Abstract
Elaeagnus umbellata dominates widely on some of gravel bars in the Yoshino River, Shikoku, Japan. This pioneer shrub is thought to be ornithochorous, because of its fleshy-fruitedness. However, for its uniform stand-structure, the possibility of water dispersal throughout the water-course during autumn fruit-ripening season was considered. The habitat characteristics (gravel size, relative elevation from low-water level) of the patches distributed in the reach 17- 77 km from river-mouth were investigated to explain their spatial distribution. The habitats were determined to be located about 2-4 m from low-water level, and to be composed of relatively large gravels, which enable the seedlings to withstand the flood disturbances. The establishment years of the cohorts corresponded well with autumn flood records. The synchronous age structure throughout the reach may be due to seed dispersal by water and also to availability of safe-sites which were provided by human activities.
