Evaluation of Mediterranean perennials for extensive green roofs in water-limited regions: A two-year experiment

Extensive green roofs (EGRs) play a crucial role in urban environments, offering numerous environmental, economic, and social benefits. However, their performance largely depends on plant selection and adaptation to local climatic conditions. This study investigates the suitability of six perennial Euro-Mediterranean species for EGRs in Mediterranean and semi-arid regions, under different water regimes. A two-year experimental analysis was conducted in Rome (Italy) assessing flowering and mortality rates. Results revealed species-specific responses to irrigation levels, with notable performances observed in Thymus serpyllum, Saponaria ocymoides, and Teucrium chamaedrys, showcasing resilience to water stress. Conversely, Lavandula stoechas and Cerastium tomentosum exhibited sensitivity to water availability, emphasizing the importance of species selection for EGRs. No species completely adhered to the expected flowering period, but showed a general tendency of anticipation, and sometimes an extended flowering period, with some differences between the species. The study underscores the complexity of plant-environment interactions and highlights the need for diversified species composition to enhance EGR functionality and resilience.