Ash dieback disease – does it spell the end for our beloved UK ash trees?
Ash dieback disease affects our common ash tree (Fraxinus excelsior) together with other ash species including weeping varieties.
Infection and symptoms
The disease is caused by a fungus Hymenoscyphus fraxineus (previously known as Chalara fraxinea). It is thought to have arrived in the UK back in the early 2000’s, with the first official case recorded in Britain in 2012. The disease is now widespread throughout the UK as can be seen on the Defra web map showing reported distribution.
Infection of the tree starts via fungal spore contact with leaves in the upper and outer canopy. This progresses through shoots, twigs and branches to interrupt the vascular function (transport of water & nutrients) within the tree. Canopy symptoms include wilted/spotted leaves, leaf loss, clumped foliage, and stimulation of shoot growth (epicormic shoots). Dark lesions, or cankers may be present on the bark, these having a characteristic elongated-diamond shape and being centered on shoots/branch junctions with the parent stem. In some cases, basal trunk lesions may be present with little evidence of dieback in the canopy.
Significance for our trees, safety and landscape
The speed of tree decline is influenced by factors including weather variation from year to year, genetic variation between trees, health and size of the tree, site characteristics and soils. Unfortunately, in most cases infection will result in a decline in the tree’s health, dieback and ultimately tree death.
Canopy dieback symptoms are also associated with wood embrittlement. This increases the risk of branch loss/branch failure and introduces unpredictable wood characteristics which may pose problems for felling by conventional techniques.
The decline in tree health may also provide the opportunity for colonization of the tree by secondary opportunistic disease-causing organisms. These can include Honey fungus (Armillaria spp) which may result in basal /root decay leading to an increased risk of tree failure from the base.
Ash dieback disease therefore has implications for tree safety. This is particularly relevant when affected trees are located in areas with high public occupancy and have significant targets (roads, railways, footpaths etc.) beneath their canopy or close by.
The disease risks the loss of ash trees from our landscape. Ash trees make up circa 12% of our woodland and are important components of many parks, gardens and hedgerows, while old and veteran ash may support unique biodiversity. Ash trees which do not pose a significant health and safety risk should therefore be retained. This is necessary to safeguard against un-necessary biodiversity loss and to maintain a viable gene pool which may in time show evidence of genetic resilience to the disease.
What to do about ash dieback in your tree population?
Is it inevitable that we must turn all ash to ashes… No!
A “one size fits all” management approach is not appropriate. Sykes Land Management Ltd offers professional advice to help you take proportionate action. We can help you to identify trees under your control, assess tree condition/risks associated and plan your response.
Gov.uk draws together extensive guidance on ash dieback which you may find useful.