The American elm (Ulmus americana), native to about two-thirds of North America, is an iconic tree and was one of the nominees for the National Tree. Although the oak received this honor, both Massachusetts and North Dakota call American elms their state tree. In the past, elms lined the streets of midwestern cities, college campuses, and the National Mall. The Oval at Colorado State University is still lined with American elms, some of which were planted in the 1880s. Elms dotted the upstate New York campus where I attended undergraduate school. I remember Dr. William Huntley lamenting the death of elms around campus, which might have been brought about by a more deadly strain of Dutch elm disease in the 1960s.*
I’m lucky to have three large elms on my property as the one on the southside tends to keep the house cool in the summer. Once a friend mentioned she considered elms the scrounge of the earth. I was surprised but then remembered the multitudinous seeds, more properly referred to as samaras, covering our sidewalk and how many seedlings I routinely yank out of flowerbeds. Without a doubt they are tenacious trees with a number of deficits, including that surfeit of seed production.
Elms may also harbor aphids which produce “honeydew,” nearly painting my white house a sticky black. European elm scale also contributes to the annoying honeydew and can debilitate a tree. Another pest, which chews holes through elm leaves, giving them a lacy look, is the elm leaf beetle. My house is now 102 years old, so I assume the trees are about the same age. I would not consider cutting them down unless they were rotten or became infected with Dutch elm disease. According to numerous sources, elms can live up to 175-200 years with an outside age of 300 years. The current oldest tree in the US listed on Monumental Trees, though, is estimated to be no older than 151 years.
Dutch elm disease started devastating stands of elms in the 1930s after the disease was carried to North America by European furniture makers in the 1920s. Known as a vascular wilt disease it can be transferred in one of two ways. First, native elm bark beetles, as well as European bark beetles, carry the disease-causing fungus. Dutch Elm Disease (DED) can also spread from the roots of closely planted trees. World-wide there are up to forty members of the Ulmaceae family but only six species are native to North America. All are susceptible to Dutch Elm Disease, but American elms are affected in the greatest numbers. Estimates are that 77 million trees were lost to the disease between its introduction and 1970. Current estimates of loss are closer to 300 million.
American elms (Ulmus americana) do still exist. Plant geneticists have created both American elm clones more resistant to DED, as well as cultivars which may prove to be less susceptible. Possibly the most famous elm tree was one which survived 14 bouts with the disease, thanks to Frank Knight, the tree warden of Yarmouth, Maine. According to the Liberty Tree Society, this elm was planted in the 1770s. Mr. Knight spent fifty years tending to Herbie, which was cut down in 2010 while the 101-year-old tree warden watched. You are able to join the Liberty Tree Society and purchase clones of Herbie, as well as support their research into viable cultivars. This site also has a timeline of the fight to save the elms
The study of DED tolerant elms continues. A cultivar developed in 1927, the Augustine Ascending elm, was once thought to have some resistance to the disease, although this has proven untrue. Of the 550 elms on the National Mall, a few of them are the Augustine Ascending cultivar. This variety may be noticeable due to its more upright nature. A specimen of Ulmus americana Augustine Ascending(B99) can be seen across the street from the tennis courts in City Park.
Another cultivar with properties beneficial to fighting scale was discovered by Fort Collins’ own Tim Buchanan, then City Forester. Scale buster American Elm (Ulmus americana Scale Buster) is located near the trolley station.
Although there is NO American elm listed on the current version of the Self-Guided Tree Tour, I have a sneaking suspicion this tree with its wooden American Elm sign is the same as the scale buster elm as a photo in the talk referenced above looks nearly exactly like the tree. This specimen is located behind the trolley station on the west side of the street. Before the leaves have bloomed it is quite easy to see its wooden sign if you are looking northeast.
*Sibley, David Allen. the Sibley Guide to Trees. 2015, Alfred Knopf.