The mink, which was introduced from North America by fur farmers and then escaped into the wild, is a typical invasive alien species.
Other such species include the East Asian raccoon dog, which has spread from fur farms on the Karelian Isthmus, the Canada goose (introduced into Finland in the 1960s) and the North American lupines that were introduced by private gardeners and now colour roadsides all over the southern half of Finland. Many marine animals have also hitchhiked into our country in ship ballast waters.
Invasive alien species compete with indigenous plants and animals for light, nourishment and living space and can drive them from their original habitats. Invasive alien species can feed on an indigenous species so heavily that the population of the latter collapses. An invasive species may also carry diseases to which it is itself resistant, but that are lethal to the indigenous species for whose ecological niche it is competing. For example, the signal crayfish that has been introduced into several water systems can carry the crayfish plague, which can easily be fatal to the indigenous European crayfish. As the more robust powerful and vibrant species variant, the North American mink has, in practice, eradicated the indigenous European mink from Finland and almost all of Europe.
Pests a threat to forests
As the climate warms up and harsh winters become rarer, it is likely that more and more southern species will gain a foothold in Finland. The nun moth and the gypsy moth are moth species, which are nowadays found only occasionally in Southern Finland, but are expected to spread hundreds of kilometres northwards in the future. These moths cause extensive damage to forests in Central Europe.
The pine wilt nematode is a dangerous forest pest that can travel with lumber shipments; stringent border inspections have so far managed to keep this pest out of Finland. The pine wilt nematode has caused extensive damages to pine forests in, for example, Portugal and China, but the indigenous pine species of its original North American habitat are resistant to it. Global warming is increasing the likelihood of forest damage caused by this worm.
Many survival methods
An invasive alien species can also be harmful to humans. An example of this is the phototoxic giant hogweed, which secretes sap that causes severe skin inflammations when the skin is exposed to sunlight. Powerful herbicides and protective clothing are required for the eradication of giant hogweed growths. Several doses of herbicide need to be administered at intervals because the plant’s seeds can remain viable in the soil for many years.
Alien species may also hybridise with indigenous species and so reduce its original level of genetic diversity; this process can even lead to the extinction of the indigenous species.
Snails ruin gardens
The Spanish slug (also known as the “killer slug”) is originally from Portugal. It has caused severe damage in gardens across many Central European countries as well as in the strawberry farms of Norway, for example. In Finland, the species was first encountered in the Åland Islands in 1990 and it has since spread, usually hitchhiking in shipments of garden products, into Southern Finland where it is considered a nuisance. Cold winters have so far wiped out most of the population each year, but this situation may change in the future.
The EU is preparing an invasive alien species strategy that has the aim of reducing the negative impacts these species have on biodiversity. One possibility is the creation of an early warning and or communication system that would be based on regular updates on the occurrence of alien species. The most cost-effective countermeasure is preventing alien species from entering our country. The strategy will also define control and eradication measures for situations in which an invasive species has already spread into a country. The Nordic countries are also cooperating to halt the spread of invasive species. Finland is drafting its own national strategy for invasive alien species; this work should be completed by the end of 2010.
Suvi Raivio, Senior Advisor (Biodiversity), Finnish Forest Industries Federation, tel. +358 9 132 6671
The UN has named 2010 as the International Year of Biodiversity. This series of articles focuses on concepts and phenomena that are related to biodiversity