Fungal disease threatens ash trees in France

A fungal disease known as chalara, caused by the fungus Chalara fraxinea, is spreading across northeastern France and killing thousands of ash trees. The disease, which is incurable, is complicating the daily lives of farmers and local communities who must prevent the falling of trees.

Expert studies the impact of the disease

In Châtillon-sur-Seine, Côte-d’Or, a technician with the public water management and development agency Sequana, Damien Dondaine, has been analyzing the effects of this fungal disease for about a decade. Observing the tops of these usually robust trees, one can easily spot some branches that are bare.

Disease symptoms are visible on trees

For younger trees, only three or four bare branches are visible, while for more severely affected trees, nearly all the foliage has disappeared. Others are half-rotted and cut in two, dead. Dondaine picks up a large branch that has fallen to the ground. "It weighs almost nothing, it's completely dry," he shows.

Disease spreads through wind and spores

The disease was first identified in France in 2008 in the Haute-Saône department. Five years later, the entire Aube department was affected. This invasive disease from Asia is carried by the fungus Chalara fraxinea and spreads through the wind.

Spores travel far and infect trees

Epidemiologist Benoît Marçais explains that "its spores can travel 60 km per year." The fungus installs itself and germinates in the leaves of the trees, then progresses into the branches. Experts observe leaf wilting, branch necrosis, and the death of the branch, or even the tree.

Ash trees are vital to the ecosystem

The situation is grim: in Côte-d’Or, ash trees provide shade for livestock, border and stabilize riverbanks, populate forests, and line small hiking trails or village squares. Dondaine observes the base of two trees, this transition area between the trunk and the root system.

Root damage leads to tree collapse

On one side, a fifty-year-old alder has a beautiful intertwining of roots, submerged in cool, shaded water. On the other, the base of the neighboring ash tree has only a small tuft of dry, short roots. The rootlets, the small extensions that anchor the tree to the ground and absorb essential nutrients, have disappeared.

Ash trees lose their ecological role

Dried out and without roots, the ash tree can no longer stand and could fall over at the next gust of wind. Under the thick root mat of the alder, fish and crayfish hide. The ash tree's roots do not even touch the water. "The rootlets also have a self-purification role," explains the technician.

Tree loss increases flood risk

Along the riverbank, "the vegetation also has a landscape role, a habitat for birds, and even produces berries and firewood." In the region, ash trees form long ribbons along the banks of roads and along the Seine, the Laignes, or the Ource. "Where you only have ash trees, it will be lunar," continues Dondaine.

Funding cuts affect riverbank management

Since two years, the Epage no longer takes charge of maintaining the vegetation along the riverbanks. "Until the 2000s, all watercourse maintenance work was funded by water agencies at 80%." Until 2024, the funding was still assured up to 40%.

Local efforts to manage the crisis

The twelfth program of the water agency has cut this, so now it is up to the owners or the local authorities to put their hands in their pockets. The bill can be steep, especially when a farmer owns several kilometers of rivers and dozens of trees.

Communes face management challenges

The same applies to the communes, often large and sparsely populated, with limited budgets. On the watershed where Epage Sequana intervenes, "there are 162 communes, for 28,000 inhabitants!" About thirty kilometers from Châtillon-sur-Seine, the commune of Les Riceys is proactive.

Communal action shows progress

Crossed by the Laignes, it has requested the counting of dead or fallen trees on the river and warned each owner. In 2022, the result was unambiguous: on the commune, 150 ash trees were on the ground and many others were dead.

Restoration projects aim for resilience

In Vix (Côte-d’Or), Epage Sequana is finalizing the restoration of a resurgence of the Seine, where the riverbanks have been reworked. Sick trees have been cut down and the diversification of species has been favored. Technicians have even deployed long ribbons to prevent cormorants from nibbling trout during their breeding season.

Disease spreads beyond France

The north, the Marais poitevin, and Great Britain are also affected. Like most fungi, Chalara fraxinea favors wet areas (where it develops) and windy areas (where it spreads). As a result, northern France and Great Britain are also affected.

Economic and ecological costs are high

In some areas of Hauts-de-France where ash trees represent 40% of the species, the disease is spreading rapidly. In 2017, the ONF took the initiative to close five affected national forests (Boulogne, Desvres, Hardelot, Vimy, and Nieppe).

Restoration is long and expensive

It took nearly a year to secure access before they could be reopened. The restoration project will take twenty years, for a budget of 20 million euros. The disease also affects the ash tree, an emblematic species of the Marais poitevin, where nearly 400,000 trees are threatened with disappearance.

Efforts to combat the disease continue

Planting campaigns are organized to counter the inevitable degradation of the natural park. The fight against chalara is also very costly. In Great Britain, the fungus would cost over 550 million pounds sterling (over 650 million euros) each year.

Hope lies in resilience and biodiversity

Fortunately, a few ash trees resist the disease. But it will take many decades before they take over. "The whole challenge is therefore to support them," says Benoît Marçais. It will also be necessary to reduce the density of sick ash trees to slow the infection within the stands and, of course, to promote biodiversity.