抄録
Nakaikemi, in Fukui Prefecture, central Japan, is a basin with an area of about 25 hectares. Rice has been cultivated in wet paddy fields throughout Nakaikemi since the Edo period (1603 -1867). The traditional wet fields always supported a diversity of aquatic and wetland plants, including threatened species. Recently, abandoned rice fields have continued to increase because the environmental conditions they provide are inconvenient for modern agriculture. A four-year vegetation survey (1997 - 2000) of Nakaikemi confirmed that the area of cultivated fields decreased from 1.2 ha to 0.3 ha. A wide distribution of tall reedy communities dominated by Phragmites, Zizania and Typha, and short herbaceous communities were observed on the abandoned wet rice fields. Non-wetland communities dominated by Solidago and creeper plants (Pueraria and Humulus} increased on drier habitats. The tall reedy communities usually developed within two to five years after abandonment. In some fields, no tall reedy communities developed during the survey period. The distribution of plant communities changed with time and soil moisture conditions. A continuous survey of threatened plant habitats showed that in cultivated and young abandoned fields, tall perennial plants succeeded and dominated the small plant species. The number of threatened species was higher in plowed plots than in non-plowed plots. These survey results suggest that the factors affecting Nakaikemi's vegetation and flora are the period elapsed after abandonment, soil moisture, management tasks and surrounding vegetation. Seed bank species composition and use of herbicides also affect plants in both the cultivated and young abandoned fields. To conserve the diverse wetland flora of Nakaikemi, appropriate land management is needed to control the vegetation.
