Non-native Invasive Plants in Wetlands -

Stopping The Invasion

What is an invasive or alien plant?

Invasive plants are sometimes native, but mostly non-native plants which have been introduced to somewhere new, and which have become over-dominant to the detriment of other native plants. Many invasive plants have been introduced deliberately or accidentally from garden centres, from exotic gardens, as a consequence of trade or through planting in gardens. Invasive plants can initially appear to be fairly innocuous until they reach a threshold level, when they become a serious threat to health, animal welfare and native wildlife. Once established, invasive species are often difficult or impossible to remove.

The invasive plant Himalayan Balsam dominating local species and shading the river course © M Davis

Why are invasive plants a problem?

Although native weeds can be troublesome, they are simply the right plants in the wrong place. Non native invasive plants however are the wrong plants, in the wrong place. They often grow vigorously due to the absence of their native predators, pests and diseases. Once established, these plants can totally take over your (wet) land. Garden ponds are particularly vulnerable as people often inherit invasive plants or transfer them accidentally from other ponds. Invasive plant pests can block and shade rivers, wetlands and ponds and out compete native plant species. They can create a flood risk by blocking waterways and can cause danger to humans and animal stock by growing thickly over water and appearing to be a solid surface. Many can reproduce from tiny root fragments, or copious seeds, which means that clearing them in flowing watercourses can actually cause an even bigger problem downstream. The control of these species has a big impact on the economy. The UK government estimates that controlling non native invasive species costs more than £1.7 billion per year. Many invasive species are listed under Schedule 9 of the Wildlife and Countryside Act 1981 as illegal to plant or cause to grow in the wild.

Why are non native invasive species a problem in wetlands?

Wetland environments are frequently disturbed (i.e. by flooding, people or boating) and are often enriched by nutrients. They provide ideal conditions for the fast growth and reproduction of non-native invasive plants. Seeds and fragments of these plants can be transported by water, or the things living in it, allowing them to easily establish along whole river catchments or floodplains. Once in, they are extremely hard to get out again. Many important wildlife species can be affected by these plants which block out light, and use up nutrients and oxygen in water. Fish, dragonflies and damselflies in particular may be affected, while mammals such as water voles may find it hard to forage.

Non-native invasive plants in Wetlands - Stopping The Invasion

What action can I take to prevent invasive aliens?

Be vigilant – If you see a plant which you think is invasive then contact Wildcall for help (01273 494777 or wildcall@sussexwt.org.uk) or register it at i record wildlife—www.brc.ac.uk/irecord

Keep out nutrients – If your pond, ditches and watercourses are suffering from nutrient enrichment from farm run off or duck feeding, then invasive plants will grow more vigorously

Stop the trade – Some of these plants are still available for sale. They may look nice but they quickly take over and can devastate natural wildlife and habitats if released into the wild. If you see them on sale PLEASE DON’T BUY THEM. Shops are making a profit selling them whilst causing expensive damage to valuable farmland, drinking water reservoirs and wildlife habitats. In April 2014 the Government banned the sale of five non native invasive aquatic plants (Water fern, Parrot’s feather, Floating pennywort, Australian swamp stone-crop and Water primrose). However, often they are still being sold ‘accidentally’ attached to the soil or roots of other plants being sold.

Don’t dump them - If you have these plants and you need to dispose of them, PLEASE DO NOT PUT THEM DOWN THE DRAIN OR IN THE RUBBISH. Seek advice on the best method of disposal for each species. Incorrect disposal can result in further spread of the plant. (See the non native species website, Wildcall or Sussex Wildlife Trust advice sheets for further advice.)

Don’t transfer plants or frogspawn between ponds/land — this helps spread problem plants. Check your boots. If you walk in different wetland sites, check and clean boots between visits. Go native – If you really want to put plants in ponds and fish tanks use native oxygenating plants

such as spiked water milfoil (Myriophyllum spicatum), rigid hornwort (Ceratophyllum demersum) or common water starwort (Callitriche stagnalis). If you can wait though, native plants will often colonise naturally within a year.

Quality control – If you are having wetland work done on your land by contractors, ask them what precautions they are taking to ensure that they do not transfer invasive plants onto your land. They may need to revise their practise. Get them to adhere to the ‘Check, clean, dry’ campaign if you can.

What can you do if you think you have invasive species on your land?

Seek advice Try not to allow machinery, fishing/netting or access by humans or animals to the area. Map the distribution of the plant and identify areas that could be at risk of new invasions. Prevent access to the area by stock, and if possible large grazing birds such as geese i.e. by using

temporary fencing. Notify your local Biodiversity Record Centre of the presence of the plant (www.sxbrc.org.uk). If the invaded area is small, removal by hand may be possible. Timing and methods of removal vary

from species to species but be aware that handling might spread it further. Any equipment should be cleaned to avoid spread to other sites and the removal of waste must be appropriately managed.

In some cases herbicides can be used as a last resort but even this is often ineffective as well as damaging to most other aquatic plant, amphibian and invertebrate species. ALL USE OF HERBICIDES NEAR WATER REQUIRES CONSENT FROM THE ENVIRONMENT AGENCY AND THERE ARE NO HERBICIDES LEGALLY PERMITTED TO BE USED IN WATER.

In some cases you may have no choice but to fill in your ditch or pond completely and dig a new one. If it comes to this, advice should be sought from your local Wildlife Trust or Environment Agency officer before infilling to ensure that the best method is used and that there are no rare and protected species which may be destroyed.

For more information on how to control specific plants see the Non Native Species Secretariat

Non-native invasive plants in Wetlands - Stopping The Invasion

Which non-native plants are a problem in wetlands?

There is an ever increasing list of aquatic (wetland) plants which are non native and are invading our wetlands. Pictures of some of the main culprits are shown below.

Japanese Knotweed © Neil Fletcher SWT

Himalayan Balsam in flower © S McIntyre

Parrotsfeather © T Renals

Crassula helmsii close up © T Hills

American Skunk cabbage © S McIntyre

Floating pennywort covering a water-course © CEH

Floating Pennywort close up with Crassula behind

© Bourne Conservation

Azolla (Water fern) © B Lavelle

Azolla (Water fern) close up © CeDaR

Non-native invasive plants in Wetlands - Stopping The Invasion

Do I have a legal obligation to clear pond pests?

Some species of invasive plant are ‘agriculturally notifiable weeds’. This means that as a landowner, if they occur on your land you are obliged to take steps to stop them spreading onto other peoples land and preferably to eradicate them. Notifiable agricultural weeds include Common Ragwort, Giant Hogweed and Japanese Knotweed. Most pond pests are not notifiable but will cause considerable damage. Landowners can now be issues with ‘ASBO’s’ which enable government bodies to obtain legal access to private land in order to tackle listed non native invasive species.

Should I tackle invasive non native plants as soon as I notice them?

Yes. Many landowners spend thousands of pounds a year to merely ‘hold the line’ with wetland plants that are invading their land. Recent clearance of Japanese Knotweed was estimated to cost £40,000 for 6 square yards requiring clearance to a depth of 3m!

Prevention is much better than cure

Once these plants are on your land, they can be impossible to eradicate without considerable expense and environmental damage. Plants like Giant hogweed can also be hazardous to humans and livestock.

Contacts

Sussex Wildlife Trust www.sussexwildlifetrust.org.uk/

Wetlands Project for advice - 01273 497555 0r Wildcall — 01273 494777

Environment Agency Ask for Fisheries or Land Drainage consent teams

03708 506506 www.environment-agency.gov.uk

Sussex Biodiversity Record Centre 01273 497521

www.sxbrc.org.uk

Centre for Aquatic Plant Management www.nerc-wallingford.ac.uk/research/capm/

index.htm

Non Native Species Secretariat www.nonnativespecies.org

Check Clean Dry Campaign www.nonnativespecies.org/checkcleandry

Freshwater Habitats Trust http://freshwaterhabitats.org.uk

References & Further Reading

Environment Agency 2003:Guidance for the Control of invasive weeds in or near fresh water.

Defra. 2008: Invasive Non-native species Framework Strategy for Great Britain. .

Freshwater Habitats Trust. 2001: Problem Pond Plants: Managing algae, duckweed and other

floating plants. Horticultural Code of Practice:

Defra & Scottish Executive: Advice and guidance on safe use, control and disposal of invasive

non-native plants for horticulture and activities that involve the use of plants.