Availability of host fish for glochidia of the freshwater unionid mussel Pronodulariajapanensis was examined for the following eleven species of fish: Zacco temminckii, Phoxinus longowskii steindachneri, Gnathopogon elongatus elongatus, Pseudorasbora parva, Cyprinus carpio, Tanakia lanceolata, Acheilognathus tabira subsp. R, Misgurnus anguillicaudatus, Pseudobagrus tokiensis, Rhinogobius sp. OR and Gymnogobius urotaenia. The hosts to which the glochidia were attached in a paddy field ditch were cultured in tanks for seventeen days. Glochidia and juveniles which became detached from the hosts were counted daily. Juveniles appeared about nine days after glochidia attachment. Rhinogobius sp. OR, G. urotaenia, Z. temminckii and C. carpio were the most suitable hosts on which over 69% of attached glochidia metamorphosed to juveniles. Three hosts, G. e. elongatus, M. anguillicaudatus and Rhinogobius sp. OR, were investigated as to the position and number of attached glochidia. Most glochidia were attached to fish fins and gills. More glochidia were attached to Rhinogobius sp. OR than to the other species. However in the study ditch, M. anguillicaudatus was most numerous and therefore the major host species.
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.
A 700-year landscape history of Himi-nisengoku-hara, a 40-ha dwarf bamboo-dominated area with Nikko fir (Abies homolepis Sieb. et Zucc.) trees, located near the 1896-m peak of Mt. Kamegamori, was revealed mainly by paleoecological analyses. Pollen and charcoal analyses were done for four sediment cores from small hollows in the dwarf-bamboo thicket. Also, the relationship between the modern pollen assemblage and vegetation was examined by using pollen surface samples collected from the dwarf bamboo thicket and Nikko fir stands. Ratios of Gramineae to Abies pollen (G:A) were useful for differentiating the dwarf bamboo thicket and fir stand pollen assemblages. A feature of all pollen assemblages from the four sediment cores was a high percentage of Gramineae pollen. The G:A ratios of fossil pollen indicated that Himi- nisengoku-hara had open landscapes during the past 700 years. Tree census data and tree-ring cores obtained from three plots suggested that Nikko fir trees were established in the periphery of Himi-nisengoku-hara at least 250 years ago, and invaded to the center of the area in synchrony with the simultaneous death of the dwarf bamboo at AD 1964. The increase of charcoal fragments with buckwheat pollen ca. 300 years ago may have been due to slash-and-burn cultivation around the area.