中部九州における母岩因子とマツ型森林の発達

抄録

The forest dominated by Pinus species often builds an edaphic climax, because the occurrence of this plant has some special reference to the petrographic factor. In Central Kyusyu, the two volcanoes, Aso and Kuzyu are adjacent to each other and with Paleozoic formations of the mountain-group of Katamuki-Sobo, thus present a suitable field for the study to elucidate the relationship between the petrographic factor and the occurrences of Pinus-type forest. Lines (Fig. 1) were drawn from the triangular point at the summit of Mt. Katamuki to that at Mt. Kuzyu(AB), and also to the summit of Mt. Neko(AC). These were used as base-lines of huge transects, and plots for actual surveys were selected within 4 sq. km taken at random along the base-lines. The area of the sample plot was(12m)^2 for forest and(5m)^2 for grassland. Within the square, the best developed stand or tree was searched for and observed as the sample. The most predominating type of plant communities other than Pinus-type were also observed in paralell. The subject was approached through four different ways. 1. Seeking after discontinuities in the distribution of species or groups of species along the base-lines. 2. Enumeration of the plant communities in series where Pinus dominates or grows in natural state, and finding of the community which is the most prominent when the area lacks any pine. 3. Growth and vitality of pine. 4. Aspect of the land and its utilization of various grade might be found in the series of sample plots along the basic lines. Among the discontinuities found in any one or more ways above mentioned, those which agree with the border line between two natural vegetational zones must be put aside to detect the special influence of the petrographic factor, and the others which coincide with the exposure of some geological formation are to be picked up. If the discontinuity is traceable in two or more different lines of considerations, it will be more and more powerful. The flora can be classified into six groups, namely, 1. Group of the Pinus densiflora forest, Pinion densiflorae. 2. Group of the montane deciduous forest, Fagion crenatae. 3. Group of the broad-leaved evergreen flora, Shiion Sieboldi. 4. Group of the secondary broad-leaved forest, Castaneion crenatae. 5. Group of the grassland, Miscanthion sinensis. 6. Group of the supra-montane heath, Rhodorion kiusiani. The sample plot AB 12 certainly surpasses the montane zone of Kyusyu and lies in the supramontane zone. Vaccinium Vitis-idaea is a characteristic species of the panboreal class of Vaccinieto-Piceetea and is also dominant in the Japanese subalpine scrub, Vaccinieto-Piuetum pumiae. Miscanthus oligostachyus is the characteristic species of the supra-montane zone of Kyusyu. It should be considered very important that Pinus pumila or the other species of pine or pinaceous family is completely absent in the supra-montane zone of Kyusyu, AB 11 and AC 23 lie very near in its altitude : Styrax-Weigela-Sasamorpha-Carex sociation in Mt. Neko lacks in the floral element of group 1,plant of Pinion densiflorae ; but Pinus-Stewartia-Symplocos-Rhododendron sociation in Mt. Kuzyu contains some of them, although, extremely surpressed by the group 5. Between the plots 8 and 9,the margin of the dissected valley of the River Oono and its tributaries is crossed by the line, where the grassland flora are replaced by those of the broad-leaved evergreen forests, and the aspect becomes dominated by the pine forest developed on the escarpment of Aso Lava. The other margin of the valiey of Oono is attained between the plots 4 and 2,where the base rock is passed over from Aso Lava to the effusive rock of Sobo Volcano. The characteristic species of the broad-leaved evergreen forest here disappear together with those of the secondary deciduous forest and are replaced by the plants of the beech forest. Along the AC-base line, the woodland on rocky cliffs and land collapses in Mt. Neko is consisted for the most pa