Invasion of black cherry and spiraea
During the Middle Ages the bogs close to the Danevirke were drained and turned into grassland. The introduction of modern agricultural-techniques destroyed previously common habitats. These habititats, however, managed to persist at special locations such as the Danevirke, although they have suffered recently from increasing atmospheric nutrient input.
This has caused plant populations to become relatively old. Losses in their biodiversity can also be observed due to sensitive species being replaced by species-poor grass communities, which are more competitive. Fast growing invasive species such as the black cherry and a spiraea species are another threat to native species.
Protection measures encompass regular mowing and adjusted grazing schemes by goats and sheep to be able to preserve the habitats occurring at the Danevirke.