Abstract
The downstream effects of water regulation by dam were investigated in the Satsunai River where a flood control darn was initially impounded in 1996. The riverbed geomorphic surfaces were classified into four groups based upon the flooding recurrence interval. Five vegetation quadrats were set in each surface to measure basal areas of trees and environmental variables. The results indicated that species distribution was different among the geomorphic surfaces representing various environmental conditions. Seedlings of late-successional tree species dominated the geomorphic surfaces being frequently disturbed in the pre-regulation scheme where Salicaceae species such as Chosenia arubutifolia occupy the canopy layer presently. After the dam regulation, about 70% of the entire riverbed was classified as few flooding areas, suggesting that Salicaceae stands will be replaced by late-successional species, such as Fraxinus mandshurica var. japonica.
