All plant and animal species in Norway are recent arrivals if we consider geological timespans – the whole country was covered with ice sheets until the ice retreated at the end of the previous ice age around 10000 years ago. After the ice retreated plant species slowly began to recolonize the country from further south in the continent, some of the more recent arrivals in the country can be as a result of this slow recolonization process. But many species would never have arrived here without human intervention. Many species were introduced as a result of farming practices (often previous to 1800), both as crops and as weeds, whilst other more recent arrivals are ornamental plants or have been brought here for other purposes (such as for the production of Christmas trees).



Not all invasive species represent a problem. Some are able to establish themselves in niches where they don’t push out native species, whilst others are only just able to survive in Norway. But unfortunately, there are some species which thrive here and establish themselves in places to the detriment of native species or ecosystems. Artsdatabanken peforms a risk assessment of invasive species in Norway every fifth year (fremmedartslista) and assesses the species on a scale from ‘No known risk’ to ‘Low risk’, ‘Potential risk’, ‘High risk’ and ‘Very high risk’. This rating is arrived at by considering the species’ potential to be an invasive species, for example the ability it has to spread in Norwegian nature, and its ecological effects such as how badly it affects native species and habitats and where it is likely to establish

Tabel 1: This demonstrates the various risk categories, considering ecological effects and invasion potential. From Artsdatabanken (



Figure 1: The garden plant the lesser periwinkle (Vinca minor) is SE catergory –  Very high risk on the Invasive Species List 2018. The species has become completely dominant in this little hollow in a noble oak forest after spreading from a local garden. 


We have selected 17 invasive species and groups of invasive species that we need to focus on in Oppland. We have produced fact sheets for each of these species and groups with information about how to control them and advice on measures that can be implemented. In addition to this we have collated lists of other registered invasive species in Oppland and invasive species that can be expected to be recorded here in the near future.



It is especially important with regional action plans to ensure that resources are used where it is most important and where they will benefit our nature the most. This is because it is society’s resources that are used to control these invasive species, because these resources are limited, and because these species can represent different levels of risk in different parts of the country.


Main photo information: Giant knotweed (Reynoutria sachalinensis) comes originally from East-Asia and like its close relatives Japanese knotweed (Reynoutria japonica) and hybrid knotweed (Reynoutria x bohemica) is one of the worst invasive species in Norway. It has the category SE – Very high risk on the Invasive Species List 2018. It forms very dense populations that push out other species and it is extremely difficult to control. Photo: Espen Sommer Værland.