The Eurasian spruce bark beetle: The role of climate

The Eurasian spruce bark beetle is one of the major forest pests in Europe, capable of mass attacking and killing Norway spruce over extensive areas during outbreaks. Here, we review various aspects of its biology in relation to climatic variables. The aim of this review was to make predictions about the potential consequences of climate change on the propensity for outbreaks across European forests. More frequent extreme winds and drier and warmer summer climate may trigger both population growth and the susceptibility of spruce stands to attack. Breeding material provided by large windfall events increase the beetle population rapidly to a level capable of killing living trees through mass attack. Such epidemics may proceed until the susceptible spruces are exhausted, or when other extrinsic conditions stop the bark beetles from further colonization. At the southern margin of the spruce distribution in Europe, lower than average precipitation seems generally to favour infestations. In central and Western Europe, even-aged plantations outside the natural range of Norway spruce are highly susceptible to disturbance events such as windthrow and bark beetle attacks. A warmer climate is expected to give a northern expansion of the area experiencing two generations per year in Europe. There have been few bark beetle outbreaks in the extensive areas of spruce forest in Finland and the northern part of Scandinavia, but increasing bark beetle populations and infestations have been observed during warm years in the last decade. The northern part of Europe may be subject to huge outbreaks if a warmer climate increases the population sizes of the Eurasian spruce bark beetle.