Understanding Invasive Species
24th – 30th May 2021 is Invasive Species week. A lot of our sand dune restoration work at Dynamic Dunescapes involves controlling or removing these pesky species. But, what exactly are they, and what harm can they cause? We sat down with Natural England Senior Coastal Specialist, Louise Denning, to mark the week and to answer all of the invasive species questions that we get asked the most.
Exotic, non-native and invasive species – what’s the difference?
Non-native species, Exotic or introduced species are species that are found outside their normal range because of human activity. Not all of these are species are invasive. Many of these can thrive in new areas and pose no threat to other organisms or the environment in which they live.
Invasive species are species outside their normal ranges that have a negative impact on other organisms or environments. They tend to have escaped controlling species (which might be predators, herbivores or parasites) in their normal ranges, which would have otherwise limited their survival, and they are often well suited to their new environment. Often, an invasive species can breed/ spread very quickly - if left unchecked they dominate habitats and smother native wildlife.
Sea buckthorn is an invasive species on many sand dunes in the UK
What problems can invasive species cause / why are we worried about invasive species?
Along with climate change and habitat loss, non-native invasive species are one of the biggest threats to biodiversity in the UK and globally. The direct costs of invasive species has been estimated to be approximately 5% of global GDP* with an estimated cost of £1.8 billion per year to the UK economy!
Non-native invasive species cause problems for wildlife and people in the following ways:
- They can out-compete native species for food, light or breeding sites.
- They can directly predate or parasitise native species.
- They can bring disease which then harms other local species.
- They can damage/ change habitats and infrastructure.
- They cause huge socio-economic costs.
What species are invasive on sand dunes in England and Wales?
There are a number of invasive species that have become established and threaten our native wildlife in dunes around England and Wales. Headline species include:
- Japanese rose – Rosa rugosa
- Sea buckthorn - Hippophae rhamnoides (at some locations
- Broad-leaved everlasting pea- Lathyrus latifolius
- Japanese knotweed - Fallopia japonica
- Crocosmia- Crocosmia montbreata
- Cotoneaster species
- Oregon-grape - Mahonia aquifolium
- Duke of Argyll's Teaplant - Lycium barbarum
- Rhododendron - Rhododendron ponticum
- Pirri Pirri - Acaena novae-zelandiae
- New Zealand Pigmyweed - Crassula helmsii
- Water Fern - Azolla filiculoides
Other plants such as Traveller’s-joy - Clematis vitalba is a native species usually found in woodlands and hedgerows. However, it can become established and dominant in areas of dune scrub where it outcompetes other native species - for example on Saltfleetby to Theddlethorpe NNR on the Lincolnshire Coast.
One moss – Heath Star Moss, Campylopus introflexus – is also a particular issue found across UK and European dune systems. This is a southern hemisphere species which has spread rapidly over the last 60-years. It is now virtually impossible to control, because it forms a dense mat when it grows.
Not all invasive species are plants! At Studland Bay in Dorset, carp is a big issue, having been illegally introduced to the freshwater lake ‘Little Sea’, where the population has grown rapidly, changed the water biochemistry and made it inhabitable for some of the area's rare, specialist plant species.
Clematis is a fast-growing invasive species on our sand dunes in Lincolnshire, in the image above, you can see how it has overtaken and smothered a mature tree.
How do we get rid of, or minimise the impact of invasive species on sand dunes?
There are a number of measures that we can use to minimise the impact of invasive species on sand dunes. The best method is to prevent them becoming established in the first place. Dune managers, volunteers and site visitors can all play a key role by recording these species when they first appear. Early intervention is really important and can save a lot of time and money in the future.
Where an invasive species has become established –a variety of methods can be used, often in combination, including:
- Mechanical removal using excavators that remove root material and top growth.
- Regular cutting using brush cutters, or mowing equipment.
- Manual removal of smaller patches or individual plants using hoes, forks and trowels.
- Grazing which helps reduce growth and vigour of invasive species.
- Spot spraying using an approved herbicide applied by a suitably qualified person.
Vegetation that is cleared may need to be burnt in a specific location on site, may be buried beneath the sand or is chipped and removed for biomass fuel. Unfortunately, invasive plants by their vey nature are quick to recover and often repeated control measures are needed for many years.
Can invasive species be a good thing?
Sometimes introduced species can full-fill an important role on our dunes. For example - rabbits! Rabbits are an important part of a healthy dune system, as they help to keep the grassland short by grazing and create dynamic areas of bare sand when they create their burrows, so sometimes we introduce rabbits to a dune system to help manage the land more naturally than by mowing mechanically.
How do invasive species arrive at a new place?
Unfortunately there are many ways new invasive species arrive at our dunes. Many species travel across the UK by 'escaping' from gardens. Garden waste and fly-tipping within dunes is a real issue; but also some plants grow from neighbouring land. Some plants have been deliberately planted on a site historically for example in the past Sea Buckthorn was planted to stabilise dunes – we now know that this causes problems – not just because Sea Buckthorn Is invasive but we no longer have Dynamic Dunes with areas of bare sand which means we are losing important early successional species.
Other plants have been planted on sites as visitors think they look nice – often bulbs and flowering plants are introduced an can cause issues. Some species are inadvertently brought to site, for example Pirri Pirri produces balls of barbed fruits which detach from the plant and catch hold of anything that passes by – that includes boot laces, socks, dogs and livestock.
Aquatic plants like the New Zealand pigmyweed and water fern can become established in dune pools and dune slacks by dogs and livestock entering these waterbodies, as dogs can inadvertently transfer plants from one location to another.
In some instances fish like carp, as we've seen at Studland Bay, and reptiles like terrapins and sliders are often deliberately released. For example, some individuals 'release' those kept as pets when they get too big for our homes.
Many of the invasive species mentioned above are able to quickly establish on dunes as the climate on the coast is generally milder, and the free-draining sand is great for seed germination/ root propagation.
Is there anything I can do to stop the spread of invasive species?
Yes, there are plenty of things!
- Take your rubbish home, and please do not bring garden waste to our sites, always take it to your local garden waste recycling centre.
- Be Plant Wise - check the plants you are buying for your garden are not invasive - http://www.nonnativespecies.org/beplantwise/
- Check your boots and socks between visits and if you go to new dune sites, and make sure they aren't carrying any mud or seeds or parts of plants.
- Check your pets' paws when travelling with them too – pet’s paws are the perfect carrier for seeds and small plants. Make sure to brush them off when traveling with your pet!
- Learn about and be aware of the invasive species in your area. You can get involved and volunteer on a local site site, where you can join a Dynamic Dunescapes volunteer team to record non-native and invasive species using our Citizen Science App, or you could lend a hand with our physical invasive species removal work.
Want to learn more?