As a boy, Harry Jones would regularly walk down to a stretch of the River Dodder that passes through Milltown and stroll its tree-lined path.
As he has grown up, so too have the exotic plants along his walking route, including those which, he later learned, are harmful to local vegetation.
Jones, now an environmental consultant, still walks his dog there every day, passing piles of rapidly spreading invasive plants.
“Everyone does. They just don’t know,” he said, on the banks of the Dodder last Saturday as he fed treats from a small plastic bag to his dog.
Invasive alien species, which are plants or animals displaced from their native habitats by humans and now harming their new environments, are one of the five significant drivers of biodiversity loss in Europe and worldwide, according to a recent European Commission report.
Along the Dodder that can mean that they squeeze out other plants, or that wildlife goes hungry.
They are spreading at an unsettling speed, says Jones, but with more resources and efforts, it is still possible to bring the situation under control. “I’m kind of optimistic but it’s going to be very expensive.”
A spokesperson for the Department of Housing said its National Parks and Nature Reserves unit does considerable work to tackle the issue. But “it does not have the resources required to extend such work to urban areas or the wider countryside”.
Dublin City Council plans to evaluate this year how its action plan to deal with invasive species, which ran from 2016 to 2020, has done, said Lorraine Bull, council biodiversity officer. “We will be able to provide further information then,” said Bull.
Along the Dodder
In Dartry Park along the Dodder, Jones points to plants, holding the fringes of some in his hand.
He stops in front of a stooping branch of old man’s beard over the river.
If even a tiny piece or seeds fall in, it means the invasive plant would travel downstream and multiply on land elsewhere.
“Waterways are the main kind of way that they’re transported,” says Jones.
Once Jones points out the invasive plants along the Dodder, they can be spotted almost everywhere, huddling over an old bridge on the river or under it, spreading their leaves.
Invasive exotic plants were often uprooted from their native habitats and transplanted to Ireland and other parts of Europe as ornamental plants, says Jones.
They can upset the balance of local biodiversity, he says. “Irish plants can’t compete with them,” says Jones, walking a steep path in Dartry Park as his dog trots alongside.
Some imported plants carpet the soil so quickly that they block the growth of existing plants.
“They are trying to get up, you know like there’s ivy there, but they kind of suffocate them,” said Jones, pointing at a few non-invasive ivy vines and a local ash tree.
Eventually, some die out, he says.
In Gardens
Exotic plants likebuddleia, also known as butterfly bush, which is everywhere along the Dodder, lure butterflies away from native plants and flowers, says Jones.
“I’ve heard them called McDonald’s of butterfly food because it’s really tasty to them, and they go crazy,” says Jones, smiling.
But buddleia is not nutritious, he says, and butterflies can’t survive on them – yet they’re hooked.
“They’re also then not pollinating the native plants nearby. They’re just going from butterfly bush to butterfly bush,” he says.
Local gardeners who don’t know that keep planting them, Jones says.
Another invasive plant called cherry laurel – considered “high-impact” by Ireland’s National Biodiversity Data Centre – is also routinely planted in private gardens, says Jones.
“Like most people have them on their gardens. I mean without knowing, Aldi and Lidl,they sell them,” he says, laughing. “And they shouldn’t, but it’s not illegal yet so …”
The Irish WildlifeActs and Europeanlegislation outlaw the planting or spreading around some invasive species. Buddleia and cherry laurel are not among them.
Jones says Massey’s Woods in Jamestown is littered with cherry laurel flowers, outcompeting native plants. It’s wreaking havoc too on biodiversity in Bushy Park, he said.
Some plants can be dangerous to humans. Likegiant hogweed, says Bull, the council’s biodiversity officer. It “spreads rapidly along waterways and is a public health risk, especially to children”.
Hard to Kill
Some invasive plants are notoriously resilient, likeJapanese knotweed, says Jones.
Leafy and ordinary-looking, it may even seem vulnerable to the untrained eye. But among environmental experts, it is known to cheat death.
“I mean, it used to grow on the sides of volcanoes in Japan. If you put it in a bonfire and burn it, it’d still survive,” says Jones.
Even buried under concrete, a microscopic hole is enough for Japanese knotweed to escape through and thrive, Jones says.
On the upper side of the river in Milltown, one patch of the plant is marked as under treatment by licensed contractors.
Chemical treatment is the only way to unburden an area of Japanese knotweed, says Jones. That might mean spraying, wiping or injecting herbicide into the plant.
Injection is safest, says Kevin Dennehy, a volunteer with Dodder Action, a volunteer group for cleaning and minding the river, who was just back from a day of river clean-up where he and fellow volunteers fished several Tesco shopping carts out of the Dodder.
“It’s far more labour-intensive,” he says, but it’s worth the effort.
Jones says it’s useful near rivers “as there is less chance of contaminating waters”.
The Challenges
Despite its notoriety, Japanese knotweed is not on the EU’s “union list” for invasive plants and animals of concern, which signals the need for prevention and control.
There was insufficient evidence that inclusion would prevent or lessen its adverse impact, says the European Commission website.
A spokesperson for the Department of Housing said if an invasive species is already prevalent “eradication is almost impossible and efforts in this regard would not be cost effective”.
There are other challenges too. If a high-risk invasive plant like Japanese knotweed grows on private land, the council can’t do anything about it.
“It is the landowner’s responsibility to treat Invasive Alien Species and ensure that they do not spread to other lands,” said Bull, the council’s biodiversity officer.
Jones says only licensed professionals can remove them. But since hiring one is costly, most people skip it or take things into their own hands.
They might spray them with herbicides that commonly have the toxic chemical glyphosate, he says.
“And chances are they’re not going to do a proper job,” he said. They can contaminate the environment in the process, says Jones.
In February, Malcolm Noonan, the Green Party minister of state at the Department of Housing,told the Dáil that the National Parks and Wildlife Services didn’t have enough resources to “provide grant funding to homeowners for the removal or eradication of Japanese Knotweed”.
At a Local Level
In itsaction plan for tackling alien invasive species for 2016–2020, Dublin City Council pledged to control and monitor Japanese knotweed, American mink and Himalayan balsam in particular on the Dodder.
The council “have organised community groups, volunteers and local companies to assist in these efforts”, it says.
The Department of Housing, Local Government and Heritagefunds councils to fight invasive species and to raise awareness.
In 2021, its National Parks and Wildlife Services granted €38,000 to Dublin City Council for its invasive species projects, said a spokesperson.
The Dodder runs into other council areas, too.
A spokesperson for Dún-Laoghaire-Rathdown County Council said it got two grants each worth €16,000 in 2021. Part of it, they said, was invested in the one-year treatment of Japanese Knotweed along the Dodder on its own lands and Dublin City Council’s lands.
Leo Magee, a senior engineer at South Dublin County Council, said its projects for tackling invasive plants and mink are generally funded by its internal budget. But they have applied for and received funding from the department under its national biodiversity action programme.
“In 2021, a sum of €5,000 was granted to produce a training video on Invasive Alien Plant Species,” Magee said.
South Dublin County Council has been liaising with Dublin city council and Irish Water for management of Japanese Knotweed and mink in the upper catchment of the River Dodder, said Magee.
Pádraic Fogarty, campaign officer at the Irish Wildlife Trust, said he doesn’t think that dealing with invasive species is difficult, “Though it is sometimes portrayed as such by cash-strapped local authorities.”
If natural heritage were prioritised and people saw the value in healthy ecosystems then the money would be provided for programmes, he says.
An invasive species such as buckthorn on Bull Island could easily be eradicated if the effort were made, he says. “But we have no management programmes for even areas like this that supposedly enjoy every protection on the books.”
Dennehy, the volunteer with Dodder Action, says that there’s a lack of coordination between Dublin City Council and the two other county councils to the south, which undermines efforts to tackle the problem.
It takes relentless follow-ups to get them to remove invasive plants, he says, and if it involves other Dublin councils then it’s especially hopeless.
“We found that the biggest problem is that they don’t have joined-up projects. They don’t work together on the rivers,” said Dennehy.
A spokesperson for Dún-Laoghaire-Rathdown County Council said it is working with other councils and agencies to address invasive species, listing several partners.
Dennehy says, though, that part of the solution is a national strategy and coordination.
During the February debate at the Dáil, Noonan said the government had “no national eradication plan at this time”.
Bull, Dublin City Council’s biodiversity officer, said that the council’s parks, biodiversity and landscape services treat the harmful species all the time.
“In its parks and open spaces, which includes river banks through the public parks,” she said.