森林群落階層構造の植物地理 : 北海道石狩低地帯野幌天然生林の事例  [in Japanese] Phytogeography of the Forest Stratification : A case of the Nopporo Natural forest, Sapporo district, Hokkaido  [in Japanese]

From the floristic regional point of view, horizontal distribution in Hokkaido belongs to "Sino-Japanese Region". Fagus crenata, characteristic species of Japanese temperate zone, distributes up to the Kuromatsunai Depression in south-western part of Hokkaido and further northern part of Hokkaido is covered by mixed forest. The mixed forests in this region, together with those in southern Sakhalin, the Amur, the Usuri, the North East District of China, and North Korea, are called "The mixed forest zone of the Far East" (TATEWAKI, 1955-57) or "Tatewakia". The mixed forest are categorized into "Hokkaido-N. E. China subregion", as a subregion of "Sino-Japanese Region" (MURATA, 1977). This study has been carried out in the Nopporo natural forest (Fig. 1), which belongs to the mixed forest zone, and has phytogeographically analyzed forest stratification. The method to classify forest stratum is developed by WATANABE (1985), based on the "Synusia" concept by H. GAMS (1918) and K. IMANISHI (1937). 7 Synusias (M1-M5, N,L-Sy) for the arboreal species and one Synusia (H-Sy) for the herbaceous species are discriminated, respectively. The determination of the Synusia for certain arboreal species is made as follows; firstly, calculate the ratio of the maximum tree height of a given species is made as follows; firstly, calculate the ratio of the maximum tree height of a given species within the stand to maximum tree height of the stand, and call it a coefficient of the rank of stand precedence (CRSP); secondly, calculate CRSP for each species, utilizing the data from 581 climax forests in Hokkaido; and finally based on the criteria shown in Table 1, the Synusia for each individual species is determined. From the phytogeographical point of view, the arboreal species in the Nopporo natural forest mostly consist of Sino-Japanese, Japanese, N.E. Asiatic elements, except for one species. N. E. Asiatic element dominates in M1-Sy, and Sino-Japanese and Japanese elements are more emphasized in the Synusias of lower strata. H-Synusia of herbaceous plants is characterized by wide distribution elements such as Circumboreal, Eurasiatic, et al., accounting for 27%. In this way, the difference in the composition of distribution elements between arboreal and herbaceous plants becomes more evident (Fig. 2). This should reflect the basic difference in the structure of the forest. Among the stands including whole species, the difference in the composition is not clear, and each stand shows relatively high ratio of Sino-Japanese element, ranging from 30% to 35% (Fig. 3). However, by analyzing the composition of distribution elements using coverage value for each Synusia, diverse distribution patterns for each stand and the stratification of the forest can be clearly identified (Fig. 4). Furthermore, compared with the forest vegetation, majority of the plants in marsh, swamp and pond consist of wide distribution elements, and they differ in phytogeographical pattern.