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Is this the beginning of the end for ash?

Paul Schofield fears another disaster for Britain’s native trees.

Set within the urban sprawl of Southend-on-sea, Essex, Southchurch Hall is a small parkland with a Tudor mansion house at its centre surrounded by mature trees and duck ponds. 

I remember going there for picnics as a child in the 1970s and sitting in the shade of huge trees with big red ‘X’s painted on their trunks. And then one day the trees were gone. 

The trees were English elms – Ulmus procera – and this was the height of the Dutch elm disease epidemic. Today, there is no trace of the elms that stood at Southchurch Hall or millions of others that were once so integral to the landscape. By the 1990s, an estimated 25 million elms had died, some 85% of the estimated UK population. 

The recent arrival of ash dieback disease brings fears that we are witnessing the gradual disappearance of another native hardwood from the countryside. Ash dieback disease was first recorded in Britain in 2012 and is now found in most parts of the UK except northern Scotland. Ash dieback is caused by a fungus, Hymenoscyphus fraxineus, which causes leaf loss and crown dieback in affected trees. The disease is usually fatal, either directly or indirectly by weakening the tree to the extent that it is more likely to succumb to other pests and diseases, most notably honey fungus, Armillaria. 

There are an estimated 10.7 million ash trees in Scotland alone. In addition to its heritage value and importance in the landscape, the potential loss of ash as a timber producing tree is serious because it establishes easily, grows fast and straight and is resistant to grey squirrel damage, all unique properties that cannot be easily replaced. It is also an important component in native woodland on more fertile soils and its loss would compound the disappearance of elm from similar sites. No native species of large stature can match the ability of ash to colonize gaps in the canopy. 

However, there are signs of hope. Some ash trees appear to tolerate infection and scientists are studying the genetic factors behind this so that tolerant ash trees can be bred for the future. 

In the meantime, the impact of H. fraxineus is likely to develop slowly as the disease advances from killing twigs and branches to extensive crown dieback and tree death in the longer term. Based on experience in Europe, particularly the recent spread of the disease in Denmark, current DeFrA guidance states the following: 

• Trees cannot recover from infection but larger trees can survive infection for a considerable time and some might not die. 

• Trees less than 10 years of age are likely to die from H. fraxineus in two to 10 years. 

• Trees less than 40 years old will die in three to five years if also infected with honey fungus and more rapidly if the tree is already debilitated. 

• For mature trees more than 40 years old, there is no direct evidence of tree deaths solely from H. fraxineus to date, but there is so far little comprehensive survey data from Europe on which to base firm conclusions. 

Mature elms survive here and there in small, isolated pockets but are still uncommon. When I do encounter one – most recently at the Edinburgh Academy – I see them so rarely that at first I’m not sure what I’m looking at. Hopefully the same won’t be true of ash 25 years from now.