A Victorian trend for keeping and trading exotic plants has given the worst invasive species time to take root across Ireland, writes Colette O’Flynn.
THE chances are you don’t have to go too far from home to see one of Europe’s and Ireland’s most invasive plants. If there is just the odd clump of these invaders in your area there is still a chance they could be eliminated, but if the infestation is more established and common, then it may be a case of looking at longer-term management options.
In reality, most alien species arriving to Ireland cause no negative effect for us and do no harm to our native wildlife. In fact, more than one third of Ireland’s wild plants are alien, with just 16 listed as invasive. But even a small number of species can cause a lot of harm.
Invasive species are alien to an area, have been introduced outside their natural range because of human intervention, and, when they thrive, they can impact on nature and the services it provides.
Therefore, the arrival of invasive species threatens our native biodiversity. They can have a socioeconomic cost and can impact on our health.
Most of our widespread invasive species are those that have been in Ireland a long time and so have had time to take hold and spread. The trend for keeping and trading in exotic (also known as alien) plants in the Victorian times can be directly linked to the first introductions of some of our most invasive plant species in the late 19th century.
Giant hogweed (Heracleum mantegazzianum), Himalayan balsam (Impatiens glandulifera) and Japanese knotweed (Fallopia japonica) were all introduced in to Ireland as ornamental plants. They grow quickly and densely in the summertime, out-compete native plants, then die back in the winter, leaving riverbank areas exposed and thus more susceptible to erosion. This in turn can cause increased sediments in the river affecting salmonid spawning grounds. As they can grow in such high densities they can also restrict access to many amenity areas with resultant economic impacts and public safety issues.
After Japanese knotweed, the most widespread and common of the invasive plants, was awarded a gold medal in the Netherlands in 1847 for being the “most interesting new plant”; it was a must-have for plant collectors. The resulting demand meant that by 1902 it was found in the wild in Ireland.
Japanese knotweed has gone from prize winner to pariah by displacing native species and is also of concern in urban environments, where its potential to impact on structures has proven costly for development sites in particular.
Japanese knotweed is not alone, with two closely related knotweed species also being invasive in Ireland: The much larger giant knotweed (Fallopia sachalinensis) and their hybrid Bohemian knotweed (Fallopia x bohemica).
What can be done to tackle these invaders?
In the first instance, the species should be recorded and reported to the National Biodiversity Data Centre and your local authority. If the species is giant hogweed, a notice should be erected warning anyone that may come into contact with it of its dangers.
Japanese knotweed should not be cut as this may aid its spread unless it is done so in accordance with best practice guidance. Movement of the plant, including soil or spoil infested with it, should be accompanied by a licence from the National Parks and Wildlife Service. Advice should be sought prior to control work on these invasive species and, where possible, biosecurity measures put in place to prevent further spread of the species.
As is the case with many invasive species, once they are reproducing and spreading in the wild, it may not be feasible to eradicate them. Therefore, prevention is better than cure — by taking measures to prevent them getting here in the first place; and early detection and warning if they do. The National Biodiversity Data Centre manages the invasive species early warning system for Ireland where species alerts are issued if a potential invader is recorded in Ireland. The aim of issuing a species alert is to trigger a rapid response to remove or prevent further spread of the species.
In September 2011, comprehensive regulations which address deficiencies in Irish law implementing the EU Birds and Habitats Directives were signed into law. The European Communities (Birds and Natural Habitats) Regulations 2011 contain important provisions to address the problem of invasive species. A black list of unwanted species is set out in the regulations. It is an offence, without a licence, to release or allow to disperse or escape, to breed, propagate, import, transport, sell, or advertise such species. Two regulations that deal specifically with these scheduled lists of species are: Regulation 49 — prohibition on introduction and dispersal of certain species; and regulation 50 — prohibition on dealing in and keeping certain species.
Regulation 50 is not yet in effect. The delay in bringing regulation 50 into effect has been caused by the need to consult with groups that may be affected by the new law and to carry out detailed risk assessments on invasive species that are traded. The National Biodiversity Data Centre and Inland Fisheries Ireland completed the assessment and consultation work on contract in 2014. It is anticipated that regulation 50 will be enacted by the arts and heritage minister this year.
On January 1, 2015, a European Regulation on the prevention and management of the introduction and spread of invasive alien species came into force. It is a legally binding tool for all EU states that lays down rules to prevent, minimise, and mitigate the adverse impacts of the introduction and spread of invasive species, and involves a phased introduction of various strategies, including an early-warning and rapid-response system with surveillance and border controls in member states.
The first milestone will be the publication of a list of notifiable species alien to Europe.
Of a big concern to Ireland and other member states are species that may be native to some parts of Europe that might invade Ireland.
Therefore, within the regulation there is scope for member states to compile lists of species where regional co-operation would be required.
Colette O’Flynn is an invasive species officer with the National Biodiversity Data Centre. Colette welcomes any queries and would be happy to receive sightings. If possible, please supply a photograph to aid verification. To view identification guides, species alerts, and to submit your sightings, go to www.invasives.biodiversityireland.ie
Native to North Africa, it is found here on roadside hedges, woodland edges, and waste ground. Due to the plant’s extensive network, removal only practical on a limited scale through a combination of excavation and herbicides. Can spread from small root fragments.
Of Chilean provenance, but not related to the garden rhubarb. Does best in milder, wetter areas which explains why it is more common in western and seaboard counties. Can be seen growing prolifically in Achill and Connemara, for example.
Its massive leaves smother other plants and it has coarse prickles. Control is feasible through chemical means that require follow-up action over a period of time.
From the Cape Region, South Africa, it has become naturalised in many parts of Ireland. Found especially in the South-West where it is common along road banks and hedgerows and by rivers and lakes. Chemical control can be difficult, but can be achieved with regular follow-up action.
Introduced in 18th century and native to Spain and Portugal. Its lilac flower stands out in May and is often admired. Does well in acid, wooded areas of Cork, Wicklow, and Kerry. There have been ongoing eradication campaigns for decades. Getting rid of the “rhodo” is seen as one of the biggest challenges in Killarney National Park where it threatens ancient oak and yew woodlands.
Despite an eradication programme over the past 35 years, it continues to grow in the park. Spreads widely and can grow up to 8m tall. It can prevent the growth of other plants over which its leaves and branches form a canopy. Also has a fungus which attacks other plants. Can be tackled by uprooting, chemically treating stumps or by continuing herbicide application. Hard to kill.
A member of the Busy Lizzy family, it introduced here as a garden plant in the 19th century. Spread swiftly along waterways and wet places. Dies in the autumn leaving ground at risk of erosion. Chemical control readily achieved, but may need ongoing control for five years, or more.
Believed to have come from China, the butterfly bush is a common garden plant and its flowers attract butterflies. Found on waste ground in the environs of cities such as Cork and Dublin, but countrywide distribution. Does well on poor soil and grows on walls, rocky outcrops and roadsides. Controlled through digging out roots and chemical application. But can regrow vigorously from the stump.
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