AgBioResearch

Michigan State University has always been green, but thanks to 10 years of research by AgBioResearch scientist Brad Rowe, the campus has become even greener. And he hopes to help the rest of the state green up as well.

Rowe, a professor of horticulture in the College of Agriculture and Natural Resources, oversees MSU green roof research on top of the Plant and Soil Sciences Building and the Communication Arts and Sciences Building, and at the Horticulture Teaching and Research Center. The program began in 2000 when MSU helped the Ford Motor Company install a 10-acre green roof on an assembly plant in Dearborn.

A green roof involves growing plants – ranging from succulents, such as sedum, to trees and shrubs – on rooftops. The depth of the soil medium influences which plants can be grown. Rowe's research has shown that, besides offering aesthetic benefits, green roofs can:

• Reduce airborne pollution, including some greenhouse gases.
• Reduce storm water runoff -- a major problem in dense urban areas – by reducing the peak runoff and by reducing the overall quantity of runoff by more than 60 percent.
• Moderate temperatures for both the building that sports the roof and structures around it, reducing energy consumption and the urban heat island effect.
• Increase roof durability and longevity.
• Provide a location to grow local produce in dense urban cities.
• Attract beneficial insects, such as native bees and other pollinators.

A typical green roof system is composed of 2 to 6 inches of lightweight, engineered soil that drains water, holds roots and nourishes the plants. Sedum's drought tolerance enables it to grow in shallow soils without additional irrigation -- the plant can survive more than 88 days without water -- and its hardiness helps it triumph over weeds.

Though green roofs aren't as popular in the United States as they are in Europe, especially Germany, Rowe said the amount of green roof space in North America has been expanding each year since his research began.  In 2010, the square footage of green roof space increased 28 percent in North America.

"Most of these systems are on government and commercial buildings, but it's a growing business, and there is a lot of interest," Rowe said.

His decade of research has helped identify particular species of plants that are best suited for green roofs.  In 2010, he began studying the feasibility of growing vegetables such as tomatoes, peppers, cucumbers, basil and green beans on the green roof test plots, but because these plants are more labor-, nutrient- and water-intensive, they may negate some of the roof's benefits.

During the summer of 2011, the research team will collect runoff samples from green roof vegetable plots to quantify nutrient runoff.  Vegetables require higher nutrient levels than sedum and the fertilizer could result in polluted runoff.

"It may be an issue, but we don't know," Rowe said. "That's why we're studying it. Unless you live someplace like New York City, it probably makes more sense to grow vegetables at ground level.”

Rowe also has tracked and analyzed how various species of sedum affect the roof's benefits, such as carbon sequestration and temperature moderation.

"We were one of the first groups doing this kind of long-term research on green roof technology," Rowe explained. "One of our current goals is to provide the U.S. Green Building Council with our results so that installing a green roof gets more points toward Leadership in Energy and Environmental Design (LEED) certification. Right now, a green roof contributes to LEED, but we'd like it to have a bigger impact."

Toward that goal, Rowe and his colleagues installed 20 new green roof test plots on the Plant and Soil Sciences Building in 2007. In the ensuing years, they have analyzed how much carbon the roof system's plants and soil are storing.

"If all the commercial and industrial roofs in metropolitan Detroit had green roofs similar to what we used, they could sequester approximately 55,252 metric tons of carbon," Rowe explained. "That's similar to removing more than 10,000 midsized SUVs or trucks off the road for a year. Of course, the final numbers depend on climate and green roof design, but green roofs can be a significant potential strategy for sequestering carbon in urban environments."

For more information on Rowe's research, visit the Green Roof Research Program Web site: www.hrt.msu.edu/greenroof/.