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Invasive Species

Non-native Invasive Alien Species

Non-native invasive alien species (IAS) are species that are introduced (intentionally / unintentionally) and / or spread threatens the environment, the economy & society including human health. IAS have been introduced outside their native habitat, where these natural management systems are not present to keep them in check. In their native habitats, predators, diseases and competitors, which have evolved in conjunction with them, to manage them. They have certain features that assist them to spread outside of their native range. They reproduce and grow rapidly; have an ability to disperse; & adapt to a wide range of new conditions and environments.


IAS plants can be spread by wind, water, movement of soil, people or animals. They are the second largest cause of biodiversity loss worldwide, after habitat destruction. Negative impacts of IAS on biodiversity can occur through a range of mechanisms, for example, competition, diseases, changes to habitats and food webs. The estimated annual cost of IAS to both the economies of Ireland and Northern Ireland is > £210 million / annum.


Council has developed a Non-native Invasive Alien Species Strategy: Council Owned Greenspaces 2020-2025, which outlines how it will manage IAS on its own land. It does not include other public owned land, private owned land or unregistered land. Council are not responsible for controlling IAS, except where it is growing on Council’s owned land. It is the responsibility of the landowner to control IAS on their land.


High risk IAS within the District include Giant Hogweed, Himalayan Balsam & Japanese Knotweed.


Giant Hogweed

It is native to Asia and was introduced as an ornamental plant to the British Isles in 1800s. Giant Hogweed is a tall plant (2 - 5 m), with white flowers on an umbrella shaped head, which are up to 80 cm across & resemble large cow parsley. Leaves can grow up to ~3 m in length. Stems are usually 10 cm in diameter that are often purple spotted or purple, with stalks covered in bristles. It produces up to 50,000 viable seeds, which disperse with the movement of wind, water, soil or spread by transportation in contaminated soil, footwear & machinery.


Giant Hogweed produces very large leaves, which cast a dense canopy that shades out less vigorous native plants. This changes the species composition and reduces species diversity of native plant communities, as it establishes dense swards that displace and suppress the growth of native flora. In the winter, the leaves die back, posing a significant increase in riverbank erosion as the soil becomes exposed to increased direct rainfall and floods. This poses a serious threat to salmon spawning habitats.


Giant Hogweed is a public health hazard as it produces sap that causes a painful and phototoxic reaction. The sap contains photosensitizing furanocoumarins, which in contact with human skin and combined with UV radiation causes severe skin burning, itching and blistering. The lesions are slow to heal and any scarring may persist for several years.


It is listed as an EU Species of Concern & landowners are legally required to control it on their own land under the Invasive Alien Species (Enforcement & Permitting) Order (NI) 2019. For further information visit Be aware of Giant hogweed and avoid contact | nidirect Also, you can report a sighting of Giant Hogweed that will be submitted to CEDAR as the official monitoring method for EU Species of Concern.


Himalayan Balsam

Himalayan Balsam is a shallow rooted IAS terrestrial plant, with its origins from the Himalayas. It produces purplish-pink flowers in summer, with large oval flowers. They have large oval leaves, which have teeth around the edges. Individual plants reach 2 m in height, with fleshy hollow stems and produce about 2,500 seeds. The seedpods explode when they are touched, dispersing the seeds by wind, water, animals and humans. Due to its rapid growth, it has the ability to reduce biodiversity, by outcompeting native plants for space, light & resources. During the summer, it competes for pollinators with native species, with its high sugar nectar content and extended flowering season. This competition can reduce native bee & plant species diversity and the ability of plants to seed set. It dies back in autumn, which leaves the ground bare of vegetation and more susceptible to erosion.


Himalayan Balsam is listed under The Invasive Alien Species (Enforcement and Permitting) Order (Northern Ireland) 2019. Therefore, the landowner is required to control it on their land. For further information visit Invasive Species Ireland


Japanese Knotweed

Japanese Knotweed was introduced in the 19th century, as an ornamental fast growing plant from Japan, but is now widespread throughout the British Isles. The vertical green leafy shoots extend up to 3 m in height, with large, broadly oval and pointed, which grow in zigzags along the branches, usually with a pale stripe down the middle of the leaf. It produces long strings of creamy-white flowers late in the summer. In winter, the plant dies back, leaving stems that resemble bamboo canes, which leaves the ground bare and more susceptible to erosion. It is associated with a deep, extensive rhizome network. It is spreading quickly throughout the island of Ireland, with the main method of distribution, from the movement of soil material infected with fragments of rhizome (root) or plant material. Also, it is spread by contaminated vehicles, equipment, colonisation from upstream areas washing it downstream and illegal dumping.

It vigorously invades natural habitats and out-competes native vegetation, by reducing light. It forms extensive monocultures / dense stands, which reduces species diversity and blocks wildlife corridor routes. Once stands become established, they are extremely persistent and difficult to remove. For further information on how to identify it & resources visit Invasive Species Ireland

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