What is Ash dieback (Chalara dieback) and what are the implications to owners of affected trees?

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Ash dieback, Hymenoscyphus fraxineus (previously known as Chalara fraxinea) is a serious fungal disease that affects ash trees (Fraxinus species). The disease was first confirmed in Ireland in 2012. Ash dieback will affect all ash trees in Ireland, causing the majority of them to die over the next two decades. Ash dieback is a significant concern in Ireland due to the prevalence of Ash trees within our hedgerow and along our roadsides. Ash is a keystone species in Ireland and accounts for around one third of our trees (excluding forestry species). A very small percentage (less than one percent) of Ash tree are resistant to the disease and researchers at Teagasc are trying to further propagate this stock.

Ash dieback is caused by the pathogen Hymenoscyphus fraxineus, which originated from Asia. It was first identified in Europe in the early 1990s. The disease spreads primarily through wind-dispersed spores (up to 35km) and can also be transported through the movement of infected plant material.

Symptoms of ash dieback include wilting and blackening of leaves, dieback of shoots and branches, and crown thinning. Infected trees can eventually die because of the disease. Once a tree is infected, there is no known cure, and management efforts focus on preventing damage to property or personal injury.

Here are some of the key risks associated with ash dieback

Tree collapse

Infected ash trees can become structurally weakened as the disease progresses. The dieback affects the crown and branches, leading to their breakage and potential collapse. This poses a risk to people and property in the vicinity of infected trees, particularly during storms or high winds.

Falling branches

As the disease progresses, branches can become brittle and prone to breakage. Diseased ash trees may shed branches even in moderate winds, posing a risk to individuals walking or working beneath them.

Tree uprooting

The root system of infected ash trees can be compromised, leading to reduced stability and an increased risk of uprooting. This is particularly concerning in areas with high foot traffic or where the trees are located near buildings, roads, or infrastructure.

Public areas and recreational spaces

Ash dieback can affect trees in public parks, recreational areas, and along roadsides. Infected trees in these locations may pose a risk to pedestrians, cyclists, and motorists, especially if they are in a state of decline or have already partially collapsed.

Habitat and ecosystem changes

Ash trees are an important component of ecosystems, and the loss of a significant number of ash trees due to ash dieback can have ecological consequences. It can disrupt wildlife habitats and impact the overall biodiversity of affected areas.

To mitigate these risks, it is important to conduct regular inspections of ash trees in high-risk areas, such as public spaces, roadside and near property. Infected and structurally compromised trees may need to be felled or pruned by professionals to ensure public safety. 

Who is responsible?

Landowners, either privately owned or by a state body (public) are responsible for all tree on their property. Annual survey should take place to identify any potentially dangerous or diseased trees and work carried out to mitigate this. 

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