Vegetation changes in the downstream floodplains of Miharu Dam along the Ohtakine River in Fukushima Prefecture, northeast Japan.

Abstract

In the downstream floodplains of Miharu Dam on the Ohtakine River (located in Fukushima prefecture, Japan), the changes of vegetation have been studied for a total of 3 years, since the dam was first filled. The findings have shown that the floodplain communities such as the Phragmites japonica community have decreased, while the upland communities such as the Pueraria lobata community and the Festuca arundinacea community have increased. The cause for this change in vegetation is considered to be erosion and the change in the flow regime. The floodplain communities occur near the edge of the streams, which is an easily eroded area. Downstream from the dam, sediment transportation is limited to a very small quantity. Since no new land forms, the habitat for the floodplain communities decreases. The amount of flowing water was controlled to less than 20m^3/sec for a year and 9 months since the first filling of water. For the grassland communities, the habitat conditions in the areas where the water level is higher than 20m^3/sec, was found to be very suitable. Under this condition, the upland communities have invaded and oppressed on the Phragmites japonica community.