Pathway analysis: aquatic plants imported in 10 EPPO countries
Pathway analyses are regarded by National Plant Protection Organizations as a very efficient way to address the risks posed by invasive alien species. A study was recently made by the EPPO Secretariat to evaluate the risks posed by the imports of aquatic plants into the Euro-Mediterranean region. Data on imports of aquatic plants was obtained from 10 EPPO countries (Austria, Czech Republic, Estonia, France, Hungary, Germany, Israel, the Netherlands, Latvia, Switzerland, Turkey) and aggregated in order to determine whether invasive or potentially invasive alien plants could be introduced in the EPPO region through this pathway. The main conclusions of this study were that this pathway was mainly consisting of imports of tropical plants for use in aquaria, and that the vast majority (90%) of these aquatic plant species did not represent a major risk due to their climatic requirements. However, a few species required thorough attention due to their known invasiveness potential.
Among the 247 species included in the study, only 10 are currently considered to be a threat for the EPPO region, representing 4% of the total number of plants imported. These invasive or potentially invasive species continue to be traded in huge quantities despite the fact that: Crassula helmsii and Eichhornia crassipes are recommended for regulation by EPPO, Azolla filiculoides, Egeria densa, Elodea nuttalli, Lagarosiphon major, Ludwigia grandiflora and Myriophyllum aquaticum should have their entry and spread prevented by countries and Hydrilla verticillata and Pistia stratiotes are recorded on the EPPO Alert List. It should be noted that among the few aquatic species which are planted outdoors, 9 out of 51 (about 17%) are invasive or potentially invasive. Only one plant, Hydrilla verticillata is used for aquarium purposes and is regarded as a potential threat.
By combining information on the behaviour of a species where it occurs, its distribution, and its records of invasiveness, it is possible to obtain a subjective indication about its future behaviour in the area where it is introduced. Such rapid assessment has to be taken with care and carries a lot of uncertainties, and only suggests species that could deserve further attention. Six (6) additional species have been identified as representing a moderate to high potential risk: Alternanthera sessilis (Amaranthaceae), Adiantum raddianum (Pteridaceae), Gymnocoronis spilanthoides (Asteraceae), Hygrophila polysperma (Acanthaceae), Limnophila sessiliflora (Scrophulariaceae) and Syngonium podophyllum (Araceae). These species could be subject to further investigation, possibly a pest risk analysis, to evaluate the risk they may represent.
Other species should be monitored to verify that they do not threaten managed and unmanaged ecosystems: Chlorophytum comosum (Anthericaceae), Cyperus alternifolius (Cyperaceae), Cyperus papyrus (Cyperaceae), Pontederia cordata (Pontederiaceae), Rotala indica (Lythraceae), Sagittaria lancifolia (Alismataceae, further investigation is needed on this species as it might have been underestimated), Hydrocleys nymphoides (Limnocharitaceae), Hygrophila costata (Acanthaceae), Ottelia alismoides (Hydrocharitaceae), Saururus cernuus (Saururaceae)
Because most of these aquatic species originate from tropical areas, it is considered that the Mediterranean Basin and Macaronesia by having the most similar climatic conditions are the most at risk. The species which have been identified based on subjective criteria of rapidly available information, need to be considered with greater scrutiny and will be considered in the next issues of the EPPO Reporting Service.
Brunel S (2009) Pathway analysis: aquatic plants imported in 10 EPPO countries. EPPO Bulletin/Bulletin OEPP (in press).