Natural Forest Reserve
Primaeval beech forest
With an area of around 970 hectares, the Sihlwald is the largest natural forest reserve on the Central Plateau. Rare species, ancient trees and fungi thrive here. Most of the natural forest is a mixed beech forest, which originally covered around 80 per cent of Central Europe.
The Sihlwald is a rare example of a large, primaeval mixed beech forest on the Swiss Plateau. For around a quarter of a century, it has been allowed to transform itself back into a wilderness. Gradually, it is taking on the characteristic features of a European primaeval forest, as it still occurs mainly in the Eastern European Carpathians.
Primeval forest or natural forest?
A Primaeval Forest is a forest that has been untouched and uncultivated by human influence. This is not the case with the Sihlwald. It was actively utilised as a commercial forest by the city of Zurich from the 14th century onwards. It was not until the year 2000 that it was no longer used. Logging stopped here. Since then, nature has been left to its own devices. The Sihlwald is therefore what is known as a Secondary Forest, which can regenerate naturally after human intervention.
A Natural Forest on the other hand consciously promotes this process, with the life cycle in a mixed beech forest lasting 500 to 800 years. At the beginning, species diversity may temporarily decline if habitats are destroyed or displaced, e.g. by a bark beetle infestation.
At an advanced stage, natural forests are characterised by a lot of dead wood: fallen trees, broken branches, perforated trunks as well as fungi, beetles, and microorganisms that decompose the wood. Different stages of decomposition promote biodiversity. Natural forests ensure the survival of rare species, provide diverse habitats and strengthen biodiversity. Natural forests are an investment in the future. They offer many different habitat structures and ensure the survival of rare animal and plant species. In this way, they promote biodiversity.
Deadwood and biodiversity
Process protection applies in the Sihlwald. This means that the forest is allowed to develop mainly free of human influence. The slow return to a natural cycle is now clearly evident: various very rare or even extinct species of fungi, lichens, mosses and beetles have been discovered. Some of these are considered Urwald relict species – meaning that they only occur in forests where the natural cycle is still intact and where there are large quantities of dead wood.
Triggered by extreme events such as heavy rainfall, dry periods, heat and subsequent bark beetle infestations, the volume of deadwood in the Sihlwald has increased significantly in recent years. In contrast to conventional commercial forests, the Sihlwald has a very high habitat structure density. The above-average number of giant trees is also a special feature and indicates a high level of biodiversity.
