石垣島の砂浜植生の成帯構造の成立

抄録

Zonation of sand beach vegetation was investigated in Ishigaki Island, southern Ryukyu Archipelago, the subtropical island. Transects were placed at thirteen points of seven beach localities. The field survey was carried out in Aug. 1983,Oct. 1983 (just after a typhoon struck) and July 1984 on four beaches, and the latter two times, on three beaches. The survey also included profiling of the beach and coastal dunes, and observing the sea conditions. The wave action influencing the beach is usually weak because the island is surrounded by a coral reef. Nevertheless, the strand vegetation was easily destroyed by storm waves caused by a typhoon, but it immediately recovered. The recovery is due to the elongation of new shoots from remaining rhizomes and seedlings from drift seeds. The zonal distribution patterns of the communities are different at the beaches. On the beach with a narrow backshore, the herbaceous zone is not developed and coastal forests grow right down to the back of the beach. The dunes are stable and covered with coastal scrubs and forests. A Spinifex littoreus community forms the platform dune only on the wide beach. There is a close relation between the zonation of coastal vegetation and shore processes and coastal depositional topography. These are based on the geographical environment and also on the regional characteristics.