Mediterranean open habitat vegetation offers great potential for extensive green roof design

• Four vegetation types with distinct climatic, geographic and soil-related properties.
• 79% of the Mediterranean species list comprise a potential source for urban greening.
• Major life forms in NW European green roof list are hemicryptophytes (75.5%).
• Besides succulents, a mixture of different life forms is an interesting option.
• Annuals can improve green roof performance and should certainly be considered.

Offering a wide array of benefits, green roofs have become an important tool for improving urban environmental quality mainly in regions with a temperate climate. However, green roofs seem to perform relatively bad in the Mediterranean, as plant species commonly used are often not adapted to cope with the additional stress factors associated with this climate. The habitat template hypothesis states that potential species can be found in habitats with similar conditions as on extensive green roofs. In this study, natural open habitats in southern France are described and variation in species composition in relation to environmental factors is analyzed. 372 local species recorded in 20 locations were grouped in four major vegetation types. These results are compared with a list of species commonly used on green roofs in NW Europe. 79% of the species found in these open habitats are currently not used on green roofs. Ten highly relevant plant traits for extensive green roofs were then used to screen the species found during the field work. 28 species scored highly in this screening procedure, indicating good potential. Annual species are currently rarely regarded for green roof purposes but in the habitat template context, this life form is an important part of Mediterranean vegetation and should be considered in green roof design. This research offers the ecological fundamental knowledge necessary for further selection and testing of species and final implementation into a successful green roof system.