Non-native species are those that have established themselves outside their natural range either past or present, with the assistance of man either intentional or unintentional.
Non-native species have been introduced to England over thousands of years. Sometimes this has been deliberate, for social or economic reasons such as forestry, agriculture and horticulture. Sometimes, however, the introduction occurs by accident; for example Dutch elm disease, which was introduced in imported timber.
The introduction of non-native species is rising sharply due to the increase in trade, transport, travel and tourism. World globalisation has offered species new pathways and increased opportunities to establish in new areas. An audit of non-native species in England in 2005, found 2721 species in the wild. Whilst most of these species are harmless or may be of benefit, small proportions of them are invasive and can have significant environmental, economic and public health implications.
Invasive non-native species have an impact on biodiversity by displacing or preying upon native species, by destroying habitats, or by introducing new diseases or parasites. The most direct implications are the threats of predation on, and competition with, native species. For example, water voles have declined as a direct result of predation from non-native mink.
Invasive non-native species can also affect ecosystems more widely. River catchments are particularly vulnerable to invasive aquatic species: these include signal crayfish and Australian swamp stonecrop. Along riverbanks, dense monocultures of plants such as Himalayan balsam and Japanese knotweed can crowd out native species. When these invasive species die down in winter, they leave the river banks bare, exposing them to increased soil erosion.
In the marine environment, the Chinese mitten crab is a voracious predator threatening many native species. It also burrows in soft sediment estuarine banks and, in high densities, can reduce their effectiveness as flood defences.
Invasive non-native species (INNS) are recognised as one of the main causes of global biodiversity loss and current evidence demonstrates that this is a problem which is increasing. Consequently there are a large number of agreements, conventions, legislation and strategies pertaining to INNS. In particular, the Convention on Biological Diversity requires Parties, ‘as far as possible and as appropriate, to prevent the introduction of, control, or eradicate those alien species which threaten ecosystems, habitats or species’.
The Invasive Non-Native Species Framework Strategy for Great Britain was launched in May 2008, and this sets out actions required addressing problems caused by these species. The GB Non-native Species Programme Board and Secretariat is looking to Natural England to show leadership in the delivery of the Strategy.
Natural England is actively supporting a co-ordinated effort to tackle the impacts of invasive non-native species in Great Britain. For more information regarding this work please visit the Non-Native Species Secretariat (NNSS) website.
Although there are concerns about many invasive non-native species, four are considered to be a particular risk: Asian hornet, killer shrimp, water primrose and carpet sea-squirt. For more on these species go to the NNSS species alerts page.
You can find out more about recording sightings of these species, and others, on the NNSS recording pages.