Can we rise from the ashes?
SINCE ash dieback was first detected in the British Isles, in the spring of 2012, the deadly Chalara infection has spread swiftly, like an autumn mist, across much of the country. Scientists have estimated that Britain may lose more than 85% of its 138 million ash trees over the next 10 to 20 years. This puts the loss of 25 million mainly English elm trees 40 years ago to Dutch elm disease into grim perspective.
Recent research from the Earlham Institute in Norfolk underlines just how vulnerable our surviving ash, the European ash, may be if only one more pathogen makes its way from east Asia to exacerbate the existing problem in our woods. This combination, say scientists, could likely wipe out what remains.
There is no cure for Chalara, although there is some evidence that the different genetic make up of ash could give a small number of trees a greater degree of resistance than others. However, there are some measures that landowners can take to give ash a chance to fight back. Dr Glynn Percival, a plant physiologist at Bartlett Tree Research Laboratory, has recently completed a three-year trial using enriched biochar, a special superheated charcoal, to treat young ash trees in controlled conditions. He says that adding biochar to the roots of ash trees suppresses dieback.
Up until recently, enriched biochar had been added to young trees via airspading, but this process does not get deep into the root system. Nor has it really been tested in mature ash trees. However, new German technology in the shape of a device called the Vogt Geoinjector is being deployed on some of the bigger estates to protect venerable trees. This is at the cutting edge of tree-root technology, with a machine that uses a pneumatic probe to penetrate soil beyond the root zone of a tree, up to 1.2m (nearly 4ft) deep. It then injects compressed air to create a cavity and vertical column back to the surface, which is then backfilled with enriched biochar.
Adding this to the roots of trees and plants seems to trigger defence mechanisms in ash as well as providing an improved habitat for beneficial soil microorganisms. And it’s not just ash. Trees treated with biochar—which is enriched with trichoderma, mycorrhizal fungi, worm casts and seaweed —appear to be resistant to a number of other prevalent, and in some cases incurable, diseases, including horsechestnut leaf miner, honey fungus and acute oak decline.
While we wait for evidence that enriched biochar is as effective on older ash trees as it is the young, and for the costs of treatment to become more accessible, it does appear that some older ash not only survive longer, but do so when they stand in open conditions, clear of the leaf and twig litter of woods and forests where the Chalara fungus fruits and spores. Steve Scott of the Forestry Commission has just returned from south-east Poland, where Chalara first took hold in 1992. He reports that ash is still evident in the wider countryside, whereas in forests, such as the mighty, primeval Bialowieza, barely 3% to 4% remains. It seems that while there is life in the ash, there is still hope.