Getting control of invasive plants in the UK
Invasive alien plant species are causing increasing problems in the UK from economic, social and ecological perspectives. It is estimated that the total annual cost of all non-native invasive species to Great Britain’s economy is approximately £1.7 billion, and there are 1350 terrestrial and 23 freshwater alien plant species now established in Great Britain.
Owing to the mounting concerns over the number and extent of alien plant species in the UK, the Parliamentary Office of Science and Technology has recently released a POSTnote describing the problems such species present and the current measures in place that try and limit their impacts.
Invasive species are ranked as the second most important driver of global biodiversity loss, mainly due to their greater abundances, densities and heightened competitive dominance against other species. Alien plant species have increased in number in Great Britain, particularly since 1850 which saw an increase in international travel and trade. However, whilst a variety of alien species exist, many are not considered to be invasive due to the fact that 80 -90% of alien plant species occupy less than 10% of suitable habitat. Therefore, 108 plant species are deemed as true invasive alien plant species (IAPs).
The environmental impacts of IAPs can be wide ranging, from simply putting native plants at risk by occupying large sections of available habitat, such as in the case of the Floating pennywort, to breeding with related native or alien species and reducing native genetic diversity. Some, such as Rhododendron and Himalayan balsam, can have large ‘ecological effects’, whereby they cause significant impacts on an ecological process. However, the lack of a robust framework which is able to quantify the effects of such invasives on habitats and ecosystem services has meant that at present there are significant knowledge gaps as to the ecological effects most invasive plant species have. It also means that prediction of where and when impacts would occur is limited, as well as uncertainty over how to mitigate such effects.
Limiting the impacts of IAPs can be dealt with in a number of ways, although uncertainty surrounds the best approach to use. The most cost-effective method is to prevent their introduction in the first place; stricter controls over the entry of plants and tighter risk assessments on imported plants are relatively simple methods that can be very effective at reducing the spread and establishment of such species. Focusing these efforts at the horticultural sector is particularly necessary given its large role in the import and subsequent role in distributing potential high- risk plants around the country. Such attempts have already been made to infringe tighter controls on this sector, as earlier this year Defra announced a ban to sell particular non-native invasive aquatic plants. The European Commission is currently developing legislation on invasive species, whilst Defra is also considering whether there should be changes made to Great Britain’s current legislations surrounding invasive plant species.
However, prevention is not always applicable as in many cases the plants are already widespread and causing numerous impacts in various locations. In such cases it may be necessary to monitor and detect occurrences in new areas and consequently act. Such early detection and eradication methods, such as the surveillance of entry pathways (e.g. airports, ports) can be used to swiftly inform eradication strategies. But, as yet no formal surveillance system exists in Great Britain. Risk assessments also have a large role to play in understanding the potential threats particular plants have. Such approaches, such as the EU Delivering Alien Invasive Species Inventories for Europe (DAISIE) and Great Britain’s Non-native Species Secretariat serve as useful platforms in identifying priority species and quantifying the magnitude of threats. However, there are criticisms with risk assessments as many feel it is too time and resource intensive.
At present, huge amounts of resources go into the immediate and longer term control of invasive species. These management activities, such as the use of herbicides, mechanical control and in some cases biological control are undertaken by conservation groups or other interested bodies such as landowners or housing developers. Yet, many consider such actions to be a drain of resources, particularly in regards to time and money, and instead efforts should focus more upon prevention and early detection. Additionally, a lack of ecological and botanical knowledge surrounding how to best control IAPs can render such actions inefficient and powerless against the dominance of these species. However, for those species which are now listed as invasive and are well established throughout the country, long term control is the only management option.
IAPs cause innumerable problems throughout Great Britain, and into the future challenges such as climate change and more plant imports increase the risk of even more alien plants establishing and becoming invasive. Whilst there are current efforts in place to mediate the impacts such IAPs can pose, it will become increasingly necessary for both our government and the wider EU to impose stricter and more effective legislations if the problems of IAPs are to be at all reduced.
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