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Posts tagged ‘disease’

Ash chapter must now be rewritten

November 10, 2012

Gabriel Hemery

Ash (Fraxinus excelsior) shoot with emerging leaves. Drawing by Sarah Simblet.

Following the devastating news that the fungal pathogen Chalara fraxinea is rampant in the British countryside, our ash chapter requires now a major rewrite.

We had completed the section on ash (Fraxinus excelsior and other ash species) just one month ago, and had included a significant section on the potential dangers from this disease which was looming in continental Europe, little-knowing that within one month hundreds of British woodlands would be discovered to have trees infected with ash dieback.

Ash (Fraxinus excelsior) shoot with emerging leaves. Drawing by Sarah Simblet.

Ash (Fraxinus excelsior) shoot with emerging leaves. Drawing by Sarah Simblet for The New Sylva.

We have now just a few months of writing and drawing remaining before the book is put together by publishers Bloomsbury. Let’s hope that the news does not get much worse for this beautiful and graceful tree species before we go to press in late 2013.


Read more about Chalara fraxinea

Chalara fraxinea has been wild in Britain for at least two years

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Lesion on young ash stem caused by Chalara fraxinea

After probably the largest-ever rapid survey of Britain’s woodlands, new incidences of Chalara fraxinea, the fungal pathogen that causes ash dieback, have been found in a possible 100 sites across the East and South of England.

After the announcement last week that Chalara fraxinea was in the ‘wild’ in the countryside of East Anglia in England, Forestry Commission staff have undertaken an unprecedented rapid survey. Every 10km square in Britain where ash trees were likely to be found was targeted, selecting four sites in each sampled square. The news is not good, as I predicted (see post).

Chalara fraxinea is present possibly in at least 100 sites, rather than the two where it was originally reported just one week ago. In addition to new confirmed sightings in Kent, possible occurrences extend to the Midlands and even Wales (see Forestry Commission latest map). Note that these are still to be confirmed officially but samples collected from many seem indisputable, even without any scientific analysis.

Today I visited Wayland Wood in south Norfolk as part of a specialist task force convened by Government. We viewed an area where hundreds of coppice stools of ash had succumbed to dieback (see pictures below).

Observing the branches of one more mature tree (with a stem about 30cm dbh) it was clear that this tree had suffered dieback during Summer 2011. This means that the Chalara fraxinea was present in Britain at least one whole year before realised, as indicated from tree physiology alone. When accounting for the life-cycle of Chalara fraxinea, then it is more likely that it was present from Summer 2010 if not even earlier. It is clear that the pathogen arrived in Britain by stealth before anybody recognised it.

Click to enlarge images

A stakeholder meeting is to be held on London today, and more details will emerge about the sightings that I report here. Scientists are working around the clock to confirm observations made in the field, by using sophisticated DNA sampling techniques on collected samples. Further expert groups are being set up and all concerned are working hard to provide practical advice to foresters, arboriculturists, nurseries and others.

Gabriel Hemery


Further information:

Ash dieback spreads in British countryside

October 25, 2012

Gabriel Hemery

Chalara fraxinea ash dieback distribution map in Britain

Ash dieback caused by the pathogenic fungus Chalara fraxinea has been confirmed on woodland trees in the British countryside.

In this case I am not happy in being proven correct in my prediction of just two days ago, see Ash dieback could devastate Britain’s landscape, that the disease was in all likelihood already loose way beyond the tree nurseries where it was first reported. As Britain’s third most common tree species, the consequences are indeed very serious.

The outbreak in East Anglia was confirmed today by plant scientists from the Food and Environment Research Agency (Fera). Ash dieback Chalara fraxinea was found at two separate sites: (1) the Woodland Trust’s Pound Farm woodland in Suffolk, and (2) Norfolk Wildlife Trust’s Lower Wood nature reserve near Ashwellthorpe. These are the first confirmed reports following the initial import of the disease on plants brought in from the continent by a Buckinghamshire nursery, which subsequently distributed ash plants to some 90 customers across the country. The location of these initial plantings is not public knowledge.

Download the latest national map of confirmed Chalara outbreak sites

Download the latest national map of confirmed Chalara outbreak sites from the Forestry Commission

[UPDATE] I prepared initially my own Google map to mark these first countryside outbreaks. The Forestry Commission have subsequently been releasing a national map of confirmed outbreak sites on a regular basis, so instead I now provide a link to their online map here (it is quite a large pdf file so allow some time for it to download).

Gabriel Hemery


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Ash dieback could devastate Britain’s landscape

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Ash in Britain

Name an iconic tree species for Britain … Did you answer oak or Scots pine? My guess is that it was one or the other. There is another species however that holds a unique place in British landscapes, not just in lowland forests, but in our uplands, in wet woodlands, among hedgerows and fields, in streets, parks and gardens – the ash Fraxinus excelsior. It may not demand our attention in the same way as some other tree species but it is extremely valuable and important in so many ways.

Ash trees at dawn in Cumbria

Ash trees at dawn in Cumbria. Photo http://www.TheTreePhotographer.com

Ash in Britain

Ash (Fraxinus excelsior) in Britain and Ireland from The New Atlas of the British and Irish Flora, Oxford University Press. Click to view an online version from the BSBI website.

Take a look at the distribution map (right) for ash – every blue dot represents a 10×10km square in Britain where ash is present. Very few places in Britain are without ash trees. It is a vital component in the ecosystems of many mixed woodlands, being an ideal companion to oak and other hardwoods. It regenerates readily being adapted perfectly to the British climate. Its wood remains one of the best materials for sporting goods, makes beautiful furniture, while its properties for firewood are unrivaled.

Imagine therefore a scenario where ash may disappear from our landscapes. Horrifying – yes; a reality – quite possibly.

Readers may have picked up the worrying news that during an official inspection carried out in February 2012, symptoms of ash dieback were observed on Fraxinus excelsior in a nursery located in southern England. Suspect symptoms were identified in a batch of 600 plants which had been imported from the Netherlands in November 2011. The presence of Chalara fraxinea (EPPO Alert List) was confirmed on the basis of the morphological characteristics of the pathogenic fungus. Eradication measures were put immediately into place and the infected lot of F. excelsior was destroyed. Further investigations on the site revealed suspect symptoms in other Fraxinus species which had also been introduced into the nursery in November 2011. Investigations have been carried out to trace-back all Fraxinus consignments originating from the same Dutch supplier which had been imported into the United Kingdom, as well as to trace-forward all plants from the infected lot which have already been sold by the British nursery.

In Denmark, around 90% of all ash trees have been affected by Chalara fraxinea, and it is rampant across northern and central Europe. Young ash trees are particularly vulnerable and can die within one year, while older trees although capable initially of surviving the dieback, are likely to die after two or three consecutive years of infection.

According to the official line (see links below) the fungal disease has not yet been found in the natural or wider environment in Great Britain, that is, outside nurseries and recent plantings. My guess is though that it is already loose and rampant in our landscape. History tells us that we usually become aware of serious pests and pathogens late in the day. Pests and diseases can appear and then take time to impact too. For instance, Dutch elm disease was first detected in Britain in 1927, and was probably present before then, yet it was not until the 1960s that millions of elm trees were affected by the disease and mature elm trees wiped from our landscape.

Chalara fraxinea is being treated as a quarantine disease under national emergency measures, and it is important that suspected cases of the disease are reported. See the links below to aid in identification.

More about Tree Health


Further information:

On the hunt to capture England’s last remaining mature elm trees

April 6, 2012

Gabriel Hemery

The authors recently travelled to East Sussex on the hunt to find some of England’s last remaining mature elm trees.

East Sussex is one of the last strongholds for the elm, where it is assisted in its battle to survive the continuing onslaught of Dutch Elm Disease by a special project run by East Sussex County Council; who employ a dedicated Dutch Elm Disease Officer. Guided by their officer Anthony Becvar, the authors saw several large English elm trees although sadly many showed signs of the disease or had been pruned by tree surgeons in an attempt to halt decline. Numerous other examples of elms including Huntingdon (a hybrid between small-leaved elm U. minor and wych elm U. glabra) and Wheatley (Ulmus minor subsp. sarniensis ) were also seen.

The tree subject chosen to be featured in a drawing by Sarah Simblet for The New Sylva were two Cornish Elms ((Ulmus minor subsp. angustifolia) that were off the beaten path. The two trees were both leaning, having had their roots disturbed, but were otherwise in very good health.

Cornish Elms and drawing in progress by Sarah Simblet

Cornish Elms and drawing in progress by Sarah Simblet for The New Sylva

Sweet chestnut blight found in Britain

March 22, 2012

Gabriel Hemery

The fungus that wiped out 3.5 billion chestnut trees in the USA has been found for the first time in Britain. Chestnut blight, caused by the fungus Cryphonectria parasitica (C. parasitica), has been confirmed by Forest Research scientists on trees in two small orchards of European sweet chestnut (Castanea sativa). The trees were imported by an English tree nursery from the same grower in France. The sites in Warwickshire and East Sussex are the first findings in Britain. Until now, the English Channel had prevented its spread from mainland Europe.

The fungus infection is usually fatal to European sweet chestnut and its North American relative, Castanea dentata, although it appears to be less virulent in Europe than it is in America. It is believed to have first originated in Eastern Asia before being introduced to North America in the late 19th Century, where it has since devastated billions of trees in the East of the country (see The American Chestnut Foundation). It was first identified in Europe in 1938, in Italy, and has since spread to most parts of southern Europe where sweet chestnut is grown, and to parts of northern Europe.

Identifying chestnut blight

The most obvious symptoms of chestnut blight are wilting and die-back of tree shoots. Young trees with this infection normally die back to the root collar, and might re-sprout before becoming re-infected. Other symptoms, such as stem cankers and the presence of fruiting bodies can also occur.

What now?

The trees where the fungus were discovered had been imported into the UK for nut production. As I have written before (e.g. Climate Change and Global Trade), the import/export of trees is potentially the most significant factor in the spread of new tree pests and diseases. Case proven I think.  Let’s hope that FERA (Food & Environment Research Agency of the UK Government) is given adequate resources to tackle this very serious fungus. Afterall, sweet chestnut is a beautiful tree species in our forests and when coppiced, as it is in commonly in Kent (see Sweet Chestnut Coppice), it is one of the few forest systems that pays well and regularly.

Gabriel Hemery


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