EPPO Prioritization Process for invasive alien plants



A brief history

When initiating the work on invasive alien plants in 2002, the EPPO Panel on Invasive Alien Plants assembled a preliminary list of approximately 500 potentially invasive alien plants in the EPPO region from scientific and technical literature, web sites and official contacts in EPPO member countries with a questionnaire survey. A preliminary prioritization of these species was made by expert judgment considering the following aspects:

  • whether the plant is considered invasive or potentially invasive by several EPPO countries,
  • whether the plant is absent or still containable by appropriate measures in several EPPO countries,
  • the potential of the plant for further spread into and causing damage in significant areas where it is absent,
  • whether the plant is reported to be actively spreading or becoming more damaging in its current distribution area.


Additional information about these selected plants was then gathered from official contacts in EPPO member countries: e.g. on typical habitats, geographical distribution within countries, identification of areas where a species is creating most problems, abundance, existence of current pathways, mode or type of spread, cultivation, official control. As there was no widely agreed method to identify those alien plants that are considered invasive and represent the highest priority for Pest Risk Analysis, the Panel decided to focus its efforts on the development of the EPPO Prioritization Process for invasive alien plants. 


After several years of development and testing by the Panel, the concepts for an EPPO prioritization process for invasive alien plants were published in the EPPO Bulletin (Brunel et al., 2010). In September 2012, the Prioritization Process was adopted as a Standard (PM5/6) by the Council of EPPO and then published in the EPPO Bulletin.





















Click on the image to enlarge it

Decision tree for the EPPO prioritization
process for invasive alien plants

Aims and structure of the EPPO Prioritization Process

The EPPO Prioritization Process is designed:

  • to assess the risk of invasive alien plants through an approved standard
  • to produce lists of invasive alien plants that are established or could potentially establish in the EPPO region, and
  • to determine which of these have the highest priority for an EPPO Pest Risk Analysis.


All invasive alien plants studied by EPPO were assessed through this Prioritization Process, allowing standardization of the procedure of listing of invasive alien plants as follows:

  • When a new species is identified as a potential threat for the EPPO region (already present in the EPPO region or absent) by a member country or by the EPPO Secretariat, the species is documented through a mini datasheet which is published in the EPPO Reporting Service and the species is included on the EPPO Alert List.
  • The species is maintained on the EPPO Alert List for a period of time (up to three years) to raise awareness to member countries.
  • Each species of the EPPO Alert List is assessed by the Panel on Invasive Alien Plants using the EPPO Prioritization Process at an individual country level and at the EPPO region level and each assessment is discussed during a dedicated meeting to reach a common opinion for the EPPO region.


Section A of the Prioritization Process scheme for the elaboration of different lists of invasive alien plants (pests or potential pests) for the area under assessment.

  • The process consists of compiling available information on alien plants according to pre-determined criteria, and can be run at the EPPO region level, at country, or local area level.
  • These criteria examine whether the species is alien in the area under assessment, and whether it is established or not.
  • The information used primarily rely on observations made in the EPPO region but, if the species is not established, the invasive behaviour of the species in other countries is also considered, as well as
  • the suitability of the ecoclimatic conditions in the area under consideration.
  • the spread potential,
  • the possible negative impacts on native species, habitats and ecosystems,
  • the possible negative impacts on agriculture, horticulture or forestry,
  • the possible negative impacts socio-economic factors such as animal and human health, on infrastructures, on recreational activities, and other trade related impacts such as market losses.
  • Uncertainty is recorded for questions on spread and impact, and summarized in an overall uncertainty rating of low, medium or high.


If the species has a high spread potential and a high impact to Plant Health or the environment and biodiversity or a high impact on socio-economic factors combined with medium impact on plant health or biodiversity, the species may be registered on the EPPO List of invasive alien plants. If information about the plant species is not considered sufficient or if the impacts appear to present a medium risk (which is defined as low to medium spread potential combined with high impact or medium to high spread potential combined with medium impact.), the species is registered on the EPPO Observation List.


Section B Prioritization Process scheme for the identification of invasive alien plants for which a PRA is needed.

  • Species that qualify to be registered on the EPPO List of invasive alien plants proceed to a second set of questions designed to investigate the efficiency of international measures (to be justified through a Pest Risk Analysis) to prevent their entry and spread. This second set of questions determines whether:
    • the species is internationally traded or enters new countries through international pathways
    • the risk of introduction is superior to natural spread,
    • the species still has a significant suitable area for further spread.
  • The species may then considered to be a priority for Pest Risk Analysis.
  • The Panel then determines which species should be the object of a Expert Working group on PRA. Depending on the outcome of the PRA, the species may be included in the A1 and A2 EPPO Lists and recommended for regulation as a quarantine pest.


The Prioritization Process can be used to provide consistent national lists of invasive alien plant species across the EPPO region, and can act as a useful tool for dialogue and information exchange between countries.



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