Distribution and ecology of the semi-mangrove, Hibiscus hamabo community in western Kyushu, Japan

Abstract

The distribution and ecology of the semi-mangrove, Hibiscus hamabo dominant community was studied in western Kyushu, Japan. Attention was paid to the community size and coastal landforms of the habitat in which it was growing. A distribution map showing both localities and size of each community stand was drawn. The H. hamabo community was widely and frequently distributed in western Kyushu. However, most localities contained fragmented or small communities. The medium-sized communities were scattered and the large were restricted in location. The most frequent coastal landforms of their habitats were inlets followed by estuaries, lagoons and sea-relic lakes. The communities whose population is more than 10 individuals were chiefly found on the lagoon and the estuary sites including downstream of rivers. The large communities were also developed only on lagoons and estuaries. The habitat of the community is normally situated on the high tide water level, but was somewhat higher on the gulf coast and lower in estuaries than the high water level. The community was phytosociologically identified as the association Hibiscetum hamabo (Nakanishi 1979) and was divided into two subassocations by the species composition and stand conditions. The one was the typical subassociation and the other was the Vitex rotundifolia subassociation. The former was composed of only H. hamabo in the shrub layer and was occasionally invaded by salt marsh elements in the herb layer. The latter is differentiated by the occurrences of the shingle beach elements and was only developed on the shore of the gulf coast. For conservation of the H. hamabo community, it is important to keep the natural conditions of lagoons and estuaries.