Is the Ash Rising from the Ashes?
Ash trees are dying across our country, but there is hope. Healthy individuals showing resistance to ash dieback are being collected and broadly tested.
Ash dieback reached Sweden in the early 2000s, and since then it has caused widespread mortality among European ash (Fraxinus excelsior) throughout the species’ distribution in the country. The situation is similar across all European nations. The disease is caused by the fungus Hymenoscyphus fraxineus, introduced to Europe through the global plant trade from Asia. In its native range, Asian ash species are resistant to the fungus, as both organisms have co-evolved over time.
Infection
The fungus spreads by wind. Spores are produced by fruiting bodies that develop in the spring on fallen leaves from the previous year. New infections occur via leaves and petioles. From there, the fungus spreads into the tree’s phloem and xylem. The infected tissue dies, disrupting water and nutrient transport, which causes dieback of the parts of the tree located above the infection site.
Typically, the trees respond by producing new shoots from epicormic (dormant) buds located below the point of infection. Repeated annual infections lead to a bushy growth form and, ultimately, the death of the tree.
