If you pay too much attention to newspaper headlines you’ll be led to believe that Britain’s ash trees are about to follow English elm trees into extinction. The truth may not be so extreme but the disease that’s spread from mainland Europe is sure to change the look of many of our woodland areas.
Chalara dieback – caused by the Chalara fraxinea fungus – attacks ash trees causing leaf loss, crown dieback and usually kills the tree. It has already led to drastic loss of ash trees in mainland Europe and has now been found in the United Kingdom.
Outbreaks are being divided into those among imported plants at nursery sites and recently planted saplings, and outbreaks in the wider environment where the fungus seems to have crossed from main land Europe. Most of the latter cases are in East Anglia and Kent caused directly by spores blown across the sea.
Until November 27, government experts had found 257 cases in the United Kingdom– 135 of those in the wider environment, mainly in established woodland. The closest recently planted case to our area is between Bristol and Chippenham.
Symptoms of the disease include browned leaf tips, bark lesions and the dying away of topmost growth. In spring mature trees can develop dense clumps of foliage below dead growth.
So what path might the disease take in our area? Savernake Forest has some established ash trees, but many have been cut down by the Forestry Commission in recent years as they fetch good money for firewood and furniture, and also for export to Ireland where they are used to make hurley sticks.
Over the past twenty years ash trees have been planted widely on Marlborough’s downlands. They are clear of the disease at the moment but ultimately land owners expect to lose those trees. More generally the spread of ash trees is difficult to quantify.
Wilton Bail wood, just north of Wilton windmill, is heavily planted with ash. About seventy per cent of the mature trees in this wood are ash. Newer plantings have used other tree species, so ash now makes up about half of all the trees in the wood. If those ash trees were all lost it would not only have a clear visible effect, but would also have a major impact on the wood’s wildlife.
The spread of the disease will almost certainly re-start next May – the season for active spores from the fungus lasts from about May to early September. But on the continent some ash trees have proved resistant to the disease with up to ten per cent surviving. So it may not result in the kind of total wipe-out that was caused by Dutch elm disease.
The broadleaf, deciduous ash tree is the third commonest tree in British woods. And while it is sometimes the dominant tree in a wood, the effect of its loss on the landscape as a whole may be very patchy.
Writing about Chalara fraxinea last week, Ashley Brady, the Woodland Trust’s head of conservation, emphasised the complexities of the threat: “The impacts on ash will be much more complex than the media headlines suggest, this goes well beyond the simple percentages of what will be lost or estimates of how many million trees are at risk. Some landscapes and habitats will be much harder hit than others, and we need to start thinking about how we respond to that now.”
Sightings of diseased ash trees should be reported immediately to the Forestry Commission Plant Health Service: email@example.com or 0131 314 6414.
Sadly our trees have many other diseases and pests to survive : lots more scary headlines coming our way. Oak trees, horse chestnuts, Scots pine and the London plane tree are among the species under threat or which are so far surviving threats.