Czechia’s ash trees decimated by invasive fungus from Asia

Hymenoscyphus pseudoalbidus

Ash trees across the Czech Republic have been dying in recent years as a result of a disease known as Ash dieback, caused by a fungus imported from Asia. Experts say there is no effective defence against its spread and warn of other invasive diseases that are threatening the country’s deciduous trees.

Hymenoscyphus pseudoalbidus, the fungus behind the Ash dieback, is believed to have found its way to Europe on commercially imported ash from East Asia. The first dying ash trees were reported in the Czech Republic in the 1990s, but the disease is common across the continent.

Ash dieback causes leaf loss, crown dieback and also bark lesions in the affected trees. It also weakens the trees, making them more susceptible to other pests and pathogens.

Experts from the Faculty of Forestry and Wood Technology at Mendel University in Brno, who have been studying the disease, first identified it in the school’s arboretum in 2007, says the faculty dean, Libor Jankovský:

"Here you can see how the infection penetrates even the healthy part of the trunk. The inner part is rotten - dry, dead. This tree, as I remember it, had a beautiful umbrella-shaped crown. Today there is only a stump.”

Ash dieback | Photo: Lamiot,  Wikimedia Commons,  CC BY-SA 4.0 DEED

The wax moth first attacks the leaves of ash trees, from which it then moves on to the branches, trunk and sometimes even the roots. The disease is airborne, which makes it difficult for foresters to defend against it.

In addition, the fungus also attacks seedlings and young trees, so there is no point in artificially planting new trees, says Mr Jankovský:

"The only way to fight against the spread of the disease is a sufficient variety of management practices, sufficient forest diversity and a large genetic diversity of the tree species we use in forests. In cities we can reduce infestation by removing fallen leaves. That way we can prevent the fungus from developing on the stems.”

The decline of ash trees is also reflected in the increasing amount of ash wood harvested. Last year, over 230,000 cubic metres were harvested in the Czech Republic, which is around five times as much as in the mid-1990s. Eva Jouklová is the spokesperson for the state-run forest company Lesy ČR.

"Ash grows on less than one per cent of the area managed by our company, from the lowlands to the mountains, mostly within mixed tree forests. The disappearance of ash trees from forests may not be noticeable, except in floodplain forests where it is an important part of the vegetation.”

Ash trees are not the only trees decimated by an invasive disease. In the second half of the 20th century, elms were devastated by an insect-borne fungus. Other deciduous trees, such as alders or maples, are also struggling with fungal pathogens at present.

Libor Jankovský of Mendel University says a major problem for Czech forests would be the introduction of a disease destroying beech trees, which are the most common deciduous trees in our forests.

Authors: Ruth Fraňková , Jana Karasová
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