SoNaRR 2025: INNS, pests and diseases
Natural Resources Wales
This webpage is part of the State of Natural Resources Report 2025
Invasive non-native species, pests and diseases are organisms that can cause damage to human health and well-being, non-human species and ecosystems. These may be native or non-native organisms.
Invasive non-native species (INNS) are any non-native animal or plant that can spread and subsequently cause damage to the environment, the economy, our health, and the way we live.
A pest is any organism that can cause damage to other organisms or human-built infrastructure, resulting in negative impacts on human health and well-being, ecosystem health or economic activity. In SoNaRR, pests usually refers to insect pests although rabbits are included here (grey squirrels are covered within INNS).
Diseases, in this context, are illnesses of any organism caused by infection by microorganisms.
Key messages
- Over time new invasive non-native species (INNS) have been establishing at continually increasing rates in Great Britain, the main global drivers are the movement of goods and people, and climate change.
- INNS are identified as one of the top five drivers affecting biodiversity worldwide; they impact all the different ecosystems of Wales, terrestrial, freshwater and marine.
- INNS are estimated to cost the economy of Wales £343 million annually (including fungi). The forestry and agriculture sectors are most significantly affected.
- Pests and diseases pose a significant threat in several ecosystems across Wales, impacting ecosystem resilience and economically important sectors such as forestry and agriculture.
- Tackling INNS, pests and diseases requires collaboration between stakeholders to improve biosecurity, target pathways of introduction, monitor the introduction and spread, ensure early intervention, and effectively plan, prioritise and implement strategic actions. It will also be important to implement INNS legislation and policy drivers and to include consideration of INNS in land management schemes.
Invasive non-native species summary
Invasive non-native species (INNS) have a significant impact on the environment, economy, and public well-being in Wales. These species are recognized as one of the leading threats to global biodiversity, with an estimated economic impact of £343 million annually (including fungi) in Wales alone. Over the past 50 years, the rate of new INNS establishment in Great Britain (GB) has surged, reflecting a worldwide trend driven by factors such as climate change and the increased movement of goods and people.
In response to the rising threat of INNS, various legislative and policy measures have been implemented in Wales since 2020 that prioritise prevention and early intervention. Key initiatives include the embedding of the Invasive Alien Species Order 2019, which restricts activities that could introduce or spread INNS, and the implementation and refresh of the GB INNS Strategy (2023-2030) including the development of the GB Pathway Action Plans. Additionally, the establishment of the Great Britain Non-native Species inspectorate (NNSI) has focused efforts on sectors most at risk for introducing these invasive species to GB.
A strategic framework for addressing INNS in Wales is essential for long-term efficacy. This framework should expand its membership and enhance collaboration among stakeholders to create a cohesive strategy. Increasing communication and supporting the establishment of strategic projects targeting specific species or geographical areas. It is also essential to continue the implementation of marine biosecurity plans that have been developed collaboratively to address INNS in marine environments.
The agriculture sector in Wales faces a substantial financial burden from INNS, estimated at £124 million annually, while the forestry sector incurs losses of approximately £167 million annually. INNS threaten productivity, damage crops and timber, and contribute to soil health deterioration and erosion. Future land management initiatives present an opportunity to promote coordinated efforts against INNS, ensuring that actions are taken at suitable spatial and temporal scales.
Particular emphasis should be placed on preventing the introduction of marine and freshwater INNS, as they are difficult to eradicate once established. Promoting biosecurity measures, early intervention measures, planning and collaboration will be vital for addressing new arrivals and curbing the spread of existing species.
Improvements in data flows, reporting and surveillance will contribute to INNS policy and legislative drivers, including Target 6 of the Global Biodiversity Framework.
Another crucial aspect of managing INNS in Wales is addressing existing evidence gaps related to their distribution, monitoring, impact, and management. Filling these gaps is essential for informing effective policy initiatives, including the State of Natural Resources Report (SoNaRR). Improved knowledge and data on INNS will enable policymakers and stakeholders to make informed decisions and allocate resources effectively, ultimately enhancing the response to the invasive species challenge in Wales.
Reducing the impact of INNS in Wales will address localised water resource and quality issues, will support the recovery of nature and will improve the resilience of ecosystems to respond to climate change.
Key changes since SoNaRR2020
In Wales, policy and legislative implementation has advanced through the embedding of the Invasive Alien Species Regulation and Order, development of enforcement mechanisms, and strategic contributions to the renewed GB INNS Strategy (2023–2030).
Targeted projects and guidance that support prevention, control, and restoration efforts across terrestrial, freshwater, and marine ecosystems have also been delivered.
Key changes have also included the growing recognition of INNS management as a public good within future land management schemes, and strengthened biosecurity promotion across sectors and ecosystems and the establishment of a collaborative INNS framework through the Wales Resilient Ecological Network (WaREN) project.
These developments reflect a maturing policy context that increasingly prioritises strategic, collaborative, and preventative approaches to INNS management.
Evidence needs
Globally and nationally, new trend data confirm that INNS introductions continue to be driven by increased movement of people and goods, and climate change. However, comprehensive trend data to describe INNS impacts across Welsh ecosystems remains limited, highlighting a continued evidence gap.
Read the full Invasive non-native species assessment in our State of Natural Resources Report 2025.
Pests and diseases summary
Pests and diseases pose a significant threat in several ecosystems across Wales, impacting ecosystem resilience and economically important sectors such as forestry and agriculture.
Over the last 15 years, pests and diseases have had a significant negative effect on tree health in Welsh woodlands, and farmland and urban trees. Pests and diseases cause a decline in tree health, which is a key determinant of the growth, composition and productivity of woodlands. The most significant diseases affecting Welsh woodlands are Phytophthora ramorum, primarily affecting larch species, and Ash Dieback in broadleaf woodlands, with the significance of oak processionary moth also increasing.
Within the marine ecosystem, the Highly Pathogenic Avian Influenza (HPAI) is a new and major threat to internationally important seabird populations in the UK. In enclosed farmland, livestock are at risk of vector-borne diseases such as Bluetongue, which is projected to have extended transmission seasons in future due to climate change. The abundance and distribution of pests and diseases are expected to increase in future due to climate change and global trade.
Key changes since SoNaRR2020
Over the last 5 years, Phytophthora ramorum and Chalara Ash Dieback have continued to cause a deterioration in tree health, but more significantly other species have emerged or have gained more of a hold since SoNaRR2020, including Phytophthora pluvialis and Oak Processionary Moth.
The first cases of bluetongue virus were detected in south-east England in November 2023. The virus has since been found in Powys and Monmouthshire.
Highly Pathogenic Avian Influenza (HPAI) caused mass mortality of seabirds in the UK and Wales for the first time in 2022 and 2023.
Key evidence sources
Explore some of the evidence we have used to inform our assessment:
- SoNaRR2020 Invasive non native species
- Costs of INNS to the United Kingdom
- Distribution and impact of INNS on the Wales Environmental information portal
- ERAMMP Report-105: Wales National Trends and Glastir Evaluation
- IPBES Invasive Alien Species Assessment
- Map of Ash dieback across the UK
- Avian flu survey in Seabird populations
- Areas of Wales with restrictions to prevent the spread of Phytophthora pluvialis
Case studies
Celtic Rainforests
The Celtic Rainforest project has facilitated INNS and non-native conifer removal, as well as conservation grazing, and restoration of plantations on ancient woodland sites (PAWS).
Celtic Rainforests Wales | Eryri National Park
Wales Resilient Ecological Network
The Wales Resilient Ecological Network (WaREN) will establish a framework for tackling invasive species across Wales. It develops linkages between stakeholders who are taking action on invasive species, with existing projects such as the Our River Wellbeing project on the river Dee and Local Action Groups in Wales.
Wales Resilient Ecological Network (WaREN) | North Wales Wildlife Trust
Marine Invasive Non-Native Species Biosecurity Planning Project
The NRW Nature Networks Marine Invasive Non-Natives Species (INNS) Biosecurity Planning Across the Marine Protected Area (MPA) Network Project contains strong elements of cross border collaboration with England. Pathway Action Plans and Species Action Plans have been produced for marine MPAs in Wales and NRW is working closely with Natural England to produce biosecurity plans for the cross-border sites (i.e. the Severn and Dee estuaries).
Other places in The State of Natural Resources Report 2025
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