A small lake covered with New Zealand pigmyweed, an invasive non-native species that was also added to the Union List on 20 June. Photo: Benjamin Blondel.
Hurrah – the seemingly ineradicable Japanese knotweed has finally made it onto the European Union List of invasive species requiring control. And 313 non-native species are waiting in the wings. Can the invasion still be stopped?
On 20 June, following a vote in Brussels, a further 26 plant and animal species were added to the Union List of invasive non-native species.1 These include Japanese knotweed and two other species of Asian knotweed, which almost everyone can see on a daily basis advancing across the Netherlands, displacing other plants and causing serious damage to sewers and foundations. Inclusion on the Union List means that trade, cultivation, transport and import are prohibited, and EU member states are obliged to locate and remove populations, or at least manage them in such a way as to minimise their spread and impact.
A horizon scan carried out in 2022 has also identified 313 high-risk species which, according to the Bureau for Risk Assessment and Research of the Netherlands Food and Consumer Product Safety Authority (NVWA), call for a prevention strategy and the application of the precautionary principle. Ideally, such newly arriving non-native species should be removed as soon as they are detected in the Dutch natural environment. The species in question include the emerald ash borer, American eel, hottentot fig, giant rhubarb, Canadian beaver, Caligus orientalis, snow goose, Obama ladislavii, and New Zealand flax. At the start of the Week of Invasive Species, the Biodiversity section of the Association of Environmental Professionals held a symposium in Utrecht on 19 June entitled: 313 new non-native species threaten our nature. How can we stop them? Bionieuws has compiled these insights on policy and the management of invasive non-native species.
Wilfred Reinhold, environmental lawyer and chair of Platform Stop Invasive Species
‘My battle against non-native species began back in 2006, when I discovered that Asian tiger mosquitoes were turning up in the Netherlands on a regular basis. That battle continues unabated: on 28 July there will be another hearing at the Council of State concerning an appeal we have brought regarding the lack of precautionary measures at ten importers of used tyres spread across the Netherlands. Between 2018 and 2021, Asian tiger mosquitoes, yellow fever mosquitoes or Korean bush mosquitoes were found at these companies, and in practice there appears to be no supervision or enforcement by the NVWA of the relevant regulations. I am a strong advocate of the precautionary principle: don’t take risks, because it is simply foolish to wait for problems to materialise. Once a species becomes established, it becomes harder, more expensive, and sometimes impossible to undo.’
Henk Groenewoud, invasive species expert at the Bureau for Risk Assessment and Research of the NVWA
‘We commissioned the horizon scans in 2014 and 2022, and these concern non-native species that pose risks of harm to nature – not phytosanitary or veterinary matters. In the case of the Asian tiger mosquito, there is no question of harm to nature, so that falls under the remit of the Ministry of Health, Welfare and Sport. What matters to us is establishing what is heading our way. In principle, that means all species from a comparable climate – an enormous number. Hitchhikers are everywhere, and species are also deliberately brought in: you would not believe how many people keep a termite farm as a hobby. On the basis of the horizon scan carried out for us by the Bargerveen Foundation, we issued advice to the Ministry of Agriculture, Fisheries, Food Security and Nature in 2024, stating that prevention is extremely important and that we must not wait until high-risk species have already become established. Control is carried out by industry, land managers, water authorities and municipalities, with the provinces playing a coordinating role. They are already doing an extraordinary amount: you see action plans or management plans for invasive non-native species everywhere, but the reality is that capacity and budgets have to compete with a great many other policy priorities.’
Christel Welles, invasive species specialist at the Province of Utrecht
‘Our reality consists of Article 17 and Article 19 species, where the former must in principle be removed immediately and the latter are subject to management, because eradication is no longer feasible. And for Article 19 species we distinguish between category a – not yet widespread – and category b: widespread. We are currently spending a great deal of time on the Asian hornet, an Article 19b species. For our approach we use a priority ladder and cost–benefit analyses for the introduction, establishment and spread of invasive species, because time, money and control capacity are not unlimited. It is extremely complex: take the Asian hornet, for example. We have cleared every observed nest, yet the situation has still got out of hand. If you miss just one nest, that means seven new nests – and you miss them easily, because in summer they are high up in the trees. But we have also had successes: the ruddy duck, the raccoon and Crassula helmsii have been eradicated from Utrecht.’
Janneke van der Loop, who completed her doctorate on the control of Crassula helmsii (pictured) in Nijmegen and is now an ecology adviser at Waterschap Aa en Maas in Den Bosch
‘Crassula helmsii, floating pennywort and Japanese knotweed are important species for a water authority. We are receiving six times as many reports in sixteen years. More disturbance, more geese causing dispersal and more nitrogen: some problems reinforce one another. An important reason for intervention is preventing damage. You want to stop plants from clogging up hydraulic structures and causing a pumping station to seize up, but we also have objectives around biodiversity and water quality. Sometimes there are conflicting interests too: a pond with invasive floating pennywort and a protected pool frog – should you excavate or not? For quite a number of invasive species there is also no clear course of action: how do you trap crayfish underwater? We also have 3,800 infestations of Japanese knotweed and 240 kilometres of floating pennywort in waterways, but we cannot work miracles. Controlling muskrat and coypu is a primary task: for that we maintain a zero-population target, and it costs 40 million euros per year. Not everything is solvable right now: the presence is too great or there is no viable course of action. So one thing is certain: invasive species are here to stay.’
1 On 2 July, the Ministry of Agriculture, Fisheries, Food Security and Nature (LVVN) announced that 26 new species had indeed been added to the Union list, and provided the following clarification regarding established invasive species for which no viable course of action exists: ‘For the species Crassula helmsii and the three Asian knotweeds, which are already widespread in the Netherlands, the ambition under the Invasive Alien Species Regulation therefore cannot (and will not) be eradication. Efforts will be directed at keeping the problems posed by these species manageable, with central government and the provinces, given limited resources, prioritising the protection of native biodiversity and therefore focusing primarily on protected natural areas.’ The implementing regulation of the European Commission concerning the ‘new invasive alien species’ is expected to enter into force in August 2025.
