Many trees are not well-adapted to the rigors of urban life. Some are highly susceptible to the effects of S02. Others, such as the oaks, grow too slowly while cottonwood and horse chestnut for example, good city trees, in most respects, produce quantities of fruit or seeds considered a nuisance by many residents. Trees best adapted to urban life appear to be those native to floodplains such as elm, ash, silver maple and sycamore. These species evolved to survive spring floods, summer droughts and therefore are better suited to the poorly aerated city soils. Since the rapid demise of elms as a result of the Dutch elm disease trees planted most frequently in Milwaukee have been maple, ash, and honeylocust. Many of these trees are now 15-25 years old and are beginning to show the effects of urban life.
Van Wyck, S. and F. Stearns. 1979. Salt and Milwaukee street trees. 12(1): 2-26.