a Pathogens


There is a small hope that unique British races of the species—isolated from continental Europe 8,500 years ago—may prove unusually resistant to the blight.

During the 19th century, as global trade increased exponentially, so did the incidence of tree blights. In the early 20th century, after rich countries instituted biosecurity regimes, the growth rates slowed, and in America, at least until recently, remained fairly linear. But in Europe, around 1960, the infection rate picked up, very likely due to the trade-boosting effect of economic integration. This not only spread diseases around the continent itself. It also made the law-abiding countries of northern Europe, such as Britain, susceptible to the sloppier customs regimes of the continent’s southern fringe.

http://www.economist.com/news/britain/21580459-arboreal-confirmation-britain-european-country-european-problems-unquiet-woods?fsrc=rss|btn

A seven-acre section of woodland near Bickleigh belonging to farmer John Greenslade has been decimated by the disease, and a major programme to uproot and destroy affected trees is under way.

Mr Greenslade began planting Byway Woods 20 years ago and has won awards for it.

By far the most interesting part of the discussion, and perhaps the more optimistic, was identifying how we might rise to the challenge of making our precious trees and woods more resilient in the face of these on going and inevitable threats. With the input of renowned woodland ecologist, Keith Kirby from University of Oxford, the group considered how the natural and cultural history of our woods has shaped them – and what we can do to give nature a helping hand.

This cannot be a ‘one size fits all’ approach and there is no simple template that all woodland owners and managers should follow – in fact the tendency to try and manage all of our woods in the same way in the past or previous suddenly shifts in management resulting from pursuit of narrow theories has probably made them more vulnerable today. A vulnerability compounded by the continuing gradual loss of woodland and the fragmentation of woods and other habitats, leaving them disconnected and isolated.

But some key principles are emerging. Our woods will be more resilient if they contain a wider range of native species, and have a more diverse structure too – so that we have a good mix of types of trees and a range of young, established and older trees.

Prof Erik Kjaer from the University of Copenhagen, confirmed that a small proportion (around 2%) of ash may be naturally resistant or tolerant to chalara. There are also good signs that this characteristic can be passed on to progeny of those surviving trees.

http://wtcampaigns.wordpress.com/2013/06/28/making-our-woods-more-resilient-tapping-in-to-the-insight-of-experts/

See what we are doing: The Natural Ash Nursery –

http://worldwidewood.wordpress.com/2013/06/17/natural-ash-nursery-cleared-and-ready-for-the-deer-fence/

Thousands of mature, native ash trees are being dug up and burned after the devastating disease ash dieback was confirmed in Devon.

About 2,000 trees at Byway Farm near Tiverton are affected, according to the Forestry Commission.

This is the first confirmed case of the disease in mature, native trees in the region – another nine cases have been confirmed in young trees that have been recently planted at sites across Devon and Cornwall, including two sites on Dartmoor National Park, according to Forestry Commission figures.

Ben Jones, of the commission’s England plant protection team, said: “It appears that the affected trees had the disease when they were planted in 1996-97. It is concerning and we are continuing our investigations into how the spread had taken place and how far it has spread.”

http://www.westernmorningnews.co.uk/Trees-burned-infection-ash-dieback/story-19481835-detail/story.html

The genetic insights could eventually be used to cross Tree 35 with breeding stock from our native ash population. Tree 35 is predominantly female and the genetic make-up could help identify a predominantly male UK tree with resistance to make a breeding pair. Or it could be used to identify both female and male UK trees with similarly low susceptibility to the fungus. A combination of crosses might be needed for a lasting comeback from the epidemic.

Ash trees are almost always fertilised by pollen from another ash tree rather than by self-pollination. This generates two copies of each chromosome in the resulting seeds. Although very similar, the chromosomes tend to have many differences when you look at the detail. This ‘heterozygosity’ makes it difficult to generate a genome sequence because in effect you have to put two genomes together at the same time.

Tree 35 has been identified as highly heterozygous.

http://www.tgac.ac.uk/home/news/54/68/Genome-sequence-for-mother-of-ash-dieback-survival/

The scientists are extremely hopeful that, having determined the tree’s complete set of genetic material – through a process known as genome sequencing – they have paved the way to identify those genes which might be connected to its ability to withstand the fungus.

Although the breakthroughs have raised hopes that a new breed of ash will be able to grow and survive in the face of the fungus, they will do nothing to protect Britain’s 80m existing ash trees, which are all under threat.

Adult clones of tree 35 grown from cuttings taken from the original trees in the 1930s were recently discovered on the Danish island of Sealand. [However] just planting this variety of Ash in the UK would result in a narrow genetic base making the species vulnerable to future diseases, experts said, adding that the latest breakthroughs still represented a giant step forward for the long-term prospects of the tree in this country.

http://www.independent.co.uk/news/uk/home-news/genetic-secrets-of-resistant-tree-gives-new-hope-over-ash-dieback-disease-8660992.html

Dutch elm disease is a tragic thing to watch, but we shouldn’t be too gloomy. Woody vegetation responds, adapts, regroups. What emerges in its recovery stage may not be the same as before, but it will always be a vital, dynamic, arboreal community.

The fungus, now known as Chalara fraxinea, is biologically mysterious, an entirely new organism of uncertain origins. It probably evolved in eastern Asia, where it appears to be harmless to native ash species. Its ancestor is a benign and widespread leaf fungus called Hymeno­scyphus albidus, native even in the UK. But at some recent date, this threw up a mutant, Hymenoscyphus pseudoalbidus, with slight genetic differences but a terrible virulence.

Natural resistance is likely to be the best hope for the survival of a core population of ashes in the UK. Isolated from the continent for nearly 8,000 years, our trees may be more genetically diverse than those in Poland.

For their part, ordinary rural people were mystified by the need for plantations, having lived for thousands of years with woods that renewed themselves spontaneously and indefinitely by seeding, or by regrowth from cut coppice stools and pollards. In place of this system of natural regeneration came the notion of trees as artefacts, biddable machines for the production of timber, programmed at every stage of their lives from planting to cutting.

The fundamental grammar of our relationship with them had been changed. Previously, “growing” had been an intransitive verb in the language of woods. Trees grew, and we, in a kind of subordinate clause, took things from them. In the forest-speak of the Enlightenment, “growing” became a transitive verb. We were the subject and trees the object. We were the cause of their existence in particular places on the earth.

Now, in the extremities of ash dieback, we can see that decades of well-intentioned planting have been not only often unnecessary, but, quite possibly, dangerous. Runtish saplings, often mislabelled and of unknown provenance, are shoved into the ground, regardless of whether they might be vectors for disease, or whether the soil is right and the site appropriate.

The existence of a large population of indigenous ashes is our best safeguard for the future and makes rather baffling the Forestry Commission’s experiment, initiated early in May, of planting out trial plots with 150,000 saplings of “15 different varieties”. The intention is to discover whether a few may be resistant and eventually propagate from them. But as 80 million ashes from probably ten times that number of genotypes are already engaged in just such an experiment across Britain, it is hard to see this as much more than a PR exercise – one that fits tidily in to our long, hubristic belief that the salvation of trees lies with us and our superior arboreal intelligence only.

http://www.newstatesman.com/sci-tech/2013/06/our-ash-trees-are-dying-dont-despair-catastrophes-are-natural-events-lives-trees

See also: http://worldwidewood.wordpress.com/2013/06/17/natural-ash-nursery-cleared-and-ready-for-the-deer-fence/

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