The Mechanism of Tree Die-Off Caused by Armillariosis and Bark Beetles in Boreal Forests

Abstract Armillariosis is a root disease that causes tree mortality and is caused by certain fungi of the genus Armillaria (basidiomycetes). As this pathogen remains hidden in the soil and within the roots, only the symptoms of the disease are visible – reddish-brown crowns and dying trees. However, these are merely symptoms of dieback and do not indicate the cause, as similar symptoms can be triggered by various factors such as needle diseases, browsing by wildlife, or drought. The situation becomes more complicated when a tree weakened by drought, such as a spruce, comes into contact with the Armillaria pathogen (e.g. Armillaria ostoyae ) and is subsequently infested by the bark beetle Ips typographus . The aim of this study is to explain the mechanism of tree dieback involving drought and dying mycorrhizae, Armillaria infection, and I. typographus infestation, as examples. Information © The Authors 2026