What is invasive alien species?
Native or alien?
Plant and animal species that are not native to Denmark are referred to as alien species. They are also known as introduced species, exotic species or non-indigenous species. A species is either native or alien; it cannot be both at the same time. The range of species is dynamic, and consequently a specific assessment is required when determining whether a species occurring close to Denmark should be considered as a native species.
Introduction and spread
Human activity has caused the spread of organisms in several different ways. Over time, travelling times between the continents have become shorter and journeys to remote destinations have become more common. Furthermore, the volume of international trade has increased significantly, which means that goods are transported across national borders in large quantities.
In our globalised world, goods and live animals and plants are exchanged across borders and continents, not only in larger volumes, but also faster than ever before. In order for a species to be defined as alien to a territory, it must be relocated by humans to a territory outside the species’ natural range.
Invasive alien species
A small number of alien species thrive so well in the territory into which they have been introduced that they have an adverse impact on biodiversity and related ecosystem services. These species are referred to as invasive alien species, or simply invasive species. By definition, invasive species have been introduced, i.e. they have been relocated by humans from their natural range, either intentionally or unintentionally; they have established themselves in their new environment; and they have an adverse impact on biodiversity.