By Robyn Stewart, ANR Agent
The American chestnut has been in existence for over 40 million years, and more than a century ago there were over three billion trees growing in the eastern United States. The American chestnut composed more than 25% of the tree population in the Appalachian Mountain range during this time. The trees were fast growing, matured into large, tall specimens that produced wood that was resistant to rot, straight grained, and used for furniture, fencing, and building. At maturity, the trees could be up to 100 feet tall and 10 feet in diameter. They ranged the majority of the east coast, from Maine down into parts of Georgia, Alabama, and Mississippi. The chestnuts produced by the trees fed wildlife like deer, bear, and turkey, humans, and livestock like hogs and cattle. The species was, for all intents and purposes, a heritage tree.
In the early 19th century, there was an epidemic of ink disease imported from Europe that killed the roots and collars of American chestnuts. It primarily affected trees in the Southeastern U.S. and it is speculated that the population and range of the American chestnut was already negatively impacted prior to the introduction of the chestnut blight, which is what the majority of chestnut decline is attributed to. Before the turn of the 20th century, a blight fungus caused by Cryphonectria parasitica was introduced to the American chestnut population causing a catastrophic population collapse. The disease originated on imported Asiatic chestnut trees and was first noticed on trees in the New York Zoological Park in 1906. The Chinese chestnut tree was able to develop resistance to the blight, but the American variety was not as fortunate. The blight kills trees by destroying their xylem and phloem tissues and causes cankers and girdling around the trunk. This damage prevents water and nutrient transport throughout the tree, leading to its death. The fungus was airborn and able to spread 50 miles per year, and within 40 years had killed up to 3 billion American chestnut trees. While the American variety is not technically extinct due to the ability of new shoots to grow from existing rootstock even after the main stem dies, these new shoots rarely grow more than 20 feet tall before blight reinfection occurs, killing them. This means that the species is functionally extinct, since the American chestnut tree cannot re-establish itself. It is speculated that the population of surviving American chestnuts with trunks over 24” in diameter is fewer than 100 in its natural range on the east coast.
Several organizations are working towards restoring the American chestnut population including the American Chestnut Cooperators Foundation, the American Chestnut Foundation, and a variety of universities. Strategies include intercrossing: breeding resistant American chestnut individuals to produce greater resistance in the population; backcrossing: breeding American chestnuts with resistant Asian chestnut varieties; inserting resistant genes from wheat into the American chestnut genome; and investigating hypovirulent strains of the fungus, which reduces the ability of the blight to impact the trees.
