The Kuju volcano Group is a volcanic field whose highest peak is Nakadake (1,791m above sea level), the highest peak on Kyushu Island in Japan. The summits of the Kuju Volcano Group have a unique vegetation which consists of shrubby forests of Rhododendron kiusianum and other trees, which are similar to the vegetation of the alpine zone. On the other hand, the summit of Sobo Mountain (1,756m above sea level), which is almost same altitude as the Kuju volcano and is located about 50km southeast of that volcano, is covered with tall forest.
In this study, the distribution of vegetation was examined from a geoecological approach, which is a methodology that tries to explain each environmental factor that defines the distribution of vegetation based on geomorphology, geology, climatology and so on. The purpose of this study is to clarify the factors that led to the formation of the unique vegetation around the summit of the Kuju Volcano Group.
As a result of multivariate analysis for geomorphological and geotechnical features, it was found that the elevation and the pH of soil involve the distribution of vegetation. The elevation is correlated with temperature, and the pH of soil indicates the degree of decomposition of organic matter in the soil. These results can be concluded as follows; 1) The tall forests are distributed in areas in which the temperature is high and the decomposition of organic matter in the soil is active. 2) The shrubby forests are distributed in areas in which the temperature is low and the decomposition of organic matter in the soil is relatively active. 3) The temperature and soil conditions at grassland are similar to shrubland.4) The temperature at the marshland is high and the decomposition of organic matter in the soil is inactive.
