Planned and Unplanned Species

In 1935, cane toads were introduced to Queensland, Australia, from Hawaii. It was hoped that they would predate and control beetles that damaged the sugar cane crop. Without natural predators and able to outbreed native frogs and toads, cane toads proved highly invasive and today occupy large parts of eastern Australia. In addition to beetles they consume native insects, arthropods, small mammals and birds, threatening biodiversity. Cane toads also emit venom through their skin which both deters and kills potential predators. Snakes, monitor lizards, even freshwater crocodiles that normally prey on frogs and toads are killed if they ingest can toad venom. Can toads have even colonised cites where they are a threat to pets and children. So far, eradication programmes have proved ineffective. While actions by community groups can reduce toad populations locally, strategies at the national scale focus on containing the spread of the toads rather than eradication.

The American mink has become established in the British countryside during the past 60 years, having escaped from fur farms. The mink is highly adaptable, and it is a strong swimmer and preys upon small mammals, fish and ground nesting birds such as ducks and moorhens. A highly successful predator and with few natural enemies in the UK< the mink outcompetes smaller carnivores such as stoats and weasels, and may be responsible for pushing water voles to the verge of extinction. Trapping programmes have had little impact nationally, but have been more effective locally in protecting endangered species such as water voles. However, there is some evidence that the return of otters to British rivers is helping to reduce mink numbers.

Oxford ragwort is a member of Senecio genus. Senecio is a yellow flowered herbaceous plant, native to the mountainous, rocky or volcanic areas. It was introduced into Britain from Sicily, where it lives as a native on volcanic ash. It was brought in 1700 to the Duchess of Beaufort’s garden at Badminton and was later transferred to the Oxford Botanic Garden. It probably ‘escaped’ into the wild in around 1720 and grew in the stonework of Oxford colleges and many of the stone walls around the city of Oxford. This gave the plant its common name ‘Oxford ragwort’. Since then it has managed to find other homes on man made and natural piles of rocks, war-ruined, rocky homeland. Oxford became connected to the railway system in the mid 1800s and the plant gained a new habitat in the railway lines ballasts (there is a high pH here), gradually spreading via the railway to other parts of the country. The process was accelerated by the movement of the trains, and by the soles of shoes, as they have many seeds, and the limestone ballast that provides a similar growing medium to the lava soils of its native home in Sicily. Oxford ragwort has been the subject of considerable controversy recently, with some people claiming that they are extremely poisonous to horses and others arguing that they are only dangerous when consumed in large quantities, so large horses would be unlikely to eat so much unless they were very poorly cared for and were grazing on land that had been seriously overgrazed and then invaded by the ragwort.

Rhododendron are often found in the grounds of stately homes, such as Chatsworth House, as they used to act as good ground cover for game birds when game shooting. They originate from northwest Spain, and came to Britain in the 1840s. They spread very easily, costing Scotland £9 million each year to keep the rhododendrons under control. They also release poison form their roots to get rid of any other competition using the soil, such as the Southern Oak Down, which can no longer have the chance to germinate the seeds in the thick mat of roots, causing rhododendrons to interrupt succession. Rhododendrons also block the light out for lichens and mosses, causing biodiversity to decrease.

Brambles are perennial plants, and therefore die and grow back regularly, which allows organic matter to be continually added year after year. It has strong roots which can break and cause cracks in walls, allowing oxygen to moisture to increase, and therefore allowing the colonisation of further plants. Even if bramble is chopped down, it is often easily re-started. Brambles have backward sloping spikes so it is able to grow over everything in its path.

Japanese knotweed is an extremely fast growing ‘weed’, growing 5 feet in just 4 weeks, and is said to be the most aggressive exotic species in the UK. They can grow up to 9 feet down, and 20 feet across in every direction, causing them to swamp other types of vegetation in their way. Japanese knotweed is spread by humans, as Japanese knotweed germinates through the rhizomes, which are exposed when humans try to dispose of it. Humans try to dispose of the weed because it can penetrate through concrete very quickly, causing catastrophic damage, and causing many houses to be unable to be mortgaged if there is Japanese knotweed within a certain radius. In order to prevent the exposure of rhizomes, the soil has to be treated, and the ground incinerated to reduce the chance of re-germination, and the waste is then controlled. It can take up to 3 to 5 years get rid of Japanese knotweed completely. This costs £1.5 billion each year in the UK, and in order to get rid of the Japanese knotweed on the wasteland that the London Olympic Park was built on, it cost £9 million. In 2010, the government agreed to using biocontrol (the first time in Europe) to try and naturally get rid of Japanese knotweed. This involves introducing the insects from Japan that keeps the knotweed in check in Japan itself. However, scientists are still unsure on the effects of these insects, such as if they are helping, and if they are causing native species to be reduced, reducing biodiversity.