To celebrate the coming of a year with three zeros in it, First Lady Hillary Rodham Clinton yesterday kicked off the “Millennium Green” campaign, which aims to plant 250 million trees, nearly one for every American. The project — which is being orchestrated by the U.S. Department of Agriculture and the EPA with much of its funding coming from the private sector — will particularly emphasize the greening of urban areas, which have experienced appreciable drops in tree cover in recent decades. The USDA is giving 100 trees to each of the 50 states to create “Millennial Groves” in their capital cities, with saplings that are descended from famous or historical trees. A similar campaign is underway in the U.K., where a “Trees of Time and Place Campaign” is urging citizens to mark the millennium by gathering seeds from a favorite tree and planting new trees.