Plant survival and growth on extensive green roofs: A distributed experiment in three climate regions.

Highlights • Plant performance on identical green roofs differed in cities 1000 s of km apart. • Climate altered plant survival, growth and phenology. • Canopy density higher in three species polyculture compared with monocultures. Abstract Green rooftops are installed in many climates worldwide to support urban ecosystem services. Across North America, green roofs often make use of the same limited set of plant species, but the effects of regional climates on the survival and growth of a core set of plant species has seldom been investigated. To identify the impact of climate on green roof plant performance, we installed an identical green roof system in three Canadian cities that experience different climate conditions: Calgary, Alberta; London, Ontario; and Halifax, Nova Scotia. The green roofs were monitored across three growing seasons for plant survival, plant height, and canopy density of three species grown in monoculture: Aquilegia canadensis , Sporobolus heterolepis , and Sedum spurium , and a mixture planting with all three species. Green roof vegetation canopy density, plant height and growth rates differed by city, plant species, substrate depth and planting type (monoculture or mixture treatment). Between sites, plant species exhibited different growth phenologies. Mixture treatments performed slightly better than monoculture plantings at each site in canopy density measures but were not significantly greater in plant height measures. The growth rate between years two and three was greatest for the mixture treatment, indicating greater potential for long term survival and performance of mixture plantings. The London, Ontario site, with a relatively moderate climate, supported the best green roof growth and performance compared to the cooler and drier Calgary and the rainier Halifax. [ABSTRACT FROM AUTHOR]