Abstract
The effect of river improvement works, including dam, revetment and groin construction, on seedling sites of Chosenia arbutifolia (Pall.) A. Skvorts, an endangered species, was investigated in the Satsunai and Tokachi River in Hokkaido. The peak, scale, and frequency of the river disturbance were greatly decreased due to the dam construction. Further, the area of seedling site for C. arbutifolia created by flood-like disturbance was also decreased. Numbers of C. arbutifolia seedlings, however, were observed at the revetment and groin sites. The study demonstrated that river improvement works, especially dam construction, would cause greater damage to seedling site for C. arbutifolia. In contrast, the works like revetment and groin construction would create the seedling site, and would perform important ecological functions, instead of natural disturbances.
