Alien species are plants and animals that purposefully or accidentally appear in the area where they had not previously been or grown. Brought to flower-gardens, orchards, and parks for decorative purposes, some alien plants have become wild over time and began to spread naturally.

- Invasive alien species are one of the greatest threats facing many regions in the world. They pose a threat to biological diversity in Europe, too.
- Invasive alien species are alien organisms that colonize a new ecosystem, expand fast, establish stable populations in natural or damaged habitats, and become a threat to nature, economy, and human health.
- Alien organisms cause major economic losses because they have a harmful impact on agriculture, fisheries, and human health. Lithuania has not yet assessed the damage done by alien organisms on its economy.
- An ever growing trade, tourism, and exports of goods to foreign countries speed up the spread of alien organisms.
- An ability to implement early prevention measures and predict possible damages could significantly help in curbing the spread of alien organisms.
- Raising societal awareness and spreading knowledge about alien species should help us resolve this problem.

Invasive alien species create many ecological problems. They also lead to ever growing economic losses in wood industry, agriculture, and tourism. According to the latest calculations by EU scholars, Europe has 11,000 alien species, and this number is growing unbelievingly fast. Every year dozens of new plant species from various parts of the world are found in Europe. In a year, such invasive alien species can cause losses in the amount of 12 million Euros, but this figure represents the damage done by only 10 percent of the invasive species.

At present Lithuania has about 548 alien plants, 46 species of which are invasive, while about 60 other species are considered to be potentially invasive and can cause serious ecological problems in the future. Our fight with alien species is a very important step toward preventing the extinction of biological diversity, one of the EU major goals.

Below are seven most dangerous alien plants:

Sosnowsky’s Hogweed (Heracleum sosnowskyi)

This plant is native to Caucasus. Since the 1950s it was grown in Lithuania as feed. Later it was disseminated by florists and bee-keepers, but soon it started spreading naturally. It is dangerous to human health because its juice can cause skin burns. Thus, it is very dangerous to children. It overgrows habitats and completely changes them. It is difficult to eradicate it in places where it flourishes.

Smallflower Touch-Me-Not (Impatiens parviflora)

This species originated in Central Asia. It began to spread in Lithuania in the 1930s, but they became especially widespread in the last 30 years. In forests, they form entire populations and overgrow many local plants. No reliable or safe eradication methods have been found yet.

Rugosa Rose (Rosa rugosa)

This species is native to eastern Asia. In Lithuania, it has been grown from the mid-twentieth century. To prevent erosion and harvest its valuable fruit, it was planted in sea dunes, quarries, and at roadsides. Now it has spread widely in the sea dunes and is close to destroying older habitats and some local plants.

False Acacia (Robinia pseudoacacia)

It is native to North America. In Lithuania, this species was introduced in parks and squares but has spread to outer and inner forests and sea dunes. Fires help these acacias spread by means of seeds and root saplings. In the Currish Lagoon’s fire-site, they take up 30 percent of the area each year, form dense overgrowth, and completely alter existing habitats.

Dwarf Serviceberry (Amelanchier spicata)

It is native to North America. At the end of the nineteenth century it was grown as a berry plant in gardens but later birds disseminated dwarf serviceberry seeds in forests. In eastern and western Lithuania, it is now a very common shrub, and in some pine forests it has formed dense overgrowth that grows ever thicker and, if cut, re-grows rapidly.

Bigleaf Lupine (Lupinus polyphyllus)

It is native to North America. It was brought to Lithuania in the early twentieth century. There, it was sown in outer and inner forests as animal feed, fire breaks, and a way to improve soil. Yet now the areas where the bigleaf lupine grows are losing their once rich natural plant habitats, while nitrogen-loving plants, mostly nettle and mugwort, are overtaking them. The bigleaf lupine poses a great threat to the biological diversity of meadows and sand habitats.

Boxelder Maple (Acer negundo)

This tree originated in North America. In Lithuania, it was introduced in 1936, and 40 years later it was spreading along the river shores, outer forests, wastelands, and roadsides. Its pollen can cause the pollen allergy pollinosis. This type of maple spreads very easily because its fruit is disseminated by wind and water. It poses the greatest threat to coastal habitats and their biological diversity.

All photos: Zigmantas Guždinskas

The most world-known invasive alien species

Grey Squirrel (Sciurus carolinensis)
The grey squirrel originated in the eastern part of North America. It was brought to Great Britain and Ireland in the nineteenth century and later to other European countries. While competing with local species for food and habitat, the grey squirrel is slowly driving out the local, Eurasian red squirrel (Sciurus vulgaris) from most parts of Europe.

Spotted Deer (Cervus nippon)
This species’ natural habitat is south Asia, from where it came to Europe, Africa, North America, and Australia. It poses a great to local deer populations because spotted deer is cross-breeding with them.

Muskrat (Ondatra zibethica)
The muskrat was brought from North America for its valuable fur. At present it spreads and breeds all over Europe. Muskrats dig their dens deep into the coasts of water bodies, which every year leads to great economic losses in the management of dams, canals, irrigation systems, and flood-prevention systems.

Zebra Mussel (Dreissena polymorpha)
The zebra mussel originated in Asia: the Black, the Caspian, and the Aral Seas. Later it spread to Europe and in the twentieth century it was introduced in North America. This is one of the most notorious invasive alien species in the world: it has a negative impact on the biological diversity of water bodies and creates huge problems for industry by polluting and clogging intake pipes in water-pumping sites.

Asian Tiger Mosquito (Aedes albopictus)
The Asian tiger mosquito is spreading fast in Europe and is a carrier of at least 22 viruses, such as dengue, Chikungunya fever, the Ross River virus, and the West Nile virus. It was brought from southeastern Asia in used tires for sale in Europe. Due to climate changes these mosquitoes will spread to the northern parts of Europe.

Canadian Waterweed (Elodea canadensis)
The Canadian waterweed was accidentally introduced in North America as a decorative plant. On the European continent, it was found for the first time in Ireland in 1836. Later, it rapidly spread to other water bodies in Central and Northern Europe. The Canadian waterweed forms dense overgrowth and pushes out local species of water plans by changing the conditions for growth.

Colorado Potato Beetle (Leptinotarsa decemlineata)
The Colorado potato beetle is one of the most well-known agricultural insect pests. The beetles originated in Central Mexico but as early as 1874 they reached the Atlantic coast in their yearly migration eastwards. During World War I the Colorado potato beetles arrived in European potato fields. Accidentally, they were brought by the U.S. armed forces together with weapons and food supplies.

Jewelweed (Impatiens glandulifera)
This plant is native to Asia. It was brought to Europe as a pretty decorative plant. It is liked by bee-keepers because of its plentiful nectar. The jewelweed is a strong rival that can push out other important local plants fortifying the soil surface with their roots. The jewelweed can induce soil erosion.

American Mink (Mustela vison)
The American mink originated in North America. At present they occur in Europe, Asia, and South America. This animal easily wins out over local species. It is no wonder that the spread of the American mink is closely associated with a rapid depletion of the European mink population. The American mink is known as a bird-nest predator and carrier of various diseases.

Raccoon Dog (Nyctereutes procyonoides)
This species are indigenous to eastern Asia. Presently they live all over Europe. They feed on birds hatching on the ground, amphibians, and reptiles. The raccoon dog is one of the major carriers of rabies and trichinellosis.

European Rabbit (Oryctolagus cuniculus)
The European rabbit is native to southern Europe. At present they appear everywhere, except for Asia and the Antarctic. Already as early as the nineteenth century the first signals of impending disaster were issued in Australia. European rabbits adapted so well to new Australian conditions and began spread so rapidly that they became the biggest enemies of the country’s agriculture. They still cause great damage to the ecosystems of the Australian continent as they compete for food with local animals. Every year Australia spends millions of dollars on the isolation or eradication of these animals.