UK elms – ‘not out of the woods yet’


Colin Tudge, the author of The Secret Life of Trees, is invited by the UK’s Telegraph newspaper to give his reaction to efforts to breed a Dutch elm disease-resistant species.

Library image from Take CoverIt’s an interesting read as he gives his reaction to this battle with nature, so here it is:

Could the English elm, so sadly laid low by Dutch elm disease, make a comeback? Paul King, who breeds trees at Raine in Essex, is on the case. Nearly 25 years ago he acquired cuttings from a few mature trees. He has now multiplied the tissues to produce a whole new generation of young elms that seem to be resistant (and are on sale for £120 apiece). Scientists at the Forestry Commission’s research centre in Surrey welcome his initiative – they are on the case, too – but are cautious. Resistance, they point out, is a tricky business.

The English elm, Ulmus procera, is probably not a “true” native – Britain has only 39 “truly” native trees – and was most likely introduced by Neolithic farmers from south-east Europe, via Spain. But it is an honorary citizen, treasured for its usefulness and its looks, favourite of landscape painters, notably of Constable; a tree of open woodland but just as happy in hedgerows where, if it was left alone, it flourished by the tens of millions. In the West Country it was known as “the Wiltshire weed”.

The first sign of trouble came in 1910 when the fungus Ophiostoma ulmi, a distant and degenerate cousin of the truffle, started killing trees in mainland Europe. It acquired its name, Dutch elm disease, in 1921 because it was first properly researched in Holland. It arrived in Britain by 1927 and looked very nasty. Happily, the disease died down by the Forties, after killing 10 to 40 per cent of our elms. Dr Tom Pearce of the Forestry Commission predicted, in 1960, that such a thing should not happen again – unless, he added, “the fungus completely changes its present trend of behaviour”.

Which it duly did. A new, closely related species of Ophiostoma appeared in North America – Ophiostoma novo-ulmi. It arrived in Britain in 1967 on imported logs, and throughout the Seventies and into the Eighties it killed about 25 million out of about 30 million elms, including most of the particular English species, Ulmus procera.

Dutch elm disease has all the biological attributes needed to be thoroughly nasty. It is one of the many “wilt diseases” of trees, which spread through the vessels of the xylem and block them. The spores are carried passively with wonderful efficiency in the sap, through the whole tree, and spread via the roots of separate trees that are often joined underground. The spores don’t live long once the tree has died and so should die out as their host succumbs – but they have a trump card: they are carried from tree to tree and from forest to forest by flying bark beetles of the genus Scolytus.

There is some innate resistance among the world’s many species of elm. The Ophiostoma fungus probably arose in Asia, so the Asian elms have evolved in its presence – and have developed considerable resistance. Breeding programmes are afoot in Europe to introduce genes from Asian species into European types by various means – and may yet succeed. Meanwhile, as Paul King has found, even within susceptible species, such as Ulmus procera, there will usually be some resistant strains. If they can be bred, perhaps we will have a new resistant strain.

So why the caution? Well, for one thing, it depends what the tree is really resistant to: the fungus or its insect vector? Paul King’s new trees are probably not resistant to the fungus itself, but are simply less palatable to the beetle. Of course, the fungus can’t usually infest the tree without the beetles – but it surely would be better to be specifically equipped with genes that would protect it even if beetles did get in.

The sad tale of Britain’s elms parallels that of the American chestnut, Castanea dentata – with some intriguing contrasts. For the American Indians and for the first immigrant Europeans, the American chestnut was a wonder tree. Its nuts were a food staple – and supported 40 million wild turkeys for good measure – and its trunks provided timber. There were so many that a squirrel could travel from chestnut to chestnut from Maine to Georgia without setting foot on the ground, or so the story went.

But the overconfident forestry “improvers” of the 19th century were still not content. They began to import Asian species with bigger nuts, to crossbreed. Inevitably, the newcomers came with their own diseases. And the American chestnuts, beset by novel pathogens, succumbed. By the end of the Twenties, the American chestnut, once perhaps the commonest North American broadleaf, was all but gone.

Again, through too much zeal, the Americans felled great swathes of chestnuts to create a firewall against the spread of infection. This failed to contain the disease – but it did, so some biologists suggest, remove the myriad genetic variations from among the wild trees, which might have included some that would have conferred resistance.

By leaving our own beleaguered elms to live on in the hedges, and nurturing the few survivors, as Paul King and others have been doing, we may avoid that final fate. (In truth, the American chestnut might not quite be dead. At least, George W Bush planted one outside the White House on Arbor Day in 2005 – but it is a hybrid: 15 per cent of its genes are from resistant Asian species. It is a sad relic, like an exhumed dodo).

Overall, the message is mixed. We could see the heroic efforts of a few growers and scientists as a triumph of human ingenuity over natural adversity – the continuing tale of “man’s conquest of nature”. Or we could see this endeavour as a desperate, last-ditch attempt to ward off the consequences of our own folly. For these are tales of hubris. We thought we could do what we liked in the name of commerce. But actually, life is more complicated than we ever supposed – and in the end, it is beyond our ken. Cause and effect relationships in nature are non-linear, which means it is intrinsically impossible to predict the outcome, beyond saying it won’t be good.

Source: Telegraph newspaper

Date: 09/06/2010

Forest Research draws up canker plan


Forest Research is to develop guidance on managing and drawing up controlling strategies for the bleeding canker tree blight, reports Horticulture Week.

“This disease has rapidly become widespread throughout Britain over the past five years,” said a representative for the research arm of the Forestry Commission.

Bleeding canker of horse chestnut was caused by the bacterium Pseudomonas syringae pv aesculi (Psa), but until recently it had only been reported in India in 1980, he said.

“It has now proved to be highly mobile and exceptionally virulent to European horse chestnut, Aesculus hippocastanum.”

Researchers were looking to provide an accurate diagnosis of the pathogen and underpin management strategies to combat the disease.

“A technique called real-time polymerase chain reaction has been developed and is being used to detect the levels of Psa on infected trees and their surroundings.”

Previously little was known about what natural resistance horse chestnut populations may have had to Psa.

“But evidence indicates that even in heavily affected locations some trees remain healthy and symptom-free.

“Disease-free horse chestnuts have been propagated and will be tested for disease resistance in inoculation trials and compared against other disease-prone individuals.

“This research will ultimately guide management and mitigation strategies. Molecular techniques developed will also be applicable to the study of other important tree diseases.”

Source: Horticulture Week

Date: 07/05/2009

Old elm ‘may help save other trees’


Experts hope an elm tree that survived the ravages of Dutch elm disease could hold the key to the species survival in the UK, the BBC News website reports.

The elm was discovered in a Worcestershire hedgerow, near Pershore, two years ago.

It had remained unnoticed because it was assumed all elms in the area had been wiped out by the disease.

The condition, which is carried by a bark beetle, has affected more than 20 million elm trees in the UK since 1970.

Now, Pershore College has taken cuttings from the newly discovered tree and has just planted the first of them.

Bob Hares, from the college, which specialises in horticulture, said that growing cuttings from old trees was difficult.

“The idea is usually to take cuttings from the young trees, which root much more readily, and build up from there,” he said.

The team will not know if these cuttings have the resistance of what they call the “mother tree” until they are about 10 to 15 years old, but they are hopeful.

Now the search is on for other elms that have survived and may also be resistant to Dutch elm disease.

The biggest problem for the college’s team is that most of us do not know what an elm looks like.

John Clarke works for Kemerton Conservation Trust, which works to preserve the natural landscape of Herefordshire, Worcestershire and Gloucestershire.

He said it would be mostly people older than 40 who would be able to recognise elms, “especially people who know trees like farmers and naturalists”.

Elms were once known as the “weed of Worcestershire”. The hope is there are more survivor trees out there to rebuild this much missed part of our landscape.

Anyone who sees a mature elmin the area is urged to contact the conservation trust.

Source: BBC News website

Date: 06/03/2009

Bleeding cankers continues to take its toll


The avenue of 43 horse chestnut trees at Barrington Court, near Ilminster, in Somerset is being cut down and replaced with a variety of oak, the Telegraph reports.

The National Trust decided the trees had do go for safety reasons, following an infection of bleeding canker that causes the trees to lose bark and branches and eventually die.

The Trust has already had to cull a number of other horse chestnuts at properties around the country, with 28 trees recently chopped down in Avebury, Wiltshire.

Home-owners around the country have also had to cut down horse chestnuts because of the disease, which the Forestry Commission say has killed 3,000 tree in recent years.

The disease is spread by spores in the ground and can cause the tree to bleed a reddish brown liquid. It can be controlled by cutting out infected areas but will eventually kill the tree.

Christine Brain, head gardener at Barrington Court, said: “Bleeding canker is rife in England’s horse chestnuts.

“It kills the tree from the inside out, and while doing so makes it susceptible to other infections which hasten the trees death.

“We’ve been maintaining the trees over the last few years in an effort to extend their life and keep the disease as controlled as possible, but removal is now our only sensible option.”

Horticulturalists have warned that conker trees are in danger of dying out in Britain unless more is done to control the disease.

The call comes as the UK government announced a £25m package to curb the spread of sudden oak death through woodlands in England, Wales and Scotland.

Source: Telegraph newspaper

Date: 03/03/2009


Firm to trial bleeding canker ‘cure’


Arboriculture specialists may have found a cure for bleeding canker in horse chestnut trees, Horticulture Week reports.

It says arboculturalist consultancy Jonathan Cocking Associates (JCA) will trial a newly patented product with English Heritage.

JCA managing director Jonathan Cocking said he was trademarking the product, which kills canker bacterium in trees’ vascular systems.

Plugs of bark are removed around the chestnut, he explains, and a tree infusion is screwed into the holes.

The process takes an hour and after a year the tree refoliates, he adds.

“We are rolling it out with a few high-profile programmes including one with English Heritage.

“The treatment is invasive, but it’s a natural product.

“It’s better to get cracking and save a few trees than run a 10-year study programme only to find at the end of it that all the horse chestnuts have died.”

JCA, based in Halifax, West Yorkshire, has worked with a Dutch firm on the cure and hopes to license the product later in 2009.

Source: Horticulture Week

Date: 16/01/2009

Sudden oak death hits UK national park


Restrictions have been introduced on visitors to the New Forest National Park in southern England after the discovery of a plant and tree-killing disease, the BBC News website reports.

Sudden oak death (Phytophthora ramorum) was discovered in a small number of rhododendron bushes along one of the park’s trails.

Visitors have been told to stick to pathways and keep dogs on a lead in signposted areas in order to prevent spreading.

The Forestry Commission said there was no risk to human health.

Mike Seddon, deputy surveyor for the New Forest, said: “As a result of routine monitoring undertaken as part of national measures to protect Britain’s trees and forests against Phytophthora ramorum, infection has been confirmed on some Rhododendron ponticum bushes.

“We are now working with Defra to determine the exact scale and extent of the outbreak, and to destroy infected plants,” he added

“In the meantime the public may continue to enjoy visiting the New Forest as usual.

“However, to help prevent the spread of the disease, we ask that in signposted infected areas they stay on the footpaths, keep dogs on leads, and do not take plant cuttings. There is no risk to human health.”

Sudden oak death was first identified in California, where it has made tan oak trees a rarity.

It causes roots and leaf discolouration, resulting in the death of the infected plants.

In the UK, rhododendron and viburnum are most commonly affected.

Mr Seddon added that, despite its nickname, sudden oak death actually poses little risk to the New Forest’s oak trees.

“There is, however, evidence that other species, such as beech and ash, are susceptible,” he said.

“Our approach therefore is to find out exactly the extent and severity of the outbreak and destroy the infected shrubs and plants to minimise the risk of the infection spreading into the New Forest’s trees.

“We have set up a survey of the area within 3.0km (1.8-mile) of the outbreak.”

Signs have been erected in the forest giving more information.

Source: BBC News website

Date: 08/01/2009

Pine beetles ‘affecting Rockies air quality and climate’


When pine bark beetles kill trees, scientists believe they may also alter local weather patterns and air quality, reports the Environmental News Service (ENS).

For the next four years, researchers will study forests from southern Wyoming to northern New Mexico to determine the precise relationship between the beetles, the trees they kill and the atmosphere.

A new international field project, led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, is exploring how trees killed by the beetles influence rainfall, temperatures, smog and other aspects of the atmosphere.

“Forests help control the atmosphere, and there’s a big difference between the impacts of a living forest and a dead forest,” says NCAR scientist Alex Guenther, a principal investigator on the project. “With a dead forest, we may get different rainfall patterns, for example.”

Preliminary computer modeling suggests that beetle kill can lead to temporary temperature increases of between two and four degrees Fahrenheit. This is partly because of a lack of foliage to reflect the Sun’s heat back into space.

Beetle kill stimulates trees to release more particles and chemicals into the atmosphere as they try to fight off the insects, Dr Guenther says. This worsens air quality, at least initially, by increasing levels of ground-level ozone and particulate matter.

The mountain pine beetle, Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia and Alberta.

Forests in Colorado, Wyoming, and South Dakota are experiencing bark beetle epidemics at a historically unprecedented scale, according to the US Forest Service.

A plan by the Service to deal with the beetles will log, burn, or spray 104,000 acres of lodgepole pines in the Rocky Mountain Region by 2011.

Researchers from the Canadian Forest Service have studied the relationship between the carbon cycle and forest fires, logging and tree deaths.

They conclude that by 2020, the pine beetle outbreak will have released 270 megatonnes of carbon dioxide into the atmosphere from Canadian forests.

The NCAR project, known as BEACHON for Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen, is funded by the National Science Foundation, NCAR’s sponsor.

BEACHON will allow scientists to gain insights into cloud formation, climate change, and the cycling of gases and particles between the land and the atmosphere, according to Cliff Jacobs, program director in NSF’s Division of Atmospheric Sciences.

The exchange of gases and particles between the surface and the atmosphere is critical in arid areas such as the western United States.

Dr Guenther says even slight changes in precipitation can impact the region.

“Here in the western United States, it is particularly important to understand these subtle impacts on precipitation,” Guenther says. “Rain and snow may become even more scarce in the future as the climate changes, and the growing population wants ever more water.”

Researchers will use aircraft as well as towers that reach above the forest canopy to measure emissions at 100 feet above the ground.

Additional data will come from soil and moisture sensors, instruments for gases and tiny particles, radars, and lidars, which are radar-like devices that use light instead of radio waves.

“BEACHON will give us a very comprehensive picture of a forest’s impact on the atmosphere,” Dr Guenther says.

“But at this point, we don’t know what the project will reveal. We may end up with more questions than answers.”

Organisations participating in the project include Colorado College, Colorado State University, Cornell University, Texas A&M University, and the universities of Colorado, Idaho, Minnesota, New Hampshire, and Washington, as well as the U.S. Forest Service, the U.S. Environmental Protection Agency, and universities in Austria, France and Japan.

Source: ENS

Date: 2/10/2008

Follow

Get every new post delivered to your Inbox.

%d bloggers like this: