Can green roofs enhance conservation of biodiversity in cities?

A-computer-generated-image-of-city-buildings-with-green-roofs-copy

Important pollinator populations grow more quickly in areas with urban and sub-urban gardens than flower-rich farmland. Allotment gardens have a greater diversity of nectar flowers compared with monocultures of crops in farmland, therefore support more populations of (for example) the buff-tailed bumblebee, Bombus terrestris terrestris. The close proximities of gardens in these urban parks allow pollinators to forage in a ‘matrix’ of gardens, each with a different floral make-up. But can roofs with built-in wild vegetation (green roofs) enhance biodiversity?

Green roofs are becoming increasingly common in cities as they absorb rainwater, regulate building temperatures (insulation), lower urban air temperatures and reduce the heat-island effect. These novel ecosystems also support generalist insect species, and scientists propose that they may also help conserve rare taxa, even vertebrates if connected to ground level habitats.

Williams and colleagues evaluated 6 hypotheses to test their effectiveness. They found that green roofs could aid rare species conservation if specific populations of species are targeted. For example, the Bay Checkerspot is an endangered species and only persists in a few fragmented populations, so populations would have to be relocated to an area within the butterfly’s range first before making use of the green roofs.

The study concluded that green roofs overall do provide important ecological and environmental benefits in the urban environment. It is also clear that green roofs support greater diversity than non-green roofs. However a policy shift towards replacing lost or declining habitats with poor-quality ones must be avoided. More research on the biodiversity of green roofs and the ecological interactions is required before policy action can maximise biodiversity gains.

Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R. R., Doshi, H., Dunnett, N., … & Rowe, B. (2007). Green roofs as urban ecosystems: ecological structures, functions, and services. BioScience, 57(10), 823-833.
Williams, N. S., Lundholm, J., & MacIvor, J. S. (2014) Do green roofs help urban biodiversity conservation?. Journal of Applied Ecology. DOI: 10.1111/1365-2664.12333

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6 thoughts on “Can green roofs enhance conservation of biodiversity in cities?

    1. entochris Post author

      Hi thanks for the comment. From what I gather you need a waterproofing membrane, with other layers built in (root barrier, drainage + irrigation). If you want a quick and easy one though just get some potted plants (although this isn’t a true “green roof”).

      You’ll need to see a specialist for a proper green roof though, to get what you actually want out of it. 🙂

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      1. Nathalie Baumann

        If I may reply to you concerning your research – since more than 15 years we’re working in Switzerland and UK on biodiversity on green roofs, green walls and rain gardens … and we can already say that it is, if it’s right greened and properly done (ecological principals) …. there are more studies about it, as you found it. As well in other languages then English! The world is bigger than the english community … don’t forget. So theres two very interesting studys, PhD’s done about the insects on green roofs and ground nesting birds – and if it’s a replacement habitat or not, compensation surface … YES it is! Long proven and we also have regulations, policy supporting green roofs …. so just go ahead and not again invent the wheel, we know how it works and can prove it.

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      2. entochris Post author

        Hi Nathalie, thank-you for your comments. I must stress that I didn’t carry out the research, I just reported what I read in the Williams et al 2014 study. Their point of view was that certain ecological considerations need to be made before making policies e.g. looking at habitat fragmentation of a species before establishing green roofs to help conserve it.

        I’d happy post an article on your research if you’d like to send me a link.

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