Invasive Plants – Prevention Is As Challenging As Cure
In my first foray into the UK, a two-week nature conservation course in the Scottish Highlands, I was met with a rather surprising activity: bracken-bashing. This aptly-named formal conservation method involved taking a large stick or rod and literally beating the plants, chopping them down as near to the ground as possible. In contrast with other more peaceful activities, such as re-planting seedlings, this violent act seemed to go against the principle of loving and caring for nature. In fact, though, conservation is often about removing or controlling the spread of what doesn’t belong as much as it is about preserving native species.
Plant Transportation
Species have native habitats and ranges in which they survive and flourish, but with the exponential increase in travel and trade, human activity has provided a vector for transporting them beyond their natural confines. This may take the form of a plant seed carried by a rat on board a transatlantic liner which would normally not find its way across the ocean. Equally, however, the introduction can be intentional, as often occurred with explorers bringing back exotic plants to Europe from their travels to the Far East or South America in the 18th and 19th centuries. In cases where such ‘new’ species become established in their new location, especially those whose introduction cannot be precisely traced, it is difficult to draw the line to distinguish the original native species from those initially considered outsiders to the region. In Europe, almost two thirds of currently established plant species were initially introduced for agricultural or ornamental purposes.
Pest problems in the UK
Bracken (Pteridium aquilinum)
Invasive plant species can be economically as well as environmentally detrimental. In the case of bracken, it outcompetes heather and other native plants, altering ecosystems and reducing biodiversity by taking over entire areas. It is also toxic to several grazing animals, including sheep and cattle, and provides a habitat for sheep ticks which carry Lyme Disease. It can even cause damage to built structures and ancient monuments with the spread of its subsurface root networks. The extent of detriment caused by the uncontrolled spread of bracken has driven the establishment of specialised organisations, such as the Bracken Control Group, as well as government initiatives, such as the Bracken Management Programme for Habitat Enhancement in Scotland.
Tree of Heaven (Ailanthus altissima)
Another invasive plant causing problems in the UK is the tree of heaven. Originally brought over from its native habitat in China in the mid-1700s, it is now commonplace to find it in parks and lining streets. Similarly to bracken, it outcompetes other plants, and can also cause architectural damage. It produces toxins which prevent other species from growing in its immediate area, with a one-up on bracken by having a nasty smell as an additional charm. It also claims the title of the fastest-spreading invasive plant in the country. Other plants can be more directly harmful to humans, such as giant hogweed, whose sap causes skin lesions upon contact.
Costs and Policy Challenges
Although it is obvious that invasive plant species cause inconvenience and ecological damage, putting figures to such a problem indicates its severity. Costs of impacts and associated management can be immense, with figures reaching £1.8bn in the UK. It is estimated that these come to a total of over €3.7bn each year in Europe. Formulating policy to manage invasive plants is particularly challenging as international and cross-border co-ordination is often required to control each step along the invasion pathway, comprising the introduction, survival, establishment and eventual invasion by the new species. Moreover, the time lag between the introduction of an alien plant species and its emergence as a pest makes it difficult to nip the process in the bud. The Forest Stewardship Council and Convention on Biological Diversity both recognise the importance of tackling this issue and present efforts to do so.
The Tens Rule
Fortunately, not all plant species introduced to a new habitat manage to survive, let alone become established and invasive. It is generally accepted that of all species introduced to the UK, 10% become established, and 10% of these become invasive. In other words, for every 100 plants introduced, only one becomes a pest. This is known as the tens rule, originating from a paper written for the Ecology journal in 1996. For animals, probabilities of becoming pests are usually higher.
When we decide to go out into the wilderness to soak up some good, pure, untouched nature, it is worth considering that actually not all species present may be natives. Neither are the trees of heaven (or hell) lining the streets. Indeed, ecology and the environment have always been subject to change, adapting and evolving accordingly. If you do, however, find yourself sweating and swearing with blistered hands from bashing bracken at any point if your life, feel free to vent about the need for better pest control. If you are even more unlucky to be covered in welts from giant hogweed, do not hesitate to blame the intrepid explorers who thought it a good idea to bring it back home.
About the Author Alexia Karageorgis
Alexia Karageorgis has an interest in exploring human relations to environmental issues. She graduated from the University of Oxford with a Geography BA, and after several nature conservation volunteering escapades, she decided to revert back to the student life. She is currently following the Science Communication and Public Engagement MSc at the University of Edinburgh while nurturing her new interest in British Sign Language.