Climate change increases the risk of damage caused by the European spruce bark beetle

The risk of considerable spruce bark beetle damage has also increased in Finland because of climate change. A warmer climate improves the living conditions for spruce bark beetles. To date, only local damage has been seen here, but even such damage can be financially significant to individual forest owners.

The Forest Damages Prevention Act obligates forest owners to remove fresh coniferous timber with bark from the forest within the period specified. Trees felled by a storm must also be removed from the forest if they account for more than 10 cubic metres per hectare.

Under the Forest Damages Prevention Act, spruce timber with bark must be removed from intermediate storage by 15 July in area A of southern Finland, by 24 July in area B of central Finland and by 15 August in area C of northern Finland.

The purpose of the act is to prevent damage, and its provisions must be taken seriously. In the worst case, failure to comply with the obligations provided for may lead to liability for damages if the spread of spruce bark beetle can be verifiably traced back to a specific forest.

Climate change favours the spruce bark beetle

Climate change is making Finnish weather conditions more favourable for the spruce bark beetle. Hot and dry summers cause stress to trees, while an unfrozen ground especially exposes spruce, which has shallow roots, to storm damage.

However, climate change may also improve the living conditions of the nun moth’s natural enemies. One of these is the ant beetle, which lives in dry standing spruce trees. This is why you should leave individual dry standing spruce trees in the forest. Natural enemies alone are not enough to control the spruce bark beetle; the epidemic will end when the beetle runs out of nourishment.

In recent years, Finnish forests have mainly been renewed with spruce. However, because of the risk posed by the spruce bark beetle, spruce trees should not be planted in very barren areas. Instead, a mixed forest may protect spruce trees from the beetle. In a mixed forest, the distance between spruce trees is longer than in a pure spruce forest, making it more difficult for the spruce bark beetle to find a target.

How to recognise the damage caused by the spruce bark beetle

  • Damage caused by the spruce bark beetle is easiest to detect in early June. Focus your attention on the base of spruce trees and look for small, round holes and sawdust of a light coffee colour.
  • Locations that are particularly exposed include sun-drenched forest edges bordering regeneration areas, where trees suffer from light stress.
  • Old spruces in poor condition are also at risk, and their renewal should be seriously considered.
  • The condition of spruce tops serve as a good indicator for assessing the risk of spruce bark beetle. If top growth is good and the needles generally dense, the forest is fine.

Photos: Natural Resources Institute Finland

Brown dust at the base of the tree and loose bark are a sign that the spruce bark beetle has attacked the tree.
Gallery patterns of the spruce bark beetle.