35 Bilstein and Rosenberg

Just outside the walls of Bilstein Castle in Olpe, the virgin forests of future are growing – the old stock of oak and beech trees is a designated wilderness forest.

Bilstein Castle (Antonius Klein)
Bilstein Castle (Antonius Klein)

Virgin forest and wilderness forest surround the castle

Bilstein Castle is conspicuously perched high above the Veischede Valley. Once the seat of the noble lords of Gevore and later the first administrative headquarters of the District of Olpe, which was founded in 1817, it is today one of the most popular youth hostels in Westfalen-Lippe. The castle is situated on the flank of the Rosenberg Mountain, whose old deciduous forests are preparing to become a "primeval forest of tomorrow". Since 1976, no management measures have been carried out in a 14.7-hectare area of natural forest. In 2013, another 44.5 hectares were designated as wilderness forest and thus also taken out of use. A 5.1 km-long circular path leads you through the area.

Geology in connection with forest communities

The rock on which the castle stands is of volcanic origin. In contrast, the slopes of the Rosenberg consist of clay, silt and sandstones, which are partly calcareous. The nature reserve therefore holds not only the widespread species-poor Woodrush-Beech Forest community, but also more demanding forest communities such as the Millet Grass-Woodrush-Beech Forest and Sweet Woodruff-Beech Forest. Although the latter community is more or less limited to the surroundings of small springs, the Millet Grass-Woodrush-Beech Forest is found mainly along the ridge of the Rosenberg and on the adjoining northern slope with its fresher soils. Here the range of nutrient-demanding plant species stretches from Wood Anemone and Millet Grass to Yellow Archangel Nettle and True Oxlip. Here, the Sycamore is a constant companion of the Beech.

Oak contra Beech

Old records and studies prove that the old-growth Beech trees of the Rosenberg are 157-176 years old, while the oldest oak trees are as much as 200 years old. "Can the oak assert itself against the beech under the climatic conditions of the Südsauerland mountains, at least on steep southern slopes, without human intervention?" That was the forestry-science question that arose in connection with the designation of the natural forest "Under the Rosenberg". Today, after just 40 years of systematic observation, it can be clearly stated that under the current climatic conditions the Oak has no chance to assert itself against the Beech in a significant proportion of the area; not even on south-facing slopes. Whether climate change will alter that remains to be seen. However, more important from today's perspective than the answer to that forest-science question is the fact that those 40 years of "doing nothing" in a comparatively modest area have played a key role in recognizing the importance of undisturbed forest development for habitat and species protection. In line with the increase in old and dead wood, there is a steady rise in the number of insects and other arthropods that are specially adapted to these habitats. Also in the case of fungi, the development is still in its infancy.

On the northern slope, a small stream valley is absolutely covered with Wild Garlic, and the Coralroot Bittercress – a plant which normally colonizes the higher altitudes of low mountain ranges – occurs repeatedly here in small stands, sometimes directly alongside the path.

Special bird species populate the ancient forests

While the Stock Dove, Great Spotted Woodpecker and Black Woodpecker are long-established residents of old-growth forests, the rare Middle Spotted Woodpecker is a recent addition. As a typical "picking woodpecker" it prefers rough-barked trees and is therefore normally regarded as a species of Oak forests. However, as the older Beech trees gradually get a more richly-structured bark, they clearly become more able to meet the habitat requirements of the Middle Spotted Woodpecker.

Contact: Kreis Olpe, Untere Landschaftsbehörde