Invasive Species | Scottish Invasive Species Initiative (SISI)

Our work

An invasive non-native species is any animal or plant that has been introduced to a habitat outside it’s native range and has the ability to spread, causing harm to the environment, the economy, human health or the way we live. Many of these species are able to spread via rivers and water courses, threatening the wildlife and landscapes of Scotland’s iconic rivers and lochs.

The Scottish Invasive Species Initiative partnership is set up to tackle invasive non-native species along rivers and watercourses in northern Scotland. Working with local partners (fishery and river trusts and boards), land managers, local communities and volunteers, we are tackling some of the worst offending invasive non-native species growing along river banks.

Our projects

As a project we are unusual in that we control both an animal (the American mink) and a suite of invasive non-native plant species in a single coordinated programme. Find out more about each of these activities below.

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. These species reached Britain when there was a land bridge connection to the European mainland. As the ice melted sea levels rose, the land connection was flooded and the natural land based movement of species stopped. Man came to Britain about 8,000 years ago and virtually all new land animals and plants which have established since then have been introduced by through human intervention. 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.

It is illegal to release, plant or allow the spread any invasive non-native species into the wild in Scotland. Currently there are around 3,000 non-native species in Great Britain with approximately 2000 of these established or “naturalised” in the wild. Around 10-15% of these are considered to be invasive and problematic.

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 or other purposes such as ornamental gardening, farming, forestry or as pets – and have then escaped and established in the wild. Other species simply hitchhike, moving to new countries via people and transport.

Practicing good biosecurity when travelling, especially with gear and equipment, is essential in stopping the spread of invasive species. 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 – around 10% of these have the potential to become invasive. This trend is mirrored across Europe and the rest of the world.

The impacts of invasive species

Invasive non-native species take hold and spread, wreaking havoc on invaded areas and causing problems for our native wildlife, our economy or our health. Once established they are often difficult and costly to remove, persistent and cause escalating problems as they spread. Their impact is so significant that they are considered to be one of the greatest threats to biodiversity worldwide.

Scottish environment

Invasive non-native species harm ecosystems by many different mechanisms; out-competing native species (Japanese knotweed forming dense stands and out-competing native flowers); preying on local wildlife (American mink decimating water vole populations); hybridisation with indigenous fauna (e.g. Sika and red deer); altering habitats (e.g. Himalayan balsam triggering erosion of river banks) and spreading disease (e.g. grey squirrels carry the Squirrel pox which is fatal to our native red squirrels). Through these mechanisms ecosystems can become unstable, unbalanced or significantly altered.

Scottish economy

Invasive non-native species impose huge economic burdens. In Great Britain they cost about £2 billion a year, with Scotland’s expense around £300 million. Damage affect agriculture, forestry, transport, construction, aquaculture, recreation and more. Japanese knotweed, for example, is able to grow through hard surfaces, such as building foundations, causing millions of pounds worth of damage in Great Britain every year.

Our health and enjoyment of the environment

Invasive non-native species also affect public health and leisure. Established pests like rats damage homes, giant hogweed cause skin burns and the aquatic floating pennywort can block waterways and prevent boat navigation. Dense stands of Japanese knotweed, Himalayan balsam, and giant hogweed can diminish countryside beauty and restrict access for walkers and anglers, reducing our enjoyment of our environment and affecting local communities.

The bigger picture

The problem of invasive non-native species causing harm is not limited to Scotland or Great Britain – it is very much a global issue. The IPBES Assessment on Invasive Alien Species (2023) and their control found that:

Invasive non-native species have a key role in 60% of global plant and animal extinctions, and
Global annual control costs are now >$423 Billion – having quadrupled every decade since 1970.

Within Great Britain 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.

Learn more about INNS management in Great Britain