Media Release - For Immediate Release

April 6 2010

Plant Diversity Improves Function of Green Roofs

Dr. Jeremy Lundholm and student Adam Harris look at plants on the University's Green Roof.

Variety IS the spice of life.

Biology researcher Dr. Jeremy Lundholm didn’t set out to test the veracity of the old adage, but three years of study by his team at the Saint Mary’s Green Roof Testing Facility seems to indicate that it is true.

In a recent study published in the scientific journal PLoS ONE, Dr. Lundholm was able to show that planting biodiverse mixtures of plants on a green roof provides greater benefits in terms of energy savings and stormwater capture on roofs planted with a single crop.

A green roof is a roof of a building that is partially or completely covered with vegetation. They are growing in number, especially in urban centres, as business and civic leaders look for environmentally friendly ways to improve city ecosystems.

Green roofs contribute to biodiversity in cities by providing a home for plants, insects and other organisms, but they also provide direct benefits to people in the form of energy savings to heat and cool buildings, and reduced stormwater management costs.

While diversity is lauded in natural habitats, Dr. Lundholm said the issue of diversity has been given very little attention in urban or artificially constructed habitats.

He said many ecologists would like to believe that there is a tangible benefit to humanity of the sheer diversity of species that transcends aesthetics, but until now there has been considerable debate about whether there is any evidence to back up the view.

Many researchers doubt that the mere level of biodiversity will determine how an ecosystem works. They believe instead the critical aspect is the interactions between particular species, so it’s not necessarily the number of species that makes a difference, but whether or not species that complement each other are present.

In the published study Lunholm’s team found after three years of observation that, on average, mixtures of nine or 15 species outperformed roofs planted with single species. A handful of species by themselves did outperformed some of the 15-species mixtures, but mixed plantings overall improved how the roof functioned.

A mixture of grasses, succulents and herbaceous wildflowers was the most successful planting, not only outperforming most of the treatments for important benefits like summer temperature reductions and storm water capture, but it was also within the top-ten treatments that performed best for all functions
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Future research will examine the mechanisms underlying these benefits of plant mixtures. This study also showed that many of the natives performed as well or better than the commonly used non-natives in the green roof industry and these should be considered in future green roof installations in Atlantic Canada.

The initial study looked at fewer than 25 native plant species on rooftop conditions, and there are over 300 species likely suited to green roofs native to Nova Scotia alone, thus many opportunities exist to optimize green roof functioning by increasing native plant biodiversity.

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For More Information:

Steve Proctor
External Affairs
Saint Mary's University
(902) 420.5513
E-mail: steve.proctor@smu.ca
www.smu.ca

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