Himalayan balsam is a very attractive tall annual plant with pink-purple flowers that grows mostly in damp habitats like riverbanks and damp woodlands. Native to the west and central Himalayas, Himalayan balsam was first introduced to the UK in 1839 and it is now widespread in Britain.
Even though it may look quite appealing to the eye it is classified as a non-native invasive species. Himalayan balsam spreads quickly due to its explosive release of seeds and forms dense stands, which can prevent flow of rainfall and lead to flooding. In the autumn and winter, as the plants die back, it can leave river banks bare of vegetation and vulnerable to erosion. The species also out-competes native species by competing for space, light, nutrients and pollinators such as bumblebees.
In order to stop Himalayan balsam disrupting habitats and altering their ecological balance, the Wildlife Trust BCN organises days out during the summer for volunteers to remove the species from waterways. This has been done for the last 8 years along Bourn Brook from the upstream end to the downstream end of the brook to prevent spreading and work towards eradication.