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Sure, a green roof is pretty and environmentally friendly. But did you know it can also be a safe haven for endangered birds, flowers, and insects? Neither did we.

Green roofs -- buildings topped with gardens rather than with asphalt, tile, or shingles -- sound (and look) good. also, in addition to cutting energy consumption and soaking up storm-water runoff that would otherwise pollute rivers and harbors, these constructed green spaces can provide a refuge for wildlife.

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THIS HAS LONG BEEN one of the arguments used in favor of this architectural innovation; unfortunately, few studies and little data have backed up the claim. Until now, that is.

Researchers in Europe have produced a small but growing body of evidence that green roofs can indeed provide living space for endangered plants and animals, especially migratory species like birds and insects. This confirms one more benefit of green roofs -- in addition to beauty, longevity, and reduced energy use -- just as their popularity in the United States and elsewhere booms.

The longest-term data comes from Germany, a country that first experimented with green roofs in the late nineteenth century. Germany probably now has more green roofs than anywhere else: approximately 50 square miles’ worth, which is equivalent to an area slightly larger than the city of San Francisco.

A study of established green roofs in the Berlin area reveals that, with very little maintenance and irrigation, roofs in both urban and rural settings can support a wide variety of plants. With varied microclimates, such as sunny and shady areas, “near-natural habitats can be constructed on roofs,” reports the study.

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And according to preliminary results from a long-term Swiss study, green roofs may not only provide food but also serve as a breeding habitat for ground-nesting birds such as the endangered little ringed plover and the northern lapwing. In 1914, Swiss designers installed green roofs to cool the buildings of the Wollishofen water plant in Zurich. The native soils they used have since given rise to thriving rooftop meadows that provide refuge to endangered orchids and to various bird species.

Research done on this green roof resulted in new design laws in several Swiss cities, including Basel, which now requires that every new flat roof be planted. The most biodiverse of the Basel green roofs offer a dense constellation of microhabitats, supporting 79 beetle species and 40 spider species, 20 of which are endangered.

The Swiss studies also inspired London planners to use green rooftops as a replacement for the wildlife habitats being lost to the redevelopment of brownfields -- once-abandoned industrial sites. Hoping to create oases for the rare and protected black redstart, biologists customized “brown roofs” of crushed concrete and brick, which appealed to the bird. While conducting a survey of invertebrate diversity -- spiders, beetles, bees, and ants -- British researchers discovered that green roofs are home to even more invertebrates than the species-rich brownfields. And about 10 percent of the rooftop species are endangered.

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ACROSS THE POND, in North America, the gathering of scientific evidence to support the benefits of green roofs is still in its early stages, but people’s desire to provide wildlife habitats in urban areas has become a common argument for installing them. And that argument has proven powerful: Nearly 90 percent of North America’s green roofs were installed between 2004 and 2006, and during that time, the number of green-roofing companies increased fivefold. Then, in 2007, the market increased by another 30 percent, according to Green Roofs for Healthy Cities, a Toronto-based organization working to promote green roofs in North America. The highest concentration of rooftop habitats is found in Chicago, which provides local ordinances that give tax benefits and speed up the permitting process for builders who install green roofs and other eco-friendly options.

“Our city has truly embraced this practice as a way to help conserve Chicago for future generations,” says Richard M. Daley, mayor of Chicago, who introduced an ambitious 150-page Environmental Action Agenda in an attempt to make his city the greenest on the continent. Chicago has approximately two million square feet of green roofs -- more than all other American cities combined -- and at least a million more in development.

Probably the most well known and ambitious of all of Chicago’s green roofs is atop City Hall, which happens to support a thriving meadow. Though the roof wasn’t originally designed as a wildlife habitat, its contours and the variety of plants on it have attracted native species. Naturalists have been tracking how many species of birds use the roof, as well as the incidence of spiders, bees, and soil insects.

Evidence indicates that native bees (which tunnel into soil rather than build hives) love the roof ’s special lightweight soil mix, which incorporates wood chips, vermiculite, and clay pellets. And while it was mostly sparrows and juncos that found their way to this park in the sky at first, the number of bird species nesting here has increased each year: Now there are warblers, vireos, woodpeckers, thrushes, and even a rare olive-sided flycatcher. To further encourage the birds, the city has installed birdhouses on the roof.

Chicago’s example (and success) inspired city officials in Minneapolis to design a green roof that mimics the plant community of the Minnesota Bedrock Bluff Prairies, a dry ecosystem that thrives on the cliffs above the Mississippi, for the Minneapolis Central Library. The hope is that the native plants on this roof, which was completed in 2005, will attract native wildlife in the same way Chicago’s City Hall has.

And in San Francisco, the design of a rooftop wetland for the endangered Bay checkerspot butterfly is under way for the city’s Transbay Transit Center. Carmel Valley–based Rana Creek, the project’s designer, is already monitoring five other completed San Francisco Bay Area green-roof projects to see whether checkerspots will use them as habitats.

“In the last few years, we’ve done 30 roofs that focus on providing habitats for hummingbirds, butterflies, and other species,” says Paul Kephart, Rana Creek’s executive director. “It’s a field of dreams, these projects. I’m a restoration ecologist. I take glass, concrete, and steel and provide more life, more fertility.”

In addition to Chicago and San Francisco, cities like Toronto, Phoenix, New York, Portland (Oregon), and Washington, D.C., have joined the movement and become hotbeds of rooftop planting. But the trend is global. Here are some of the most inspiring examples from around the world.


During a 2007 renovation, this independent school (prekindergarten through eighth grade) just south of San Francisco planted more than 2,500 square feet of native grasses over the cafeteria and 7,500 square feet of native plant species over the library. The site will be monitored for the presence of the Bay checkerspot butterfly.


Guinness World Records has pronounced this 454,000-square-foot roof the largest green roof in the world. Nine varieties of drought-tolerant sedum thrive in just one inch of porous stone, sand, and organic material. Scientists have done insect surveys of the roof, and Canadian geese use it as a nesting site.


For this three-story building, which houses a boutique, designers took botanical architecture far beyond the green roof, covering even the exterior and interior walls with plants.


At the new art school here, two curved, sloping green roofs mix grasses and native greenery to provide a parklike environment where students can gather.


Rather than using tents or canopies to house this year’s summer music festival, this modern art museum has chosen to use a temporary living roof. A series of cardboard tubes, none more than a yard tall, will be assembled to form a large platform and then planted with flowering and fruiting plants, including everything from mint to peas.


Utility plants don’t usually add to wetlands, but this sinuous facility, featuring a green roof, is an exception. Completed in 2007, it boasts the largest eco-roof in Connecticut.