Abstract
Invasive alien species is one of the biggest problems threatening biodiversity. In order to reduce its negative effects on biodiversity, the “Invasive Alien Species Act” was enacted in 2005 in Japan. Amorpha fruticosa L. is a woody species, which was introduced from North America and used for revegetation of artificial slopes, most commonly in Japan. Even though negative effects of A. fruticosa for other native species in riverbeds have been reported in the western states of the U.S.A, where A. fruticosa was not distributed originally, A. fruticosa is not designated as an “Invasive alien species” by the act in Japan, due to its usefulness for revegetation. In this study, the authors investigated A. fruticosa's present ecological status in and around artificial slopes, which have been revegetated by this species, and its escape status in Hattogawa River, Tottori prefecture, in southwest Japan. Additionally, invasiveness of A. fruticosa was evaluated using two different risk assessment models. Consequently, it became clear that A. fruticosa has survived more than 25 years on artificial slopes and has escaped to surrounding areas. Also, A. fruticosa made patches in the riverbed, and the increases in their numbers might have happened by secondary seed dispersals. Both risk assessment models judged the invasiveness of A. fruticosa as high
