The decline of the American elm is an example of what the cost of a monoculture can be to our cities. Encourage diversity and continuous experimentation so that we can expand the list of available trees for our cities. Experiment not only with new species but with tree cultivars within these species identified as having greater tolerance of particular urban soils. With proper design and space allocation, your menu of trees from which to select increases. It is better to invest in smaller trees and plant them properly than to spend your limited funds on large trees and not install and maintain them properly.
Smaller trees are preferable for more reasons than money.
Smaller trees are easier to transplant and establish and often out-grow larger transplanted trees within the first 2 to 3 years. Be careful not to select trees that are small enough to be subject to vandalism or mechanical injury. For mass plantings, research that is promising and ongoing is using seed or small seedlings with the protection of tree shelters for site plantings. Look for new research releases from the Horticulture Department and School of Forestry at Auburn University. Be sure the trees you purchase are from a reputable nursery and consult the American Association of Nurserymen's American Standard for Nursery Stock.