Natural disturbances are key factors in the coexistence of species. Some riparian species were adapted to large disturbances throughout their reproductive characteristics. However, the recovery processes and coexistence mechanism after large disturbances have not yet been fully explored in relation to seedling establishment at early stage. We research the forest structure and environment after debris flow 15 years ago. Alnus hirsute and Salix sachalinensis were dominant riparian species in young forest. They established large gaps. On the other hand, Pterocarya rhoifolia and Cercidiphyllum japonicum formed small patches in dark conditions. Seed dispersal of Pterocarya is restricted around the mother trees. Tree ring analysis suggested that Pterocarya and Cercidiphyllum had begun to establish in some years after debris flow. On one hand, Alnus and Salix had established immediately after debris flow. At the next year of debris flow, we observed the severe dryness by a strong light in research site and found that only pioneer species can grow quickly after a debris flow. In results, the causes of coexistence of these species are 1) different response to light condition among species, 2) different soil environment in seedling established sites, 3) limitation of seed dispersal.