Cities possess several intrinsic characteristics that act to limit the success of urban trees.
Trees growing in urban areas are smaller and shorter-lived than trees growing in undisturbed environments. The larger, more healthy the tree, the more functional it is. Thus, any problem which limits growth will decrease the benefits in a direct manner. The value of benefits provided by trees is difficult to estimate, but may reach several billion dollars for energy conservation alone. Since there is room enough for 60 million additional trees along U.S. streets, the potential exists for doubling this figure.