Abstract
A dynamic model associated with water depth has been developed to simulate the growth dynamics of Phragmites australis. The biomass of shoots and rhizomes are analyzed with respect to various water depth. Phragmites australis have to grow over the critical height beyond the water depth while early season growing by stored material of rhizomes. There exists a severely influenced zone that aboveground and underground biomasses are sharply decreased as the water depth increases over the critical height. The severely influenced zone is varied with respect to initial rhizomes biomass. The density ratio per one shoot is decreased as the water depth increases, and the strength is also decreased. Morphological change of rhizomes contributes so as not to decrease the biomass under the critical height
