Ask the Tree Expert: Healthy Diversity

By Bill Eck
ISA Certified Arborist MA-4657A
 
Who decides which kinds of city trees to plant and where? And how do they make their decisions? I did a little research online and it looks like DC’s Department of Urban Forestry has the responsibility for planting along the city streets. I’m very curious about how they pick what kinds of trees they will plant.

For Forest Hills, for example, I wonder why ginkgo trees line Cumberland and Appleton streets (west side of Connecticut) and why sawtooth oaks line Chesapeake Street (west side). Walking around downtown you will come to a block that is all Linden trees, turn a corner and it’s all willow oaks, turn a corner and it’s all ginkgos. I love looking at the beauty and diversity, and am curious about how the decisions to plant certain types of trees are made. – Jen Beeson

The science of choosing street trees is not a simple one. There are so many factors that go into choosing these trees that they would be hard to summarize in just a few paragraphs, but here we go:

No matter where you are planting a tree, the most important decision is picking the right tree for the right place. This involves many factors, including the height, crown spread, form, growth rate, hardiness, and soil, sun and moisture requirements. Certain species of trees have different attributes that make them more or less appropriate for use as street trees. In general, you want trees that grow with an arching form that grow up and over parking spaces and the sidewalk without interfering with cars or pedestrians. If the trees are planted beneath wires, the final height and form of the tree are important considerations. Street trees also have to deal with stressful conditions such as soil compaction, infrequent supplemental watering, ozone pollution and physical damage.

In the early 1900s most street trees in most American cities were American Elms. They were planted for their growth rate, stress tolerance and most importantly their form. When you think of the classic tree lined street with trees arching together, you are probably thinking of American Elm. In 1928 Dutch Elm Disease was discovered in New England and began a destructive march across the US, reaching Minneapolis in the 1970s. Virtually every city in the northeastern U.S. lost the majority of their street trees. Because of this, city planners and arborists wisely decided that a monoculture should be avoided when replanting these cities to avoid a similar incident from occurring and thus we have a huge diversity of street trees being planted today. It is still desirable to have single species lining individual streets for aesthetic purposes, but too many streets of the same species could spell disaster in the event of a destructive pest infestation.

The DC Urban Forestry Administration (UFA) plants between 3,000 and 4,000 street trees each year. Residents may request a tree for an existing, empty tree box in front of their residence or trees for an entire block by calling 311. All planting requests must be submitted before June 15th to be processed for the upcoming fall/winter planting season.

Thanks for your question, Jen! Bill Eck has the answers on tree care. He is taking your questions at info@foresthillsconnection.com.