抄録
The purpose of this study is to investigate the relation which related studies have not made clear between the soil water qualities, the ground level and the distribution of Bruguiera gymnorrhiza and Rhizophora stylosa in the south-east coast of Iriomote Island in Okinawa Prefecture. The investigations were carried out on the distribution of B. gymnorrhiza and R. stylosa, the ground level and the soil water quality at the fringe that was chosen as the main object in this study to replace the riverine which related studies have focused on. As a result, a strong relation was observed between the distribution and the ground level. The ground level of the seaward edge of the range of R. stylosa stand showed 102±2cm, that of the border between R. stylosa stand and B. gymnorrhiza stand showed 133±1 cm and that of the landward edge of the range of B. gymnorrhiza stand showed 167±0 cm (0 cm is set to be the same as the datum line in Ishigaki Is. in 1990) . A strong relation was observed between the distribution and the soil water qualities, too. The soil water salinity from the depth of 60 cm of the seaward edge of the range of R. stylosa stand showed 31.5±1.6‰; that of the border between R. stylosa stand and B. gymnorrhiza stand showed 25.7±0.9‰; that of the landward edge of the range of B. gymnorrhiza stand showed 19.3±2.2‰. The soil water qualities were influenced by the fresh ground water from the landward side. Small stands of R. stylosa were found surrounded by the vegetation of B. gymnorrhiza. Judging from the ground level, B. gymnorrhiza must grow in those areas, but the soil water quality in those areas were suitable for R. stylosa. This suggests that the relation between the distribution and the soil water qualities is stronger than the other.
