Abstract
From the results of the investigations during six years from 1953 to 1958,the writer sought for the decisive factors for the establishment of a Phragmites community among the abiotic habitat in a reed swamp, situated in Asuwa Subprefecture, Fukui Prefecture. The swamp lies at about 10m above sea-level. It has developed around a small pond by the sudden and striking increase of spring water after the Fukui Earthquake in 1948. The swamp is invaded by Phragmites all over, but four facies are recognized by the dominance of the following species respectively ; Phragmites communis, Zizania latifolia, Scirpus preslii and Alnus japonica (Fig. 1). It is noticed from the three years observations that the interspecific competitions in the Phragmites and the Zizania communities are so serious that an almost pure stand of each plant has been established and annuals have substantially been excluded from it. From the distribution of component species and their successional trends in this swamp the writer came to the following conclusion that, the water depths (Tables 1 and 2), the scarcity of soluble phosphorates and the excess of active alumina in the soil (Table 4) may be responsible for the occurrence of these, especially the Phragmites communities. Furthermore, he assumes that actual acidity, organic matter content as well as mechanical texture of soil (Tables 3 and 4) are only indicative, but some critical conditions caused secondarily by them are essentially effective to the establishment of the swamp communities.
