Urban Ecosystems

, Volume 18, Issue 2, pp 419–430 | Cite as

Exotics on exotics: Pollen analysis of urban bees visiting Sedum on a green roof

  • J. Scott MacIvorEmail author
  • Ally Ruttan
  • Baharak Salehi


Numerous bee species were collected from a single green roof over the blooming period of the dominant exotic plant type, Sedum, a succulent stonecrop widely used in the green roof industry. As green roofs become more common in cities, an understanding of the potential positive and negative impacts of widespread use of this exotic but useful plant is needed. In this study we sampled bees visiting a green roof in downtown Toronto and compared the proportion of Sedum pollen in the loads they were carrying back to nesting locations. It was found that smaller bees (e.g. Lasioglossum, Hylaeus) were significantly less common on the roof compared with medium (e.g. Apis, Megachile) and large-sized bees (e.g. Bombus, Andrena). The proportion of Sedum pollen in the pollen loads of foraging bees collected was high amongst all bees (average of 80.5 % of total pollen load), but significantly greater for exotic bees compared to native bees. Moreover, native bees had significantly greater numbers of non-Sedum pollen types comprising more than >20 % of their pollen loads, meaning bees could be visiting flowers at ground level and on the roof in the same foraging bout. As the number of green roofs in cities increase, the characteristics of their designs, including the vegetation type and diversity, could have a significant impact in shaping local urban bee communities.


Pollination Urban Native Vegetated roof Enhancement Extensive Diversity Habitat design 



We thank Dr. Laurence Packer for comments and feedback. Sheila Dumesh and Tom Onefurko for help confirming bee identifications, Jonathan Huang for help mounting pollen slides, Matt Perotto and Catherine Yoon for maintaining the green roof plants and Liat Margolis for coordinating the GRITlab. Funding for the research was provided by an NSERC awarded to Scott, and CANPOLIN funding to Bahar and Ally. Additional support was made available by an NSERC Discovery grant (Laurence Packer), and a MITACS award in collaboration with Scott Torrance Landscape Architects Inc.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  • J. Scott MacIvor
    • 1
    Email author
  • Ally Ruttan
    • 1
  • Baharak Salehi
    • 1
  1. 1.Biology DepartmentYork UniversityTorontoCanada

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