Invasive species bans show a step in the right direction

Yesterday marked a historic day for the control of non-native invasive species in the UK. From next spring, five species of non-native aquatic plants will no longer be allowed to be sold within the UK. The ban is the first of its kind and represents the growing recognition of the impact that these species have on native species and ecosystems, as well as the economy.

Non-native invasive species have long presented problems to ecosystems in the UK. In recent years, one of the most prolific and fast-spreading of these has been Japanese knotweed, Fallopia japonica. Introduced from Japan in the mid-nineteenth century, it has become widespread across a range of habitats, from roadsides to riverbanks. Growing more than a metre per month, it outcompetes and excludes native species. The impact on other species, however, is not the only cost the Japanese knotweed has posed to the UK and huge amounts of time and resources are spent controlling and limiting its spread. A report by CABI, commissioned by Defra in 2010 (The Economic Cost of Invasive Non-native Species to the British Economy) highlights just how costly this can be. They estimate that Japanese knotweed costs the economy £166 million per year, and is the second most costly invasive species after rabbits (£263 million per year).

These individual costs for the control of one species are huge, but it is the total cost of invasive species to the economy that is most worrying. Every year, all invasive species cost the UK £1.7 billion. Direct costs, such as management control schemes and the cost increased flooding in areas with species present are relatively easy to quantify, and can be readily included in these analyses. Indirect costs, such as the knock-on effects of an invasive species in an ecosystem are not so simple to calculate, and are often excluded. This means that the true cost of invasive species to the UK could be even higher.

The 2010 report by CABI highlights the cost differences between early and late intervention when tackling invasive species. Water primrose (Ludwigia grandiflora), one of the species to be banned from sale in the UK next year, is a rapidly spreading aquatic weed originally from South America. It forms dense mats on the surface of water, affecting photosynthesis rates and oxygen levels for other freshwater plants. It is currently only present in southern England, but eradication of the species at its current level through chemical methods is estimated to cost £70 000. If the species becomes more established, however, as it currently is across the continent, eradication is likely to cost £242 million.

The benefits of intervening early in the spread of a non-native invasive species are clear. Defra’s recent announcement shows a bold step in the right direction for invasive species policy in the UK. As the environment minister Richard Benyon MP highlights, “Tough laws to curb the sale of these plants could save the country millions of pounds as well as protecting wildlife such as fish and native plants.”

In addition to water primrose, the species to be banned from sale next year are: water fern, parrot’s feather, floating pennywort, Australian swamp stone-crop (New Zealand pygmyweed).