Thielenbruch und Thurner Wald, Nature reserve in Dellbrück district, Cologne, Germany

Thielenbruch und Thurner Wald is a 59-hectare nature reserve in Cologne's Dellbrück district, on the western edge of the Paffrather Kalkmulde between the Mutzbach and Strunde streams. It holds the region's only surviving calcareous fen, fed by limestone springs near the Katharinenkammerweg, next to a purple moor-grass meadow. Alder carr woods stand by the water, drier ground carries oaks and birches, and elsewhere are reed beds, willow scrub and a transitional bog with quaking Sphagnum. The S11 railway, a gas pipeline, a high-voltage line and the Paffrather Straße cut through it.

The Thurner Wald section was designated a nature reserve in 1969, covering 59.00 hectares between the Bergisch Gladbacher Straße, Duckterather Weg, Katharinenkammerweg, Heinrich-Strünker-Straße and Waltherstraße. It lies on the western edge of the Paffrather Kalkmulde, between the Mutzbach and Strunde streams. Together with parts of the adjacent Thielenbruch reserve in Bergisch Gladbach it forms the FFH area Thielenbruch (DE-5008-301).

The reserve lies on the Bergische Heideterrasse at the western edge of the Paffrather Kalkmulde, between the Mutzbach and Strunde streams. Its eastern side, near the Katharinenkammerweg, holds several limestone springs that feed the only preserved Kalkflachmoor (lime-rich flat fen) in the whole region, next to a Molinia meadow. Visitors can look for the Helm-Azurjungfer damselfly and the Sumpf-Stendelorchis orchid.

The area is accessible via several marked walking paths and visits are best during early morning or evening hours when wildlife is most active. Sturdy footwear is recommended since the ground can be muddy and uneven in wetter sections.

The reserve shelters 12 dragonfly species, among them the Helm-Azurjungfer (Coenagrion mercuriale), a damselfly dependent on the calcareous spring-fed fen near the Katharinenkammerweg. This small fen is the only preserved Kalkflachmoor of its kind in the region, which is why the insect survives here.