We conducted a survey on vegetation change and performed a germination test for the topsoil seed bank after vegetation management of the herbaceous community dominated by the invasive alien species Coreopsis lanceolata on the riverbed of the Kiso River. We observed that although a large number of C. lanceolata seedlings were established, few flowering shoots emerged in the year following vegetation management (removal). The extended summed dominance ratio of C. lanceolata decreased, while that of Potentilla chinensis and Galium verum-domestic species growing on the gravelly riverbed-increased. However, the number of alien species of annual and biennial plants markedly increased after the removal. The germination test showed that this increase was caused by germination and establishment from the seed bank in the disturbed area after the removal. The test also showed that the seed supply of Artemisia capillaris and Dianthus superbus var. longicalycinus-domestic species growing on the gravelly riverbed and, in small numbers, in the surveyed and surrounding areas-was low. In this study, the removal proved effective in controlling the flowering of C. lanceolata; however, the problem of increase in the number of alien species of annual and biennial plants remains to be resolved.
