Invasive Species

A definition of an invasive species is a plant, fungus, or animal species that is not native to a specific location (an introduced species either deliberately or accidentally).

Invasions by non–native species are a major threat to global biodiversity second only to habitat destruction. Invasive species negatively affect terrestrial and aquatic habitats and they cost the Irish economy by damaging our fisheries, blocking navigation, reducing agriculture outputs and wasting resources. Invasive species also have negative impacts on economic interests as well as civil infrastructure.

Human activities are the main cause of the arrival of invasive species. As well as having impacts on the environment and the economy, invasive species may impact on our lifestyles.

Gardening, boating, angling and the keeping and trading of pets are all activities that can unintentionally spread invasive species

Many species are deliberately released like species of fish for angling or the Muntjac deer for hunting.

Others have escaped from gardens and farms like Japanese Knotweed and the American mink.

Some arrive as hitch hikers and stowaways with imported goods or other species!!

The Convention on Biological Diversity website gives the following information:

  • Since the 17th century, 40% of all animal extinctions have been because of invasive species
  • The U.S the U.K. Australia, South Africa, India & Brazil have suffered economic and environmental losses well over €100 billion as a result of introduced species
  • The structure and composition of ecosystems can be negatively transformed by invasive species by repressing or excluding native species is an information website run by the Irish Government & the Northern Irish Government. Here, some 47 non-native invasive species are listed; they are listed as being either established threats or potential threats. Of the established threats there are 30 and the potential threats 17. They are grouped into habitat in terms of freshwater, marine or terrestrial.

Japanese Knotweed is among the 30 established threats as is Giant Hogweed, Giant Rhubarb, (Gunnera) and Himalayan Balsam.


Invasive Species - Giant Hogweed


Invasive Species - GIANT RHUBARB


Invasive Species - HIMALAYAN BALSAM


Invasive Species - Giant Knotweed


Invasive Species - Bohemian Knotweed


All types of knotweed grow vigorously and out-compete native plants. They all form tall dense stands that exclude all other vegetation, shading the area below. Native plants can rarely compete with these invasive species and local plant biodiversity is reduced.

Rivers, hedgerows, roadsides and railways can form important wildlife corridors for native plants and animals to migrate and disperse along and large infestations of knotweed and other invasive species can block these routes for wildlife.

Invasive Species - All types of knotweed grow vigorously

Japanese knotweed can also seriously damage buildings, hard surfaces and infrastructure in some cases.

Once established Japanese Knotweed can be particularly hard to control and it has the potential to undermine concrete and tarmac and other areas of hardstanding if there are any weaknesses if these surfaces already present.

When Japanese knotweed colonises riverbanks, it can damage flood defence structures and reduce the capacity of channels to carry flood water.

If you find Japanese Knotweed on your property it should be dealt with as soon as possible, if it is not, stands of the plant can quickly become established, there by making it more difficult to control and manage.

Invasive species - damage flood defence structures


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