alien invasive species

Alien species, introduced deliberately or accidentally, that prove to be invasive. AISs include pests and pathogens to which native species have no resistance, causing the more or less complete destruction of a taxon (eg. Dutch elm disease, chestnut blight), and plant and animal species that spread to the exclusion of natives eg. Japanese knotweed, rhododendron, Himalayan balsam, giant hogweed, false acacia, buddleia, American mink and grey squirrel. Some AIS plant species are noxious weeds and some pose a direct threat to human health. More than 10,000 species in Europe are thought to be non-native, of which at least 15% are invasive. Many potential AISs not present in Britain could easily be introduced.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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