Alien invasive species occur in all major taxonomic groups from micro-organisms to mammals. The Invasive Species Specialist Group (ISSG) of the Species Survival Commission (SSC) of the World Conservation Union (IUCN) has gathered information on 326 alien invasive species including 157 that negatively impact forests and the forest sector (www.issg.org/database [accessed on 23 August 2005]). Annex 1 provides a list of 204 species known to affect forests and the forest sector including the 157 species identified by ISSG.
ISSG has also compiled a list of the One Hundred of the World’s Worst Invasive Alien Species (www.issg.org/database/species/search.asp?st=100ss&fr=1&sts=#SpeciesList) which aims to collectively illustrate the range of impacts caused by biological invasion. Although incomplete, this list is a first attempt to rank the impact of alien invasive species. Included are 62 alien invasive species - four fungi, one flatworm, 10 insects, two molluscs, two amphibians, one reptile, two birds, 13 mammals, two grasses, six plants and 19 trees and shrubs - that impact forests and forestry. Annex 2 provides a more detailed discussion of these species.
