View article

Compared to neighboring green space, urban centers are associated with increased stormwater runoff, rising temperatures, air pollution and decreased biodiversity (Mentens et al. 2006; Oberndorfer et al. 2007; Currie and Bass 2008; Bowler et al. 2009). Since the world urban population is projected to increase from 3.9 billion in 2014 to 6.3 billion by 2050 (United Nations 2014), there is a need to reduce some of the negative effects associated with urbanization. Numerous studies have demonstrated that green roofs can help mitigate some of these effects and this has lead to an increasing demand for their construction (Oberndorfer et al. 2007). However, more research is necessary to determine which species native to individual ecoregions are suitable for the green roof environment.

Green roofs are composed of layers; they usually contain a waterproof membrane, a root barrier, a drainage layer, a growing medium, and a vegetation layer (Castleton et al. 2010). There are several different ways a green roof can be constructed: complete or" loose laid" systems, where each green roof layer is a fundamental part of the roof; modular, where vegetated trays are installed on top of an existing roof; and pre-vegetated mats, where the vegetation is established off site and rolled onto the roof (Oberndorfer et al. 2007)(Figure 1). Out of these three green roof systems pre-vegetated mats offer instant cover and represent a good choice for windy and sloped locations as the physical structure provided by the mat may reduce erosion. Pre-vegetated mats have also been suggested as one of the best methods for reducing weeds on newly established green roofs …