Many plants that we see and love in the U.K. are not native to us. They are either long established and have become part of our ecosystem with the damage done further back in history or they are non-invasive meaning they pose no current threat to the ecosystem. Many invasive plants were released in the 18th and 19th century when budding botanists collected plants from around the world, continuing to grow them here in the UK not knowing the damage some can do when released into the environment.
There are currently around 70 NNIS (non-native invasive species) of plants and wildlife that are causing damage around the U.K. The ones I mention here are some of the more common or dangerous ones found in our gardens and countryside, most are a criminal offence to plant or sell, if you discover any of these plants then please contact the relevant body for advice on removing. You can find this list of NNIS here.
Plants
Giant Hogweed – Originally from Russia, giant hogweed looks like our native hogweed except, as the name suggests, it’s giant. Regular hogweed grows up to around 2m and poses no threat to humans. Giant hogweed however, can grow up to 5m!
It’s sap, when skin is exposed to it, can cause blistering of the skin and permanent damage because it removes the skin’s ability to process UV light. Even tiny amounts of sap are dangerous with the effects lasting at least 20 years!
It also, like many invasive species, out competes other local flora and it’s roots damage the soil around riverbanks leading to unnecessary erosion and an increased flood risk. The flower heads (umbels) can produce 50,000 seeds each which makes control of giant hogweed difficult.
Himalayan Balsam – A stunning plant in its own right, Himalayan balsam comes from west and central Himalaya and can grow up to 2m tall. It loves river banks and damp woodland and establishes quickly in clumps. It’s seed pods explode and fire small seeds that are then carried by the wind. Because it spreads easily and grows along riverbanks it can slow the flow of surface water entering the river when it rains and as a result can cause localised flooding. There is a popular trend amongst some of the more ecologically minded to go ‘Balsam Bashing’ where teams of people attempt to control the spread. Conveniently It is easily removed, as it has a small root structure and can be pulled by hand from the soil.
Japanese Knotweed – This is a hugely successful plant at reproducing. It does this by using rhizomes. Rhizomes are underground plant stems that send out roots and shoots to produce more plants) or viable parts of it’s stem.
Knotweed grows in clumps as it spreads using it rhizomes and its roots have the power to work its way into, split apart, and destroy concrete and asphalt. Therefore it is extremely difficult and costly to remove. Houses that have Japanese knotweed on its land are usually unmortgageable because of the structural damage this plant can cause. To remove every trace of knotweed the soil for 2m below and around the plant must be removed and disposed of correctly, usually by a specialist company, as any fragments of the plant are viable and could create new plants thus spreading the plant. After that strong chemicals are used to try and control the growth of any remaining fragments. This process of removal can take up to four years to complete. If you think you have knotweed please visit this government site for more information.
Rhododendron – Native to south west Europe and southwest Asia. This beautiful plant is loved for its large vivid purple flowers and is commonly found around the U.K. in woodland and ecologically sensitive areas. Rhododendron is something most people will have seen growing wild at some point. Being so pretty It can still be found in many people’s gardens all over the country. It spreads easily as its small seeds are carried on the wind.
If left alone It can grow to cover a large area reducing sunlight and as a result restricting the growth of other plants beneath it. This has a knock-on effect to insects and wildlife that rely on those plants for life. Although it’s not illegal to plant rhododendrons I would suggest not doing it and removing it if you already have it.
Trees
Non-native oak trees – Worldwide there are over 600 species of oak tree, all of which can be found in the northern hemisphere. Of the 600 oaks only two are native to Britain with a further three commonly found non-native oaks. Native oaks are the English oak and sessile oak. The three non-native oaks are holm oak, red oak and turkey oak. Holm oak is the only evergreen oak to be found in britain and is used for firewood and it’s acorns for pig feed. The red oak is native to America and gets its name from the colour of its leaves in autumn which turn a deep shade of red. The turkey oak is native to parts of Asia and southeast Europe. The main concern is that it is the host of a type of wasp called the knopper gall wasp, which in spring forms small galls (a reaction from a plant or tree to grow a home for insects, very clever) within the catkins of the Turkey Oak. The female wasps that develop from these galls on the turkey oak then lay eggs within the acorns of the English Oak causing galls to develop and therefore affecting the fertility of the English Oak and reducing the viability of the acorns.
False Acacia – there is a road near me called Acacia walk and it has about half a mile either side of the road planted with these stunning trees. That is half of the reason why they are so popular, they are stunning with big golden cascades of flowers. The acacia spreads by ‘suckering’ that is that it sends new shoots up from around its base and spreading that way, more so than by its seeds. This suckering effect can damage, pavements and homes as it sends up shoots. The false acacia also has a tendency to rot and then drop the rotten branches causing obvious problems. It also casts shade, as many non-native species do, over the native trees and plants of Britain reducing their ability to grow.
For factsheets on NNIS then please visit this site where they are listed by common name.