The bark beetle - a piece of the puzzle in the natural forest cycle

The clearly visible infestation of spruce trees by the bark beetle begins with bore dust at the base of the trunk and holes in the tree bark - the spruce bark beetle, the most widespread bark beetle species, is almost always at work. It attacks spruce trees that have been weakened by storms or have just fallen. The beetle and its larvae feed in the sap-bearing part of the bark, the so-called bast. This makes it more difficult for the tree to transport nutrients. Because the spruce bark beetle reproduces very quickly, infested spruce trees have no chance of surviving. Shortly after the infestation, the first pieces of bark lie on the ground and the crowns turn brown. Pale green spruce needles fall to the ground. Dying trees - and at the same time a new habitat for plants and animals. The dying spruce trees suddenly bring light down to the ground in previously dark locations. Young trees that were previously in the shade move towards the light. Pioneer species such as elder, birch and willow begin to grow in larger areas. A new generation of forest emerges.

The bark beetle plays an important role in the natural forest cycle: it starts the natural cycle of decay and growth. In the Sihlwald, this development is left to nature. As part of the so-called process protection, those tree species that are best suited to the location and local conditions at that moment grow on the newly created areas. "Bark beetle infestation is a natural method by which the Sihlwald is transformed over decades into a unique mosaic of different tree species and tree generations," explains Isabelle Roth, Deputy Managing Director and Head of the Natural Forest Division at the Zurich Wilderness Park Foundation. The bark beetles and the associated death of the spruce trees are therefore part of a long process that the Sihlwald is undergoing on its way from commercial forest to natural forest.

In the Sihlwald, natural processes can and should take place undisturbed. For the primeval forest, the death of the spruce trees means a change in the composition of tree species. In addition, new deadwood habitats are created for countless beetles, fungi, mosses and lichens. The bark beetle is also a source of food for other forest animals. It is a popular food source for woodpeckers, ichneumon wasps and beetles.

In commercial forests, spruce infestation by bark beetles means a financial loss for forest owners. The owners try to limit the increase in the beetle population by felling trees with additional debarking. This management is also implemented at the edge of the Sihlwald Nature Discovery Park.

The spruce is originally a mountain tree that prefers a damp and cool climate above 800 meters above sea level. The conifer grows faster than other tree species. For this reason, and because spruce wood could be harvested for a long time to cover costs or even make a profit, forest owners and foresters planted the tree far beyond its natural range in the Swiss Plateau.

Information:
Monday, September 16 from 3 to 5 p.m., Isabelle Roth, Deputy Managing Director and Head of the Natural Forest Division, tel. 044 722 55 22 (head office)