CABI scientists found that invasive non-native species (INNS) – such as the aquatic water weeds floating pennywort and Japanese knotweed as well as signal crayfish – cost the UK economy an estimated £4 billion a year.
However, when considering species only covered by the GB Non-native Species Strategy – for instance with fungi excluded from the estimate – the total cost was estimated to be £1.9 billion.
CABI researchers in the UK, Switzerland and Kenya found a 135 per cent increase in comparable costs since the last assessment in 2010. Annual estimated costs in 2021 were £3.02 billion, £499 million, £343 million and £150 million to England, Scotland, Wales and Northern Ireland respectively.
The cost to forestry increased eightfold. The cost to aquaculture and agriculture increased by 139.5 per cent and 112.7 per cent, respectively. Meanwhile, the cost of most of the other sectors increased roughly in line with inflation (47.6 per cent for Great Britain and 55.7 per cent for Northern Ireland).
Agriculture is the most affected industry, with estimated costs for the UK at £1.088 billion followed by construction, development and infrastructure at £270 million and tourism and recreation at £136 million. The impact upon forestry is £123 million.
A growing problem
The study, published in the journal Biological Invasions, updates the earlier assessment using the same methodology and the diversity of changes among sectors and species highlights the value of such a detailed approach.
There are currently around 2,000 INNS in the UK with 10-12 new species establishing themselves every year. The list includes well-known established species such as grey squirrel, killer shrimp, giant hogweed, mink and parakeets. It also includes recently arrived but highly impactful species such as the sea squirt Didemnum vexillum and ash dieback.
The fungus Hymenoscyphus fraxineus, which causes ash dieback disease has become the costliest species in the past decade. In the UK, it has cost an estimated £883.5 million, followed by Japanese knotweed (£246.5 million), rabbits (£169.7 million), rats and mice (£84.4 million), cockroaches (£69.8 million) and deer (£62.9 million).
As a group, fungi were the costliest to the UK, accounting for 52.9 per cent of the total estimated costs, followed by mammals, plants and terrestrial arthropods (21.9 per cent, 15.5 per cent and 7.5 per cent of the total, respectively).
Solutions to address invasive species
Dr Rene Eschen, lead author and Senior Scientist, Ecosystems Management, said, “Our research illustrates the usefulness of repeating economic cost assessments for INNS, as INNS are dynamic and their impacts vary.
“Repeat assessments like this one are important to maintain a focus on the impact of INNS, changes in impacts as a result of new or spreading species, as well as the identification of potential impacts of management or policies.”
The researchers recommend continued investment in sustainable, long-term solutions for widespread damaging species. For instance, classical biological control, they say, has been a cost-effective, safe and environmentally sensitive management option when other methods prove ineffective or are no longer feasible.
Dr Richard Shaw, co-author and Senior Regional Director, Europe and The Americas, said, “This assessment again shows the important costs of INNS to the UK economy. Few effects of INNS-specific management efforts can be seen in these results. However, they highlight the need to continue prevention and early detection, followed by eradication of the highest-risk species prior to establishment.”
In February, the GB Invasive Non-native Species Strategy, which draws upon CABI’s research, was published. It provides a strategic framework for government departments, their related bodies and key stakeholders to better coordinate action.
Policy action against invasive species
Defra Head of GB Non-Native Secretariat, Niall Moore, said: “Invasive Non-Native species pose a serious threat to our natural environment and this Government is taking action through the recently launched GB Invasive Non-Native Species strategy, to protect our native animals and plants from INNS.
“CABI’s research, funded by Defra, reveals the significant financial impact of INNS. It is vital that we work together with researchers, scientists, and others, who are working to tackle INNS, to prevent their entry into and establishment in Great Britain and, when they do become established, to mitigate their negative impacts.”
The paper can be read in full open access here: https://link.springer.com/article/10.1007/s10530-023-03107-2.
This article originally appeared on the CABI blog and has been edited for length and clarity.
Header photo: Floating pennywort is one invasive non-native species of concern. The aquatic weed causes dense mats that cover the water’s surface – such as here on this water course on the River Wey, Weybridge, UK (Credit: Djami Djeddour).