Invasive Non-native Species in Scotland
An audit by Scottish Natural Heritage in 2001 found 988 non-native species occurring in Scotland. Whilst the majority of non-native species are not invasive, there is clearly the potential for a vast amount of ecological and economic damage from those that are. A number of invasive species that are currently causing problems in Scotland are described below.
American Mink ( Mustela vison)
This species is listed on Schedule 9 of the Wildlife and Countryside Act 1981, which makes it illegal to release or allow its escape into the wild. Many mink escaped or were released from fur farms during the 1930s onwards and have since become widespread across Scotland. They are thought to be a significant factor in the water vole population crash, and the huge losses suffered by several seabird colonies on Scottish islands. For more information, see the GB Non-native Species Secretariat Website.
Grey Squirrel ( Sciurus carolinensis)
This species is listed on Schedule 9 of the Wildlife and Countryside Act 1981, which makes it illegal to release or allow its escape into the wild. The Grey Squirrel was first introduced during the late 1800s and is now widespread across the country. It is a major pest of forestry, where they strip bark from deciduous trees. They are also considered to be responsible for the catastrophic decline of the red squirrel, by competing for food and passing on disease. For more information, see the GB Non-native Species Secretariat Website.
Non-native Aquatic Plants
A large number of aquatic plants, for both aquaria and outdoor ponds, are available to buy in garden centres and pets shops. Most of these plants are harmless and will not survive outdoors or in unsheltered habitats. However, some invasive plants escape into the environment where they can quickly take over streams, rivers and lochs. Invasive pond plants generally won't be a good choice for your pond as you will find that they grow rapidly and soon overgrow your pond and out-compete your other pond plants.
To stop invasive aquatic weeds becoming a problem in the wild you can ensure that you:
• Dispose of pond plants carefully - compost or burn, never tip the water down a drain or into a watercourse as some of these plants can regenerate from very small fragments.
• Don't buy known invasive species - even if you are careful about how you dispose of your pond waste, birds and animals can transport plants to watercourses.
• Try to buy native pond plants which won't be a problem in the wild.
Plantlife Scotland has produced a number of leaflets concerning problem invasive aquatic plants and recommending alternative native species. Further information can be found on the Plantlife website.
Japanese knotweed ( Fallopia japonica)
Japanese knotweed was originally introduced to Scotland as an ornamental plant in the mid-nineteenth century. It is listed on Schedule 9 of the Wildlife and Countryside Act 1981, which makes it an offence to plant or otherwise cause it to grow in the wild. Japanese knotweed is able to regenerate from very small pieces of plant (fingernail size) and its rhizome system can be up to 3 metres deep, making it extremely difficult to eradicate once established. It is easily spread to new sites through illegal fly-tipping or the careless disposal of "infected" soil and as a result of natural processes such as flooding and erosion. Japanese knotweed causes ecological problems as a result of out-competing native plants. It can also be commercially damaging because of the cost of eradication on development sites and its ability to damage structures and road surfaces.
Refer to the NetRegs Website for information on how to identify and control Japanese knotweed.
Rhododendron ponticum ( Rhododendron ponticum)
Rhododendron was introduced into Britain in the mid 1700s as an ornamental plant. Since then it has become widespread, particularly in woodland habitats on the west coast of Scotland. Although the flowers give a colourful display, it creates dense thickets and shades out native plants. Its root system and leaf litter is also toxic to other plants and it will eventually come to dominate the habitat, to the total exclusion of virtually all other vegetation. As a non-native species it provides few compensating benefits for native birds or animals. For more information, see the GB Non-native Species Secretariat Website.
Himalayan Balsam ( Impatiens glandulifera)
This attractive plant is a garden escapee that can be often found along riverbanks. It can outgrow native grasses and other plant species, creating an ecologically-harmful monoculture in which native species are unable to thrive. It is able to project its seed over a radius of up to four metres and spreads readily to new areas. The seeds remain viable for years, making eradication a time-consuming and difficult long-term project. For more information, see the GB Non-native Species Secretariat Website.
Giant Hogweed ( Heracleum mantegazzianum)
Another garden escapee, this was introduced into Britain in the late 1800s and can often be found on waste ground and riverbanks. It grows up to 5 metres tall and each flower head produces thousands of seeds that are readily dispersed by wind and water. If sap from the plant gets on to the skin and is then exposed to sunlight, it can blister and cause severe skin irritation. Children in particular are at risk and there are a number of cases each year of injuries caused by contact with this plant. Refer to the NetRegs Website for information on how to identify and control Japanese knotweed.