<国立科博専報>日高山系幌尻岳における森林の垂直分布

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Mt. Poroshiri is the highest peak in the Hidaka range, Hokkaido (42°43′NL, 142°41′EL, 2,052m in altitude, ) and is situated in the area of broad transitional zone between cool-temperate and subarctic zones (Pan-Mixed Forest zone). In this mountain the altitudinal changes of species composition, forest structure, and species diversity were investigated. 1) Distribution of dominant species along the elevation gradient : - Main dominant species in each plot from lower to higher altitudes were Picea jezoensis, Abies sachalinensis, Betula ermani, Sorbus spp., Alnus maximowiczii, and Pinus pumila (Figs. 3 & 4). In this mountain the prominent feature was that B. ermani occupied a considerable part in the Picea-Abies type forest. 2) Forest sturcture : - As the indicator of the biomass of forests, the basal area (BA) of forest trees at breast-height or the product of BA and the vegetation height (i. e., BA・H) were used. Vegetation height and BA decreased with increasing of altitude (Fig. 4). The maximum of BA was 0.5% of land area at the lowest plot (1,000m in alt.). Population structure of the main dominant species, B. ermani, P. jezoensis, and A. sachalinensis, were analyzed as shown in Fig. 9. In this chart every individual of each species is arranged with the sequence of the diameter at breast-height (DBH), and the gradient of the regression line and the number of points in each plot indicate the stability of the population structure of each species. B. ermani is more stable in higher altitudes and P. jezoensis and A. sachalinensis, in lower altitudes. 3) Species diversity in each community : - The species diversity of each plot has no intimate relation with elevational gradient. This result indicates that the species diversity of a certain community is controlled not only by habitat conditions but also by the interrelation of the component species. The information-theoretical measure of diversity was calculated in each plot (Table 2 and Fig. 6). It was mainly controlled by the relative dominancy of the dominant species (Fig. 5) and not so affected by the altitudinal gradient. As shown in Fig. 7 the basal-area sequence of the component species of each plot has a usual type of subalpine forests, consisting of a few superior dominants and subordinate species. 4) Ordination of Betula phase : - In each plot along elevation gradient, the two species groups were distinguished according to their competitive relationship (Fig. 10) i. e., the Betula group and the Picea-Abies group. The Betula group is a species group consisting of deciduous broad-leaved species, such as B. ermani, Sorbus spp., and A. maximowiczii. The Picea-Abies group is the another one, consisting of evergreen conifers, such as P. jezoensis and A. sachalinensis. As the Betula group was present in every plot except the alpine pine shrub, basal area of the Betula group in each plot was used as the axis of ordination. In this ordination all plots were separated into two groups according to the presence or nonpresence of the Picea-Abies group, and these two groups of plots were arranged symmetrically according to the basal area of the Betula group (Fig. 11). According to this phase ordination, we can understand the transitional trend from the Betula group to the Picea-Abies group, irrespective of spatial or temporal pattern of vegetational change. By plotting the number of species, diversity index, and BA・H in this figure, we can understand the change of each characteristic along the transition from the Betula group to the Picea-Abies group. As shown in Fig. 11,the number of species and the diversity index were higher in the transitional zone, and they fell in the parts of the maximal basal area of both groups. In contrasting to the change of diversity, BA・H was monotonously increased along the ordination except the transitional zone, where the BA・H or at least its rate of increment seems to fall. 5) Altitudinal zones in Mt. Poroshiri : - The altitudinal zones of
国立科学博物館の論文
1973-12-20

<国立科博専報>日高山系幌尻岳における森林の垂直分布

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