Autecology, distributional expansion and negative effects of Amorpha fruticosa L. on a river ecosystem: a case study in the Sendaigawa River, Tottori Prefecture

摘要

Amorpha fruticosa L., introduced from the eastern part of North and Central America as a revegetation material for artificial slopes, has escaped into riverbeds in Japan, and its negative effects are of concern. In this study, an attempt has been made to clarify the actual extent of escape and establishment of A. fruticosa, through a case study of the Sendaigawa River, Tottori Prefecture, coupled with a survey of national distribution using the National Censuses on River Environments. The autecology of A. fruticosa, including phenology, germination, allelopathy and coppicing ability, was also studied by observation and experiments. The following conclusions were drawn: A. fruticosa preferred sunny sites; the total established area in the study site was 7,500 m2; A. fruticosa showed strong coppicing ability; there was lower species diversity in and around areas populated by A. fruticosa; and A. fruticosa has been expanding its area both in the watershed of Sendaigawa River region and nationwide. The authors emphasize the importance of quick control of A. fruticosa.