Research article Assessing chilling and drought tolerance of different plant genera on extensive green roofs in an arid climate region in Iran Navid Vahdati, Ali Tehranifar * , Fatemeh Kazemi Department of Horticulture Science and Landscape, Ferdowsi University of Mashhad, Iran article info Article history: Received 15 July 2016 Received in revised form 11 January 2017 Accepted 12 January 2017 Keywords: Chilling Drought Environmental stress Plant selection Seasonal response Urban landscaping abstract The harsh and stressful growing environment of extensive green roofs especially in arid environments allows a limited range of plant species to survive. Therefore, achieving plantings to survive in such conditions is a significant challenge. This paper describes an experiment investigating plant selections for extensive green roofs based on chilling (cold season) and drought (warm season) conditions of Iran. Nine species were selected from the three major taxonomic and functional plant groups that are commonly used on extensive green roofs including grasses, groundcovers and sedums. The species namely Agro- pyron cristatum, Festuca aurundinacea, Festuca ovina, Potentila sp., Frankinia thymifolia, Vinca minor, Sedum acre, Sedum spurinum, Carpobrotus edulis were imposed to natural chilling in autumn and winter using a randomized complete block design. For spring and summer, irrigation regimes at levels (48, 72 and 96 h intervals) in a factorial experiment based on a randomized complete block design with four replications were applied. The results showed that Agropyron cristatum, Frankinia thymifolia and Carpobrotus edulis were the best plants from each class. Carpobrotus edulis was the best choice for cold and warm seasons and this was followed by Frankinia thymifolia and Potentila sp. Vinca minor performed well in the cold seasons and Sedum spurinum appeared to be excellent in the warm seasons. The plants of the experiment showed significantly different appearances in different watering regimes. Little differences in drought tolerances were observed among the forbs and grasses, which must be watered during warm seasons. However, the succulents responded very well to the drought and low watering regimes. Overall, suc- culents and groundcovers were considered more appropriate for application in warm and cold seasons, respectively. According to the findings, drought and cold weather conditions cannot be a major obstacle for developing extensive green roofs in Iran if considerations are made on selecting its plant species. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Green roof development is an important strategy which ad- dresses some key urban environmental issues, hence is increasing in cities in recent years. Green roofs can reduce surface water runoff, provide habitats for wildlife, moderate urban heat island effects, improve building insulation and energy efficiency, improve air quality, create aesthetic and amenity values, provide opportu- nities for urban food production (English Nature, 2003; Dunnett and Kingsbury, 2008). Limited water availability, wide tempera- ture fluctuations, high exposure to wind and solar radiation create highly stressed, and sometimes disturbed, environments for plants in these green infrastructures. As a result, a relatively small range of plant species can normally survive in extensive green roofs systems. The ability to withstand summer droughts would be a main factor in selecting the plants for green roof systems (Dunnett and Kingsbury, 2008), particularly where irrigation is limited or not applied. Consequently, the survival during drought periods de- termines plant species suitability for green roofs (Bousselot et al., 2009), especially in hot and dry climates. Because of the thin sub- strate layer, extensive roof environment is a harsh environment for plants to grow and survive. As a result, a relatively small range of plant species are normally used on extensive green roofs. Previous plant selection studies for green roofs tended to focus only on performance of individual plants on the systems (Boivin et al., 2001; Durhman et al., 2007). Sedum species are the most commonly used green roof plants (Dunnett and Kingsbury, 2008), as they are highly adapted to the dry environments (Gurevitch et al., 1986; Cook-Patton and Bauerle, 2012; Terri et al., 1986). The * Corresponding author. E-mail address: tehranifar@um.ac.ir (A. Tehranifar). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2017.01.027 0301-4797/© 2017 Elsevier Ltd. All rights reserved. Journal of Environmental Management 192 (2017) 215e223