Bark beetle surge threatens spruce forests in Ostrobothnia after storm damage

Storm-felled spruce trees in Finland’s Ostrobothnia region have created ideal breeding grounds for the destructive spruce bark beetle, with monitoring traps showing a threefold increase in beetle numbers compared to last year, Yle reports.

The Hannes storm that struck around Christmas 2025 downed an estimated 500,000 cubic metres of timber in Ostrobothnia, primarily in coastal areas north of Pedersöre and southern parts of Kristinestad. The fallen trees now risk accelerating beetle infestations unless removed before the insects’ swarming season begins.

Pohjanmaa Forest Management Association has cleared 37,000 cubic metres of storm-damaged wood so far, but field supervisor Jami Pirttimäki notes this reflects only part of the effort, as private landowners and other operators have also been working to remove vulnerable trees. “The numbers we report are just what the association has handled,” he said.

Monitoring traps in Kruunupyy, Närpiö, and Mustasaari—each with three traps emptied four times between spring and summer—revealed over 1,600 live beetles in Mustasaari’s May collection alone, triple the count from the same period last year. While below the 15,000-beetle risk threshold set by the Natural Resources Institute Finland (Luke), the rise signals growing pressure.

The beetles target living or recently fallen spruce, using pheromones to coordinate mass attacks that can kill healthy trees within weeks. “One beetle won’t fell a spruce, but when they swarm the same tree, it’s overwhelmed,” Pirttimäki explained. Warmer winters and climate change further favour their spread, though Finland has yet to see the large-scale damage observed in Central Europe.

Authorities urge landowners to inspect forests regularly for yellowing crowns or needle drop—signs of irreversible infestation. “Fancy maps and software help, but the best tool is still putting on your boots and walking the woods,” Pirttimäki advised. The Forest Centre has also mailed risk alerts to affected property owners, using aerial imagery to identify high-risk zones.