Increasing the resistance of Mediterranean extensive green roofs by using native plants from old roofs and walls

Background: While the use of extensive green roofs (EGRs) is increasing worldwide, Mediterranean conditions complicate EGR design due to their long, dry summers with intense solar radiation. Aim: To inform sustainable EGR design for Mediterranean regions, we explored the use of resilient, drought tolerant species in experimental EGRs. Methods: We selected four native species that are known to spontaneously establish themselves on urban structures, including roofs, in Lisbon, Portugal: Antirrhinum linkianum, Asphodelus fistulosus, Centranthus ruber, and Sedum sediforme. We evaluated growth and aesthetic value under two irrigation treatments (100 and 60% ETo, reference evapotranspiration). The presence of moss covering for the lower level of irrigation was also evaluated. Results: Antirrhinum linkianum presented the highest number of flowers, most extended seed production duration, and the highest area coverage. Irrigation level did not significantly affect flowering and green coverage for any of the species. Conclusion: Antirrhinum linkianum is an ideal starting species for Lisbon EGRs. Irrigation costs can be reduced by starting at a 60%ETo irrigation level.