Planting trees in urban and suburban environments is generally good. There has been a steady decline in recent decades in the number of trees that line the streets in American cities and we need to reverse this trend, according to the nonprofit group America Forests. Urban trees absorb pollution and keep air quality reasonably good and new research shows that if our air is cleaner, we live longer. Planting just one tree on your front lawn, your curb or in your backyard helps. In case you're like me and all the trees you plant in your backyard turn brown and die, you can also give money to an organization that plants urban trees. The New York Restoration Project, the Earthworks Project in Boston and Friends of the Urban Forest in San Francisco are all involved in re-greening their cities with new trees. But urban shade doesn't come cheap. At NYRP, tree-related donations start at $100 for a sapling and go up to $2,500 for a fruit tree. At Prospect Park, the urban oasis down the street from me, I would have to pay $750 to $1,000 to have one tree planted or $10,000 for a grove. For that price I get to have some say over what type of tree is planted and where in the park it's planted, so I can visit it when I want to. But even so -- ouch! A spokesperson for American Forests explains that planting trees costs more in the city because they need to be more mature than the seedlings you can plant in friendlier rural environments. Additionally, these prices often are meant to cover several years of pruning and fertilizers to make sure the tree thrives.