One of the major transformations of the planet from human activities is the redistribution of species to areas outside their native range. These “alien” species have in many cases caused substantial harmful impacts to the recipient environment.
All alien species cause changes to the ecosystems to which they are introduced. Such impacts are of many types - some are dramatic and obvious and can easily be classified as desirable or undesirable. However, for the vast majority of alien species, no information on impact is available. This greatly complicates the task of objectively assigning priority to management.