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Invasive Non-Native Species and UK Law

American mink

As ecologists, we have to ensure that we record any invasive non-native species when carrying out surveys and PEAs. A non-native species (NNS) is any plant or animal that has been introduced, deliberately or by accident, to a location outside of its natural range. Some of these are relatively benign and have little or no impact on the biodiversity of their new home.

Certain species, though, have a detrimental effect on the existing flora and/or fauna of the local environment. These are known as invasive non-native species (INNS). They may outcompete native plants or animals, prey on endangered species, cause local extinctions or be hazardous to human health. A lack of natural predators in an introduced setting can lead to rapid population growth, exacerbating the problem.

Because of their potential for damage to the environment or humans, and because they cost the economy over £1 billion per year, there is UK legislation on INNS. Consequently, their presence on a site can affect planning decisions, cost substantial amounts of time and money to eradicate and even affect the chances of a house buyer getting a mortgage. It is therefore essential to be aware of INNS and the law surrounding them.

INNS and the Law – England, Wales and Northern Ireland

In England and Wales, section 14 of the Wildlife and Countryside Act 1981, as amended, is the main piece of relevant legislation. This states that it is an offence to release any of the 30 non-native birds or animals listed on Schedule 9 of the act into the wild or to allow them to escape from captivity. These are all species that have become established in the wild to a greater or lesser extent. However, because of the threat they pose to native wildlife and habitats, there is strict regulation of any future releases.

Grey squirrel invasive non-native species
Grey squirrels are an invasive non-native species in the UK

It is also an offence to plant any of the 36 listed plants in the wild or allow them to spread from a private collection. Although it isn’t illegal to have a proscribed plant growing in a garden, it can make the owner vulnerable to prosecution as a nuisance neighbour under the Anti-social Behaviour, Crime and Policing Act 2014 if the plant/s in question are likely to spread to neighbouring gardens. As such, both commercial and residential landowners must control invasive species on their property and, if possible, eradicate them. They may need a special licence to carry this out, depending on the species and location.

In Northern Ireland, the corresponding legislation is the Wildlife (Northern Ireland) Order 1985, as amended. This follows the same format, with their own Schedule 9 list of the non-native species to be controlled.

INNS and the Law – Scotland

In Scotland, the approach is different in that it is an offence to release any non-native plant or animal into the wild outside of its native range, not just those classed as invasive. The Wildlife and Natural Environment (Scotland) Act 2011 (WANE) and a Code of Practice on Non-Native Species, require landowners to prevent any NNS on their property from spreading to the wild. They must also prevent any NNS spreading to adjacent privately owned land.

Japanese knotweed
Japanese knotweed is one of our most invasive plant species

The overriding aim with Scottish legislation is prevention rather than cure when it comes to NNS. This is in recognition of their potential for causing irreversible environmental damage, and the huge costs involved in eradication or relocation programmes.

In addition, despite the UK’s exit from the EU, the Invasive Alien Species (Enforcement and Permitting) Order 2019 enacted EU legislation on invasive species into UK law. This applies in all the devolved nations. The order makes it illegal to keep, breed, transport, release, allow to escape or sell any invasive species on the EU List of Union Concern.

In all regions of the UK, it is possible to apply for a licence from the relevant body (Natural England, NatureScot, NRW or DAERA) to keep, move or grow an INNS. They may grant a licence for certain reasons such as for eradication or animal welfare purposes.

Additional Island Controls

Because some of the UK’s native species aren’t naturally present on all its offshore islands, there are also some controls on island releases. Northern Ireland’s Schedule 9 list contains four mammals (stoat, red fox, hedgehog and brown rat) native to the mainland. It is illegal to release any of these on the region’s islands due to the potential for predation of vulnerable ground-nesting birds and their eggs. These include waders, terns and corncrakes.

Brown rat invasive non-native species
Brown rats can be a huge problem for ground-nesting birds on islands

Likewise, because WANE in Scotland prohibits the release of species into the wider environment outside of their native range, a species cannot be released on an island if it is not naturally occurring there. Stoats, hedgehogs, rats and mice species have all become established on some islands they would not naturally live on. When travelling to certain islands, biosecurity is therefore extremely important to ensure their numbers are kept at a minimum. As in Northern Ireland, the main concern is for ground-nesting birds.

Island biosecurity
Island harbours often highlight the need for strict biosecurity
Island biosecurity

Eradication programmes have proved both controversial and costly in the past. A cull of non-native hedgehogs in the Western Isles was replaced by a relocation scheme as a result of an outcry against lethal control. North Uist is now hedgehog-free, but work still needs to be done on South Uist and there are concerns they may have arrived in Barra in June 2022. Elsewhere, stoats have been present in Orkney since 2010 and NatureScot is currently developing a project to address the issue.

Island biosecurity
Biosecurity For Life aims to highlight the risk of invasive species to island bird communities

Worst Offenders – Plants

Almost certainly one of the most destructive and invasive non-native plant species in the UK is Japanese knotweed. Brought to the UK as an ornamental plant, it is now regarded as highly invasive due to its rapid growth rate and the difficulty in removing it. In the spring it can grow up to 10 cm a day and it also spreads very easily from small pieces of its underground rhizomes. In addition, it impedes other plant species from growing.

While it isn’t illegal to have it in your garden, you must control it and ensure it does not spread elsewhere. When it comes to selling a property, the seller must check for it and commit to removal if present. The buyer, meanwhile, may not be able to get a mortgage if this commitment is not in place. As a result, being able to correctly distinguish it from some of its less harmful forms and similar-looking plant species is important.

Japanese knotweed
Japanese knotweed has purple-flecked stems and heart-shaped leaves

Giant hogweed is another garden escape. This is now found predominantly along riverbanks and is a huge plant, able to grow up to five metres tall. The plant is a rapid spreader, with individuals able to produce tens of thousands of seeds. One of the main concerns with this species is that its sap can cause skin to react to sunlight, producing blisters, burns and scarring.

Himalayan balsam
Himalayan balsam gives off a distinctive sickly smell

Himalayan balsam is another plant that spreads easily along watercourses. It is fast-growing and quickly crowds out other plant species. In the right conditions, seed pods explode, spreading large numbers of seeds over great distances. They also float so form new populations along rivers.

Rhododendron is a huge problem, especially in the west of Scotland

Rhododendron has extremely dense foliage that shades woodland floors to the point where nothing can grow beneath it. The roots systems are toxic to other species even after removal, so native plants may not be able to grow for years afterwards. Seeds disperse easily on the wind or by water, and plants are extremely difficult to remove once established, costly millions of pounds.

Other problem species are montbretia, giant rhubarb and cotoneaster.

Montbretia is a common garden escape

Worst Offenders – Animals

American mink were first recorded breeding in the wild in the UK in 1956. These animals came from a combination of escapes and intentional releases from fur farms. This is an extremely aggressive predator and its rapid spread along the UK’s waterways has led to huge declines in water vole populations. Water voles were already under pressure from habitat loss and pollution, and the mink proved to be the final straw for some populations. Concerted trapping operations have had some results. Research published in 2006 suggested that as otter numbers bounced back from previous declines, they were displacing mink.

American mink
American mink have had a huge impact on water vole numbers

Grey squirrels are so numerous and so well established in much of the UK that many people might not even see them as non-native. First introduced in the 19th century from North America, they outcompete our native red squirrel as well as carrying squirrel pox, a disease that is fatal to reds but not to greys. Red squirrels now only succeed where there are no greys, such as parts of Scotland and islands like the Isle of Wight and Brownsea. In some places grey squirrels are culled to provide a buffer zone between reds and greys.

Grey squirrels
Grey squirrels outcompete our native red squirrels

Signal crayfish are also North American in origin and were brought here in the 1970s with the aim of starting a commercial fishery. Once in our waterways, though, it quickly outcompeted the white-clawed crayfish, our native species, due to its larger size. They almost certainly passed on crayfish plague, as well. The American crayfish also impacts the wider environment. As aggressive predators, they eat a number of native fish, frogs and invertebrates. Their large burrows can destabilise riverbanks and lead to increased flood risk.

Other species of concern include racoons, racoon dogs and Asian hornets, although these are not as widespread as the above.

Next Steps

Landowners have a legal responsibility regarding the potential spread of INNS from a site. It is therefore important to be aware of any that may be present when looking to buy a residential property or begin a development project. Another important point is that even when a species has been established in the UK for some time, it may still be listed on Schedule 9 and require control.

It is also important to be aware that construction projects risk contributing to the spread of INNS. Machinery, soil, building material and people often move frequently between sites. Good biosecurity is vital so that invasive species don’t inadvertently move with them from one project to another. Garden waste fly-tipping is also a huge spreader of plant INNS.

Although there are useful ID guides from organisations such as the Non-Native Species Secretariat, ecological surveys are the best way to be sure that no invasive species are present. Early detection is crucial in limiting the impact of INNS and can save vast amounts of time and money. Prevention is always a better and less costly option than cure.

Purple Plover offers a range of surveys that include invasive species detection and identification. We can also advise on prevention and mitigation strategies, as well as recommending specialist eradication companies should we find any INNS on site.