Abstract
The authors reviewed articles on two invasive alien woody species in Japan, Amorpha fruticosa L. and Triadica sebifera (L.) Small., A. fruticosa was introduced from eastern part of north and central America as a revegetation material for artificial slopes, has escaped into rivers in Hokkaido, Honsyu, Shikoku, Kyusyu and Okinawa. An experiment implemented on the artificial slope showed that cutting and spreading herbicide a year failed to control community of A. fruticosa and it recovered two years later. Application of weed risk assessment for A. fruticosa suggested that it should be “reject” by Pheloung model and “extremely highly invasive” by John and Linda model. Triadica sebifera, an endozoochory type woody species, is native to southern areas of China and it was introduced into Japan in 18 th century for ornamental or economical purposes. In recent years, spatial distribution of this species is expanding in various places including river basins, forest gaps and other open spaces in Japan. For instance, in Nara Kasugayama Forest Reserve and Awajishima Island, where the population density of sika deer is extremely high, the number of this species is rapidly increasing because of its unpalatability to deer. There is an epidemic of oak wilt disease in forests of warm-temperate area in Japan. The population of sika deer also is increasing in many places as well. There is a concern that the interaction of these events may enhance the expansion of spatial distribution of this invasive species.
