Journal Article

Performance of dryland and wetland plant species on extensive green roofs

J. Scott MacIvor, Melissa A. Ranalli and Jeremy T. Lundholm

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 107, issue 4, pages 671-679
Published in print April 2011 | ISSN: 0305-7364
Published online February 2011 | e-ISSN: 1095-8290 | DOI:
Performance of dryland and wetland plant species on extensive green roofs

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry


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Background and Aims

Green roofs are constructed ecosystems where plants perform valuable services, ameliorating the urban environment through roof temperature reductions and stormwater interception. Plant species differ in functional characteristics that alter ecosystem properties. Plant performance research on extensive green roofs has so far indicated that species adapted to dry conditions perform optimally. However, in moist, humid climates, species typical of wetter soils might have advantages over dryland species. In this study, survival, growth and the performance of thermal and stormwater capture functions of three pairs of dryland and wetland plant species were quantified using an extensive modular green roof system.


Seedlings of all six species were germinated in a greenhouse and planted into green roof modules with 6 cm of growing medium. There were 34 treatments consisting of each species in monoculture and all combinations of wet- and dryland species in a randomized block design. Performance measures were survival, vegetation cover and roof surface temperature recorded for each module over two growing seasons, water loss (an estimate of evapotranspiration) in 2007, and albedo and water capture in 2008.

Key Results

Over two seasons, dryland plants performed better than wetland plants, and increasing the number of dryland species in mixtures tended to improve functioning, although there was no clear effect of species or habitat group diversity. All species had survival rates >75 % after the first winter; however, dryland species had much greater cover, an important indicator of green roof performance. Sibbaldiopsis tridentata was the top performing species in monoculture, and was included in the best treatments.


Although dryland species outperformed wetland species, planting extensive green roofs with both groups decreased performance only slightly, while increasing diversity and possibly habitat value. This study provides further evidence that plant composition and diversity can influence green roof functions.

Keywords: Green roofs; ecosystem function; biodiversity; Sibbaldiopsis tridentata; Danthonia spicata; Empetrum nigrum; Kalmia polifolia; Scirpus cespitosus; Vaccinium macrocarpon

Journal Article.  7858 words. 

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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