What is an alien species?
The term "alien species" includes all species that have been propagated outside their natural range by means of human activity. This also includes subspecies, local varieties of species, and man-made varieties such as livestock breeds and cultivated plants. The spread is not limited to national borders, but can also include spreading within the country, such as the launching of pike in waterways where the species could not spread to itself.
Alien species harm local nature in several ways: For example, new species coming in can change the environment and outperform indigenous species. This is especially critical if it affects species that are already threatened for other reasons. Alien species can also bring their own stowaways, such as parasites and new diseases. They can also interfere with indigenous species and in some cases reduce overall genetic diversity.
It can be hard to define an alien organism, especially when this applies to variants of a species. In order to best map and monitor alien species, we need a good overview of the natural diversity of Norway to begin with and the history of a species: For example, how do we treat the return of wild boar to Norway after a period of national extinction? Or the roe deer that first wandered into the country in the 20th century?
Whatever the reason for the spread of a new species, it is important for the management of nature that they are monitored, and that we investigate the effect on indigenous nature. Many species will be impossible to remove from ecosystems once they have established themselves. So the most effective measures are those of early detection and mapping of the spread for continued monitoring and management.