Great British Elm Experiment: nurseries and tree managers work to re-establish trees resistant to Dutch elm disease

Gavin McEwan asks how tree managers are re-establishing elms in Britain after the ravages of Dutch elm disease.

Elms often seen in hedgegrows because roots of diseased trees don't die. Image: HW
Elms often seen in hedgegrows because roots of diseased trees don't die. Image: HW

The elm, a native British tree rich in heritage and folklore, and with its own associated invertebrates, was ravaged by Dutch elm disease in the 1960s and 1970s, with losses put at 25 million trees.

But ever since the disease emerged as a major problem in Europe and North America, there have been efforts to isolate resistant strains and to breed and promote hybrid varieties that can withstand attack.

The Elms Across Europe campaign, which began 30 years ago, funded planting of hybrid elms across the continent. But now a British charity, the Conservation Foundation, is attempting to find resistant native trees through its Great British Elm Experiment.

Last month the first elms, micro-propagated from surviving native English trees, were delivered to 250 schools and to other organisations that will monitor their growth over the years to come. The charity hopes to double the number of participants in the project by autumn this year.

The charity's director and co-founder David Shreeve admits: "It's an experiment and it may show it doesn't work. There will be no instant results - it has to be a long-term study. Pupils will go through school, but new ones will continue to look after the trees. After 10 years it will get exciting, though some won't survive."

Plans to control the disease have traditionally been hampered by the fact that the beetle responsible for spreading the pathogen only bores into mature wood, meaning that even susceptible trees may appear healthy for decades.

Part of the aim of the study is to look at populations in different conditions around the UK. Shreeve adds: "People were telling us: 'We still have one,' so we started recording them. We want to know why they have survived - are they freaks? A subspecies? They are probably all a bit odd."

At the instigation of Colchester MP Bob Russell, 40 MPs signed an early day motion in the House of Commons last month supporting the project - although this intervention came as a surprise to the Conservation Foundation, Shreeve adds.

Native elms have never entirely disappeared from commercial production. However, one commercial nursery admits: "The tree is said to usually succumb to the disease again after about 25 years, but if we all keep growing it from new suckers, then we will keep the species going."

According to native tree specialist nursery Alba Trees sales director James Hepburne Scott: "There is a fair amount of hope involved in planting them. We have been growing them since we started in 1988, so some of those will be getting to the vulnerable stage - though no-one's been in touch.

"It's a minor tree for us, though it always sells out. People creating native woods will often include a small percentage of elms, though it wasn't ever grown as a plantation tree like oak."

Alba mostly sells the wych elm (Ulmus glabra), rather than the more disease-susceptible English elm (U. procera). "There are quite a lot of healthy wych elms in Scotland," Hepburne Scott notes. "My own theory is that there is a small residual disease-resistant population in Scotland and the north of England."

Such planting initiatives receive the cautious approval of Forest Research. A representative says: "We welcome efforts to restore elm trees to their rightful place in Britain's rich collection of native trees, although we would caution that proponents of projects such as this need to take care that their efforts don't actually help spread the disease."

But many tree managers have been understandably reluctant to chance potentially vulnerable trees in high-profile sites such as trees and parks. Fortunately, hybrid elms offering resistance to Dutch elm disease have been and continue to be developed.

Among these is U. 'New Horizon', which was awarded Best New Plant Variety in the Horticulture Week Awards on its UK introduction five years ago.

The Royal Borough of Kensington and Chelsea in west London planted 11 of the trees in the middle of Kensington High Street last year. The borough's arboricultural officer James Burton says: "We considered three alternatives, but we already had a large number of them.

"The fact that elm is a traditional tree in this country was also a factor, as was the success of the three that we had already planted elsewhere in the borough. They were a bit more expensive than, say, a London plane, but that comes down to the production quantities."

So far, all but one have put on good growth in their first year, he says. "It's the worst place you could plant a tree, in terms of soil, nutrients, air quality and so on. Fortunately, there were specially designed pits of around 2cu m from the previous trees. I could see us planting more in the borough - they have a nice habit and are quick to establish in what is a difficult area."

Elsewhere, the north London borough of Enfield is embarking on a programme of planting 100 hybrid elms, principally for their conservation credentials, to encourage the white-letter hairstreak butterfly (Satyrium w-album). A further 100 'New Horizon' will form part of the mix of trees at the Olympic Park currently under construction in the east of the city.

Hampshire-based Hillier Nurseries has sole distribution rights for the trees in the UK. Amenity director Hossein Arshadi says: "It would be great to get a resistant English elm for the Olympic site, but you have to go for the next best thing, and they have a proven track record.

"You have to be ever so careful - you can't just take a cutting from a tree that happens to have survived and go out and plant it. That may work, but the chances are it won't - you can't go selling it as 'resistant'. There is no quick fix - it needs many years of proper scientific research to ascertain whether that individual truly is resistant.

"We don't want to lose credibility as an industry. Fortunately, thousands of (hybrid trees) have been planted since the 1980s without problems."

'New Horizon' is just one of a family of US-bred varieties, with several "brothers and sisters", Arshadi explains. Propagated in Germany, a microchip containing a unique number that can be read by a scanner has been embedded inside each tree.

One German nursery was hit with a EUR250,000 (£220, 000) fine or a six-month prison sentence for passing off fake Resista elms, he adds.

"Without protection, the whole thing becomes a mixed bag - you could have any elm, since no one knows which is which. Yet we have to have the trust of customers like local authorities or they will stop planting Ulmus altogether," he warns.

Some groups, such as Buglife, the invertebrate conservation trust, would rather see authorities take their chances with native trees, however.

"We would prefer to see native stock," confirms biodiversity officer Duncan Sivell. "We wouldn't say 'no' to imported hybrid elms - it's just not yet clear what their effect on biodiversity might be."

BRIGHTON

For more than 40 years, Brighton has been a test bed for the maintenance of elms, which account for three-quarters of the East Sussex town's amenity trees and include what are thought to be the oldest English elms in Europe.

Brighton and Hove Council is also the national collection holder for Ulmus, with more than 100 species and varieties.

Arboricultural manager Rob Greenland says results with hybrids have been mixed. "We have tried lots of different elms - from Holland and Japan as well as the USA, though among the Dutch ones we only continue to plant Ulmus 'Lobel'. Some of the hybrids are semi-fastigiate so suitable for planting in streets. But they don't all accept pruning as well as English elms do and look less natural afterwards."

With a tight control regime in place, the town has also continued to plant native elm species despite the risks.

"We still put a large effort into our control programme," says Greenland. "We are planting English elm (U. procera) and smooth-leaved elm (U. minor) in prime locations such as parks. Even though we have the national collection, we don't actually have very many English elms, but we are looking to build up numbers."


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