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Invasive non-native species ‘Invasive non-native species’ formed the second group of species for which management was deemed necessary to benefit nature. Here, targeted action is focused on species that are not native, and which are harmful to the wider biodiversity of a given area. The hierarchy of action in dealing with such invasive species is: prevention, containment and then control. The most effective action is to prevent the spread of invasive non-native species into Scotland in the first place - those species that present a recognised but imminent threat need to be targeted in particular. In Scotland the Non-Native Species Action Group currently provides a lead in coordinating necessary action for such species. However, the SAF concentrated on species that had already established themselves in Scotland. Actions for invasive non-native species can include control measures to reduce their population or limit their spread, or efforts to modify the human activity contributing to their spread (through enactment and enforcement of legislation, voluntary agreements or through education and promotion of codes of practice). SNH’s priorities related mainly to the control of such species where they affected sites, habitats and species of high nature conservation importance, including genetic as well as ecological threats. Six out of the 32 SAF species were included here. These became the focus of new, targeted effort and resources over the five year project. These met the SAF criterion of being ‘non-native species present in Scotland and assessed as presenting the greatest risk to biodiversity of high conservation value.’ The following species became the focus of new action under this heading: Plants • New Zealand pygmyweed • Rhododendron ponticum and its invasive hybrids • Wireweed American mink © John MacAvoy Grey squirrel © Laurie Campbell North American signal crayfish © Lorne Gill/SNH Wireweed © Lorne Gill/SNH Vertebrates • American mink • Grey squirrel (see chapter 8) Invertebrate • North American signal crayfish