In recent years, the forestation in rivers is one of the biggest problems for river administrator. In this study, the factor analysis on the forestation about the willow and bamboo communities in rivers is conducted for the long-term and appropriate management. The twelve first-class rivers in Chugoku District are divided into small drainage basins, where a rate of trees and seven parameters: distance from a weir, total nitrogen, total phosphorus, maximum discharge divided by ordinary discharge, distance between levees divided by average water surface width, slope of the river bed and bed deformation are allocated. The correlation analysis and the cluster analysis between the rate of the trees and these parameters were performed to find the contributing factor of the forestation in rivers. These factor analyses indicate that the deformation of riverbed is a main factor for the river forestation about the willow.
