Many species of wildlife that can be found throughout the UK originate from countries outside the British Isles. Non-native species can become established if their biology is suited to their new environment. Prominent non-native species are usually great at adapting. If you don't think you know of any non-native species, think again, as there is an abundance of non-native species in the UK, from Canada geese (branta canadensis) to apple trees (malus x domestica). In fact, the UK is home to over 3,000 non-native species.
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| River Douglas (image source: Wikimedia Commons) |
However, some non-native species that become naturalised (established in the wild) can have devastating effects on pre-existing ecosystems. These organisms are referred to as invasive species and cause damage to other species and their new environment. They commonly outcompete indigenous species and dominate habitats. They disturb the balance of delicate ecosystems and can often have a destructive effect on biodiversity.
The occurrence of invasive species is almost always the result of human interaction. It is often the case that we underestimate the potential for foreign species populations to grow wildly out of control following naturalisation. A lot of invasive species are brought into new lands with no disruptive intentions, by collectors and affluent globetrotters. One famous example is the occurrence of the grey squirrel in the UK.
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Eastern grey squirrel, sciurus carolinensis
(image source: Pixabay) |
Herbrand Russel, a conservationist and former president of the Zoological Society of London, was a prolific spreader of the grey squirrel. Russell often gifted associates with grey squirrels and was known to introduce them to both Kew Gardens and Regents Park. Blissfully unaware of the damage that his actions would go on to cause. Imported from North America, grey squirrels were viewed as exotic to landowners. However, they were perfectly suited to Britain's climate and populations quickly spread. As you read further into the article you will see that the introduction of invasive species is commonly attributed to the ignorance of collectors and enthusiasts.
The victim of this was the red squirrel. Reds are smaller and more timid than greys and fail to outcompete the greys for food and habitat. Greys also brought squirrelpox to the UK. Whilst they had developed an immunity, reds were highly susceptible to the virus. Sadly the introduction of grey squirrels has caused mass displacement of red squirrels in the UK. In England, grey squirrels now outnumber red squirrels 18:1.
You can find invasive species across the globe but this blog will focus on the top offenders that can currently be found along the River Douglas. This blog will begin with invasive plant species, split into two sections, flora and fauna.
1) Giant hogweed (heracleum mantegazzianum)
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| Giant hogweed, heracleum hantegazzianum (source: Pixabay) |
Origin: Caucasus Mountains, Eurasia
How it got here: First recorded in the Kew Seed List of 1817, giant hogweed quickly became popular in the horticultural trade as an ornamental plant. It wasn't long before the plant established itself outside of gardens with the first naturalised population being recorded in Cambridgeshire in 1828.
Where can it be found: Giant Hogweed is widespread across the UK and Europe. It is commonly found along riverbanks, using the water to transport its seeds.
Identification: Giant hogweeds defining quality is its towering height, reaching up to 5m tall. It is an umbellifer and its flowers form clusters known as umbels. the leaves are extremely large and have spikey edges. The stems are thick with white hairs and are blotted with colours of red and purple. There is a native species of hogweed (heracleum sphondylium). It is notably smaller, reaching about 2m in height. Although still poisonous, it is not nearly as dangerous to humans nor as invasive towards other wildlife.
How it spreads: Giant hogweed can produce up to 50,000 seeds that are carried via wind or water. They are quick to establish and effective at competing against rival species.
Threatening qualities: The sap contains the chemical furanocoumarins and is poisonous to humans as it causes photodermatitis. This causes painful burns and removes the skins ability to protect itself from UV rays, meaning victims often have to stay out of the sun for months following an incident with sap. Giant hogweed requires masses of energy due to its immense size, outcompeting the surrounding flora to die out due to lack of resources. It reduces biodiversity by up to 90%. Furthermore, giant hogweed creates bare soil which leads to soil erosion and prevents plants other plants from taking root.
Control: The Wildlife and Countryside Act 1981 states that it is an offence to grow giant hogweed in England and Wales and the local authorities can request that giant hogweed be removed. Giant hogweed can be treated using weedkiller or pulled/dug up from the soil (wearing protective gear). Due to its toxic nature, it is classed as 'controlled waste' under the Environmental Protection Act and should be disposed of accordingly.
2) Japanese knotweed (reynoutria japonica)
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| Japanese knotweed, reynoutria japonica (source: Pixabay) |
Origin: Japan, Taiwan, Northern China.
How it got here: in 1854 the Botanist, Philip von Siebold, sent a shipment containing Japanese knotweed to the Royal Botanic Gardens in Kew. The plant was originally used for ornamental purposes but was also used as animal feed. It is also suggested by Ann Connelly, a knotweed expert, that the plant was used in welsh mining valleys to stabilise loose soil. The first naturalised reported sighting of Japanese Knotweed in the UK was located in Maesteg, Wales in the year 1886.
Where can it be found: Japanese Knotweed's natural habitat is on volcanic earth but now it is commonly found in the UK alongside railroads. Victorians originally planted knotweed alongside railroads as lining due to its rapid growth. However, it is an extremely adaptable species and can be found in both rural and urban areas inhabiting a large variety of environments including along rivers and streams. The worst affected area in England is the North West, which explains Japanese knotweeds prominence along the River Douglas.
Identification: Japanese knotweed has leaves that are light green, smooth and in the shape of a heart or shield. Stems can reach 3m in height and in summer will resemble bamboo shoots with a red/purple colour. In late summer small cream coloured flowers will be produced on long spikes that form in clusters. Over winter months Japanese knotweed will become dormant but will begin to grow again in spring forming asparagus looking shoots.
How it spreads: Japanese knotweed makes use of rhizomes to spread, rhizomes are horizontal subterranean stems that can create new shoots and roots. Rhizomes store plenty of proteins and starches making Japanese knotweed particularly resilient during poor growing conditions. Furthermore, Japanese knotweed can grow from rhizome fragments as small as 1cm, making propagation and distribution an easy process. In the UK Japanese knotweed does not spread via seed as we have an exclusively female population, each plant is a clone of the original female plant brought to the UK.
Threatening qualities: One of the biggest problems that Japanese knotweed to humans is the rhizome and its ability to spread and extend up to 7m and reach a depth of 3m. Rhizomes can penetrate small cracks and gaps causing a serious threat to the structural integrity of buildings and infrastructure.
Japanese knotweed can have destabilising effects on river banks as it dies off in Autumn and dead stems can prevent the flow of floodwater. Furthermore, the rhizome causes damage to flood defences. No other UK species can compete with its exponential growth and the plant causes a heavy decline in the surrounding biodiversity where present.
Control: It is illegal to cause the growth of Japanese knotweed in the wild under the Wildlife Countryside Act 1981. In its native land, Japanese knotweed is controlled by predators such as the sap-eating psyllid, aphalara itadon, but as there are no natural enemies in the UK weed killer is the most effective way to treat the plant. Glysophate is commonly used but may take up to 3 years for complete removal. It is important to deal with Japanese knotweed appropriately as rhizome fragments are extremely talented at forming new plants. Japanese knotweed must be treated as 'controlled waste'.
3) Floating pennywort (hydrocotyle ranunculoides)
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| Floating pennywort, hydrocotyle ranunculoides (source: Wikimedia Commons) |
Origin: North and South America
How it got here: Floating pennywort was brought into the aquatic plant trade in the 1980s. It was often sold by garden centers as 'marsh wart' (hydrocotyle vulgaris), a native and non-invasive British species. The first naturalised sighting of floating pennywort in the UK was recorded in 1990 on the River Chelmer.
Where can it be found: Originally found in the south-east of England but it can now be found throughout The Midlands, Wales, and increasingly in areas of The North West. It can be found in still and slow-flowing areas of water such as streams, ponds lakes and canals.
Identification: Floating pennywort has fine roots and fleshy stalks. It can form thick and intertwined mats on top of water bodies weighing up to and proceeding 80kg. Leaves of the pennywort can be both floating and emergent. Leaves are often thicker than they are long. Floating pennywort will also produce small white flowers that form in clumps occurring between July and August. A failsafe way to identify floating pennywort against marsh wort is to compare the leaves. Marsh leaves form a round shape and the leaves are smaller than the kidney-shaped leaves of floating pennywort. In addition, the stems of marsh wort are much thinner.
How it spreads: Floating pennywort can be transported through waterways, by boats or even by people. Pennywort spreads using stolons, horizontal stems which connect organisms. Stem fragments as small as 1cm are able to regenerate within the space of a week, making them extremely expansive. Plus, floating pennywort can grow up to 20cm a day in the correct conditions. In the space of 20 years, the amount of recognised sites of infestation has increased from 29 to 1,500+.
Threatening qualities: The adaptability of floating pennywort is of its most intimidating features, it can compete with its freshwater contenders. The combined surface area of floating pennyworts leaves often cover large areas of the water suffocating and starving any submerged life of sunlight which is crucial in the process of photosynthesis. Due to the mass amounts of area floating pennywort can grow to inhabit, crowding is also an issue for surrounding plant life. It can also induce a reduction of oxygen creating problems for aquatic animals. It can also cause migratory problems and block naturally and non-naturally occurring drainage systems.
Furthermore, floating pennywort can cause issues for fishermen, deter tourists and block access routes. It can also be the cause of flooding. It is estimated to cost Europe and great Britain £25 million per year.
Control: It is illegal to cause the growth of floating pennywort in the wild under the Wildlife Countryside Act 1981. Certain charities, organisations and volunteer groups have success in removing floating pennywort. Cutting and imminent removal alongside pulling and chemical treatment are effective techniques, best implemented between May and October. The use of chemicals should be reserved for seasons during which other plant species have died back.
CABI is currently working on a project which has established a suitable and effective natural enemy for floating pennywort. One which will not interfere with other organisms or throw ecosystems out of balance. Through the use of exploratory surveying, CABI has found the South American weevil, listronotus elongatus, to be an effective and non-disruptive natural enemy of floating pennywort. A trial release is being coordinated to take place in the summer of 2022 in an attempt to establish a population of listronotus elongatus.
4) Himalayan balsam (impatiens glandulifera)
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| Himalayan balsam, impatiens glandulifera (source: Pixabay) |
Origin: The Himalayas, north-west Pakistan to northern India.
How it got here: It was first introduced in 1839 by plant hunters in the British Isles as a greenhouse favourite. Collectors and enthusiasts were enticed by its large pink flowers and hanging explosive seed pods. Popular amongst the public and beekeepers, it was released into the wild and the first naturalised sighting was recorded in 1855 in Middlesex.
Where can it be found: Since its introduction to the UK it is estimated that Himalayan Balsam has spread at a rate of 645km² per year. Populations can now be found throughout all of the UK, even reaching off-shore and isolated areas such as the Isles of Scilly. Himalayan balsam grows in damp and wet habitats, along river banks, near ponds, and in wetter meadows and woodlands.
Identification: Himalayan balsam reaches heights of 2-3m (up to 10ft) between June and October, height alone can act as an effective means of identification. Another distinctive feature comes in the form of its helmet-shaped pink flowers, brandishing it with the nickname 'policeman's helmet'. It has serrated oval-shaped leaves with a pinkish-red vein.
From July, the plant will produce dangling seed pods. Stems are tall, rough and have a red colour. Himalayan balsam often grows in dense large patches.
How it spreads: One of the main issues with Himalayan balsam is how easily it can spread. One of its defining features is its exploding seed pods. It is estimated that each plant can produce up to 800 seeds per year with an 80% germination rate, making Himalayan balsam extremely prolific. The pods are sensitive and will explode if touched or knocked, dispersing seeds up to 7m away from the plant. If seeds are carried by wind or water they can germinate miles away from the parent plant and can lay viable for up to 2 years.
Threatening qualities: Himalayan balsam has a catastrophic impact on local biodiversity, as it grows in dense and tall stands it smothers many native species, outcompeting them for local resources and sunlight. Bees are attracted to the large colourful flowers and as a result neglect smaller and less bright native flowers, preventing the spread of pollen. Himalayan balsam's roots are ineffective at stabilising earth and can cause erosion problems alongside riverbeds, furthermore, the dense stands can lead to flooding problems through blockages.
Control: Like the other invasive species of this blog, Himalayan balsam is listed under section 9 of the Wildlife Countryside act of 1981 and it is illegal to introduce it into the wild. Hand pulling, mowing and cutting are all effective measures of deterring growth. It is important to ensure roots are completely unearthed if pulling and that plants are cut below the lowest node if being mowed or cut, otherwise this stimulates the growth of auxiliary buds. These methods should be completed before the end of June to ensure effectiveness. Herbicides are also a popular solution, with glysophate being a lead contender.
CABI conducted a study to establish a biological control measure. They found that rust mould was an effective and targeting natural enemy of Himalayan balsam, sadly UK trials found low levels of infection and some stands to be completely immune to the effects of the fungus.
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