Invasive species


An Invasive Non-Native Species (INNS) is any non-native animal or plant that has the ability to spread causing damage to the environment, the economy, our health or the way we live.

In particular these invasive non-native species are a big threat to the native wildlife of Scotland. Many of these invasive species are able to spread via our rivers and water courses and threaten the iconic wildlife and landscapes of our rivers and lochs.

Working with the local fishery trusts we are tackling the worst offending plant species, which typically grow on river banks, and one invasive mammal - the American mink. 

American mink

Mink control project

American mink impact on native species through predation, competition and as vectors of disease. Significant population declines of ground nesting birds and small mammals (e.g. water vole) have resulted from mink predation.   

Using mink monitoring rafts we will be locating mink and contolling them with the aim of seeing native wildlife populations recover. 

Find out more about our Mink control project

Invasive non-native plant

Invasive plant project

Invasive non-native plants are causing a big problem in the countryside. They grow readily and spread forming dense stands, which out-compete native flowers and in turn change the habitat for insects and other small creatures. 

Working at a local level with communities and through training volunteers we aim to work at a catchment scale to put in place sustainable invasive plant control.

Read more about our Invasive plant project


What are invasive non-native species?

Native species are generally taken to be those that were present in Britain at the end of the last ice age, which got to Britain under their own steam when there was still a connection (a land bridge) to the European mainland. As the ice melted sea levels rose and the connection was flooded and the natural movement of species stopped. Man came to Britain about 8,000 years ago and virtually all new land animals and plants that have become established since this date have been introduced by man. These are known as non-native (or alien) species.

Not all non-native species cause problems, only a minority go on to have serious negative impacts on our native species, our health or economy, these species we call invasive non-native species.

There are now almost 2,000 non-native species established in Britain, 10-15% of these are invasive. (Defra 2012)

It is illegal to release, plant or allow to spread any invasive non-native species into the wild.


How do they get here?

Invasive species are introduced either directly or in-directly by man. Trade, transport, travel and tourism can all move species around the world. Many species have been introduced intentionally for commercial purposes such as ornamental gardening, farming, forestry or as pets and have then escaped and become established in the wild. Other species simply hitchhike, moving to new countries via people and transport.

Biological invasions impact every landmass and ocean on the planet.

The number of new arrivals is increasing, with 10-12 new non-native species becoming established in Britain each year. This trend is mirrored across Europe and the rest of the world.

Practicing good biosecurity when travelling, especially with gear and equipment, is essential in stopping the spread of invasive species.

Help stop the spread of invasive plants and animals by practising good biosecurity

The impacts of invasives

Invasive species take hold and spread, wreaking havoc on invaded areas and causing problems for our native wildlife, our economy or our health. They are often difficult and costly to remove, being persistent and causing escalating problems as they spread.  Their impact is so significant that they are considered to be one of the greatest threats to biodiversity worldwide – even more than pollution or climate change. 

Red squirrel with squirrel pox virus

Impacts on the Scottish environment

  • Competition; invasive species are often better adapted to their new environment, growing faster and out-competing our native species for space and food/nutrients. Example; Japanese knotweed forms dense stands along river banks out-competing native wild flowers.

  • Predation; a predatory invasive species can have a significant effect on reducing the population of a native species.  Example; the American mink was largely responsible for a 94% decline in the native water vole population.

  • Hybridisation; invasive species can interbreed with native species, diluting the native gene pools. Example; non-native Sika deer can interbreed with native Red deer.
  • Habitat alteration; invasive species can alter invaded habitats. Example; Himalayan balsam forms dense stands on river banks, these die back in the winter leaving bare soil which is prone to erosion, which can contribute to flooding problems. 
  • Spreading disease; invasive species can carry pathogens and parasites to which our native wildlife have no resistance. Example; the grey squirrel carries the Squirrel pox virus, which has no effect on grey squirrels but is fatal to our native red squirrels.
Japanese knotweed growing through pavement

Impacts to the Scottish economy

Invasive non-native species are having a significant cost to our economy.  They are estimated to cost in the region of £2 billion a year in Great Britain. In Scotland, this figure is around £300 million 1. Costs are incurred by the agriculture, forestry and horticulture sectors, but also by many other sectors including transport, construction, aquaculture, recreation and utilities.

Japanese knotweed in infamous in its ability to grow through hard surfaces, such as tarmac car parks or building foundations, it is estimated to cost millions of pounds worth of damage in Great Britain every year.



giant hogweed burn

Impacts to our health & enjoyment

Some invasive species threaten our health or enjoyment of our environment. Rats, house mice and cockroaches are all invasive non-native species that can be serious house pests. Oher species, such as Giant Hogweed, can cause severe skin burns. 

Invasive species that grow forming dense stands such as Japanese knotweed or Himalayan balsam can spoil our enjoyment of the countryside, making it less appealing and restricting access for walkers and anglers.


1 A 2010 study estimated the figures to be £1.7 billion in GB and £246 million in Scotland, these have been adjusted to allow for inflation. (Williams et al, 2010, The Economic Cost of INNS on Great Britain)


The bigger picture

The problem of invasive non-native species causing harm is a global one.  Within Great Britian there are various agencies involved in co-ordinating the approach to tackling  invasive non-native species, and several organisations lead on this work within Scotland. 

Read more about the management of invasive spcecies within Scotland and the UK


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