EPPO Global Database

EPPO Reporting Service no. 03 - 2011 Num. article: 2011/066

Pest risk analysis on invasive alien plants in the United Kingdom


Within the Great Britain non-native species risk analysis mechanism established in 2006, risk assessments are carried out by independent experts and are reviewed by a panel of experts. Following this process, risk assessments are available online for comment before being finalized. Risk assessments for the following plant species have been completed. For each species, the overall assessment and its uncertainty as well as the major conclusions are presented below.

Allium triquetrum (Amaryllidaceae) – Medium overall risk (Low uncertainty)
A. triquetrum is a highly invasive plant in areas where the climate is mild and where favorable habitats occur (i.e. road verges, hedge bases and disturbed waste ground). The species is very likely to spread to new areas in Great Britain. Climate change is likely to markedly increase the suitable areas to be colonized by this species.

Azolla filliculoides (Salviniaceae, EPPO List of IAP) – High overall risk (Medium uncertainty)
The species represents a high risk to static and slow moving water bodies in the southern half of England and in low lying areas of Northern Ireland. The plant is spread by flood waters and by the movement of birds, animals and man. The plant has a high impact on biodiversity reducing populations of submerged macrophytes, fish and invertebrates beneath the mats. Dense infestations, which completely cover the water surface, are a danger to children, pets and livestock who may mistake water for land.

Crassula helmsii (Crassulaceae, EPPO A2 List) - High overall risk (Low uncertainty)
The high volume of plant trade means that the plant is imported widely into the UK. Its ability to grow from fragments of stem has enabled it to spread from ponds and ornamental pools into the wild. In addition, it is very difficult to control. This species has an impact on biodiversity and increases flood risk.

Eichhornia crassipes (Pontederiaceae, EPPO A2 List) - Low overall risk (Low uncertainty)
The establishment of this species in the UK is very unlikely under current climatic conditions unless cold-hardy varieties are developed.

Fallopia japonica (Polygonaceae, EPPO List of IAP) – High overall risk (Medium uncertainty)
The species is well established throughout the UK and is still spreading. It can thrive in a wide variety of habitats and is likely to continue to establish in new sites throughout the UK. It is readily transported as fragments in soil or transported by water through river systems. It can have major impacts on biodiversity, as well as on integrity of river geomorphology in localized areas. Impact can be high in urban areas where it can damage foundations of buildings.

Fallopia sachalinensis (Polygonaceae, EPPO List of IAP) – High overall risk (Medium uncertainty)
The species is already established and widespread in the UK and climate change is likely to increase its growth, as it prefers warmer wetter conditions in summer. As F. japonica, it is usually transported as rhizomes in soil and down flooding rivers. It causes serious impacts on biodiversity with losses of native plants and animals due to the dense thickets formed.

Hydrocotyle ranunculoides (Apiaceae, EPPO A2 List) – High overall risk (Low uncertainty)
H. ranunculoides has been introduced into many countries worldwide for ornamental purposes. It is very widely established in the UK, having spread from its first recorded occurrence in the wild in 1990 to more than 50 km² in 2008. It has a very high capacity for vegetative reproduction through fragmentation and high potential for spread by natural or mechanical means. The most important potential economic, environmental and social impacts in the UK are the interruption of waterway use for commercial activities such as fishing, damage to conservation initiatives and species, recreational purposes, flood hazard due to build up of vegetative mass, and aesthetic problems.

Lagarosiphon major (Hydrocharitaceae, EPPO List of IAP) – High overall risk (Low uncertainty)
The potential for ecological and recreational damage caused by the presence of this species, combined with the paucity of control methods makes this species a threat to native ecosystems and the recreational use of water bodies. The ability to change dramatically the chemical status of water bodies, including nutrient and pH changes, means that water quality is also affected by the presence of the species.

Ludwigia grandiflora (Onagraceae, EPPO List of IAP) – High overall risk (Low uncertainty)
The high volume of plant trade means that L. grandiflora is imported widely into the UK. Its ability to grow from fragments of stem has enabled it to spread from ponds and ornamental pools into the wild. Its can establish large stands in water bodies.

Myriophyllum aquaticum (Haloragaceae, EPPO List of IAP) – High overall risk (Low uncertainty)
The species is already present and established in Great Britain. It is traded extensively in the UK, and fragmentation is important over winter. Shallow ponds and margins of all watercourses are at risk from invasion by this species.

In addition, 2 risk assessments are close to completion: one for Elodea canadensis (Hydrocharitaceae, EPPO List of IAP), and another for Elodea nuttallii (Hydrocharitaceae).
Risk assessments have been initiated for the following species: Ailanthus altissima (Simaroubaceae, EPPO List of IAP), Allium paradoxum (Amaryllidaceae), Ambrosia artemisiifolia (Asteraceae, EPPO List of IAP), Buddleia davidii (Scrophulariaceae, EPPO List of IAP), Cabomba caroliniana (Cabombaceae, EPPO List of IAP), Carpobrotus edulis (Aizoaceae, EPPO List of IAP), Egeria densa (Hydrocharitaceae, EPPO List of IAP), Gaultheria shallon (Ericaceae), Heracleum mantegazzianum (Apiaceae, EPPO List of IAP), Impatiens glandulifera (Balsaminaceae, EPPO List of IAP) and Lysichiton americanus (Araceae, EPPO List of IAP).

Sources

GB Non-native species Secretariat.
https://secure.fera.defra.gov.uk/nonnativespecies/index.cfm?sectionid=51