Invasive alien species are plants and animals that have been introduced outside of their native range by humans and have a negative effect on the new ecosystem. Many invasive alien species cause harm to native flora and fauna. Others have a direct economic cost. Invasive non-native species pose a significant risk to Yorkshire’s waters. Find out about the major invaders.
Annual flowering plant
Himalayan Balsam quickly establishes dense growths along riversides and ditches.It out-competes native vegetation leaving riparian areas with low habitat diversity. Himalayan Balsam dies back in the winter leaving bare banks which are easily eroded.
Currently, pulling Himalayan Balsam is the only effective way of eliminating it. Efforts need to begin at the top of the catchment because seeds spread downstream. Pulling is very time consuming and needs to be repeated for several years until all plants have gone. Scientists are currently investigating using rust, a natural pathogen of the plant, to control Himalayan Balsam. Find out more here
Japanese knotweed was introduced to Europe from Asia. It colonises quickly and is common on road verges and river banks. It outcompetes native plants and its strong root system can damage concrete foundations, buildings, flood defences and roads.
Japanese Knotweed reproduces only from fragments of stem and root, not from seed. It is therefore essential that fragments of Japanese knotweed are not spread between areas. It is an offence under the Wildlife and Natural Environment Act 2011 to plant or otherwise cause Japanese knotweed to grow in the wild. The most effective control method is herbicide.