Accredited official statistics

20. Pressure from invasive species

Updated 7 May 2024

Applies to England

Data last updated: November 2023

Introduction

Non-native species are those that have reached Great Britain by accidental human transport, deliberate human introduction, or which arrived by natural dispersal from a non-native population in Europe. Species that have arrived since 1500 are included within this indicator.

Most non-native species are considered benign or positive, but some have a negative impact on native species through the spread of disease, competition for resources, or by direct consumption, parasitism or hybridisation; such species are termed invasive. Invasive non-native species have one or more of these negative impacts and a high capacity to spread to natural and semi-natural habitats.

This indicator shows the change in number of invasive non-native species established across 10% or more of the land area of Great Britain, or along 10% or more of the extent of its coastline.

Type of indicator

Pressure indicator

Assessment of change in the number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline

Freshwater invasive species:

• Long term (1969 to 2022): Deteriorating
• Short term: Not assessed
• Latest year: Not assessed

Marine (coastal) invasive species:

• Long term (1969 to 2022): Deteriorating
• Short term: Not assessed
• Latest year: Not assessed

Terrestrial invasive species:

• Long term (1969 to 2022): Deteriorating
• Short term: Not assessed
• Latest year: Not assessed

Note on indicator assessment

Analysis of the underlying trends is carried out by the data providers. Long- and short-term assessments are based on a 3% rule of thumb. The base years for these assessments use a three-year average, see Assessing Indicators.

Invasive species in Great Britain

Trend description for Figure 20.1

There are 3,343 non-native species in Great Britain, 2,074 of which are classified as established (reproducing in the wild). This indicator contains 195 non-native species that are considered to be exerting a negative impact on native biodiversity (48 freshwater species, 39 marine species and 108 terrestrial species). The majority (189) of these species are established; six are long-term residents but not known to breed in the wild, (two species of terrapin (Emys orbicularis and Trachemys scripta) and four freshwater fish (Ameiurus melas, Leuciscus idus, Salvelinus fontinalis and Oncorhynchus gorbuschas)).

Over the period 1969 to 2022, invasive non-native species have become more prevalent in the countryside. Since 1969, the number of these species established in or along 10% or more of Great Britain’s land area or coastline has increased in the freshwater, marine (coastal) and terrestrial environments, thereby increasing the likely pressure on native biodiversity (Figure 20.1).

Comparing the latest data point from 2022 with the previous one, 2019, the number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline has increased in terrestrial (from 60 to 61 species), in freshwater (from 13 to 14 species) and remained the same in marine environments (29 species).

Figure 20.1: Number of invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline, 1969 to 2022.

Source: Botanical Society of Britain & Ireland, British Trust for Ornithology, Marine Biological Association, National Biodiversity Network, UK Centre for Ecology & Hydrology.

Download the data for Figure 20.1 in ods format

Notes on Figure 20.1:

1. Each data point reported for this indicator represents the count of invasive non-native species for the preceding 10 years rather than annual data, i.e., the data point for 1969 relates to the count of invasive species present in the period 1960 to 1969.
2. The square marker on the line chart (figure 20.1) shows the 2022 data point which covers a shorter time period than the triangular markers on the line chart (currently three years, 2020 to 2022).

Relevance of indicator 20

The indicator shows progress with commitments to improve the status of our wildlife and habitats. It is relevant to outcomes 1, 2 and 3 in Biodiversity 2020: A strategy for England’s wildlife and ecosystem services ; it is also relevant to a number of international targets (see Annex A and B of the aforementioned publication for further details).

The United Nations Convention on Biological Diversity (CBD) identifies invasive non-native species as a major threat to biodiversity. Many non-native species do not threaten biodiversity, but invasive non-native species can spread disease (for example, signal crayfish Pacifastacus leniusculus), modify ecosystems (for example, rhododendron Rhododendron ponticum), drastically reduce populations of native species (for example, American mink Mustela vison), or hybridise with native species (for example, ruddy duck Oxyura jamaicensis).

Under the CBD, the United Kingdom has an international obligation to address the impacts of invasive non-native species. The UK government has published 3 strategies, with the current one starting in 2022, under the Invasive Non-native Species Framework for Great Britain

The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets, and the new Kunming-Montreal Global Biodiversity Framework Targets , when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.

Background

The indicator and background charts are based on species distribution data available through the National Biodiversity Network (NBN), supplemented by expert knowledge and in house datasets of the Botanical Society of Britain and Ireland (BSBI), British Trust for Ornithology (BTO), UK Centre for Ecology & Hydrology (UKCEH), the Environment Agency (EA) and Marine Biological Association (MBA). Trends in the extent of invasive non-native species, as presented in Figures 20.1 and 20.2 were derived through a two-stage process. The number of invasive non-native species included within the indicator was substantially expanded from the 49 species used in the indicator published in 2009 (Hill et al., 2009). An initial list was derived from the GB Non-native Species Information Portal (GB-NNSIP) (Roy et al., 2014) by selecting all non-native species within the database that are noted to have, or potentially have, a negative or strongly negative ecological effect, including all 49 species from the original indicator. This list was subsequently reviewed by experts. Species for which there was a high degree of uncertainty with respect to negative impact were removed and new species were added as deemed appropriate. The revised list in 2014 comprised of 179 species, but has been subsequently amended in 2015, 2017, 2018, 2019, 2020, 2021, 2022 and 2023 to now comprise of 195 species (see technical background document).

Invasive non-native species were categorised according to the extent of the land area or coastline of Great Britain in which they were found in the decades of 1960 to 1969, 1970 to 1979, 1980 to 1989, 1990 to 1999, 2000 to 2009, 2010 to 2019 and the present period of 2020 to 2029 (see below). The categorisation was achieved by combining assessment of modelled distributions based on data available from the NBN with expert opinion and the use of additional datasets where available (for more details see the technical background document).

Invasion extent of non-native species

The extent to which the non-native species in this indicator are considered invasive is divided into the following 5 categories:

Definition: Not present in territory; Interpretation: Absent; Extent: 0.

Definition: Present in territory and either not established or with established populations that have not spread more than 10km from their source; Interpretation: Not or scarcely established; Extent: 1.

Definition: Established populations represent less than 10% of territory, with some having arrived from further than 10km from their source; or if more widespread then populations scattered and sparse; Interpretation: Established but still generally absent or at most occasional; Extent: 2.

Definition: Established populations present in 10% to 50% of the territory; Interpretation: Established and frequent in part of the territory; Extent: 3.

Definition: Established in more than 50% of the territory; Interpretation: Widespread; Extent: 4.

Figures 20.2a, 20.2b, and 20.2c shows the number of species in each decade in each extent category listed above.

Figures 20.2a, 20.2b, and 20.2c: Changes in the extent of invasive non-native species in freshwater, marine (coastal), and terrestrial environments of Great Britain, 1969 to 2022.

Figure 20.2a: Freshwater

Figure 20.2b: Marine

Figure 20.2c: Terrestrial

Source: Botanical Society of Britain and Ireland, British Trust for Ornithology, Marine Biological Association, National Biodiversity Network, UK Centre for Ecology & Hydrology.

Download the data for Figure 20.2 in ods format

The indicator is compiled from those invasive non-native species established in or along 10% or more of Great Britain’s land area or coastline (that is, extent categories 3 and 4). There are limitations to this approach:

• First, the list of invasive non-native species has been derived through the rapid assessment of impacts based on expert opinion. A semi-quantitative approach is currently being developed to improve the certainty and reliability of the list.
• Second, the extent value is based on relatively broad categories. The extent of some species can increase multi-fold within a single category, for example, the number of invasive non-native species in 10% to 50% of the land area of Great Britain, which can reduce the sensitivity of the indicator.
• Third, the occurrence data obtained from the NBN may not be representative of the species distribution in each decade, especially for both the earlier and most recent time periods, because there is often a time lag before occurrence data appear on the NBN. Furthermore, the availability of occurrence data reflects the intensity of survey effort applied in a time period that has subsequently been submitted to the NBN. The attribution of extent categories has, however been supplemented by expert opinion and in some cases by more complete datasets.

Further information on invasive species

Further information on invasive species is available through, the:

• The Defra website on Developing an indicator of the abundance, extent and impact of invasive non-native species (PDF, 382kb)
• The Delivering Alien Invasive Species Inventories for Europe (DAISIE) on the EC 6th Framework Programme
• The EU Invasive Alien Species Regulation on the EC website
• The NBN Atlas produced by the National Biodiversity Network (NBN)
• The technical background document produced by the UK Centre for Ecology & Hydrology
• The GB Non-native Species Secretariat for the UK Government
• The Invasive Non-native Species Framework Strategy for Great Britain produced by the UK Government

References

Hill, M. O., Beckmann, B. C., Bishop, J. D. D., Fletcher, M. R., Lear, D. B., Marchant, J. H., Maskell, L. C., Noble, D. G., Rehfisch, M. M., Roy, H. E., Roy, S. and Sewell, J. (2009). Developing an indicator of the abundance, extent and impact of invasive non-native species. Final report. Defra.

Roy, H. E., Preston, C. D., Harrower, C. A., Rorke, S. L., Noble, D., Sewell, J., Walker, K., Marchant, J., Seeley, B., Bishop, J., Jukes, A., Musgrove, A. and Pearman, D. (2014). GB Non-native Species Information Portal: documenting the arrival of non-native species in Britain. Biological Invasions, 16(12), 2495–2505.