Page 18 - Tree Line - North Carolina Forestry Association - Third Quarter 2021

PART 1
Restoring Giants: American Chestnut Tr
BY FRED P. HAIN,
PROFESSOR EMERITUS & DIRECTOR OF FOREST RESTORATION ALLIANCE,
NC STATE UNIVERSITY
This is part 1 of a two-part series. The next issue of TreeLine will report on the work of the Forest Restoration Alliance and the Hemlock Restoration Initiative in saving and restoring eastern hemlocks killed
by the hemlock wooly adelgid.
A merican chestnut trees were once distributed from Alabama to Maine,
and they numbered in the billions. Where they were most dominant — the Appalachian Mountains — it has
been estimated that one in every four hardwood trees was an American chestnut. Because of its resistance to decay, the wood was used for fence posts, poles, split rail fences, piling, railroad ties, and log structures. The tree was also popular in the furniture industry and served as an important food source.
And then they were gone! Around 1904, a parasitic fungus, Cryphonectria parasitica, was accidentally introduced into the United States and by 1940, most mature American chestnut trees were wiped out by the blight. A few scattered trees have survived, and a few chestnut stands planted outside the natural range exist.
The blight came from East Asia, where the native chestnut trees have resistance to infection and survive the disease. Since American chestnuts did not evolve with the fungus, most, if not all, trees were highly susceptible to the blight. If there was any resistance
in the American trees, it may have been lost through harvesting. The root systems of the fallen trees remain alive to this day because soil microorganisms suppress the blight. Thus, chestnut sprouts are commonly found in areas where once mature stands of chestnuts existed.
An earlier version of Darling 58, Darling 54, is shown to be doing well, while the wild-type American chestnuts on the left are wilted 30 days after infection with Cryphonectria parasitica.
These sprouts can become quite large, but usually succumb to the blight before reaching sexual maturity.
Efforts to restore American chestnuts began in
the 1930s with limited success. Those interested in saving the tree could only perform sanitation and chemical applications on a small scale in areas such as city parks. Biological control through hypovirulence is not widespread in the United States. The virus
that prevents the blight from being lethal does not readily spread from tree to tree. Initially, hybridizing surviving chestnuts with resistant Chinese chestnut trees showed little promise until a technique called “backcrossing” was employed by The American Chestnut Foundation (TACF) in the 1980s.
16 ncforestry.org / THIRD QUARTER 2021
ANDY NEWHOUSE, CC BY-ND
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