Invasive Alien Species

An Invasive Alien Species (IAS) is a terrestrial or aquatic plant, animal, insect, or microorganism that has colonised and invaded a new country or environment and causes substantial environmental and economic damage.

Plants and animals all over the world vary in their competitiveness. Their capacity to spread is normally controlled by their local environment, soil or climatic conditions, or by the interactions with other plants and animals. When a plant or animal is moved to a new environment such as a different country, and that new environment suits them, they can colonise invasively and take over making it impossible for the original, native species to continue living there. In fact, IAS are considered to be the second most important cause of global biodiversity decline after habitat loss.

Japanese Knotweed
Japanese knotweed is one of the more recognisable of Ireland’s Invasive Alien Species.

This problem has become so serious over the last thirty years that Governments across the world have introduced legislation in an attempt to prevent IAS from being introduced to new countries and, once introduced, to actively stop their spread.Legislation varies across countries and continents. Ireland has adopted a suite of EU measures which can be viewed here.

However, some alien invasive species not controlled by  legislation may pose significant problems locally in individual member states.; an example is winter heliotrope. Winter heliotrope (Petasites fragrans) has become severely invasive in Ireland over the last five years but it is not included in EU-wide lists because it appears to be a problem which is specific to this country.

Winter Heliotrope
Winter heliotrope can rapidly colonise road verges, woodlands and river banks and out compete native vegetation.

In Ireland, the National Biodiversity Data Centre (NBDC) does a superb job recording our flora and fauna, including the occurrence of non-native species and their potential invasiveness. Well known, highrisk species include Japanese Knotweed, Giant Hogweed, Grey Squirrel, and Mink. There are many others which are less visible initially but cause significant environmental damage; for example, the fungus Aphanomyces Astaci has caused a plague in our native crayfish, and the ash die back fungus Hymenoscyphus Fraxineus, which is thought to have originated in Asia, has nearly destroyed our native ash population within 8 years. Also, there are many invasive alien freshwater aquatic plants and animals which may not become obvious until the native ecosystem is overwhelmed.

All records submitted to the NBDC are mapped on their comprehensive mapping system which can be accessed here.

The table shows the most frequently encountered and highest risk IAS in County Limerick.


Where Found

Legislation for Control

Japanese knotweed (Fallopia japonica) and its relatives

All habitats, throughout Ireland. Spreads rapidly along water and road corridors

High risk. EU legislation

Giant hogweed (Heracleum mantegazzianum)

River margins, field boundaries, road verges

High risk. EU legislation

Indian balsam (Impatiens glandulifera)

Riverside habitats

High risk. EU legislation

Rhododendron (Rhododendron ponticum)

Woodland, old estates, gardens. Increasingly found in raised and blanket bogs

High risk. EU legislation

Cherry Laurel (Prunus laurocerasus)

Woodland, old estates, gardens.

High risk

American Mink (Mustela vison)

River and stream corridors, lake margins

High risk. EU legislation

Grey Squirrel (Sciurus carolinensis)

Woodland, urban areas, gardens

High risk. EU Legislation

Winter Heliotrope (Petasites fragrans)

Road verges. Almost anywhere

High risk, but not controlled under EU legislation

Butterbur (Petasites hybridus)

River and stream corridors, Almost anywhere.

Medium risk, but not controlled under EU legislation

Buddleja (Buddleja davidii)

Waste land, gardens, road margins. Still planted as an ornamental

Medium risk

Traveller’s joy (Clematis vitalba)

Scrambles over hedges and small trees

Medium risk

Himalayan honeysuckle /pheasantberry (Leycesteria formosa)

Almost anywhere. Frequently in gardens where it is planted as an ornamental. Beginning to infest woodland and bog habitats

Medium risk

Lonicera nitida

Old hedgerows, field boundaries, gardens. Used as hedging in the past.

Medium risk

Snowberry (Symphoricarpos alba)

Old hedgerows, field boundaries, gardens. Used as hedging in the past.

Medium risk

Some of these plants, such as Buddleja and Cherry Laurel are still commonly planted in gardens, which is a matter of real concern, as they can readily 'escape' into the countryside where they cause havoc with our native vegetation.