Vegetation changes and topographic feature in the delta of Obitsu River in Tokyo Bay

Abstract

This reseach aims at investigating about vegetation changes and topographic feature in the delta of Obitsu estuary, while comparing this time (2001) and the past vegetation maps (1974, 1995, 1984). The change of geographical feature using the vegetation maps in 1974, 1984, 1995 and 2001 was found that in north sandbar, the creek connected with seaside in 1974, but it was closed a part by deposition of sand in 2001. In south sandbar, the distribution of Pinus thunbergii community was confirmedon the south in 1974, but a part of Pinus thunbergii community was eroded in 2001. The sandbank was expanded from 1974 to 2001. Compared with vegetation maps in 1974, 1984, 1995 and 2001, the area of the back marsh vegetation was expanded from 1974 to 2001. In regard to the area of each vegetation type in 1974, 1984, 1995 and 2001, the salt swamp plant community of covered water type at high tide, such as Phragmites australis community, Carex pumila corrununity, Calystegia soldanella community were reduced, and that of uncovered water type at high tide, such as Phacelurus latifolus community was expanded. Sand dune community, grassland plant community and woody plant community were reduced. Ruderal plant community such as Pueraria lobata community, Solidago altissima community was expanded.