兵庫県北但馬地域における低位ブナ林とその存立条件

Beech forests characterized by Fagus crenata of F. japonica are distributed at abnormal low altitudes, down to 150 meters above sea level, in the northern Tajima district on the Japan Sea side, southwestern Japan. The abnormal low-altitudes are investigated to have been resulted from (1) marked lowering of the beech zone in snowy area, (2) large snow depths in the northern Tajima district and (3) escaping from severe human disturbance since the beginning of agriculture, particularly during the high economic growth period. The following two factors promote the lowering of the beech zone in snowy area: Creeping and avalanching of deep snow tend to destroy most small trees, but young beech can endure through crawling and triangulating their stem profiles. While large animals as hares and serows feed preferably winter buds and sprouts of deciduous trees, especially of beech, deep snow cover in the district protects from the browsing of animals. In addition, the large longevity of beech up to 400 years probably contributes to preserve the lowered distributions. Deep snow in the district is attributable to the large relief of the Hyonosen mountain mass behind. The mountain mass elevates the water-saturated winter wind that has traveled over the warm Japan Sea water from the cooled and dried Asian continent. Human activities destroyed most of natural forests in Japan, but small human population in the mountainous northern Tajima district reduced the destructive effects. The spot forests of beech are thus preserved as relicts of previous one extensive over the district. Many of them are left to protect villages from slope disasters. The spot forests seem to have potentials to grow over the snowy area, so that it is not impossible for us to revive them with suitable supports.