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Chestnut Hills, West Salem, WI
Our research site is located about 15 miles east of La Crosse, WI. It is the largest remaining stand of American chestnut (Castanea dentata)
in North America. Eleven chestnuts were planted in about 1900 by a farmer from either Pennsylvania or Virginia. This site was apparently ideal for the growth of these
trees because at its height, the stand consisted of more than 6,000 trees with a dbh greater than 5 inches. Because this stand is outside of the native range of chestnut,
it remained blight free until about 1988. The stand is now in decline but still remains relatively healthy. This may be the
last opportunity to study the forest ecology of the American chestnut tree. |
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The chestnut blight, caused by Cryphonectria parasitica, is a classic example of the devastating effects of an
introduced pathogen. Prior to 1900, shipments of Asian chestnut (Castanea crenata or Castanea mollissima) trees were coming into North America
that were being planted in nurseries and sold as specialty trees. With some of these Asian chestnut trees came the chestnut
blight fungus. The blight was first discovered at the Bronx Zoo in 1904 by Hermann W. Merkel. Asian chestnut trees carry resistance
to Cryphonectria, while the American chestnut was no resistance to this deadly canker disease. From the Northeastern U.S.,
the blight spread rapidly through the native range of the American chestnut. It completely
decimated the native population, approximately 3.5-4.0 billion trees, in less than 50 years. The fungus traveled by the wind
and on the lumberman that logged these trees. William MacDonald, a professor of plant pathology at West Virginia University and the treasurer of the
American Chestnut Foundation, wrote "The devastation of the American chestnut by the chestnut blight, represents one of the greatest recorded changes in natural plant population
caused by an introduced organism." |
| Given the success and importance of chestnut in the east (Read more about the history of the American chestnut tree here),
it is likely that chestnut was planted elsewhere in the Midwest, yet other chestnut stands are extremely rare. Our hypothesis
is that this particular stand thrived because the correct mycorrhizal fungi were present in the soil. So our study aims at
identifying the mycorrhizal fungi associated with this particular stand of American chestnuts. It is also interesting to see
if local fungi have adapted to grow on or with the chestnuts or if species of fungi from the native range have found the disjunct
stand here in Wisconsin. We have examples of both scenarios, obviously the Cryphonectria has found the stand, but also
Ciboria americana, a small cup fungus specific to chestnut burs, has found the stand as well. It is also likely that the local
mycorrhizal fungi have made a host jump from closely related tree species such as Oak or Hickory, both of which are found in
the chestnut stand. |
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| There are a number of other research projects going on at this particular stand of chestnuts, the largest being a cooperative effort between researchers from the Wisconsin DNR, Michigan State University, and West Virginia University,
looking at trying to save these trees using a hypovirulent strain of the chestnut blight fungus. The hypovirulent strain of Cryphonectria has a dsRNA (double stranded) virus that renders the strain "less virulent". This "sick" strain can still cause disease, but is
unable to kill the trees. |
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