Years ago, I clearly remember the tall, Elm trees that lined many streets and boulevards in Midwest towns. Eventually, most if not all were eventually destroyed by the Dutch Elm disease (DED) that went from tree to tree, destroying all Elm trees in its path. From the information I could gather at the time, once the tree was infected, the beetle would look for other nearby Elm trees to infest. If your street or boulevard had many Elm trees on the parkway or nearby, most, if not all these trees were in peril.
According to Wikipedia research, the DED spread slowly from New England westward and southward, reaching the Detroit area by 1950, continued west to the Chicago area by 1960 and within 10 years infecting trees in Minneapolis by 1970.
Arborists and common sense thinkers have certainly learned a thing or two over the years. In other words, try to avoid the errors of those tree planters or communities of years ago.
When you plant along the parkway, avoid the temptation of planting just one species of tree even if the price is right. Two potential advantages: One, if you only plant one species and that species becomes infected after 15 or 20 years, there is a chance the disease or bug will travel from tree to tree eventually wiping out all trees on the parkway. What a difference you would find when a mature tree parkway eventually looks sparse with newly planted trees. Certainly less beauty and certainly less shade during hot weather. The second reason you avoid one species of tree is that by staggering a few species, you are providing a fighting chance the bug infestation will not successfully infest (or take a lot longer to accomplish) the entire species.
Over the last few years, I have seen at some corporate parks in the Chicago area where landscapers and developers are planting strictly ash trees – one after another. If these trees are susceptible to the emerald ash borer, one by one the ash borer could easily move from tree to tree. It may be a different infection or invasive species but without appropriate planning, we are compounding the problem by how we’re planting the trees.
There’s no way this can be completely avoided, but with appropriate planning and forethought, we might be able to stop the spread of this disease or at least slow it down considerably.