多良間島の御嶽林に関する調査研究

摘要

The two aims of this study were, firstly, to investigate the total number of trees, tree height, diameter at breast height (DBH), tree age, and tree distribution in a Fukugi (Garcinia subelliptica ) forest in Shiokawa-utaki, where the artificially planted Fukugi tree is dominant, and to investigate the history of this tree plantation. Secondly, we applied a phytosociological approach to compare the characteristics of a man-made Fukugi plantation in Shiokawa-utaki and an artificial forest and a natural forest in the Futenma-utaki on the coastline. In Shiokawa-utaki and along the entrance path leading to it, 2,457 woody trees were found, with approximately 70% being Fukugi trees. The oldest of these was estimated to be 248 years of age. The proportion of young Fukugi trees was high, with 85% of them being younger than 100 years of age. The reason for this small proportion of 100 year-old trees may be the continuous natural regeneration during the course of establishing this plantation. In particular, the distribution chart of the tree age demonstrates that the somayama (government administered timber forest) governance reinforcement of 1742 during the reign of the Ryukyu Kingdom and damage from the Meiwa tsunami in 1771 triggered the development of the Fukugi tree plantation. When examining the distribution chart of the Fukugi trees in Shiokawa-utaki, we found that old-growth trees occur at the outer periphery of the ground, with the spirit rock in the center. This indicates that the Fukugi forest was initially planted from the outer periphery of the utaki grove. Our phytosociological examination found that the Fukugi forest in Shiokawa-utaki can be classified as a Diospyros egbert-walkeri-Garcinia subelliptica community, consisting of differential species like Diospyros egbert-walkeri, Flagellaria indica and Paederia scandens. The Calophyllum inophyllum forest in Futenma-utaki can be classified as an Antidesma pentadrum-Calophyllum inophyllum community that consists of differential species like Calophyllum inophyllum, Antidesma pentandrum, Callicarpa japonica var. luxuriam, and Ficus erecta. The natural Hernandia nymhaeaefolia forest in Futenma utaki can be classified as an Allophylus timorensis-Hernandia nymhaeaefolia community, consisting of differential species like Hernanida nymhaeaefolia, Allophylus timorensis, Euonymus japonicus and Planchonella obovata. It can be assumed that the Fukugi forest in Shiokawa-utaki and the artificially planted Calophyllum inophyllum in Futenma-utaki have developed by replacing an original Psychotria manillensis-Diospyros maritima natural forest alliance.%沖縄の御嶽林の構造を植生上から観察すると、いろいろなタイプに分けられる。ある御嶽にはより自然林が優占し、またある御嶽は主に人工林で構成されている。御嶽によって自然林から人工林の構成頻度の違いも、多様に存在する。さらに樹種構成をみても、その地域の自然植生の代表種から、人工的に植栽された樹種まで様々である。なぜ、このような違いが出てくるのか。また、この植生上の違いは、どのようなプロセスを経て形成されたのか。このことは、言い換えれば、御嶽林と地域の人々が、どのようにかかわつてきたか、という森林と人間との関係史の問いかけでもある。