2011 Volume 16 Issue 1 Pages 1-15
The vegetation of abandoned rice fields and factors influencing it in small valley ('yatsu', in Japanese) heads in the east plain of Lake Kitaura, Ibaraki, Japan, were examined to evaluate the potential of the fields as habitats for indigenous wetland plants. The floristic composition in a 15×5m study area and the importance value of each species, which was evaluated as the frequency of occurrence in 39 0.5×0.5m quadrats set at each study site, were recorded in 32 abandoned rice fields. In total, 230 indigenous (site average 32 spp.) and 25 alien (site average 3 spp.) species were recorded. Seven species that were listed on national or regional red lists were recorded at nine sites. Analyses of environmental factors affecting the vegetation properties using a generalised linear model showed that groundwater level (GWL), light availability index, which was calculated from a spherical photograph taken above the vegetation, and the time since abandonment, had significant effects on both the richness of indigenous species and indigenous wetland species. A significant positive effect of the GWL was also detected for the occurrence of the endangered species. In contrast, the GWL had a significant negative effect on the importance value of the invasive alien species Solidago altissima, which often dominates the fields. The GWL was significantly lower in the fields abandoned with remaining drainage facilities. In conclusion, abandoned rice fields in 'yatsu' valley heads can provide a habitat for wetland plants, including threatened species, unless the drainage facilities remain.
