Evaluation of the development of five Sedum species on extensive green roofs in a continental Mediterranean climate

Because of their easy implementation and low maintenance, extensive green roofs have become established during the last few decades as one of the best options for integrating vegetation on the built environment. The success of these systems involves having of a plant species palette well adapted to extreme conditions, especially in drought environments. Among the available ones, the Sedum genus has stood out due to its tolerance to climate extreme conditions and its use has been widespread throughout the world. In previous research, efforts have been mainly concentrated on selecting the most drought tolerant Sedum species, without considering other important parameters for the suitable provision of ecosystem services from the green roof, such as coverage capacity, shape and structure or growth strategy, among others. In this study, five species of Sedum (Sedum album, S. sediforme, S. sexangulare, Sedum spurium cf. oCoccineum' (syn. Phedimus spurius cf. oCoccineum') and Sedum spurium cf. oSummer Glory' (syn. Phedimus spurius cf. oSummer Glory') were tested in a dry continental Mediterranean climate with the aim of observing their patterns of growth and development. Results revealed that Sedum album, S. sediforme, S. sexangulare are recommended species for their use on extensive green roofs in this climate, whereas both varieties of S. spurium, particularly var. "Coccineum", present some limitations for their use, basically due to their shape, plant structure, pigmentation and lack of adaptation to winter conditions. Shape Index could be an adequate tool for decision-making in the selection of plant species in the design of green roofs because it provides information not only about the shape and size but also related to the growth strategy of these plants.