徳之島の板根林について

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1) The clarification of the structure of the buttressed-tree-forest in the central part of Isl. Tokunoshima, the Ryukyus, is aimed at in this study. 2) The citation of the data on the temperature and rainfall was made from those furnished by Isen meteorological station (70 m above the sea-level). 3) To make the investigation more effective, the location of six quadrats (each of them being 25m×25m) was made in the forest. The differentiation of 6 strata was carried out, according to the height of the forest-trees, with the performance of the measurement of all the trees upward of 2cm in diameter at the breast-height. In the respective quadrats were located six belt-transects of 2m×24m. Acquisition of any information concerning the floristic composition, cover degrees and frequemcies of all the species belonging to the shrub and herbaceous layer, was aimed at in setting these belt-transects. 4) The structure of the natural forest in Isl. Tokunoshima was ascertained by these studies, with the following results obtained : At the district zoned from the valley to mountain slope 250m〜370m above the sea-level, the stand is represented by 1. Quercus miyagii-Arachniodes pseudo-aristata sociation. Plot 1,Plot 2. 2. Quercus-Turpinia ternata-Colysis wrightii sociation. Plot 3. 3. Quercusmiyagii-Schefflera octophylla-Ctenitis subglandulosa sociation. Plot 4. 4. Quercusmiyagii-Rhododendron tashiroi-Arachniodes pseudo-aristata sociation. Plot 5. At the district stretched on the mountain ridge, the stand is represented by Castanopsis sieboldii-Distylium racemosum-Dryopteris erythrosora var. koidzumiana sociation. Plot 6. In Table 5 are shown the structural characteristics of each of those forests. 5) Transverse-section of the stem immediately above the buttresses, and the direction of the buttresses of Quercus miyagii, and diagrammatic profile of the buttresses, are shown Fig.3〜Fig.10. 6) Buttresses are not only of considerable ecological significance but are so important a physiognomic feature of tropical rain-forest tree. In general, tropical-regions-buttressed-trees lack a tap-root, and usually have well-developed superficial root-systems. Buttress-formation is the direct response of the tree, answering to the mechanical stimulation of strain set up by the wind. At the district situated at 250m〜370m above the sea-level in the central part of Isl. Tokunoshima, the soils are extremely shallow and rock-layers are exposed here and there in the forest. Quercus miyagii, a main buttressed tree, at the district, usually lacks tap-root, owing to the shallowness of the soil and is in possesion of the well-developed lateral roots. Buttress-formation of this oak in the district, as seen in the photographs, is so elegant as may be compared to those in the tropical-rain-forest. It is noteworthy that such buttress-phenomenon appears in Isl. Tokunoshima which belongs to sub-tropical region. As to the causes of buttress-formation, several hypotheses have been proposed. But in-so-far as, I am informed of there is no hypothesis applicable to all instances. It seems highly probable that, as far as, the buttress-formation in Isl. Tokunoshima is concerned, it is attributable to the shallowness of soils through which the tap-root-formation is exhibited.
鹿児島大学の論文
1971-09-25

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迫静男
Laboratory of Silviculture

徳之島の板根林について

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