A STUDY ON THE GRASSLAND UTILIZATION OF THE VOLCANIC SLOPES OF KIRISHIMA

Abstract

The island of Kyushu is well characterized by the abundance of volcanoes such as Unzen, Aso, and Kirishima. Major land uses on the slopes of these volcanoes are cultivated fields, grasslands, and forests. According to the ratio of these land uses, these volcanic areas can be divided into three types: cultivated-field-dominant, grassland-dominant, and forest-dominant. Unzen belongs to the cultivated-field-dominant type, and Aso grassland-dominant, whereas Kirishima represents the forest-dominant type in general. The primary aim of this paper is to analyze the reasons why the forest-dominant type is to be found in the Kirishima volcanic region with reference to physical conditions, historical changes in land use, ownerships of the land, productivity, and so on. The reasons for this trichotomous division may be explained by both physical and social factors. The physical factors are closely related to the nature of surface features and rocks of respective volcanoes; whether the slopes are gentle and wide or not, or the valleys in unit area are many or not. Social reasons are equally important for making this division, because, if the physical factors are decisive, the ratio between the three types of land uses will not differ from place to place. Therefore we also have to study social factors. Among them productivity of land is the most important, because the owner of the land will like to use it so as to attain the highest possible income. Like the opinions of many other researchers, the present writer thinks that forest land is the most productive or profitable among the three types of land use on volcanic slopes. For this reason many grasslands have changed to forests on Kirishima. In the volcanic region of Aso, however, most grasslands have not so changed to forests as in the case of Kirishima. This is primarily because of the fact that many of the grasslands of Aso have long been and are even now owned by a great number of farmers in common and so the subdivisions and aff orestations have been largely checked for the farmers of the area. On the contrary, grasslands and forests have been widely owned by the national govenment in the Kirishima volcanic region, which fact has enabled considerable afforestation there. In short, it is known that both physical and social factors are decisive for the formation of present land uses on the volcanic slopes in Kyushu. Such factors were surveyed in the volcanic region of Kirishima in comparison with Aso and, to a lesser degree, with Unzen.