Jason Aloisio, a graduate student at New York City's Fordham University, sees the city's air as swirling with life. And to prove it, he has grown gardens on the city's rooftops without planting a single seed. .... The plots were set up in spring, but planting wasn't scheduled until autumn. So Aloisio laid out plots on eight roofs across the city. ... Over the weeks, the plots caught seeds carried by wind and birds. After just a few months, the most successful plots were jammed with plants, with biomass rivalling that of the prairies of the Great Plains. The plants were diverse, too, with 30 species showing up in total, one-third of them native to the area. ...Charlie Miller, founder of the company Roofmeadow in Philadelphia, Pennsylvania, says that Aloisio isn't the first to be curious about what might show up on an unseeded green roof. "That has been a sort of fad in Europe for the past six or seven years," he says. "In Germany, they call them Naturdächer — nature roofs.""I go around the city and wherever I am, I see plants growing in these tiny little crevices," says Aloisio. "They look like weeds, but they are still green."
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