NON-NATIVE, INVASIVE SPECIES

Surrey Biodiversity Partnership

Position Paper Series

NON-NATIVE, INVASIVE SPECIES

BACKGROUND

DEFRA defines a non-native, invasive species as: “Any non-native animal or plant which has the ability to spread causing damage to the environment, the economy, our health or the way we live.”

Non-native species can be defined as those species that have been introduced by humans, deliberately or accidentally.

Non-native, invasive species are widely recognised as a major threat to biodiversity, second only to habitat loss. They can also have serious impacts on health and safety, social and amenity resources, flood risk management and development. As a consequence, there are huge economic impacts due to the large costs of trying to eradicate, or at best control, these invasive species.

Some non-native species are not invasive and cause no such threats. For example, little owls were introduced into the UK in the 19th century and are now naturalised, but pose no threat to any of our native species. Also, perhaps due to climate change, some species such as little egrets found their own way to the UK and now breed here. It is therefore important to keep things in perspective.

This position statement sets out the reasons why the Surrey Biodiversity Partnership (SBP) supports the control of some of the more problematic non-native, invasive species.

WHY DO THEY BECOME INVASIVE?

Most of the invasive, non-native species in the UK are not invasive in their countries of origin. This can be for a number of reasons including the fact that their natural predators and diseases that would normally keep them under control, are not present in the UK. They also tend to have effective and rapid reproduction rates and aquatic plants in particular are often able to spread faster than terrestrial species.

HOW DO THEY THREATEN NATIVE SPECIES?

• Out-competing them for the same habitat, e.g. Himalayan balsam grows on river banks and other damp places and out-competes the more diverse natural plant communities.
• Taking over their breeding places, e.g. ring-necked parakeets nest in holes in trees created by woodpeckers.
• Over-shading, e.g. Japanese Knotweed can soon become a monoculture due to its tall and vigorous growth that shades out all other species trying to grow beneath it.
• Preying on native species, e.g. American mink prey on water voles and are the only predator of this protected mammal that can swim and are small enough to enter their burrows.
• Spreading disease, e.g. the American signal crayfish carries a fungal disease that can wipe out populations of our native white-clawed crayfish.
• Interbreeding / hybridising with native species, e.g. the Spanish bluebell can hybridise with our native bluebell, resulting in a different genetic make-up.

OTHER IMPACTS OF INVASIVE SPECIES

• Flood risk, e.g. floating pennywort can grow into huge, thick rafts of vegetation from bank to bank of a river that can clog up weirs and sluices.
• Structural damage & commercial impacts, e.g. Japanese knotweed can grow through walls and tarmac and is extremely difficult to eradicate. This can be especially problematic on development sites.
• Health & Safety, e.g. the sap of giant hogweed causes severe blistering of the skin when exposed to sunlight.

WHAT DOES THE LAW SAY?

The Wildlife and Countryside Act 1981 states that it is an offence to plant or otherwise cause to grow in the wild any plant listed in Schedule 9, Part II. Under Schedule 9, Part I, it is also an offence to release or allow to escape into the wild, certain non-native animals, or any animal which is not ordinarily resident in, and is not a regular visitor to, GB in a wild state.

Additional legislation may be relevant, for example as all parts of the Japanese knotweed plant and any soil contaminated with it are classed as controlled waste, it comes under Part II of the Environmental Protection Act.

WHOSE RESPONSIBILITY?

The strategic, widespread control of invasive species is currently not the sole responsibility of any statutory organisation, although this may change in the future. The responsibility for dealing with invasive plants therefore currently rests with individual landowners. However, there are some organisations that can offer help. For example, the Environment Agency does control species such as Japanese knotweed and floating pennywort, where they may cause a flood risk to properties. Some Wildlife Trusts may also carry out control of species such as mink, as part of a wider water vole project.

TO CONTROL OR NOT TO CONTROL?

Prevention is better than cure, so as soon as a non-native, invasive species is recorded, it is preferable to eradicate it at any early stage before it spreads. For some species, they are now so widespread and difficult to control that eradication may be impossible, but rather they should be kept at a manageable level. In addition, effort should be focused on the most sensitive sites, where rare species are present or where there is a flood risk or other serious impact.

THE FUTURE

There are many different ways of controlling non-native, invasive species, dependant on a number of factors. For example, to date, the only practical way to control Japanese knotweed has been with the use of herbicides. However, herbicides are not specific to a particular species and in addition, the list of herbicides that can legally be used, especially near water, are gradually being reduced. There is considerable ongoing research into biological control methods and indeed 2010 has seen the controlled release of two biological controls for Japanese knotweed, namely a sap-sucking insect and a fungus. Biological control methods are unlikely to ever completely eradicate their hosts, but will keep them under control, as they would be in their native countries.

In April 2010, a number of new non-native, invasive species were added to the Wildlife and Countryside Act. Future legislation will hopefully ban the sale of some these species. Co-ordinated strategies for invasive species control will also be required for the more problematic species.

NON-NATIVE, INVASIVE SPECIES IN SURREY

There are a number of non-native, invasive species in Surrey, some of which are particularly problematic for a variety of reasons. Below are details of just five species that the SBP considers to be the most important with regards to their impacts on the biodiversity of the county. All are listed on Schedule 9 of the Wildlife and Countryside Act.

Himalayan Balsam

Himalayan balsam was introduced to the UK from the Himalayas in the early 19th century and has since escaped from gardens and colonised many of our river banks and damp grassland habitats. In Surrey it can be found on all of our river catchments and out-competes our native flora due to its prolific seed production and fast growth. It can be easily removed by uprooting the plant before it sets seed, but this needs to be done throughout the catchment to prevent recolonisation from seeds shed from upstream. The SBP believes that this plant is a serious threat to our native plants and the variety of animals that rely on them, so would like to see strategic programmes for its control set up in each river catchment.

Japanese Knotweed

Japanese Knotweed was introduced to the UK as an ornamental plant in the mid 19th century and is widely believed to be the most invasive plant in the UK. It has a deep-rooted underground rhizome system and hence can be difficult to eradicate. As well as being listed on Sch.9 of the WCA, all parts of the plant and any soil contaminated with it are classed as controlled waste. It can grow in virtually any situation including through tarmac, and is commonly found along road verges and particularly river banks, where it over-shades our native flora and can rapidly become a monoculture. It can be found in all of the river catchments in Surrey and the Environment Agency (EA) controls it on river banks where it has the potential to cause a flood risk. It is also controlled by landowners such as local authorities.

Japanese Knotweed. Environment Agency

Australian Swamp Stonecrop/New Zealand Pigmyweed

Commonly known by its scientific name of Crassula, this plant is widespread in Surrey and is probably the hardest to control. This is because it spreads rapidly and has three different forms: one can survive completely submerged under water, an emergent form grows in shallow water and a third type is completely terrestrial. It is frost resistant and spreads rapidly, and can quickly dominate an area. Being small, it often grows between larger plants, which makes it difficult to control without damaging the non-target plants. This is a particular problem where it grows alongside rare plants. An example in Surrey is where it grows in ponds on a Site of Special Scientific Interest that supports starfruit. This is a nationally rare plant protected under Schedule 8 of the WCA and this Surrey site is one of only three sites in the UK. There has therefore been a strict programme to control the Crassula for a number of years using a herbicide, which is done under licence, with timing and the method of working being crucial to protect the starfruit.

Brown galingale is another plant protected under Schedule 8 of the Wildlife and Countryside Act and is found in a pond in the borough of Spelthorne, one of only seven sites in England. This pond is also invaded by Crassula, but Spelthorne Borough Council is working hard with Plantlife and with the support of the SBP, to control its spread.

Crassula is also present on the Basingstoke Canal SSSI, along with a number of other invasive plants that are partly responsible for the unfavourable condition of the SSSI. In addition, it is found on many other wetland sites in Surrey, both statutory designated sites and those without designation, but in all locations is a serious threat to our native biodiversity.

American Mink

Water voles are the UK’s fastest declining mammal, with approximately 95% of populations having been lost in the last 20 years. This national trend is true in Surrey and they are continuing to decline, with only a very small number of communities left in isolated pockets, whereas pre-1990 they were widespread in the county. The loss of their wetland habitats was a major cause of their decline, but this was exacerbated by mink escaping from fur farms, that predate on water voles. Water voles and their burrows are now fully protected under the Wildlife and Countryside Act 1981 (as amended) and the water vole is a priority species in the UK Biodiversity Action Plan (BAP) as well as in the local Surrey BAP. As river and wetland water quality and habitats are enhanced, mink remain the major factor in the decline of the water vole. Mink also prey on other native species such as waterfowl, amphibians, fish and other small mammals.

The SBP believe that mink should be monitored and controlled and support the work of the Surrey Water Vole Project, hosted by Surrey Wildlife Trust. While individual landowners are responsible for controlling mink on their own land, the project can offer help and advice. While a strategic mink control programme is desirable, this is currently not possible so the project monitors mink in strategic areas. This includes areas where water voles still exist and those sites for potential water vole reintroduction.

There is some evidence from the 2009-2010 national otter survey that mink numbers appear to be declining in those areas where otters are increasing.

Signal Crayfish

Signal crayfish were introduced to Europe from North America in the 1960s for commercial fisheries reasons and have since escaped into the wild. They are now present in all river catchments in Surrey and are the main cause of the decline of our native white-clawed crayfish, now thought to be present in only one or two sites in Surrey. Signal crayfish are much larger and more aggressive that our native crayfish and out-compete them for food and habitats, as well as infecting our native crayfish with a fungal disease called crayfish plague that our native crayfish have no resistance to. Signal crayfish can be trapped under licence from the EA, but are now present in such large numbers in Surrey rivers and lakes, as they are in much of the UK, that at present eradication is not deemed possible.

CONCLUSION

The SBP is concerned about the impact of a number of invasive, non-native species in the county, particularly their effects on our native flora and fauna. They are helping to control these species by:

• Supporting the local Surrey Habitat Action Plans, many of which have actions to control invasive, non-native species.
• Organising training days where the latest methods of control are discussed.
• Organising site visits where partners can share problems and solutions.
• Supporting the work of CABI , an international organisation that carries out vital research into the biological control of invasive, non-native species.

Through partnership working and commenting on up to date policy and legislation, the SBP is playing a large part in controlling invasive, non-native species, which in turn is helping to protect the native wildlife of Surrey.

For more information and advice on non-native, invasive species on the Environment Agency website, click on this link

For more information on the work of CABI on non-native, invasive species, click on this link

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