Invasive alien species in Europe

Indicator definition

The indicator 'Invasive alien species in Europe' comprises two elements: 'Cumulative number of alien species in Europe since 1900', which shows trends in species that can potentially become invasive alien species, and 'Worst invasive alien species threatening biodiversity in Europe', a list of invasive species with demonstrated negative impacts.

1. 'Cumulative number of alien species in Europe since 1900'

The cumulative number of alien species established in Europe from 1900 onwards is estimated in 10-year intervals. Pre-1900 introductions are also estimated. Information is broken down by major ecosystems (terrestrial, freshwater and marine) and selected 'taxonomic' groups: vertebrates, invertebrates, primary producers (vascular plants, bryophytes and algae) and fungi.

2. 'Worst invasive alien species threatening biodiversity in Europe'

The list of worst invasive alien species threatening biodiversity in Europe distinguishes a number of the most harmful invasive alien species in Europe, across ecosystems and major taxonomic groups, with respect to their impacts upon European biodiversity and changing abundance or range. The list of worst invasive alien species threatening biodiversity in Europe covers the pan-European area. Two criteria were used to select species for the list:

The species is recognized by experts ^₍₁₎ to have a serious adverse impact on biological diversity of Europe.

The species, in addition to its adverse impact on biodiversity, may have negative consequences for human activities, health and/or economic interests.

^{_{(1) Note: this recognition is based on expert view rather than quantifiable data and is therefore subject to debate. The reason for this is lack of quantitative data that lends itself to analysis and comparison among species.}}

Units

number of species
cumulative number of species

Policy context and targets

Context description

The Convention on Biological Diversity defines _⁽²⁾ an alien species to be 'a species, subspecies or lower taxon, introduced outside its natural past or present distribution; includes any part, gametes, seeds, eggs, or propagules of such species that might survive and subsequently reproduce' while an invasive alien species is 'an alien species whose introduction and/or spread threaten biological diversity'.

The potential threat that alien species pose to biological diversity can be illustrated in the cumulative number of alien species. Although not all alien species become invasive, the number of alien species introduced to an environment has a direct correlation with the number of species which may become invasive at a later date.

Invasive alien species may affect and reduce native biodiversity in various ways, such as through competition for food and space, predation, disease transfer, and changing habitat structure and functions. Many invasive alien species are weeds and animal pests in agriculture/aquaculture and forestry. Invasive alien micro-organisms may create severe problems to human health and to production crops. Intentionally introduced alien species for production in agriculture, forestry and fisheries/ aquaculture, horticulture or for biological control, can also become invasive, causing negative impact on native biodiversity. There is a growing concern that with climate change and further deterioration in the environment, invasive alien species may benefit and increasingly compete with native species to the latter's disadvantage.

Increase in trade and tourism and transport on land and in particular at sea, as well as developments in agriculture, plantation forestry, aquaculture, fisheries, game management and the pet trade, have provided new and enhanced pathways for the spread of invasive alien species. Although European states have a comprehensive regulatory framework to protect economic interests against diseases and pests, these are often inadequate to safeguard against species that threaten native biodiversity.

Although, over time, thousands of alien species have been introduced to Europe, most are considered more or less harmless _⁽³⁾ and only a relatively few genuinely problematic. There is no precise limit to draw the line between 'invasive' and 'non-invasive' alien species. Hence, it is presently impossible to compile a complete inventory of invasive alien species in Europe. The genuinely problematic ones are more easily identifiable and there are several reasons to consider those worst invasive alien species to prioritize actions and to be able to communicate the issue to a wider public _⁽⁴⁾.

_{^{(2) See http://www.biodiv.org/invasive/terms.shtml (Accessed March 2007).}}

^{(3) See e.g. http://www.gisp.org/ecology/threat.asp.}

_{^{(4) The IUCN Invasive Species Specialist Group has thus presented a global list of '100 of the worlds worst invasive species' with a main objective to create awareness of the wide range of invasive species from different taxonomic groups and of impacts caused, see http://www.iucn.org/dbtw-wpd/edocs/2000-126.pdf.}}

Relation of the indicator to the focal area

Invasive Alien Species have been recognised as one of the major threats to biodiversity. The indicator 'Invasive alien species in Europe' covers significant aspects of the CBD/EU indicator 'Trends in invasive alien species (Numbers and costs of invasive alien species)'.

Targets

2010 biodiversity target

Related policy documents

• 2010 biodiversity target
  2010 biodiversity target 'to significantly reduce the rate of biodiversity decline by 2010'

Methodology

Methodology for indicator calculation

Two different approaches were used in compiling the elements for the indicator 'Invasive alien species in Europe':

Cumulative number of alien species in Europe since 1900

Data were compiled by existing networks according to the following criteria specified by the SEBI 2010 Expert Group on IAS:

1. The indicator is populated with data 1900-2007 at 10-year intervals and older 'pre-1900 aliens'.

2. Only the first record in the wild of a particular alien species for the different regions in Europe is included (i.e. no multiple records).

3. Only verified (by experts) records will be included.

4. 'Casuals' (organisms that are introduced to the wild but do not reproduce) are excluded ^₍₆₎.

5. Synonyms are checked.

The basis for the calculation of the terrestrial and freshwater data was the 11 country lists recording the alien species of different taxa with information on year of establishment. First year of establishment recorded in a country was considered to be the year the species established in Europe. The cumulative species numbers for the main taxonomic groups was then calculated.

The marine data were compiled in cooperation with main experts on the European regional seas, see above. Each regional sea was considered separately; otherwise the calculations were performed as above _⁽⁷⁾.

Worst invasive alien species threatening biodiversity in Europe:

Candidates for a tentative list were initially selected from national lists and other sources by experts in the SEBI 2010 Expert group on trends in invasive alien species. Species were selected from the terrestrial, freshwater and marine environments as well as from a range of taxonomic groups. The criteria used were the following:

1. The species is recognised by experts to have a serious impact on biological diversity of Europe. 'Serious' refers to, e.g.:

• severe impacts on ecosystem structure and function;
• replacement of a native species throughout a significant proportion of its range;
• hybridisation with native species;
• threats to unique biodiversity (e.g. endemic species).

2. The species, in addition to its impact on biodiversity, may have negative consequences for human activities, health and/or economic interests (e.g. is a pest, pathogen or a vector of disease).

The list was then subject to an informal technical specialist consultation involving e.g. the Bern Convention's Group of Experts on Invasive Alien Species, contacts at IUCN/ GISP (Global Invasive Species Programme), the partners of relevant EU and regional research networks (e.g. NOBANIS, DAISIE) and other experts. Additional information was provided in a technical consultation on the EC Clearing House Mechanism in February-March 2006. This technical specialist review added a few new species and removed another few. The 2006 list was finally established at a meeting of the SEBI 2010 Expert Group on trends on invasive alien species in October 2006 _⁽⁸⁾.

Maintaining, revising and updating the list should be the responsibility of the SEBI 2010 Expert Group on trends on invasive alien species or a similar forum of experts nominated by countries. The list should be updated every five years _⁽⁹⁾.

_{^{(5) A species, subspecies or lower taxon, introduced outside its natural past or present distribution; includes any part, gametes, seeds, eggs or propagules of such species that might survive and subsequently reproduce. An invasive alien species is an alien species whose introduction and/or spread threaten biological diversity www.cbd.int/invasive/terms.shtml, accessed on 2 December 2008).}}

^{_{(6) However, the marine data include a number of 'casuals', i.e. species which have not be proven to establish and/or breed through records over a number of years.}}

_{^{(7) Actually, for marine data also accidentally recorded species are presently included.}}

_{^{(8) http://biodiversity-chm.eea.europa.eu/information/indicator/F1090245995/F1115192484/F1115817422/fol521326 (Accessed March2007).}}

_{^{(9) A first review may be necessary already by end 2007, as significant additional information is expected to be published by the EU DAISIE project in 2007, see http://www.daisie.ceh.ac.uk/.}}

Methodology for gap filling

No methodology for gap filling has been specified. Probably this info has been added together with indicator calculation.

Methodology references

No methodology references available.

Uncertainties

Methodology uncertainty

No uncertainty has been specified

Data sets uncertainty

No uncertainty has been specified

Rationale uncertainty

MAIN DISADVANTAGES OF THE INDICATOR

Cumulative number of alien species in Europe since 1900

• The indicator covers alien species without distinguishing those aliens that have become invasive. Although there is a relation between total number of alien species established and the number of invasive alien species, it is desirable to focus on the latter. Presently, this is not possible as no harmonized and officially accepted criteria to identify the share of invasives are available.
• The limited geographical coverage for the freshwater and terrestrial environments does not provide a representative indicator for European-level assessments. The eleven Nordic and Baltic countries have specific climatic and biogeographical features - being the northern part of Europe - which differ considerably from other regions. For a limited number of Species the time of introduction is not known.

Worst invasive alien species threatening biodiversity in Europe

• These species have been identified in an extensive and open expert consultation. In spite of this there is an element of subjectivity in the selection of species.
• The indicator 'Invasive alien species in Europe' presently also suffers from not more precisely measuring the impacts of the invasive alien species, including costs, details on the geographical spread of (at least selected) species within Europe and on management and other response measures.

ANALYSIS OF OPTIONS

The suggested sub-indicator 'Cumulative number of alien species in Europe since 1900' has been designed to show development according to the three main ecosystems - marine, freshwater and terrestrial. Data can also be broken down to more specific environments (wetlands, forests, agricultural lands, urban areas etc.). Another option is to present the indicator according to means of introduction, thus connecting to driving forces.

The list of 'Worst invasive alien species threatening biodiversity in Europe' could alternatively include also species which (mainly) threaten human interests. Some of these are of great economic importance and widely known. The advantage from an awareness point of view of expanding the list to include these species should be balanced against the objective of presenting effects on native biodiversity (the present list).