Mire Development in the Daisetsuzan Mountains, Central Hokkaido, Northern Japan

Abstract

A lot of mires are distributed in the Daisetsuzan Mountains, especially above the forest line where Pinus pumila community is dominant. According to some pollen analyses and radio carbon datings, the initiation of a mire formation dates back to about 7, 500y. B. P., but most of mires have developed after about 5, 000y. B. P. when the climatic condition began to get cooler. The climatic condition seemed to delay snow melting above the forest line. This caused a decrease of Pinus pumila community whose existence is often controlled by snow depth, and caused an increase of water supply from snow patch through summer, which provided a favorable condition for mire development in the Daisetsuzan Mountains.The distribution of mires under the climatic condition mentioned above was controlled by a surface condition of land such as topography and vegetation. Below the forest line located around 1, 500m a. s. l. in the Daisetsuzan Mountains, volcanic activities and landslides caused the destruction of forest vegetation and the formation of depressions leading to mire development. Above the forest line the favorable condition for mire development was provided by periglacial processes which formed microtopography such as solifluction lobes and terraces. These features make water easier to stagnate on a gentle slope. In addition to these conditions, a size of catchment area, a distribution of snow patches and an existence of permafrost which controlled water supply decided the distribution of mires in the Daisetsuzan Mountains.