Scientists are rapidly developing technology for genetically engineering fast-growing supertrees. The economic advantages for timber companies seem clear. The environmental repercussions are less certain. Forest biotechnology, scientits predict, will ultimately transform such disparate industries as housing and fuel; some even suggest that this technology may help humankind colonize Mars. “Genetically engineered trees could produce gasoline or alcohol or almost any other chemical from sunlight,” says Freeman Dyson, a professor of physics at the Institute for Advanced Study in Princeton, N.J. “Think of tapping trees for chemicals the way you tap them for maple syrup — the possibilities are marvelous.”