawa, Chiba and Ibaraki Prefectures and on the foot of mountains in Kanagawa, Tokyo, Saitama, Tochigi and Ibaraki Prefectures. It is an important fact that they are small in number in Gunma Prefecture, whilst they are few in the central parts of the Kanto Plain because of destruction by human activities. (2) Next, thermal condition controlling the distribution of evergreen broad-leaved forests was surveyed as follows : The warmth index (W.I.) was estimated by monthly air temperature with a lapse rate of 0.61°C per 100m. Topographical map (1:1, 000, 000) was used for base map. The areal mean values of the heights with various warmth indicies within an area of 30km×30km were calculated for each square using the estimated temperature at the 159 climatological stations in this district. The distribution of the warmth index is shown in Fig. 2. By the same method the distribution map of coldness index (C.I.) was drawn as given in Fig. 3. If we superimpose Fig. 2 on Fig. 3, it can be observed that the isolines, running along the foot of the mountainous area in Kanto District, are C.I. -5°C, W.I. 105°C, W.I. 90°C etc. from the Pacific Ocean to the inland and the isolines of W.I. and C.I. run roughly in parallel with alternal pattern. Comparing the distribution map of the remnant forests (Fig. 1) with them (Figs. 2, 3), the boundary of the remnant forests are found between the lines of W.I. 105°C and 90°C and it coincides with the lines of C.I. -10°C in Kanto District. For the actual heights of the upper limits of vertical distribution of evergreen broad-leaved forests, mostly the Cyclobalanopsis forests, the warmth and the coldness indices in Kanto District are calculated (Table 1), showing that they are approximately represented by C.I. -10°C. Therefore, the inland boundary of the evergreen broad-leaved forests of this district is expressed by C.I. -10°C as the same for Tohoku District. (3) Field observations were tried at 15 stations in this district as show in Fig. 1. Quantitative data by quadrat method was taken at places as given in Table 2. Size of quadrat was 100m2 - 400m2. All trees with a diameter more than 3cm at breast height were checked in a quadrat as well as stratification, forest floor vegetation, and the number of species and of individuals. Basal areas at breast height were calculated from the trees with a diameter more than 10cm (A group), 3-10cm (B group), as shown in Table 2. Three types of evergreen broad-leaved forests are recognized from the dominant species on the table: Cyclobalanopsis type (with Abies firma or Torreya nucif era) on the slope of Mt. Takao Mt. Nishikanasa, Mt. Sengen A, Mt. Dokko, and at Iko Shrine. Shiia type on the slopes of Mt. Sengen B, Mt. Takadate, and Mt. Butchozan. Machilus type at Kozaki Shrine. Basal area at breast height of the Cyclobalanopsis spp.