This month’s topic is ash dieback, a disease that is currently affecting our native ash tree, Fraxinus excelsior. Like Dutch elm disease before it, it is expected to change the appearance of the English landscape and much research is under way on how to manage it and mitigate its effects. The disease is caused by a fungus, originally called Chalara although now known as Hymenoscyphus fraxineus, which originated in East Asia. It has spread to affect ash trees across Europe, Great Britain and Ireland.
The disease is particularly deadly to young and coppiced trees, which die quickly. Older trees have more resistance and some trees are totally resistant to it. The first signs in an affected tree are blackening and wilting of the shoots and leaves, which are most easily spotted between July and September. Dark patches appear on the bark and typically are elongated diamond shapes of dark brown or black. If occurring near the base of the tree it is at risk of falling. The disease spreads via wind-blown spores.
Managing the disease depends on the age of the trees, their use and situation. There is no obligation to report or to act if you own a diseased tree, but public safety is of primary importance and any tree with a potential to cause harm, such as one alongside a road, footpath or building should be carefully inspected for signs that limbs or the whole tree might fall. Public bodies are currently felling many trees that fit this category. In woodland, a number of strategies may be undertaken, including doing nothing, depending on the diversity of species and tree-age on the site. Felling living trees is not recommended but taking out stands of young trees where the majority are infected may allow beneficial regeneration by more resistant types of the tree. However there must be nearby healthy trees over thirty years old for there to be enough ash seeds to achieve this.
Stopping spore spread is time consuming. Gathering and burning leaves or composting them with plenty of soil on top may interrupt the fungus life-cycle but is not practicable in most situations. Visitors to woods are advised to brush plant material off their shoes and wheels, e.g. bicycles, prams etc before leaving the site and to wash them at home before entering another wood, but again this is a cumbersome task.
The good news is that as some ash is totally resistant to the fungus, these strains should out-compete and eventually replace the susceptible types. Opening up woodland and allowing in more light to aid natural regeneration is a sensible strategy to promote this and, sad though it is to see trees dying, it can be rewarding to see traditional wood-management in action. Two such traditional wood-workers are seen in the accompanying photograph, Woody and Twink are their names. Horse-logging is an ancient skill in tune with the woodland environment, we’re lucky to have some practitioners of the art living here in the Teme Valley.