Norway's first official foray into evaluating the impacts posed by alien species was with the publication of the “2007 Norwegian Black List” by the Norwegian Biodiversity Information Centre. Only 217 species were assessed in this first effort.

The publication “Alien species in Norway – with the Norwegian Black List 2012” includes impact assessments for all 1180 known reproducing alien species in Norway. The 217 species assigned to the two highest impact categories – severe and high impact – are what comprise Norway’s Black List of alien species.

The work also includes information on the 1140 non-reproducing species known from Norwegian territories, including Svalbard, as well as data on distribution and pathways (vectors) into Norway. All information is found using NBIC’s alien species search online (in Norwegian).

Which species were considered?

Nearly 50 experts from different scientific institutions have participated in preparing this assessment, which considered a total of 2595 species. These species were divided into four groups:

  1. 1180 species which by definition are considered alien species in Norway, including Svalbard and Norway’s territorial waters, and which reproduce or have the potential to reproduce in the wild in Norway within the next 50 years.
  2. 203 ‘door knockers’, or alien species that have the potential to establish themselves and reproduce in Norwegian nature.
  3. 1140 alien species which are recorded in Norwegian territories, but that are not thought to be able to reproduce in Norwegian nature in the next 50 years.
  4. 72 species that have been previously considered to be or have been treated as alien species, but that fell outside the delimitations of the 2012-project.

Groups that have not been treated in this categorization are native species that are being introduced to new areas in Norway, species that are introduced and have existing native populations, genetically modified organisms and genetic variants, subspecies or lower taxa (with the exception of vascular plants), and single-celled organisms.

10 on the most invasive species list

Ten of the alien species recorded as capable of reproducing in Norway are also among the 100 species on the International Union for Conservation of Nature’s list of the world’s most invasive alien species (Lowe et al. 2000, 2004).

Of these, eight species are listed in the two highest impact categories, five of which are assessed as having a severe impact (SE). These are:

  • Ophiostoma ulmi, the fungus that is involved in Dutch elm disease;
  • Eriocheir sinensis, the Chinese mitten crab;
  • Mnemiopsis leidyi, the warty comb jelly or sea walnut;
  • Oncorhynchus mykiss, the rainbow trout; and,
  • Sus scrofa, the wild boar.

The species that were ranked as having a high impact (HI) are:

  • Ulex europaeus, common gorse;
  • Linepithema humile, the Argentine ant; and,
  • Bemisia tabaci, the silverleaf whitefly

Two of the species that are regarded amongst the ‘100 of the worst  invasive species’ in the world are assessed as having a low ecological impact (LO) in Norway. These are Oryctolagus cuniculus, the European rabbit, and Euphorbia esula, green spurge.

More than half with low or no known impac

Of the 2595 species considered, all 1180 alien species capable of reproducing in Norway and 134 of the 203 potential alien species for Norway have had their impact assessed.

Of the 1180 species that can reproduce in Norway:

  • 106 species are considered to have a severe impact
  • 111 a high impact
  • 198 a potentially high impact
  • 399 a low impact and
  • 366 no known impact.

Of the 134 door knocker species:

  • 7 are considered to have a severe impact
  • 23 a high impact
  • 9 a potentially high impact
  • 67 a low impact, and
  • 28 no known impact.

Where do they come from?

Most alien species in Norway are native to Europe, followed by Asia and North America.

These are areas that to some extent have similar climatic conditions as Norway.

Half of the alien species that can reproduce in Norway are present as a result of escapes or naturalizing. A large proportion have arrived as stowaways, but often it is not know how the species got here, and it is assumed that the cause is human activity.

Most alien species have come to Norway via unintentional introductions, and species that came as stowaways with imported plants account for more than one-third of these introductions.

Garden centres and nurseries are collectively the largest source of deliberate introductions of alien species into Norway.

Species used in production for various commercial activities represent the largest single group of species deliberately introduced. Most of Norway’s alien tree species fall into this category.

Where are they found?

The southeastern parts of Norway are home to the largest recorded numbers of alien species. Oslo and Akershus have the most alien species for which an impact assessment has been conducted, followed by Vestfold, Østfold and Buskerud. These are counties with generally high diversity and a favourable climate.

The largest proportion of alien species are found in constructed sites, including residential areas, industrial areas, sand quarries, roads, and golf courses/sports fields.

Human influenced habitats such as meadows and pastures, arable land and woodland are also habitats for a considerable proportion of alien species.