Choosing perennial plants for extensive green roofs in a semi-arid climate

Abstract

Abstract The main challenge in establishing and maintaining shallow, extensive (non-irrigated) green roofs in semi-arid climate is plant selection. The chosen species should cover the roof and remain green all-year round and at the same time to survive the long, hot and dry summer in this harsh microhabitat. Three perennial species were selected for the present study conducted on a green roof at Haifa University, Israel: Sedum sediforme, Carpobrotus edulis and Portulacaria afra. These succulents were planted in non-irrigated plots, in a 17 cm deep substrate that consisted a mixture of 90% perlite and 10% compost. All three species have survived two consecutive summers and manifested notable spreading ability. Their groundcover area has increased between 3-5 times during the 18 months monitoring period of this study. These results suggest that they are suitable for the design of extensive green roofs in the semi-arid areas of Israel. Two additional species Aptenia cardifolia and Malephora crocea showed varying results, but nevertheless should be regarded as reasonable candidates. In contrast, ten other perennial plant species that were tested in the same conditions did not survive the dry summer. The results suggest, that a main factor of extensive green roofs design in semi-arid areas is species selection, namely identifying, choosing and monitoring of the fittest plant species for this harsh microhabitat.