Knotted up
Britain's ecosystems are under threat from leafy invaders. We find out how community volunteers are helping to revive dying river environments.
Words by Sam Bradley.
Illustration by Bethany Thompson.
Every Tuesday, Sandra Boyle heads out to the banks of the Water of Leith and begins pulling up plants. Accompanied each week by as many as 25 volunteers, she works in a race against time to disrupt and eradicate a spreading menace before it can appear once more and undo the work of her and her team. The Water of Leith winds through Edinburgh to the capital's old port, where it meets the Forth in a puzzle of quays. But the ecosystem surrounding the river, like watercourses across the rest of the UK and Europe, is under threat from invasive species that out-compete natives and destabalise the environment.
Boyle, Trust Administrator at the Water of Leith Conservation Trust, plans her sweeps of the riverbank with operational precision. "I've got all these maps all over my wall – it looks like a military operation. I come back and I put a circle on the patch we've done and I date it. And that way we know we've got to go back in a couple of months at least and re-do that bit," she explains. Despite the seriousness of the approach, Boyle enjoys the work. "I love it. I absolutely love it," she says.
Boyle's campaign has three principal targets in mind. Himalayan balsam, which originates from the foothills of Uttarakhand, is the first. Called "a contentious plant" by the writer Richard Mabey – its prettiness is overshadowed by its ability to out-compete native plantlife – it increases soil erosion in the riverbank ecosystems it occupies. Second, there's the grandly named Heracleum mantegazzianum (Giant hogweed to you and me). Hogweed has been successful in migrating from its original home in the Caucasus across to North America, by way of ornamental gardens in Europe, where it's displaced native species and reduced the habitats available for wildlife. In particular, the sap of hogweed is phototoxic - it stops skin from protecting itself against ultraviolet light, leading to harsh inflammation. Finally, there's Japanese knotweed (Reynoutria japonica), considered an official public menace. It weakens foundations, road surfaces and flood defences. If there's evidence of knotweed within just seven metres of a property, most lenders won't give you a mortgage to buy the place. The stuff is literally treated as toxic by the UK government - it's considered 'controlled waste' and it's an offence to plant it or help it grow in the wild.
The trio – knotweed especially – have earned themselves a bit of a bad rep. After all, other invasive species from China and east Asia have been welcomed and accepted as part of the furniture, if not the landscape. There's barely an ornamental garden worth its salt without a rhododendron, while gardeners up and down the country cultivate bamboo shoots in order to block out their awful neighbours. Neither species get such harsh treatment from the country's financiers and waste disposal experts, nor alarmed reporting of their threats to native species (rhododendron nectar, for instance, is toxic to honeybees). 169 years after the first knotweed cuttings arrived in the UK, perennial moral panics about the plant still proliferate. The Daily Mail, which values the stability of house prices above Queen, country, God and law has reported on japonica's threat to homeowners six times this year already. The only effective way to kill knotweed is with a glyphosate, a herbicide. It's nasty stuff, and dangerous to use near a river given the risk of affecting environments downstream. "We inject it into the stem," Boyle explains. Using a tool that looks "vaguely like a water pistol but with a needle on the end," she and her volunteers fire glyphosate into the veins of the weed, hoping to kill it. "You've got your paper suit on, your waders – with all the gear you kind of look like a nuclear scientist."
Unusually for an invasive species, knotweed's spread can be traced back to one man: Philipp Franz von Siebold, a doctor, traveler and a botanist. Working for the Dutch East India Company, he travelled widely in Japan in the 1820s, when the country was still formally closed to foreigners. He's credited with introducing vaccination and setting up a medical school; his daughter Kusomoto Ine was the first female Japanese doctor. He also spent his years in Japan amassing a vast botanical collection and naming the plants he 'discovered' after himself. When he returned to Europe after being accused of spying by the shogun's government, he cashed in on the speaking circuit and spent his time establishing botanical institutes in the Netherlands. One sample from his collection, a single specimen of knotweed that Siebold retrieved from a volcano, was given to the Royal Botanic Gardens in Kew, in 1850. Every specimen of knotweed in the UK is a clone of that single sample.
“You've got your paper suit and waders on, your waders... with all the gear you kind of look like a nuclear scientist.”
Siebold's gift to Kew came at a crucial moment. Gardening for pleasure had become popular among the middle classes, along with a vogue for all things Japanese. And since knotweed stalks look a bit like bamboo, budding gardeners went nuts for the stuff. It was planted in private gardens and along riverbanks, part of efforts to prevent soil erosion. And within 10 years of its arrival in then UK, it was everywhere.
Back in Japan it grows widely in the wild, spreading across the archipelago's rocky hills and covering slopes in a carpet of green and white. It's foraged as a wild vegetable and the young shoots are used in pork, fish and sweet dishes (supposedly it tastes like rhubarb) – it's also an important source of nectar for honeybees and is an ingredient in traditional medicines.
In the UK, it is far less benign. Its roots burrow deep and wide into the weak spots in brickwork and concrete, growing between the cracks in walls and then expanding over time.
Boyle's task is complicated by the resilience of her foe. Balsam and hogweed can be pulled out of the ground and buried, but knotweed is especially tough due to its deep roots and prolific reproduction; even uprooted it can live on and reseed itself. While Boyle says "we're winning" the fight against invasive plants on the banks of the Water, she wants to cut down on its use of chemicals and so the Trust has been running a study with Napier University, mapping and surveying the environment along the river and testing out different strategies for controlling the invaders. "At the moment it's looking successful. We're hoping that it'll be published and it's something that will have broad impact for other people," she says.
Wider afield, others are using similar tactics to combat invasive plants. The Scottish Invasive Species Initiative, a project run between Scottish Natural Heritage, the University of Aberdeen and local environmental groups, is working to set up community teams across 29,500km of northern Scotland to monitor and manage their local ecosystems. Vicky Hilton, a spokesperson for the initiative, tells us it aims "to create a sustainable long-term solution to controlling invasive species" by supporting activities like conservation days, surveying and plant spraying.
The legacies of Victorian gardeners and amateur colonialists like von Siebold have been miserable for riverbank ecosystems across the world. But the work of Boyle and the Invasive Species Initiative is helping to undo their mistakes. As Hilton notes, "many hands make light work."
