The greening of America, one roof at a time

Francis Clines has an editorial in The New York Times about a growing phenomenon:

From the 15th floor you can see all manner of Manhattan eccentricities on the street below. But how did the humdrum rooftop of a nearby apartment house suddenly become covered with a blanket of suburban grass? “No, not grass— you don’t want grass,” explains Stuart Gaffin, a research scientist tracked down at Columbia University who turns out to be the city’s rooftop Johnny Appleseed. A specialist in something called the Urban Heat Island, Mr. Gaffin has successfully campaigned to have over a half-dozen rooftops, including four at green-minded Columbia, entirely matted with small plants called succulents.
They sop up and vaporize rainwater before it can jam the city sewage treatment plants; they cut summer heat that can exceed 170 degrees on a roof. No mowing required. “They’re nature’s geniuses at staying cool,” Mr. Gaffin says, while stepping across the resilient mat of sedum plants flourishing high over West 112th Street. He gestures to the city panorama and estimates thirty square miles of unused rooftop acreage that could be vegetating. “Twenty times Central Park!” he declares, sounding like a producer coveting Broadway.
Mr. Gaffin’s gardens range from vegetation plain as the top of a pool table to more advanced mixes that resemble pointillist abstractions atop two roofs at the Bronx’s Fieldston Middle School. Students tend instruments measuring insulation, water conservation, and other virtues of green roofs, which Mr. Gaffin says far outlast normal roofs. They have a weird urban serenity. Far from streetwise rats, the worst critters that have shown up are butterflies and crickets.
The city lags far behind Europe in green-roof savvy, but Mr. Gaffin is as patient as his succulents. He evangelizes roof by roof, delighted to uproot a stray weed above 112th Street. “Field work,” he says.