Invasive non-native species are one of the top 5 drivers of global biodiversity loss and are estimated to cost the UK economy up to £2 billion annually. Over 2000 species have been introduced to the UK; these are known as non-native species. Not of these are harmful, however, around 10-15% have become invasive non-native species, meaning that they can have negative impacts on native species, human health, and the economy. Management of invasive species can be costly and time-consuming, but early detection and regular monitoring of sites can help improve chances of eradication.
Norfolk is home to internationally important wetland habitats, including chalk streams, pingo ponds, valley fens, and floodplain grazing marshes; all of which are vulnerable to invasive non-native species. At Norfolk FWAG, we regularly provide advice on wetland management and oversee wetland restoration projects. As part of our regular staff training, we spent a day focusing on the identification and management of some of the most problematic aquatic invasive plant species in the region.
We started the day in Norwich on a backwater of the River Wensum. Here we found floating water fern Azolla filiculoides and the least duckweed Lemna minuta, both are non-native, however, the latter is not considered invasive. Floating water fern is native to North and Central America and was first recorded in Britain in the late 19th century. This species spreads rapidly across the surface of water bodies, depriving submerged plants of light and reducing oxygen levels in the water.
Before moving onto the next site we also looked at some common native aquatic plants such as arrowhead Sagittaria sagittifolia, yellow water lily Nymphaea lutea, gypsywort Lycopus europaeus, Water forget-me-not Myosotis scorpioides and water mint Mentha aquatica.
Next, we headed into the Yare valley and visited a small farm pond that has been colonised by the invasive non-native Parrot’s feather Myriophyllum aquaticum. It was originally brought to the UK from Central and South America during the late 19th century to grow in water gardens; the first wild record was in 1960. Since then, it has spread throughout much of lowland Britain. It grows rapidly and forms dense mats on the water’s surface, shading out native plants and altering the physical and chemical characteristics of the water body. In the UK, it only reproduces vegetatively, and even the smallest fragment can regrow and spread. As a result, it can be very difficult to eradicate.
The last stop was a nearby stream, where we encountered large stands of Himalayan Balsam Impatiens glandulifera. This species is one of the most common and widespread invasive non-native plants found along waterbodies and damp habitats in the UK. It was originally imported from the Himalayas as a garden plant, owing to its attractive pink flowers. It is very fast growing and can rapidly outcompete native marginal vegetation. It forms dense stands that may reach over 2m in height. Each plant can produce over 500 seeds, which are dispersed up to 7m from the parent plant by its ‘explosive’ seed pods. This species has been successfully eradicated from some sites by regular hand pulling before the plants set seed. The seeds can persist for 2-3 years in the soil, meaning that several years of management are required to fully eradicate it.
Before moving between sites, we undertook a thorough check and clean of our footwear and clothing to ensure that we were not inadvertently spreading these species. It is an offence under Schedule 9 of the Wildlife and Countryside Act 1981 lists to plant or otherwise allow these species to grow in the wild in England, Wales, and Scotland.
