Joint efforts to bring ash back to Nordic and Baltic forests

Only about 1-2 percent of the ash trees in the wild seem to possess some degree of resistance to the invasive pathogen causing ash dieback.

Text: Mats Hannerz Scientific contact: Mateusz Liziniewicz


A joint SNS-supported project has established a series of trials with selected healthy ash trees across Norway, Sweden, Denmark and Lithuania. The aim is to speed up the genetic breeding of ash, and thereby provide a bank of tested trees that is tolerant to the disease.

Resistant and non-resistant ashes. Photo: Michelle Cleary

In nature, healthy ashes can be found side by side with trees attacked by the fungal pathogen Hymenoscyphus faxineus, which is causing the ash dieback. Selection and testing of ash trees have shown a large genetic variation in susceptibility to the disease, and a great potential for breeding. The need to bring back ash to the wild is urgent. The species, once a common tree in the Nordic-Baltic deciduous forests, is home to hundreds of organisms depended on ash, and it is a keystone tree species in many habitats.

The new series of trials, established in all the four involved countries, is based on already selected, screened and phenotypically defined trees from the wild. It will allow a strong forward selection of healthy offspring, thereby creating a second-generation population of ash trees with a higher tolerance to ash dieback. Since trials are spread among the countries and in their natural environment, offspring from the mother trees will be well adapted to their local conditions.

The trials will provide strong support to bring the ash back to the Nordic-Baltic forests. They will also be valuable for future research on genetic diversity and resistance to new threats and diseases. For example, the emerald ash borer (Agrilus planipennis) that is spreading east in Europe, can become a new problem for the ash forests. To be prepared to combat such threats, transfer of knowledge and genetic sources is necessary. The trial series provides such a preparation.


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