高度経済成長期を画期とした西中国山地の植生景観変化とその背景について : 広島県北西部八幡高原と山口県秋吉台の場合

森林や草原の景観はふつう1～2年で大きく変わることはないが，数十年の単位で見ると，樹木の成長や枯死，あるいは草原の放置による森林化などにより，しばしば大きく変化する。本稿では，高度経済成長期を画期とする植生景観変化とその背景について，中国山地西部の2つの地域の例について考えてみた。その具体的な地域として取り上げたのは，広島県北西部の北広島町の八幡高原と山口県のやや西部に位置する秋吉台である。その2つの地域について，文献類や写真，また古老への聞き取りなどをもとに考察した。その結果，八幡高原では，たとえば，今はスキー場などの一部を除き，草原はわずかしか見られないが，高度経済成長期の前までは，牛馬の放牧などのためなどに存在した草原が少なからず見られた。その草原の大部分は森林に変わり，また，高度経済成長期の前の森林には大きな木が少なかったが，燃料の変化などにより，森林の樹木は高木化した。なお，その地の草原は，高度経済成長期の直前の頃よりも少し遡る昭和初頭の頃，あるいは大正期頃まではさらに広く，その面積は森林を上回るほどであった。その変化の背景には，そこで飼育されていた馬の減少もあったが，別の背景として，大正の終り頃から製炭が盛んになり，山林の主な運用方法が旧来の牛馬の飼育や肥料用などのための柴草採取から，炭の原木確保のための立木育成へと変わったことがあった。一方，秋吉台には，今も草原が広く見られるが，それはそこが国定公園などに指定されている所で，草原の景観を守ることが観光地としての価値を維持するためにも重要であるためである。しかし，その秋吉台の草原も，高度経済成長期の前と比べると，草原面積は少し減少している。また，草原やその周辺の山林への人の関わり方の大きな変化により，植物種の変化など，その草原には大きな質的変化が見られ，また草原を取り巻く森林も高木化が進むなど大きく変化してきている。

Vegetation landscape changes since the rapid economic growth period and their backgrounds of two areas in the west Chugoku Mountains Region in Japan were studied based on literatures, photos, interviews of elders and old maps. One of the studied area is Yawata Highland which is located in the northwest of Hiroshima Prefecture, the other is Akiyoshidai, a famous limestone area which is located in Yamaguchi Prefecture. Results are as follows.In the Yawata Highland, grassland is now rarely seen except for a ski resort etc., however before the rapid economic growth period, grassland was commonly seen there as it was used for grazing cattle and horses etc. Most of the grassland transformed into forests, and most trees of forests have become high and much bigger due to the changes in fuels etc. after the rapid economic growth period; big trees were not commonly seen before the period. The grassland was more wider in the area until the Taisho era or the very beginning of the Showa era, which go back some decades; the grassland area was at least nearly equal to that of forests or it might exceed the forest area in those days. One of the backgrounds of the change was the thriving of charcoal making from the end of Taisho period, and another one of the backgrounds was the large decrease of the number of cattle and horses kept in the area; the main uses of the land changed greatly from keeping cattle and horses and gathering grass for fodder and fertilizer to making forests to secure wood for charcoal.Meanwhile, in Akiyoshidai, grassland is still widely seen. This is because the area is designated as a quasi-national park etc., and it is important to keep the landscape of grassland to maintain the value as a tourist spot. However, the area of grassland in Akiyoshidai has been also decreasing and that of forests has been increasing after the rapid economic growth period, although the speed is rather slow. Moreover, large changes in quality have been observed in the grassland; the plant community has been changed and some species are rare now. Furthermore, forests surrounding the grassland also have been changed greatly; the rate of tree species has been changed greatly and most trees have grown bigger. Such changes are due to the great changes of people's engagement in the grassland and its surrounding forests.

source:https://www.rekihaku.ac.jp/outline/publication/ronbun/ronbun9/index.html#no207