Abstract
We investigated the fen communities and their hydrochemical environments in Abiragawa, which embraced the largest area of fens in Yufutsu district, and compared with communities growing in neighboring seven mires. Three groups were identified; Group A (Calamagrostis langsdorffii) predominantly occurred in floodplain mires and Group C (Carex lasipcarpa var. occultans) in valley mires. Two types of Group B dominated by Thelypteris palustris occurred exclusively in lower water level areas of Abiragawa. B1 had mixed species composition with Group A, and B2 with Group C. The EC and pH values in B2 were lower than B1. After the modification of river course in 1956, water supply to Abiragawa had interrupted. In Abiragawa, Group A is growing and one type of Group C was described on 1975. The dominance of Thelypteris, which grows in drier habitats indicates that the hydrological change could develop the communities of Group B by deteriorating the communities of Group A and C. The alder forest (Alnus japonica) has increased by 50% for the last 29 years and replaced fens, provably owing to hydrological changes. Accordingly, recovering the hydrological conditions before modifying rivers would be effective to restore fen communities in Abiragawa.
