Hopes that the wet spring in Germany has damaged the spruce bark beetle are fading. The pests are multiplying rapidly and it has become a real problem.
In recent years it has already caused billions in damage and now the spruce bark beetle is on the rise again, as reported from many places including Bavaria. "The cool and wet spring has not brought the relief that was hoped for," says Andreas Hahn, head of forest protection at the State Institute for Forestry (LWF) in Freising: "It's at least as strained as in previous years."
The danger of spruce bark beetles: They lay their eggs under the bark. When the larvae hatch, they eat the main layers of the tree and destroy its lifeblood. The animals benefit from global warming: according to Hahn, there used to be an average of 1.5 beetle generations per year. Now there are two to three. At the same time, trees are suffering from drought, making it harder for them to survive an infestation of spruce bark beetles. The damage is enormous; in 2022, many infested trees had to be felled.
Trees felled due to insect infestations are four times as many as ten years ago
In 2022, the Federal Statistical Office estimated that insect damage accounted for four-fifths (81.4 per cent) of the harvesting of damaged timber in forests. This is a new record and represents a fourfold increase over ten years. Damaged timber refers to trees that are felled prematurely, for example due to disease, pest infestation or storms.
In 2022, a total of 50.5 million cubic metres of wood was felled in German forests due to forest damage. Insect damage accounted for 41.1 million cubic metres of the damaged wood. Almost exclusively conifers such as spruces and pines were affected.
Gigantic growth: each female bark beetle has laid up to 300 eggs since May
The first beetle generation of the year is about to swarm out to bore into the bark of new trees and lay lots of eggs. "The warmer it is, the faster they develop," Hahn explains. Franconia and parts of Lower Bavaria are particularly affected, as shown by LWF bark beetle monitoring. Using data from bark beetle traps and the propagation forests laid out, forest owners can see how often they should check their trees.
In southern Bavaria, too, a remarkably large number of spruce bark beetles had fallen into the traps at two-thirds of the sites. These are bark beetles from last year that survived the winter. According to the expert, they have been able to lay eggs twice since May - 80 to 150 per female. And their offspring are now laying eggs again - an exponential growth.
Concerns for the forest: bark beetles also in higher mountain areas
Other German states are also sounding the alarm: "In the still green forest districts of the Harz, the alarm has now gone red and we are intensifying control measures," said a young forester from Lower Saxony in a press release. In the Harz, the spruce bark beetle in particular has destroyed around 80% of spruce forests over the past six years.
Foresters and forest owners in Saxony are very concerned as the spruce bark beetle is spreading to higher and higher altitudes. "So far, mainly mountainous and hilly areas up to 400 metres as well as medium-altitude areas up to 600 metres, for example in Eastern Saxony, Oberlausitz, Zittauer Gebirge and Sächsische Schweiz, have been affected," says Renke Coordes, spokesperson for the Saxony Forests. There are now also increasing reports of damage in low mountain areas above 600 metres in the Vogtland and Westerzgebirge.
Current claims at historically high levels
For the past five years or so, forests in Saxony have found it increasingly difficult to resist the massive spread of these pests. Despite a decline last year, current damage is still "at a historically high level", emphasises Coordes. In some regions, damage had recently been less because the majority of threatened trees - especially spruces - had already died.
According to the experts, conditions at the beginning of the year were initially favourable for stopping the spruce bark beetle. However, after abundant rainfall in March and April, the dry month of May caused drought stress to the trees and weakened them significantly.
A more accurate forecast of damage development this year is not yet possible. It largely depends on the continuation of the weather and the effectiveness of countermeasures, Coordes explains: "A dry, hot summer could lead to high spruce bark beetle population densities causing damaged wood figures to rise again." Forest owners are urged to check their forests for new infestations now, and to quickly remove affected trees from the forest or render them harmless, he adds.
