Vegetational Landscape of an Isolated Peak

Abstract

Mt. Hakkoda-Odake (1584m a.s.l.), is the main peak of the North Hakkdda Mountains, Aomori Prefecture. The peak, like other peaks of these mountains, is nearly conical and has a relative height of about 200m. Geologically it is almost homogeneous and valleys dissecting it are rather shallow. In the present research, species composition, coverage of each species and height of plant communities were surveyed at survey sites placed at intervals of 200m (Fig. 1).As to the vegetation of these mountains many studies have been carried out. According to these studies we can say as follows : Three altitudal zones arc distinguished in these mountains in general. The lowest of them is the area below 900m a.s.l. and is occupied by Fagus crenata forest, the mediate, 900-1500m, by Abies mariesii forest and the highest, above 1500m, by Pinus pumila scrub. Therefore the present survey area belongs to the upper half of the Abies mariesii forest zone and the Pinus pumila scrub zone. These altitudal zonations, however, are often disturbed especially on the east slopes. The upper limit of the Abies mariesii forest, on these slopes, is lower than on other slopes, and, Sasa kurilensis community, deciduous broad leaved community and snow patch community, a particular one dominated by peculiar herb and dwarf scrub species, often occupy the area between the Abies mariesii forest zone and the Pinus pumila scrub zone (Fig. 2). It has been observed that these phenomena are connected with local heavy snow, and that the distribution of plant communities are eventually well correlated with the topography -altitude, exposure, inclination and so on.Through the present survey, considerably clear correlation between plant communities and topography is found quantitatively as well as qualitatively. In this area, centering the top of the peak, communities of low height are radially distributed (Fig. 3). The NE-extending part of them falls on a snow patch. However this figure does not show except the NE-extending part, another snow patch is to the SE of the summit and there the plants are very low in height, too. The rest parts, extending to NNW, W and S, are seemingly not due to heavy snow, but to local strong wind. In winter, the snow cover, which protects plants, is blown away by the strong wind, and in summer, there is an excessive transpiration. The low height vegetations, extending to NNW, W and S, are supposed to be the results of these effects. This assumption well agrees with the estimated direction of prevailing wind (Fig. 5) and the distribution of wind speed around a conical mountain assumed by Ozawa and Yoshino (1965) (Fig. 4).