Elm envy

The devastation wrought by Dutch elm disease in the middle of the last century left Americans largely bereft of our favorite street tree. We lost no time in trying to find substitutes that could reproduce the look of American elm and resist Dutch elm disease. Japanese Zelkova, Zelkova serrata, was seized upon as a tree that could replace American elms along roadways.

Zelkova was little known until a few decades ago. It is rare to encounter a mature one. In the last few decades the tree has become a very popular elm substitute. The tree shares the American elm's vase-like habit, but Zelkova's vase is typically squatter. The habit is also stiffer. American elm limbs undulate as they ascend. Not so the limbs of Zelkova, which lacks the elm's sinuous grace.

The tree has a handsome and distinctive bark. The young bark has very prominent lenticels(1), horizontal striations, that are reminiscent of the bark of some cherry trees. Older bark is rough and peeling.

The unusual bark and vase-like habit make this species easily recognizable even when it is leafless.

One peculiarity of Zelkova that has the potential to cause trouble as the tree matures is the density of its branching pattern. An entire forest of limbs emerges from the trunk a short distance above ground level. The Central Avenue tree pictured above illustrates the tremendous branching density. The Putnam Avenue Zelkova pictured below shows how numerous limbs typically originate in a bunch.

One wonders what is going to happen to all those limbs when they get large. You would have to bet that some will be crowded out and will drop to the street. Professor Edward. F. Gilman of the University of Florida (formerly of Rutgers) has drawn attention to this problem. In a presentation at the New Jersey Shade Tree Federation meeting in 2006, Professor Gilman spoke of Zelkova as a special case among shade trees in that it needs careful pruning for the first two or three decades of its life in order to develop a healthy form. Is he being overly pessimistic? Hard to know. There just aren't that many mature Zelkovas around on which to base a judgment. If he is right, the enormous vogue that Zelkova now enjoys is going to lead to large maintenance expenses for the municipalities planting them in great numbers. The only mature Zelkova I know is at 9 Remington Avenue in Edison (off Park Avenue). That tree has a diameter at breast height of about three feet and is quite a beautiful specimen. Pruning history? I haven't a clue.

Another American elm substitute that is growing in popularity, but still a rarity, is lacebark elm, Ulmus parvifolia. Like Zelkova, lacebark elm is resistant to Dutch elm disease. Kathryn Uhrich and Jeff Holmes recently planted two lacebark elms in the curbside strip in front of their house at 1441 Evergreen Avenue. They are the only lacebark elms I know in Plainfield. The peeling bark of this species is exceptionally beautiful. These two elms are an exciting addition to Plainfield's urban forest.

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Siberian elm, Ulmus pumila, is yet another elm with resistance to Dutch elm disease. There is an example of this species near the Muhlenberg Hospital Park Avenue parking lot. The first tree on your right as you turn off of Park Avenue onto Laramie is a mature Siberian elm.

Michael Dirr's Manual of Woody Landscape Plants, the Bible for many gardeners, calls this species "one of...the world's worst trees" because of its susceptibility to damage by wind and insects.(2) I think Dirr is exaggerating. I have seen many attractive Siberian elms (not in Plainfield, where it is uncommon), and I find the coarse, chaotic bark quite attractive.

Finally, some people are still planting American elms. Dutch elm disease-resistant varieties include 'Princeton', 'Liberty', and others.

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(1) Lenticels are loosely bundled groups of cells that permit gas exchange, allowing the tree to "breathe" through its bark.

(2) Manual of Woody Landscape Plants, fifth edition, Michael A. Dirr, Stipes Publishing 1998, p. 1048.

Copyright Gregory Palermo

American Elm

Once the most common street tree in the northeastern United States, the American elm has become something of a rarity. This beloved native was almost wiped out by Dutch elm disease in the middle of the last century. One of the early victims of globalization, the elm was attacked by a foreign fungus: Dutch elm disease was carried to the U.S. by elm bark beetles in imported logs. The disease continues to destroy elms to this day. When you see a mature elm, it’s hard to know whether it has survived because it is disease-resistant or because it is lucky enough not to have been attacked.

An American elm is easily recognizable. Its doubly toothed leaves are unusual for being asymmetrical. The tree usually has a distinctive vase shape. The gentle undulation of its limbs as they reach for the sky gives the American elm a sinuous grace that is unmatched by any other tree. Those characteristics are exemplified by the elm at the Drake House Museum on West Front Street.

The American elm at the rear of 116 Watchung Avenue (visible from Parking Lot 6 on Second Street between Park and Watchung Avenues) was recently cited by the City as a specimen tree at the 2007 Arbor Day celebration. The tree measures 47 inches in diameter at breast height. I estimate its age at 100 years.

The two elms on Park Avenue near Muhlenberg Hospital (1267 and 1303 Park Avenue), have a more pronounced limb curvature than one thinks of as classic. When I drive by those elms in winter, their exaggerated curves against the sky always bring to mind dancing girls.

The best example of a local American elm that I know is in the 3800 block of Park Avenue in Edison. Its arching limbs reaching across the street are visible from a quarter mile in either direction. The elm is on the left side of the road when one is heading away from Plainfield.

Seeing this beautiful tree I understand very easily why people once planted elms to the point of overabundance. Sadly, the huge numbers of those elms and their close proximity to each other made it easy for Dutch elm disease to spread from one tree to the next. Michael Dirr, author of the plant bible known as the Manual of Woody Landscape Plants draws a lesson from the story of the elms: “The extensive use of one tree such as the American elm is an example of foolhardy landscaping. The tree is enormously ornamental and was overplanted. The diseases caught up with the tree and the results were disastrous. Unfortunately, people do not seem to learn by their mistakes and now Honeylocust, Bradford Pear, Green Ash, Red Maple, and Planetree are being used in wholesale fashion for cities, residences, and about everywhere. I strongly urge a diversified tree planting program encompassing many different species and cultivars.”

I have included photographs of every mature Plainfield elm that I know. I would be glad to hear about others. I am also on the lookout for dawn redwoods and for outstanding examples of white oaks and red maples (Acer rubrum).

Copyright Gregory Palermo