Czech ash trees decimated by invasive Asian fungus

It is believed that Hymenoscyphus pseudoalbidus, the fungus that causes ash dieback, found its way to Europe on ash imported commercially 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 damage to the bark of 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 studied the disease, first identified it in the school’s arboretum in 2007, said the dean of the faculty, Libor Jankovský:

“Here you can see how the infection penetrates even into the healthy part of the trunk. The inner part is rotten – dry, dead. This tree, if I remember correctly, had a beautiful umbrella-shaped crown. , there is only one stump. “

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

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

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

“The only way to control the spread of the disease is with a sufficient variety of management practices, sufficient forest diversity and high genetic diversity of the tree species we use in forests. In cities, we can reduce the infestation by removing dead leaves, this way we can prevent the fungus from growing on the stems.

The decline of ash trees is also reflected in the increasing amount of ash wood harvested. Last year, more than 230,000 cubic meters were harvested in the Czech Republic, about five times more than in the mid-1990s. Eva Jouklová is the spokesperson for the public forestry company Lesy ČR.

“Ash grows on less than one percent of the area managed by our company, from plains to mountains, mainly in mixed forests. The disappearance of ash trees from forests may not be noticeable, except in floodplain forests where it is a significant part of the vegetation.

Ash trees aren’t the only trees decimated by invasive disease. In the second half of the 20th century, elms were devastated by a fungus carried by insects. Other deciduous trees, such as alders or maples, are also struggling with fungal pathogens today.

Libor Jankovský of Mendel University says that 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.

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