Abstract
In May 2004, the "Invasive Alien Species Act" was enacted in Japan with the aim of preventing adverse effects to ecosystems, human safety, agriculture, forestry, and fisheries caused by alien species. Here, we present a list of invasive alien vascular plant species that should be designated as Invasive Alien Species (IAS). Invasive alien vascular plant species were categorized according to the following four criteria: (1) the national or international status of invasiveness; (2) the total amount of riparian habitat that the species can invade; (3) adverse effects on biodiversity and ecosystems; and (4) the implementation of countermeasures by administrators or local residents. We selected 108 vascular plant species as IAS candidates and categorized them into three ranks (A, B, or C) according to the summed scores of the four criteria. Rank A consisted of the 16 most invasive species: Ambrosia trifida, Eragrostis curvula, Robinia pseudoacacia, Sicyos angulatus, Solidago altissima, Egeria densa, Festuca arundinacea, Myriophyllum aquatica, Elodea nuttallii, Eichhornia crassipes, Dactylis glomerata, Bischofia javanica, Taraxacum spp., Veronica anagallis-aquatica, Stenactis annuus, and Pistia stratiotes. These 16 species have demonstrated strong adverse effects on biodiversity and ecosystems, and programs have been implemented to control them. Almost all of these species are included in lists of the world's worst 100 invasive species and Japan's worst Invasive Alien Species, and most of them dominate large areas of riparian habitat. Rank B consisted of 34 species, including Barbarea vulgaris, Amorpha fruticosa, Gymnocoronis spilanthoides, Iris pseudacorus, and rank C consisted of 58 species. Some IAS candidates are currently used in landscaping and gardening. For conservation of biodiversity and ecosystems, all listed species, particularly those of rank A, should be designated as IAS, and active management must be implemented for their control.
