All things invasive with the Scottish Invasive Species Initiative

14 May 2019

As it’s national Invasive Species Week (13-17 May) this week’s blog has been written by Vicky Hilton, Volunteer & Communications Officer for the Scottish Invasive Species Initiative (SISI). 

The SISI is a four-year partnership project led by Scottish Natural Heritage (SNH) and is funded by SNH and the National Lottery Heritage Fund. Partners in the project include a number of Fishery Boards and Trusts, and the University of Aberdeen. The project is developing invasive species management skills among a network of enthusiastic volunteers and partners, who are supported, trained and equipped to take on invasive species control at a local level.

What is an invasive species?

There are around 2,000 non-native plants and animals in the UK. Only around 10-15% of these non-native species go on to cause problems - these are termed as invasive non-native species (INNS). INNS pose a significant threat to the environment, the economy and in some cases human health.

They are problematic as they thrive in their introduced environment and disrupt the delicate balance of natural ecosystems. Their impacts can be large and obvious, like the presence of a stand of Japanese knotweed, or subtle, like the reduction in invertebrate biodiversity in a river where the banks are dominated by Himalayan balsam.



What makes a successful invader?

Most non-native species that go on to become invasive share several characteristics that make them successful in their new environment. They lack predators, reproduce quickly and can disperse easily across a large area. 

The most significant impacts invasive species have are on our natural environment, where we see; 

  • Competition; invasive species are often better adapted to their new environment, growing faster and out competing native species for space and food/nutrients.
  • Predation; a predatory invasive species can have a significant effect on reducing the population of a native species. For example, invasive American mink predate on water voles. 
  • Hybridisation; invasive species can interbreed with native species, diluting the native gene pools. For example, invasive Sika deer are interbreeding with our native Red deer.
  • Habitat alteration; invasive species can alter invaded habitats. Himalayan balsam forms dense stands on riverbanks, these die back in the winter leaving bare soil, which is prone to erosion and can contribute to flooding problems. 
  • Spread of disease; invasive species can carry pathogens and parasites to which our native wildlife has no or limited resistance. Invasive grey squirrels carry the Squirrel pox virus, which has no effect on grey squirrels but is fatal to our native red squirrels.

A combination of any of the above characteristics make successful invasive species formidable opponents to native species – and difficult to remove or dislodge once established. INNS are also expensive to remove and are estimated to cost the UK economy in the region of £2 billion a year. 

The most effective measure to prevent the spread of INNS is to prevent their introduction in the first place. However, once established there are a number of ways in which we can manage and control them: 

  • Be Plant Wise – by not dumping garden waste in the countryside, you can prevent non-native species escaping from your garden.
  • Practice good Biosecurity – “Check, Clean, Dry” all of your equipment and footwear when undertaking outdoor activities in the countryside.
  • Volunteer – Join in a conservation volunteer activity, undertake habitat restoration work or adopt a mink monitoring raft on a nearby watercourse. 
  • Record sightings  - you can use the “iRecord” website and App to report problem species 

To find out more about the project and to get involved, visit where you can also sign up to the e-newsletter, follow on social media (Facebook, Twitter and Instagram) or contact us on