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.

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The objective of this study was to investigate the growth factors of grassland plants in semi-natural grassland under artificial management by various mowing frequency per year. As for grassland plants, most species (including the registered species in Red Data Books (vascular plants) of Chiba Prefecture and Ministry of the Environment, Government of Japan) were found at a mowing frequency of 1 time per year, second most commonly at 2 times, and extremely few at 4 or more times. Plant volume of grassland plants was the highest at 0 times (section that has not been mown for over a year), and became lower as mowing frequency increased. Instead, that of ruderal plants was high at 4 and 8 times, and ruderal and exotic plants were only founded at 14 times. The upper rank of dominant species by mowing frequency per year were Miscanthus sinensis at 0 times per year, Solidago altissima, Eccoilopus cotulifer and Miscanthus sinensis at 1 time, Imperata cylindrica at 2 times, Digitaria ciliaris at 4 and 8 times and Paspalum dilatatum at 14 times. As mowing frequency increased, the upper rank of dominant species changed from grassland plants to ruderal and exotic plants, except for Solidago altissima of 1 time. We propose to conduct continuous mowing management that tall herb Miscanthus sinensis community is formed by mowing of 0 times per year, or mesocotyl grasslands including the registered species are formed by mowing of 1-2 times in order to maintain semi-natural grasslands which are historical and cultural landscapes in Shiroi-City, Chiba Prefecture.

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The Oguraike area is now planned for natural environmental conservation and restoration under the Grand Design about Urban Environment Infrastructure in the Kinki Region. Actual vegetation at the Ograike area is expected as a seed source to conserve and restore wetland environment. The purpose of this study was to reveal species composition of actual vegetation in river bank of the Uji River, the Yokoojinuma and the Oguraike drained lands, Kyoto prefecture, Japan. Five quadrats were placed in these areas and all the vascular plant species were recorded. Two hundred and eight species including 10 endangered plant species and 71 alien plant species were recorded. Actual vegetation in the river bank of the Uji River and the two drained lands were useful seed sources of floodplain species and wetland species, respectively. Especially, we found the desirable vegetation with only one alien plant species and some endangered plant species at the center part of the river bank of the Uji River.

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