Invasive species

The following invasive plants can be found in the territory of Žemaitija National Park:

Sosnowsky’s hogweed (Heracleum sosnowskyi). It is a perennial, monocarpic perennial plant of the family Apiaceae, 2.5-3.5 m tall, sometimes up to 4.5 m. The taproot is thick, up to 10 cm in diameter, often branched. The stem is ribbed and covered with coarse hairs. The leaves are large, feathery, with a coarsely toothed leaf margin. The flowers are clustered in large compound umbels at the apex of the stem and lateral branches. The central umbel is the largest, the lateral umbels slightly smaller. The petals are white or barely pinkish. The fruit is a schizocarp, consisting of two single, ovoid, very flattened laterally parts, called mericarps.

Origin and distribution. Sosnovsky’s hogweed  is native to the central and eastern Caucasus, and is also widespread in Transcaucasia. As a weed and invasive species it is widespread in the Baltic States, Belarus, Russia, Ukraine, Poland and Germany. Sosnovsky‘s hogweed covered areas reach 10 000 hectares in Lihtuania alone. In the territory of the Žemaitija National Park, Sosnovsky’s hogweed  is so far distributed around the town of Plateliai. The largest area is in the village of Kruopiai, close to the park territory.

Threats. In areas where Sosnowsky’s hogweed begins to grow, biodiversity is greatly reduced and plant species native to the area disappear. By maturing and dispersing a large number of seeds, growing rapidly and forming large stands in places, it outcompetes almost all other plants.

Control. Individual plants can be dug up, or roots can be cut, or a field can be ploughed up or treted by herbicide application. The best way to stop the spread of the plants is to cut them back when they are young, before the seeds have matured. When eradicating Sosnowsky‘s hogweed it is essential to use personal protective equipment to prevent the sap from getting into the respiratory tract, eyes and on bare skin.

Sosnowsky‘s hogweed brochure

Large-leaved lupine (Lupinus polyphyllus). A perennial 60-110 cm tall, bush-forming plant with thick roots. The clustered flowers are usually blue or purple in various shades, less often white or variegated. It flowers from late May to late June, with single or cut individuals flowering during other summer months. The flowers produce fruits, hairy pods with seeds. A single larger plant can produce more than 5 000 seeds during the growing season. The seeds remain germinable for many years, while the hard seeds, which usually account for 20 % of the total number of seeds, remain germinable for 50 years or longer. The large-leaved lupin can also reproduce by rhizomes, for example, if it is divided by ploughing the soil.

Origin and distribution. The species is native to western North America. It was introduced to Europe in 1826 and quickly spread throughout Europe as an ornamental plant, sown for animal feed or to improve the soil.

The first occurrence of fruiting large-leaved lupins in Lithuania was in 1931, but they became more widespread in the late 20th century, when large areas of unused land – abandoned meadows and cultivated fields – became available. Lupines are now widespread throughout the country, forming large stands in places and are the dominant plants in communities.

It is widespread throughout the Žemaitija National Park area: in meadows, slopes, undergrowth, where there is abandoned, uncultivated land.

Threats. Lupines form a symbiosis with nitrogen-fixing bacteria, altering the soil by adding nitrogen compounds. In areas where lupins become established, competition-prone native plants disappear.

Control methods. In order to control and eradicate the spread of large-leaved lupins, the plants are mowed (to prevent the seeds from maturing) and dug up.

Brochure for the Lupinus gaussiana

Canadian waterweed (Elodea canadensis). A perennial, fully submerged aquatic plant with a branched stem growing up to several metres. Leaves 6-15 mm long and 2-4 mm wide, ovate-lanceolate, dark green, translucent, straight or oblanceolate but not curled in the middle, in whorls of 3. The flowers are pale purple or off-white and emerge on long pedicels. Seeds do not mature as only female individuals grow. Canadian waterweed reproduces vegetatively by stem parts of various sizes and by overwintering buds.

Origin and distribution. The Canadian waterweed is native to North America. It was introduced as an aquarium plant in Europe in the first half of the 19th century and was accidentally introduced into water bodies and spread throughout Europe. At present, the Canadian waterweed has taken over all suitable habitats. The species does not produce seeds in Europe, as only females grow, but can easily reproduce vegetatively. Overwintering buds or stem parts are carried by water to new locations. Waterweed are quite common in the Žemaitija National Park. They are found in lakes, ditches and peat bogs.

Threats. Canadian waterweed, which form thickets, outcompetes native small aquatic plants, especially those adapted to shallow water.

Control. The abundance of Canadian waterweed in small pools is reduced by herbivorous fish. In swamps and other artificial water bodies, abundance can be reduced by mechanical means through periodic scraping of plants. The extracted biomass can be used to produce compost.

Canadian waterweed brochure

Rugosa rose (Rosa rugosa). A shrub of the rose family, which can grow up to 2 m tall. Stems are numerous and erect, usually 1-1.5 m, sometimes up to 2 m tall. Branches are thick, abundantly prickly and hairy. The spines are straight, fluffy, with many needle-like spines between them. The leaves are compound, consisting of 5-9 very wrinkled leaflets. The flowers are fragrant, large, 6-8 cm in diameter, solitary or grouped in apical clusters of 2-6, sometimes more. Petals 5, rather large, red-violet, pink, sometimes white. Blooms from May to late autumn. It differs from other types of roses in its dense, variously long spines and clearly wrinkled leaves.

Origin and distribution. The species is naturally widespread in East Asia. In Central Europe, it began to be cultivated in 1860, and in Lithuania in the first half of the 20th century – as a decorative, food and medicinal plant. The first recorded occurrence of this plant in Lithuania was in 1937. These plants became most widespread in Lithuania in the second half of the 20th century, when they were used to green up slopes and strengthen coastal sandbanks. Now this plant is widespread throughout the country, especially common in the southeastern and western parts, and somewhat rarer and less abundant in the northern part. Currently, it is found throughout the country in open, dry soil habitats (very common in coastal dune habitats). The greatest influence on the spread of the species was the fact that it was planted in the wild and widely grown in green spaces. Quite common in the territory of the Samogitia National Park. Found on roadsides, slopes, and forest edges.

Threats. Rugosa roses have a negative impact on native plants, animals, communities and habitats by reducing the diversity of native species.

Control. Rugosa roses are very difficult to control and eradicate. There are no effective and environmentally friendly methods. Individual bushes can be dug up and destroyed. It is important to know that once the bushes are cut down or cut, they begin to grow rhizomes and begin to spread even more widely.

Rugosa rose brochure

Black cherry (Padus serotina). A tree of the rose family up to 10-20 m tall, also grows as a shrub. The bark is dark brown or brownish-gray. The leaves are oblong-ovate or lanceolate, 5-7 cm long with a sharply pointed apex. The upper side of the leaves is dark green, shiny, glabrous. The flowers are white, fragrant, gathered in narrow, rather dense, 10-14 cm long clusters. The drpe fruits are pink when they begin to ripen, and become black and shiny when fully ripe. When the fruits ripen, the sepals remain unfallen at the fruiting stem. It blooms in the second half of May, sometimes until the beginning of June, much later than the native bird cherry (Prunus padus).

Origin and distribution. The species is naturally widespread in North America. Black cherry began to be cultivated in Europe at the beginning of the 17th century, and in the 19th century. At the end of the 19th century, they began to be planted in forests for their timber and in the hope that they would prevent the spread of fires and improve the soil. The fact that they were planted in forests and ornamental gardens had a great influence on the spread of these plants. Black cherry reproduces by seeds and spreads by root sprouting. Birds feed on the fruits, so their seeds can be carried over long distances from the parent plant. In Lithuania, black cherry has naturalized and is rapidly spreading in forests. While it is rare in the territory of the Samogitia National Park, it can be found in Babrungėnai, on the edges of the forest.

Threats. As the density of black cherry increases in habitats, species diversity decreases not only in grasses and mosses, but also among shrubs and trees. Black cherry inhibits the spontaneous regeneration of local trees. All parts of the black cherry contain cyanide, so their droppings can affect various animals, and cases of animal poisoning have been recorded.

Control. Black cherries can be destroyed by mechanical means – cutting down trees and uprooting stumps and young plants. The most effective method of destruction is a combination of chemical and mechanical means of eradication.

Black cherry brochure

Box elder (Acer negundo). A fast-growing tree 10-20 m tall. The branches are widely spread, the bark is gray-brown, shallowly furrowed. The leaves are compound, consisting of 3-7 coarsely toothed or irregularly lobed leaflets. The flowers are uniform, small, greenish-pink. The male flowers are gathered in tufts, the female flowers in drooping clusters. It blooms from late April to mid-May. The flowers are pollinated by the wind.

Origin and distribution. Naturally widespread only in North America. In Europe, these trees began to be grown in the 17th century (mainly in parks). Now, the box elder is widespread throughout Europe and is considered an invasive species in many countries. Its rapid spread was greatly influenced by the fact that it was often planted in green spaces. The fruit is easily carried away by wind and water, so invasive box elder spread successfully, especially along river banks. In Lithuania, box elders cultivation began around 1930, and were registered in 1963. However, box elders are quite rare in the territory of the Samogitian National Park.

Threats. The greatest threat is posed by riverside box elders. Once established, box elders form dense stands, eventually crowding out native plant species. Box elder seeds that enter rivers can travel long distances and establish themselves in new areas. Wind-borne box elder pollen can cause allergies in some people, so sthis species growing in cities might have a negative effect on human health.

Control. Eradication by felling trees is not, as box elders quickly regrow and produce many offspring. The most reliable method of eradication is with chemical means.

Box elder brochure

Low juneberry (Amelanchier spicata). A multi-stemmed shrub about 6-8 m tall. The first-year shoots are hairy, then bare. Leaves are ovate, bluish-green with a toothed margin. Flowers are white, in clusters. Blooms in May. Fruits are pink at first, then bluish-black with erect stamens at the apex. The berries ripen between July and August.

Origin and distribution. The species is native to North America. In Europe, the low juneberry was introduced in the early 19th century. It was planted for its edible berries and as an ornamental plant. In Lithuania, in the mid-20th century, the low juneberry was planted in various landscapes as a useful berry shrub.  The berries are eaten by birds and their seeds are carried far and wide, and also reproduce by root sprouting. The low juneberry is rare in the territory of the Žemaitija National Park.

Threats. Forms dense thickets in or near forests, changes the nutrient composition of the soil, loss of sun loving plant species, and outcompeting other trees.

Control. Control by clearing shrubs is ineffective as the plants regrow very quickly from the stumps and produce many root sprouts. A combination of chemical and mechanical control is the preferred method of eradication.

Low juneberry brochure

Devil’s beggarticks (Bidens frondosa). It is an annual, 10- to 150 cm tall, heavily branched plant. The leaves are compound, pinnate, composed of 3-7 leaflets, with a long, unfeathered petiole. The graces at the apex of the branches consist only of tubular reddish-yellow flowers. Flowers from mid-July to October.

Origin and distribution. The species is native to North America. In Europe, the devil’s beggarticks was first recorded in France in 1762. The plump fruits of the devil’s beggarticks are adapted for distribution by terrestrial animals, waterfowl and humans. The fruit is carried far by water currents. The species was first recorded in Lithuania in 1982 in Kaunas, the banks of Nemunas.

Threats. Compared to the native species, the devil’s beggarticks is less demanding of soil moisture and therefore grows well in relatively dry areas. Devil’s beggarticks grow rapidly and form fairly dense stands, competing with native herbaceous plants and often becoming the dominant species.

Control. To prevent the further spread of the species and to prevent the seeds from ripening, it is recommended to cut back stands regularly (at least monthly throughout the summer). If the number of Devil’s beggarticks is low, they can be uprooted before or at the beginning of flowering. The grass cuttings can be used for compost if no seeds have been produced.

Devil’s beggarticks brochure

Canada goldenrod (Solidago canadensis L.). A perennial, 50-200 cm tall, dense shrub. The stem is erect and covered from the bottom to the top with coarse hairs. Leaves are ovate, lanceolate or linear, toothed or equilateral. The racemes are small, clustered in apical panicle-like compound inflorescences. The tongue flowers are yellow, rarely white, and sometimes the racemes are without tongue flowers. Tubular flowers yellow. Fruit is a cylindrical or ovoid drupe. It flowers from July to October.

Origin and distribution. The species originates from North America and is widely distributed as an alien plant in Europe, spreading to Asia and other continents. The mature Canada goldenrod was first found in Lithuania in 1983 and is now widespread throughout the country. It grows in moderately moist and dry soils in open areas.

Threats. The rapid spread of the Canada goldenrod is due to the fact that it has been cultivated in flowerbeds throughout the country for a long time. It produces a large number of wind-dispersed seeds, which germinate under favourable conditions and within a few years new invasions are established. Sedges are perennial, dense bush plants that are not demanding of soil conditions. Because they form large stands, they outcompete most native grassland plants.

Control. It is recommended that individual plants be uprooted and the remaining plants sprayed with herbicides. Established stands shoudl be eradicated by mowing before flowering (to prevent seed dispersal), and agrochemical and chemical control measures.

Canadian goldenrod brochure

Black locust (Robinia pseudoacacia). A tree of the legume family, usually 10-15 m, sometimes 25-30 m tall. The trunk is straight, often low-branching, up to 1 m in diameter, with deeply furrowed brownish-grey bark. The leaves consist of 9-25 ovate leaflets. The flowers are white or slightly yellowish, scented and clustered in clusters. Pods are 5-12 cm long, reddish-brown, bare, with 3-15 seeds. It flowers in June and ripens in October.

Origin and distribution. Native to the southeastern USA but widely introduced in Asia and Europe. Black locust was introduced as an ornamental tree in parks, towns and roadsides, and from the mid-19th century it was introduced into forests and used to plant eroded hillsides and sandy areas. Black locust was first found in Lithuania in 1958 and is now widespread throughout Lithuania. It is quite rare in the territory of Žemaitija National Park. It grows on forest edges, roadsides and landfills.

Threats. Black locust is a very vigorous tree that reproduces both by seed and by root and stump sprouting. The seeds can be carried very far by the wind, while the tree can spread 20 metres per year by sprouting. Black locust, which grows in dense clumps, changes the soil chemistry and, where it grows, it produces uncharacteristic nitrogen-rich plants. Sandy habitats are particularly affected by this, with the eventual loss of sand species.

Control. Balck locust is best controlled by chemical means. A herbicide solution should be injected into holes drilled in the trunk and main roots. The trees should only be cut back once they are completely dead (preferably after a year).

Black locust brochure

Armenian dock (Rumex confertus). A perennial 60-150 cm tall, large plant with thick, branched rhizomes. The lower leaves are oblong-ovate, obtuse, deeply cordate, with a long petiole. The leaf margins are distinctly wavy. The underside of the leaves and petioles are covered with dense, short but coarse leaflets. It flowers in June-July with small, greenish flowers clustered in a panicle.

Origin and distribution. It is native to south-eastern Europe and western Asia. In central and northern Europe, the spread of the Armenian dock began in the late 19th century, and is thought to have occurred accidentally in agricultural produce. In Lithuania, Thick-flowered Sorrel is a widespread and spreading invasive plant. It spread most rapidly in the mid-20th century, especially in river valleys.  It is quite rare in the territory of Žemaitija National Park. Found in Žemaičių Kalvarija, meadows, roadsides.

Threats. Thick-leaved sorrel is a plant with strong competitive properties. It often grows in solitary clumps, but sometimes forms dense thickets that cover large areas. Armenian dock outcompetes native grassland plants, especially the low-growing ones.

Control methods. To control the spread of the species, meadows are mowed to prevent seeds from maturing. The plants are destroyed by uprooting.

Armenian dock brochure

Scotch broom (Sarothamnus scoparius). A profusely branched shrub of the legume family with compact, broom-like branches, growing up to 1–2 m, sometimes 3 m, in height. Young bushes have green stems, the stems of large old bushes are woody. The leaves are trifoliate, composed of oppositely ovate leaflets. The flowers are bright or light yellow, sometimes with an orange tint. It blooms in May–June, the seeds ripen in August–September. The fruit is a pod that is initially green, almost black when ripe, flattened, covered with hairs.

Origin and distribution. The species is naturally widespread in Western Europe, the southern parts of Central and Eastern Europe and Scandinavia. It was first observed in Lithuania in 1898. The species began to spread particularly rapidly in natural habitats in the second half of the 20th century, because it was purposefully planted in order to strengthen the soil affected by erosion. Now found almost throughout Lithuania: in light pine forests, forest edges, sandy areas. Rare in the territory of the Samogitia National Park.

Threats. Has the most negative impact in sandy areas: changes the composition of the soil, overshadows local plants, which reduces species diversity.

Control methods. In order to stop spontaneous seed spread, the above-ground part should be cut off at the beginning of summer, but the broom will not die and will regrow for many years. The most effective way to destroy Scotch broom is by digging and uprooting it (preferably in spring).

Scotch broom brochure

Small balsam (Impatiens parviflora) An annual plant of the Balsaminaceae family. The stem is erect, glabrous, branched. The leaves are 8–17 cm long, 4–8 cm wide, ovate, pointed, with short petioles. The flowers are small, light yellow, clustered on the tops of long stems. It blooms from June to September. When the seeds ripen, the capsule bursts, its leaflets suddenly twist spirally and scatter the seeds. It grows in medium-humidity and moist mixed, deciduous forests, spruce forests, less often pine forests, it is often found in riverine thickets and grass communities, wastelands, gardens.

Origin and distribution. It is native to the mountains of Central Asia. As an alien plant, it is widely distributed in many European countries. These plants were first discovered near botanical gardens, in whose collections they were grown. Since the 19th century. In the mid-1970s, they began to spread rapidly in forests. In Lithuania, small balsams were rare until the mid-20th century, and began to spread rapidly from the mid-1970s. Human activity had the greatest influence on the spread of the species in Europe. It is believed that the spread of this plant was mainly determined by vehicles used in forests (by seeds sticking to the wheels). It is quite common in forests of the national park.

Threats. Small balsam are quite shade toleant, but can grow in grows in well-lit areas as well. They can grow even where only 5 percent of sunlight reaches the ground. As a result, these plants are able to occupy free ecological niches formed in forests – areas where the cover of herbaceous plants has been destroyed or is absent due to lack of light. In forests, small balsam compete with herbaceous plants and often become the dominant species of herbaceous weeds.

Methods of control. The plant is an annual, so if it is widespread in a small area, it is advisable to uproot it. In large areas, another effective method of destruction is frequent cutting.

Small balsam brochure

Annual fleabane (Erigeron annuus). An annual or biennial, rarely perennial, plant of the Asteraceae family, 50–120 cm tall. The stem is erect, hairy. The leaves are narrow, 10 cm long. The inflorescence is in white or pink panicles. It grows in rivers and moist meadows. It blooms from early June to October.

Origin and distribution. The species is naturally widespread in almost all of North America. In Europe, the species was first observed in the early 18th century, in Germany. It is believed that the annual fleabane spread from a botanical garden. This species began to spread most rapidly in the 19th century, and is now widespread almost throughout Europe. In Lithuania, annual fleabane were sometimes grown in flower beds at the beginning of the 20th century. Until the early 1980s, the species was rare in Lithuania, but later it began to spread very rapidly. Now it is very common throughout the country. It grows in various habitats, but most often settles in soils, meadows and pastures, and roadsides.

Threats. The greatest danger is posed to natural meadows. Annual fleabane spread rapidly and overshadow local flower and herbaceous species.

Control. It is best to uproot single annual fleabanes at the beginning of flowering. The abundance of this species can be controlled throughout the growing season by mowing the grass at least once every three weeks to prevent these plants from ripening seeds.

Annual fleabane brochure