1990 Volume 06 Pages 15-23
The development of subalpine conifer forests in Japan is closely related to climatic changes since the Last Glacial Age. However, it is also related to the development of mountain slopes. So, the relation between slope development and subalpine conifer forests is discussed first. Block slopes, which were formed during the Last or late Glacial Age, were distributed extensively in subalpine zones. Though most of these block slopes were covered with subalpine conifer forests, some parts were treeless. There, only saplings or isolated short trees, such as Larix leptolepis are able to observed. It is considered that the lack of forest is due to the delay of plant succession on extensive block slopes. Treeless block slopes are distributed, for example, near the Sensui Pass in the southern Japanese Alps, and on Mt. Kimpu in the Kanto Range. In both areas, the lower limits of block slopes were at about 2000 m a. s. I. Fossil periglacial block slopes are dissected at their lower limits. Such parts, named " the postglacial dissected line " by Hatano (1986), offer unstable habitats for plants. Betit/a ermanii shrubs are often observed in such habitats. They seem to be adapted to an unstable geomorphic conditions. Forest line extends to about 2500-2600 m in central Japan. However, considering the climatic conditions it could ascend to about 2800 m. Normally, the limiting factor for forest growth is considered a mean temperature of approximately 10°C for the warmest month of the year. But in the Japanese Alps, an isotherme of 10°C for the warmest month runs about 2800 m. So the height of present forest line is lower than the estimated limit. The author concluded that the presence of periglacial block slopes probably caused the lower forest line.
