A Consideration on the Development of a Colony of Shrubs in Rivers

Abstract

A process and conditions of development of shrub colonies in rivers are discussed with field observation and experiments. An observation in YOSHIDA river suggests that the divergence of branches after a break near the root by flood flow is a major cause for the development of a colony of shrubs of S. Gilgiana which is a common species in rivers in Japan. Experiments on drag and on bending characteristics of S. Gilgiana lead to an estimation of critical flow velocity at which S. Gilgiana is broken by flood flow (and then develop a colony).