Ash trees on Barnes Common
The Ash tree (Fraxinus excelsior) is widespread on Barnes Common but is facing an uncertain future due to ash dieback or chalara, a disease caused by a fungus Hymenoscyphus fraxineus. First recorded in Poland in 1992 and identified in Britain in 2012, it is thought to have arrived via imported saplings from the Netherlands and by spores carried on the wind from Denmark, where 90% of ash trees have already been lost.
Dieback is usually apparent through leaves wilting and dying in summer along with twig and branch dieback and distinctive diamond shaped bark lesions. The disease is spread by spores released from the fruiting bodies of the fungus that forms on the dead leaves of the ash and then infects the new leaves.
Due to its ability to withstand shocks, ash has been used for hockey sticks, hammers and axes and produces some of the best firewood available. It also supports more than 100 species of insect, while lesser stag beetles, owls, woodpeckers, bullfinches and bats are all known to use it for homes and food.
However, of the UK’s estimated 126 million ash trees, there is hope that some will show resistance. Encouragingly, researchers have already identified a 200 year old female ash in Norfolk that is untouched by the disease which has so far killed half the trees in the county.
Scientists have further been able to develop three genetic markers which can predict a tree’s likely tolerance, raising the possibility of using selective breeding to develop strains of disease-resistant trees. So far, the prediction is that 3% of British ash trees will show a fairly high level of tolerance, although scientists at the John Innes Centre have recently predicted that losses could now be reduced to 50% in Britain. However, it is now a race against time to identify a wide genetic mix of tolerant ash trees before the next deadly threat, the emerald ash borer beetle strikes. This is moving quickly westwards through Russia and is now top of the UK’s plant risk register.
So how is FoBC helping? Ash Tag was developed by the University of East Anglia and now run by the Sylva Foundation as the Living Ash Project where small numbered aluminium plates are nailed to a selection of ash trees throughout the country. By regular monitoring, trees that have tolerance can then be identified. FoBC has tagged six trees around the Common, all ranging in size and age so now we will just have to see how they fare.