Could Somerset site give hope for ash dieback disease?

28th Oct 2013

Trees in a Somerset plantation have survived with ash dieback (Chalara fraxinea) for far longer than previously thought possible, suggesting there may be potential to slow the spread of the disease in the British countryside after all.

Only ten per cent of the six thousand ash trees at the Holnicote plantation are showing any signs of the disease, despite having been infected for five years longer than any other tree in the UK so far.

The disease is present in one other small plantation nearby but doesn’t appear to have spread any further – which is at odds with Government predictions which suggests it should have spread further and infected more trees in this time.

These findings suggest that tackling the disease in the UK is not a lost cause – and control measures could slow the spread of the disease from South East England where the disease appears to have been windblown from mainland Europe. 

With ash making up one third of the UK’s tree cover, this could be good news for the British landscape which would be radically changed by the disease if it is allowed to spread rapidly across the country in the coming decades.

Dr Simon Pryor, natural environment director with the National Trust said: ‘It’s important that the disease has not appeared to have spread very far at all. Even the trees affected have not suffered as much as we’d have expected, and very few have died, despite apparently having had the disease for nearly a decade.

‘Whilst we don’t want to be too optimistic on the basis of this one outbreak, this does confirm the view we’ve held from the outset that it is worthwhile removing infected trees in order to try to slow the spread – especially in places like this so far from the main area of the disease in the South East.

‘We will be asking Government to look again at its control strategy in the light of this new evidence – which to us does not appear to fit well with current modeling.’

More on the situation at Holnicote

We discovered the outbreak of ash dieback at its Holnicote Estate in September when undertaking routine inspections for the disease.

The trees were planted back in 2001 to mark the millennium, and pre-date other outbreaks of the disease by five years.

It’s likely that these trees – like thousands of others imported to the UK at the time – were infected whilst being grown on in central Europe.

Mark Courtiour, countryside operations manager at Holnicote, said: ‘Discovering the disease at such a large site is particularly heartbreaking. Like others, we were shocked to discover that the trees we thought were being grown in British nurseries were actually being grown on and imported from the continent.

‘We will be felling all the infected trees as a matter of priority and filling the gaps with other species.

‘However, there is a real glimmer of hope and we are continuing inspections at the site.’

Nevertheless, some scientists remain sceptical. Dr Richard Buggs, who heads the ash tree genome project at Queen Mary University of London says:

'I really hope this is true, but from what I can piece together at the moment I remain unconvinced. I am guessing these are UK genotypes of seed that were exported to the continent (probably the Netherlands) to be grown, then returned to the UK as saplings. The NT Press office have tweeted to me that the trees were only diagnosed last month and the majority of trees in the site are not showing symptoms. From what I can make out they are inferring that the trees have had the disease for 12 years because they were imported 12 years ago, and because there are no other local outbreaks of ash dieback in Somerset.

'However, 12 years ago ash dieback had not been found in the Netherlands (where most tree nurseries are based). Some trees on the continent have survived many years with ash dieback, but it tends to be mature trees that can do this. For young trees to survive and grow for so long with ash dieback would be impressive, but even more impressive would be the fact that their neighbouring trees have not been infected. It seems to me that recent long range dispersal of spores within the UK is a more likely explanation for what the NT is seeing at the moment. I would love to be proved wrong though. If they are right then these trees would appear to be quite resistant, or the strain of fungus they have been infected with is of low virulence.'

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