Forest Characteristics determining probability and magnitude of spruce bark beetle damage in forest stands

Spruce Bark Beetle ( Ips typographus L.) is a notorious pest of spruce forest. In the recent decades the damage by the species has increased as a result of the increase of use of spruce in plantation forestry and changes in the climate. Management of spruce forest needs to be adapted to reduce the susceptibility to spruce bark beetle outbreaks. Climate change will result in more frequent extreme events, like severe drought and windfellings, increasing the possibility of large amounts of stressed, weakened or dying trees in the landscape. In order to support decision making Nordkvist et al (2023) developed a susceptibility index that can be used to compare stand management options for susceptibility to spruce bark beetle. This study evaluates probability of attack and magnitude of damage using forest characterisation as commonly used in the (Swedish) forest industry. The data is used to calculate and assess the index values in the context of incurred damage (probability and magnitude). The study finds that volume of spruce (m 3 h -1 ) and average stand size are the strongest predictors for probability and magnitude of damage. Magnitude of damage is also affected positively by stand density and negative by volume of broadleaves. The index values explain both observed probability and magnitude of damage.