The Ecological Characteristics of Ludwigia stipulacea in Urban River

Ludwigia stipulacea is one of the endangered plants in Japan. To make clear the ecological characteristics of L. stipulacea, we studied its population in an urban river in east Kanagawa Prefecture. The seasonal change of its biomass showed three periods in the lifecycle of L. stipulacea; a period of erect shoot growth (May-August), a period of level shoot growth (September-October), a period of decline (November-January). The flowers were observed from May to beginning of December, and the flowering peak was in early summer. Distributions of L. stipulacea were interspersed in about 6 km area of Kasio River. The results surveyed 44 vegetation sites in 1998, the total communities size was about 1, 500 m2. Many sites of sandbar were dominated by L. stipulacea. It is characterizing the landscape of this urban river, that its communities are spreading leafs on the surface of the water. From the structure of species, we discussed the succession of L. stipulacea community. It was separated two types, early and late communities on succession, by the presence of Andropogon virginicus, Persicaria thunbergii. And it is considered that L. stipulacea community will be decline by invasion tall herbaceous species.