Resistance of ash trees affected by ash dieback and Armillaria root rot to uprooting and stem breakage

Ash trees (Fraxinus excelsior) infected by the fungus Hymenoscyphus fraxineus show crown dieback but may also exhibit basal stem lesions, which are often colonized by secondary fungi. Infected ash trees often have a reduced stability and may be uprooted during a storm. This poses a major safety risk for people and infrastructure. Typically, the uprooted ash trees show only moderate crown damage, while their roots are heavily degraded by Armillaria spp. To better understand the impact of H. fraxineus and Armillaria spp. on the resistance of ash trees to uprooting and stem breakage, non-invasive static pulling experiments are conducted. If possible, simple criteria to evaluate the stability of ash trees in the field will be developed.