Green roofs for biodiversity

Green roofs that are designed to increase biodiversity should feature indigenous vegetation local to the area. Biodiversity roofs should also incorporate different vegetation layers and landscaping features to increase opportunities for wildlife to feed and shelter. These may include hollow logs or twig bundles, rocks, different substrate types, such as areas of sand or rubble, and spaces for shelter, such as roof tiles and nesting boxes.

The value of green roofs for biodiversity will depend on their characteristics and location. In general, larger green roofs on relatively low buildings closer to natural areas will be more valuable than small, high green roofs in dense urban areas remote from parks or native vegetation remnants.

In the Northern Hemisphere, biodiversity roofs often have only a shallow (< 150 mm) depth of substrate, and receive little to no irrigation or maintenance. In most parts of Australia, the longer growing season and typically hot, dry summers make it unlikely that herbaceous vegetation on shallow green roofs could be sustained in the long term.

Irrigation may need to be provided during hot dry periods to ensure greater vegetation success. The vegetation must not create a fire hazard or block drains, so non-vegetated areas around the roof perimeter, drains or other fixtures must be kept clear.

If a low to no-maintenance approach is taken for a biodiversity roof, there must be an understanding that some plant species may be short-lived. Species’ persistence can be improved through plants that readily seed and self-sow, or produce underground storage organs (bulbs or tuberous roots) that are dormant for part of the year.

Planting a diverse range of species on a green roof is more likely to attract a broad range of invertebrates, birds and other wildlife than a monoculture of a single species.

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Biodiversity green roof at The University of Melbourne, Burnley campus