Chestnut Blight

Once an important hardwood timber tree, the American chestnut became overwhelmingly susceptible to chestnut blight. This was caused by an Asian bark fungus accidentally imported into North America. The disease was first noticed on American chestnut trees in 1904 at the Bronx Zoo by Hermann Merkel who at that time was their chief forester. He estimated that by 1906 this blight would overtake 98 percent of the chestnut trees in all of the Bronx, New York.  It seemed unstoppable. Even though the Chinese chestnut evolved with the fungus blight as a disease with a strong resistance, the American chestnut’s resistance to this “blight” was very weak. The bark fungus became airborne and spread 50 square miles a year. In only two decades it’s killed three billion American chestnut trees. The very large American chestnut can be monoicous (bisexual), producing both eggs and sperm or dioicous (unisexual), either female (producing eggs) or male (producing sperm). They generate many small, pale green (nearly white) male flowers found tightly occurring 6 to 8 inch long. These female parts are called catkins (twig-like) and appear in late spring to early summer.

A young tree in its natural habitat grows rapidly, reaching nearly one-hundred feet and almost 10-feet in diameter. From Maine, Ontario, Mississippi, the Atlantic coast, the Appalachian Mountains through the Ohio Valley, these majestic trees were once the most prevalent in the Northeastern United States. In Pennsylvania, they comprised 25–30% of all hardwoods. When the tree’s nut production begins between 7–8 years, it causes rapid growth as compared to oaks that don’t produce huge numbers of acorns yearly. Other hardwoods like oaks were not affected by such rampant disease.

Reduced population

The total number of chestnut trees in eastern North America was estimated at over three billion, and 25% of the trees in the Appalachian Mountains were American chestnut. The number of these very large hundred feet surviving trees, with two-foot diameters within is probably fewer than 100. American chestnuts were also a common part of the forest canopy in southeast Michigan.

Although large American chestnut trees are now rare east of the Mississippi River, they can be found in the “blight-free” West, where the habitat is agreeable for planting. It also turns out that early settlers during the 19th century planted American chestnut seeds prior to this fungus. Huge planted chestnut trees can be found in Sherwood, Oregon, as their typically Mediterranean climate discourages the fungus, which relies on hot, humid summer weather. American chestnut also thrives as far north as British Columbia.

Revitalization Attempts in America

The reason plant researchers and consumers have wanted to renew this nearly extinct breed of fruit tree is that man and wildlife have ecologically relied on this as a “circle-of-life” food. In the woods, the American chestnut is vital for wildlife, providing extremely edible fall food for white-tailed deer, wild turkey and passenger pigeons. Black bears are also known to eat the nuts to fatten up for winter hibernation. Its leaves contain more nitrogen, phosphorus, potassium, and magnesium compared to other trees sharing the same habitat. This means they return more nutrients to the soil when these animals die or excrete, helping future growth of other plants and animals. Men have also hunted the animals who feast on these chestnuts and leaves. This is a key factor why the “blight” has had to be reversed by science.

While it is believed that survival of this species past the next decade its native range is almost impossible, much effort is being done to help them. Some years ago Dr. Wayne Weidlich,  Director at the American Chestnut Foundation, (ACF) noted that chestnut blight will grow on chestnut roots if they are exposed. He thought to try packing soil over trunk canker sores.  And, amazingly it worked.  Something in the soil effectively eliminates the blight fungus and allows the tree to heal.  Other successful methods are reviewed in this article. As mentioned in the link above, backcrossing is being used by the ACF to restore the American chestnut to its original habitat. Several other organizations are attempting to breed blight-resistant chestnut trees that adapt to their particular ecosystems as is happening with the Canadian Chestnut Council in Ontario.

Intercrossing surviving American chestnuts

The American Chestnut Cooperators Foundation (ACCF) doesn’t inject Oriental genes for blight resistance. Instead, their researchers employ an elaborate breeding strategy using intercrossing developed by John Rush Elkins, a research chemist at Concord University, and Gary Griffin, professor of plant pathology at Virginia Tech. Many of the strategies are safer than typical bioengineering to keep the trees from becoming cross-bred.

While this work continues on many levels, it’s evident that the entire species would face permanent jeopardy were it not for science and mankind’s intervention.