Comparative Study of Perennial Mixtures on Sheep's Wool-Coir-Vegetation Mats versus Sedum in Carbon Sequestration and Cooling Effect of Green Roofs

Urban areas characterised by high population density often lack sufficient green spaces, which diminishes their ecological and climatic benefits. Green roofs as additional ecosystems can make a positive contribution to the urban climate. In Germany, extensive green roofs, which are usually characterised by Sedum vegetation, are predominantly used. Sedum is suitable for sunny and semi-shady locations, requires low-maintenance and needs few nutrients and water. However, the urban climatic effect of Sedum is low. In this study, sheep's wool-coir-vegetation mats (SW-C-VMs) pre-cultivated with a perennial mixture was compared to a conventional Sedum vegetation using the example of Berlin (Germany). The perennial mixture showed a 7 times higher carbon sequestration than the Sedum vegetation. Due to the good water storage and fertilising effect of the sheep's wool, the perennial mixture did not need to be irrigated or fertilised and was self-sustaining on the green roof. The temperatures on the surface of SW-C-VMs with perennial mixture and at a depth of 0.1 m in the substrate were significantly lower and more balanced in summer than on the substrate surface and at a depth of 0.1 m in the substrate of the Sedum vegetation. On days with high air temperatures, the maximum temperatures on the SW-C-VMs with perennial mixture were up to 17.0 K lower than on the substrate surface of Sedum. In future, SW-C-VMs with a perennial mixture are recommended for semi-shaded green roofs and are preferable to Sedum.