Adding trees to urban landscapes can beautify an area and help convert carbon dioxide into breathable oxygen. But, simply planting more and more young trees is not the most efficient way get good results. Leda Marritz explains that trees need both time and room to grow.
"[M]ost urban trees are planted in small openings where they receive a mere fraction of the soil needed to survive. Unless they can access additional soil or water nearby, these trees usually don't survive to maturity. As a result, they are replaced on a short cycle [PDF], an avoidable recurring expense and - when you consider that a tree with a 30-inch diameter removes 70 times more air pollution annually than one with a 3-inch diameter - a very serious missed opportunity. And that's just one measure of a tree's contribution. They also help with stormwater interception, urban heat island effect reduction, crime reduction."