Impacts of riparian alien species on aquatic habitats and species

What impact do riparian invasive non-native plant species (Rhododendron ponticum and its hybrids, Japanese knotweed (Fallopia japonica), Himalayan balsam (Impatiens grandulifera), and giant hogweed (Heracleum mantegazzianum) have on freshwater habitats and species?

This report summarises the documented impacts of riparian alien plant species on aquatic habitats and species. There is growing interest surrounding the idea that invasive non-native riparian plants may exert substantial effects on stream habitats and species by altering both in-stream processes and terrestrial-aquatic linkages. These changes can influence community structure by altering productivity and nutrient cycling which can ultimately compromise ecosystem functioning. Impacts on stream habitats and species may be direct (e.g. providing poor quality litter), or indirect (e.g. through displacement of native vegetation). The magnitude of impact can depend on factors such as invading plant attributes, extent of invasion, characteristics of the system being invaded and climate. This information will help inform policy decisions by the UKTAG Alien Species Group on how riparian alien species are taken account of in Water Framework Directive classification and risk assessment.