Not all alien species in Norway are risk-assessed. The assessment encompasses primarily alien species that have become established in Norway after the year 1800. In addition, there is a selection of species that are likely to become established in Norway within the next 50 years.
Over the years, a great many species have come to Norway with human assistance, either as stowaways or the result of a deliberate introduction. Ox-eye daisy Leucanthemum vulgare, common buttercup Ranunculus acris and yarrow Achillea millefolium are examples of species that most Norwegians view as being a natural part of the native flora, even though they probably came to Norway with human assistance.
Stably reproducing populations after the year 1800
It would be impossible to risk-assess all alien species because we have too little knowledge about species that came to Norway a long time ago. It has therefore been necessary to develop explicit guidelines with regard to which species shall be risk-assessed:
Only alien species that are established in Norway shall be risk-assessed. The term established refers to species that can produce viable offspring, outdoors, without human intervention. However, alien species that were stably reproducing in Norway, by the year 1800, are not to be risk-assessed. Such species are to be considered native in Norway.
To be established as stably reproducing means that the species must have reproduced, without human intervention, for more than 10 years.
Read more: Introduced to Norway before or after 1800?
Door knocker species
Some alien species are nevertheless risk-assessed even if they are not established in Norway. This applies to alien species that will probably become established in Norway within the next 50 years. Such species are called door knocker species. They have been classified into three groups:
1) Species that are present in Norway but which currently only reproduce indoors or with the help of humans. Examples of such species are insects in greenhouses, garden plants or aquarium fish.
2) Alien species that are present in neighbouring countries and which will probably come to Norway through natural dispersal.
3) Alien species that are not present in Norway but which live in areas with nature types and a climate that are similar to Norwegian conditions. Such species can become established in Norway via different means of dispersal.
The door knocker species to be risk-assessed are selected by the relevant authorities in consultation with the expert committees and the Norwegian Biodiversity Information Centre.
Species used in production
Species used for the production of food, timber, other animal or plant products, and also for recreation, are referred to as production species.
If a production species was in extensive use in Norway, in the year 1700, it is not to be risk-assessed. Examples of such species are the mallard duck Anas platyrhynchos, domestic cow Bos taurus, domestic goat Capra hircus, domestic cat Felis catus, domestic pig Sus scrofa domesticus, oat Avena sativa and rye Secale cereale.
Production species that were not in extensive use, in the year 1700 or earlier, are to be risk-assessed. The species production area is not to be included in the assessments. It is the ecological risk of the species outside its production area that is to be assessed. This means that escapees and wild stocks of production species are to be assessed.
A small number of production species can influence Norwegian nature even though they do not disperse outside the production area. Examples are species that can contribute to genetic pollution through wind pollination (anemophily). Species that do not leave their production area but which nonetheless have an impact outside it, are to be risk-assessed.
The production area of a species is the defined area which is set aside for the actual production eg. a field, a forest stand, grazing land for livestock, a fish pond, a fish farm, or a private garden.
Groups (taxon) below species level
Groups below the species level, such as sub-species, varieties, cultivars and hybrids, can be risk-assessed. Those taxon below species level which are to be assessed are selected by the relevant authorities and the expert committees, in consultation with the Norwegian Biodiversity Information Centre.
Regionally alien species
Species which are native in parts of Norway but which (after the year 1800) have been dispersed by humans to places in Norway where they do not belong, can also be risk-assessed. Such species are described as regionally alien.
Regionally alien species which are to be assessed are selected by the relevant authorities and the expert committees, in consultation with the Norwegian Biodiversity Information Centre.
Read more: Regionally alien species