Abstract
Escaped garden plants, although they may affect indigenous plants and tip the balance of a local ecosystem, can give natural, favorable touch to urban spaces covered with concrete. It is of great importance to evaluate possibilities and limitations of those plants in sustaining naturalness and biodiversity in the city landscape. This study is to investigate Pink Knotweed (Persicaria capitata (Buch.-Ham. ex D.Don) H. Gross.) growing wild on the surface of urban river revetments and to discuss how this species should be incorporated into the urban river landscape. A field survey was conducted for the Mikasa River (catchment area: 94km2, length of the mainstream: 24km), which runs through densely populated areas in Fukuoka (population: 1.46 mil), Japan, to obtain information as to how Pink Knotweed grows on the concrete surface of the river revetment. The findings obtained are as follows: 1) communities of Pink Knotweed are found throughout all parts of the main stream and concentrated especially in the upstream parts of the channel, which are located close to residential areas. 2) The mean length from the edge of the water to the upper end of a community is 1.69m, and the mean area of a community is 0.17m2. 3) Over three-quarters of the communities face north or northwest, which fact implies the species tends to avoid scorching sunlight on the revetment.
