Abstract
In 1980's, there occurred a luxuriant growth of submerged macrophyte, Ranunculus nipponicus (Makino) Nakai var. submersus Hara, in Tagimi River, Hyogo Prefecture, Japan. However, its distributional range has been diminishing recently with the progressive growth of emergent Phragmites japonica Steud. To improve and restore the habitat quality for R. nipponicus, we attempted to conduct several methods of P. japonica removal and evaluated the effectiveness. In the field, we carried out hand-cutting using sickles with various frequencies of cuttings from once to four times from May / June to August 1997. In addition, we compared effects of two removal methods of P. japonica using back-hoe on the regrowth of R. nipponicus; one method that excavated the plant wholly with bottom sediment (excavation method) and the other dug out only plant shoots (shoot removal method). Frequent hand-cuttings with more than three times during growth were effective in reducing the growth of P. japonica, and R. nipponicus recovered noticeably with decreasing P. japonica growth. While the plant cover of R. nipponicus increased after the application of either removal method of P. japonica, earlier recovery of R. nipponicus was observed after the application of shoot removal method than after the application of excavation method.
