The warm weather last week was the starting point for this year’s spruce bark beetles. Now they begin to swarm and lay their eggs under the bark of the fir trees.
Last year, forest owners in Sörmland were hit the hardest, but when the fir is removed, new forests are planted with both hardwoods and conifers.
In the vicinity of Bettna in Sörmland, Johan Nilsson runs forestry. He stands by a clearing and shows where he and his father planted spruce thirty to forty years ago. Now every single fir has been removed after massive attacks by the spruce bark beetle in recent years.
– It feels frustrating, and is also a feeling of powerlessness, you have no control. Everything I had planned for my time on the farm has been overturned, because I have been ruled by an insect.
Financially, the attack has led to SEK 250,000 less income last year than expected for Johan Nilsson.
Last year, the spruce bark borers destroyed five million cubic meters of spruce in Sweden, and the hardest hit were Sörmland and Örebro. The figure can be compared to the large forest fires in the summer of 2018, which destroyed two million cubic meters.
Likes stressed firs
The spruce bark holes are so small that they are barely visible. They are attracted to spruces that are exposed to stress, such as drought, and make their way under the bark where the females lay their eggs. When the new spruce bark beetles hatch, they eat the inner bark of the spruce. The tree tries to defend itself by secreting resin, but when there are thousands of bark beetles in the tree, there is a great risk that the tree will die.
– We think it will be a difficult summer, says Erik Waltersson at Mellanskog, who is an adviser to affected forest owners.
The food – and the spruce barker – are running out
A really cold summer would dampen the spruce bark beetles. But there are other solutions as well. One is not to plant spruce on dry land, which was done on a large scale in the 1970s. Another is that forest owners do not invest unilaterally in spruce.
– There will be much more mixed forests now, and pine and fir are planted in the right place. And there will be more deciduous trees on these lands, says Erik Waltersson.
But eventually, when the spruce bark beetles have killed all the large, older spruces, they will not survive any longer, because then there is no food for the larvae.
– In a few years’ time, they will have cut off the branch they are sitting on, believes Erik Waltersson.