In the first half of the Twentieth Century our mighty American elms (Ulmus Americana) began to shrivel up and die in huge numbers. It was indeed a mystery until someone discovered that an introduced invader, the elm bark beetle had arrived on the scene and brought with it a botanical plague. This was the microscopic fungus which causes the Dutch elm disease (Ceratocystis ulmi). It infects the trees simply by stowing away on the legs of the beetle as it burrows into the tree bark. Once there it infects the host just as effectively as if it were injected with it.
Dutch elm disease is essentially one of many which are categorized as wilt diseases. What happens is that the fungus chokes off the circulation of water and nutrients via the cambium layer. This is manifested by the spring or mid-summer yellowing and wilting of the foliage giving the appearance that it was October and time for the leaves to turn color and fall. But by the fall in most cases the tree has died.
During the 1930s and ‘40s, vast amounts of labor was target against this disease. Millions of diseased elms were cut down, their stumps dug out, and all of this was heaped into bonfires and burned. It was to little avail as the disease continued on its destructive path. Eventually it was learned that a systemic chemical which killed the fungus could be used to inoculate the tree before they were infected or infected to a 10% or less degree.
The Elm Research Institute in Harrisburg, New Hampshire has promoted this method and makes available to the public the vaccine and the injecting apparatus for an appropriate fee. But alas, this method can be costly and laborious as it must be applied annually. I have seen trees which have been religiously inoculated each year which have died anyway, so it is far from 100% effective.
The ERI has also developed a resistant subspecies known as the liberty elm. They are promoting plantings of this hybrid as a means of restoring elms throughout the United States. Although this method will work given the wide-scale application that is hoped for, but nonetheless it is still a different species from the native American elm.
It has been said by imaginative folklorists that centuries ago a squirrel could have journeyed from the Hudson Valley to the Ohio Valley without ever having to leave the treetops. Additionally, as many as half of these individual trees could have been American chestnuts (Castanea dentata). That squirrel, as well as many other species of animals in that ancient forest, would have enjoyed an abundant food supply from those trees. By the 19th Century those nuts were also being marketed for human consumption. Today's chestnuts "roasting on an open fire" are from the Spanish chestnut (Castanea sativa). The American chestnut also provided a valuable lumber forest species was altered suddenly and dramatically, by what was to become one of the most infamous plant diseases in North American history. This was and is the chestnut blight.

First diagnosed in the Zoological Park in New York City in 1904, the blight is caused by the fungus Cryphonectria parasitica. This fungus was ostensibly introduced with imported plants from Asia about a century ago. This fine lumber was used extensively for construction and furnishings around the nation

Due to inactive and negligent legislatures ample programs to combat the disease were never implemented. Within 50 years it had spread throughout the natural range of the American chestnut, forever altering a vast ecosystem and destroying the economic and aesthetic value of one of America's most versatile trees.

Chestnut blight is one of the group of wilt diseases which disrupts the tree's ability to conduct water. Infection occurs when spores of Cryphonectria parasitica which finds an ideal home in wounds that penetrate to living bark (insects are responsible for most of these wounds). Hyphae then grow into and between cortical cells and disrupt living bark and cambium. Cells are killed by macerating enzymes and by the acidification of tissues by other fungal secretions.
Very shortly thereafter the disease began to spread, researchers observed that the Chinese and Japanese chestnuts were resistant to infection. We now know that while both Chinese and American chestnut barks contain inhibitory chemicals which counteract fungal enzymes, this capability is much stronger in the Chinese trees. Incredibly, the tannins in American chestnut bark which inhibit growth of most microorganisms, actually supports the growth of Cryphonectria parasitica. In addition, the Asian chestnut species also respond faster and more efficiently in isolating lesions with a cork barrier.

The cankers that characterize the disease destroy vascular tissues in twigs, branches, and trunks. Chestnut blight does not, however, affect the roots. So it is that the species persists in our forests, as sprouts. These sprouts grow to perhaps 20 feet in height before becoming diseased and quickly die.
Once a mighty giant of the eastern forests, the American chestnut has been literally destroyed by a microscopic spore from the other side of the planet. Relinquishing its position in the canopy to oaks and hickories, the chestnut survives as an understory species in the company of striped maple and mountain laurel.
These two magnificent species were once so dominant that all towns named streets after them. Today in the aftermath, the street names continue on, but their namesakes are for the most part extirpated species.

Bibliography

Carrol, K. Journal News. 4/17/89. West Nyack, New York. A Tree Still Grows in Tomkins Cove.
Smith, A. 1989. Museum Papers. Bear Mountain, New York. A Small Victory For Nature.
Smith, D. 7/14/01. The Journal News. West Nyack, N.Y. The American Elm Makes a Comeback.
Tattar, T. 1989. Harcourt, Brace, and Jovanovich. New York, New York. Diseases of Shade Trees.
Trotta, K. 1996. Museum Papers. Bear Mountain, New York. The Chestnut Blight.
Copyright © 2000 AJS