As we are apparently about to lose our American ashes to the emerald ash borer of Southeast Asia, which literally eats them from the top down, it seems appropriate to reflect on other trees that we have lost to invasive species of one sort or another. While the ash borer is an insect and the chestnut blight is a fungus, the “Dutch elm” disease is a fungus spread by an insect, namely the elm bark beetle (there is more than one species).
The disease arrived in the United States in 1928 with some European lumber destined to be used as veneer. It spread west and south from New England. When I was a child in the 1960s there were still a few elms along the streets of some New England towns and when I arrived at St. Lawrence University in 1978 in the North Country of New York State there was still two double rows of elms along the half mile drive that passed for a grand entrance to the campus. Some of them were already dead, but the majority were still alive. (Now it is not even mentioned on the school’s website.)
It was just this kind of monocultural planting that made the American elm (Ulmus americana) succumb so quickly to the disease. Once the fungus is in an individual tree it pervades all the living tissue, including the roots. The specimens that lined both sides of every Elm Street in the United States had intergrown root systems.
While the chestnut was predominantly a forest-grown species, the American elm is best known as a street tree. It has a “vase” habit, which is to say that its trunk divides into several large boles a good 20 feet above the ground and each of these then veers off at a high angle successively producing more minor branches with the same geometry. The finest branches then succumb to the pull of gravity, arc over and begin to plunge, eventually hanging straight downward or nearly so, creating a vast vail foliage that is at its most beautiful in the early spring when the unfurling leaves are a bright yellow-green.
In other words this is a tree whose very shape made it perfect for streetscaping. In addition to a welcome habit, the tree also grew relatively rapidly and to great size (100 feet) within decades, and tolerated the increasingly bad air in urban settings and the root binding caused by underground urban infrastructure. The result was iconic avenues lined with trees the branches of which formed great arches that were blocks long. What American village, town, or city in the eastern two-thirds of the country is without an Elm Street?
Somewhat ironically it now survives best in its native habitat, which was most commonly riverbanks and bottomlands, although it is found in upland areas. It is not that uncommon to be driving along a country road in upstate New York and suddenly see the characteristic vase shape beside the road. As long as the tree is isolated from others of its kind, it stands a change of reaching a good size and old age.
Even in areas where Dutch elm diseases exists new elms often grow. Unlike the chestnut, the elm seeds are samaras and dispersed great distances by the wind. Once the seed germinates, elms grow much more quickly than chestnuts and tolerate a much broader range of physical environments. So, although they will not reach impressive size, they will reproduce several times before dying.
Unlike chestnut wood, which was good for almost anything, elm wood was good for very little. Entire houses could be built of chestnut, but even splitting elm for firewood was difficult and annoying. It was first and foremost a piece of living sculpture and people miss it in its living state, not for the usefulness of its parts.