Planting the Seeds of Invasion

The spread of non-native plants can undermine flood protection systems.

A car stops in a country lay-by... a bag of garden waste is fly-tipped in the undergrowth beside a half-hidden stream... and within a few years local watercourses are overrun with an aggressively spreading tropical plant.

"It's the sort of scenario that's already happened in hundreds of places across the UK," says Dr Jonathan Newman, who's investigating the threat posed by invasive aquatic plants as part of the Centre for Ecology & Hydrology's LWEC-accredited Biodiversity Programme. "Most of the problems we're seeing are due to human, not natural, action."

Plants such as parrot's feather and floating fairy fern, originally introduced into this country to adorn garden ponds and aquariums, are increasingly making their presence felt in the wild and affecting native ecosystems. Some can even pose a serious flood risk. In the Gwent levels, when storms ripped up floating pennywort that had become established there, drainage ditches and sluices were blocked and water levels rose by over 1.5m. Moreover, with winters becoming milder due to climate change, tropical plants could find it increasingly easy to gain a foothold in the UK.

"Once they're established, little can be done except digging or dredging them out," Jonathan Newman explains. "The key is to improve people's understanding of the risks of non-native species invasions, as the Environment Agency's 'Check, Clean, Dry' campaign aims to do."

And there's no doubting the need to succeed. Take the challenge facing the Black Sluice Internal Drainage Board, which maintains 500 miles of watercourses in part of Lincolnshire.

"Normally, we would remove weed growth from drainage channels annually, but with weeds such as pennywort it will need to be removed up to five times each year," says Stuart Hemmings. "With limited resources, we need to restrict the spread of these invasive plants in our drainage systems".