Today marks the start of this year’s Invasive Species Week. It is organised by the Non-native Species Secretariat to raise awareness of invasive non-native species (INNS) and how everyone can help to prevent their spread. Paul Walton, RSPB Scotland’s Head of Habitats and Species, explains more about the problems and what actions the Scottish Parliament must take to tackle the threats of invasive non-native species in Scotland – preventing damage to our wildlife and landscapes, helping to restore them, and saving future generations from major environmental repair costs.  


The United Nations oversees two major initiatives on the global nature crisis facing our planet. The Inter-governmental Panel on Biodiversity and Ecosystem Services (IPBES) gathers and collates humanity’s best scientific and cultural understanding on the living world, and the threats it faces. The Convention on Biological Diversity (CBD) brings national and sub-national governments together in a shared mission to address the crisis. Both agree that there are five key overall drivers of biodiversity loss across the world: damage and fragmentation of wild places); climate change; pollution; over-use of natural resources ; and the impact of invasive non-native species (INNS).  

Invasive non-native species are animals or plants which have been moved and introduced to places where they do not occur naturally, directly through deliberate or accidental human actions, causing negative environmental, social and/or economic impacts in those areas. 

Why is moving animals, plants and fungi around the world and releasing them, such a problem? Can’t we just welcome all the newcomers into the environment? Unfortunately, we cannot: the natural barriers to the movement of species that exist on earth – including the oceans between land masses and around islands, mountain ranges and deserts, ocean currents – mean that plants, animals and other life  have developed independently in different regions of the world, adapting to local conditions and through interactions with other local species. This effect generates much of the biological diversity on Earth: for example, we have kangaroos as plains grazers in Australia, but antelope fill this role in Africa. When people move plants and animals around, we effectively break down those barriers and often damaging impacts emerge. 

 The introduction of new animals and plants introduces new diseases, new predators, new competitors for food and shelter. INNS impacts affect all major habitats and all major groups of animals and plants across the world – Scotland is no exception. For example, Scotland’s precious and threatened rainforest on the west coast has suffered massive degradation through invasion by non-native rhododendron, escaped from gardens and spreading rapidly, smothering the habitat and its unique wildlife species. The impact of INNS is not only on nature. In 2010 the economic impact of INNS across the UK countries was estimated to be at least £1.7bn each year, generally taken to equate to well over £2bn each year now. 

 A sea of bluebells in native woodland

Act fast and act early  

The two UN global biodiversity initiatives (IPBES and CBD) also agree that when tackling INNS, the best way is to act at the earliest invasion stage possible – that the emphasis should be on preventing releases and establishment of damaging species in the first place – and this will require establishing effective national and local skills and resources for INNS biosecurity – preventing the arrival of new species and detecting and acting on new species that arrive before they become a problem. This avoids the damage to nature and is hundreds of times cheaper than addressing issues once the damage has happened. The UN initiatives also agree that control (reducing the numbers and impact) or eradication (complete removal) initiatives are needed for the most damaging INNS already established, and that these must follow best practice guidelines if they are to be effective. 

 International trade is the single most important mechanism moving INNS around the world. As the globalisation of trade has accelerated, so has the movement of INNS. Other parts of the world – notably Australia and New Zealand – have succeeded in slowing the rate of arrival of INNS significantly through the introduction of strong national biosecurity policy, legislation, staffing and infrastructure.  

The establishment of new non-native mammals in Europe and New Zealand over 500 years. New Zealand began to implement strict biosecurity public policy in the 20th century. The curve representing New Zealand starts to flatten at around 1900, the Europe curve is still increasing.

The establishment of new non-native mammals in Europe and New Zealand over 500 years. New Zealand began to implement strict biosecurity public policy in the 20th century.

Source: Armon R.H., Zenetos A. (2015) Invasive Alien Species and Their Indicators. In: Armon R., Hänninen O. (eds) Environmental Indicators. Springer, Dordrecht

How about Scotland? 

 Currently, INNS biosecurity arrangements in Scotland, however, are inadequate. At least 10-12 new non-native species are establishing on the island of Britain each year. Northward movement of INNS currently established in the south of Britain continues. New and highly damaging non-natives are arriving on Scottish islands, such as stoats in Orkney, which are now eating the Orkney voles, a species found nowhere else in the world, and potentially making it harder for native predators such as short-eared owls, to find enough food to thrive. Too often, INNS control and eradications projects either fail to operate at the right scale or to employ best practice, are not funded and seen through to completion, or are too short-term to establish an effective legacy.  

Number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline, 1960 to 2018. The graph shows increasing numbers. 

Number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline, 1960 to 2018.

Notes: The most recent time period covers a slightly shorter period than the other bars (from 2010 to 2018). Source: Botanical Society of Britain & Ireland, British Trust for Ornithology, Centre for Ecology & Hydrology, Marine Biological Association, National Biodiversity Network.


Investment in a National INNS Inspectorate for Scotland would be preventative spend and represent a precautionary national approach to this principal driver of biodiversity loss. It would ensure government support in the long term, rather than a reliance only on short-term projects. The inspectorate would also inform and underpin a ‘Polluter Pays’ approach to INNS responses and management, minimising costs for expensive action to repair the damage done. And in developing and promoting best practice in local INNS control, eradication and biosecurity initiatives – for example on Scotland’s internationally important, yet highly vulnerable seabird islands – would be a key cornerstone in delivering the badly needed step-change in action against the new UN Decade on Ecosystem Restoration. 


As part of our joint Nature Recovery Plan, we are asking the Scottish Parliament to establish a Scottish Invasive Non-Native Species Inspectorate by 2025. 

  • Good blog. One question/concern. One of your colleagues wrote an update 're Orkney stout trapping. A small number of feral cats were caught as well as stoats. Both are non native and kill voles and birds. One was seen as an achievement to trap. The other was written as an apology and unfortunate occurrence. Why is removing cats wrong?