Bullensee, Nature reserve in Kirchtimke, Germany

Bullensee is a drained raised bog with a single lake set into its eastern edge, southeast of Ostertimke on the Stader Geest. Peat cutting has left water-filled hollows across the bog, which is covered by moor forest of bog birch, sand birch and Scots pine. The lake cuts into mineral ground in the east and is silting up from its west bank.

The area was first protected as a nature reserve on 4 December 1937; a larger reserve of 32 hectares followed on 16 December 1983 under the code NSG LÜ 027. On 1 October 2018 it was merged with the neighbouring Hemelsmoor reserve to form "Bullensee und Hemelsmoor". Peat cutting had earlier drained and hollowed the raised bog, and the flooded peat pits now carry renewed bog vegetation.

The name Bullensee refers to the lake on the eastern edge of the former reserve, which gives the protected area its name. The surrounding drained raised bog was heavily pitted by peat digging, and the old peat cuttings have filled with water where raised-bog vegetation is growing again. The bog woodland is dominated by bog birch, sand birch and Scots pine.

The area lies southeast of Ostertimke, bordered to the north by Kreisstraße 111, with the surrounding woods and farmland accessible on foot. The lake fills former peat cuttings and shallows from the west bank, so the wetter ground is best avoided there. The site is now part of the larger Bullensee und Hemelsmoor reserve, where conservation rules apply.

The lake gives the reserve its name and lies at its eastern edge, where it cuts into the mineral subsoil; from the west bank it is silting up, and there the raised-bog vegetation is still relatively vigorous. The surrounding bog was heavily pitted by peat digging, and the old peat cuttings have filled with water where bog plants are returning.