Update on the pest risk assessments on invasive alien plants in Great Britain
Within Great Britain, a non-native species risk analysis mechanism was established in 2006. Risk assessments are carried out by independent experts and reviewed by a panel of experts. Following this process, risk assessments are available online for comment before being finalized. Since 2011, new risk assessments for the following plant species have been completed. For each species, the major conclusions of the risk assessment are presented.
Ambrosia artemisiifolia (Asteraceae, EPPO List of Invasive Alien Plants) is so far only recorded as casual in Great Britain and occurring on less than 100 ha. The probability of entry is considered as very likely as a contaminant of bird feed. It seems likely that at least in some of the warmest regions in Great Britain, the species could establish. If the species establishes, it would also be very likely to spread from established populations producing seed. The main impacts are expected on human health and agriculture.
Elodea canadensis (Hydrocharitaceae) is already a widely established aquatic plant and is regarded as naturalized in most parts of Great Britain. The pathway of entry is through trade of the species for horticultural purposes. Given the long establishment history of this plant in Great Britain, it is unlikely to cause much further damage, but it has the potential to invade new habitats, especially man-made water bodies such as drainage channels and gravel pits. In addition, movement into areas currently uncolonised cannot be ruled out.
Elodea nuttallii (Hydrocharitaceae, EPPO List of IAP) is also already a widely established aquatic plant in Great Britain, in particular in England. The pathway of entry is through trade of the species for horticultural purposes. It is considered to be in an expansion phase and has the potential to spread further. The plant should be regarded as having a high risk of being invasive and should be strongly recommended as a priority target for eradication or control in new sites. It also has the potential to move into areas currently uncolonised, particularly in north-eastern England, Scotland (north of the Central Lowlands) and Wales, in either new habitats or in habitats currently occupied by E.;canadensis, which it displaces.
Eucalyptus glaucescens, E. gunnii and E. nitens (Myrtaceae);are widely established as ornamental garden trees and trial plantations. Entry pathway is by intentional importation of seed. Due to increased interest in growing these species for short rotation forestry and cut foliage, imports may increase in the future. There appears to be no evidence of natural regeneration of E. glaucescens, E. gunnii and E. nitens in Great Britain and the potential for spread currently appears to be low. The most important environmental impacts may be on loss of biodiversity, increased fire risk and lowering of water tables, and these impacts would be greatest at sites of high conservation or social value. The overall risk for these species is considered to be low, but given the potential for rapid developments in both the volumes that may be grown, and new varieties which could quickly be developed, the situation should be closely monitored.
Rhododendron ponticum (Ericaceae, EPPO Observation list of Invasive Alien Plants) is already widely established accross the whole of Great Britain and is spreading. The main pathway of introduction for R. ponticum has been ornamental horticulture. This species is causing massive economic losses within its existing geographic range. Losses are due to management and control costs for the species, losses of biodiversity, impacts on landscape aesthetics, loss of grazing land, impacts on forestry, and the species' role as a reservoir for the pathogens Phytophthora ramorum (Peronosporaceae, EPPO A2 List) and P. kernoviae (Peronosporaceae, EPPO A2 List).
Sargassum muticum (Sargassaceae) is an algae which occurs throughout southern England, and has also been found in Wales, and recently on the west coast of Scotland. The species entered as a contaminant of oysters. No negative impacts on biodiversity have been observed, but the species may be able to change community (biotope) structure and dominance (having a visual impact where it forms dense beds). The species is considered as a potential ‘nuisance species’.
Wasabia japonica (Brassicaceae) is currently grown commercially in Great Britain and traded as a commodity from overseas suppliers. The species has highly specific requirements for growth and could only establish in small stream margins in open areas, most likely in the Sussex and London area. Spread by seed and fragmentation are unlikely. Impacts are expected to be low as the species is not tolerant of competition with other species. The overall risk that this species represents is considered to be very low.
Sources
GB Non-native species Secretariat. http://www.nonnativespecies.org/index.cfm?pageid=143
2011/066 Pest risk analysis on invasive alien plants in the United Kingdom.