Chestnut Allelopathy

By James Egenrieder

[reprinted with permission]

There was a short but very interesting interview on NPR (public radio) on November 8, 2005 that quickly caught my attention. This interview was part of the daily All Things Considered program; the interviewee was botanist Erik Nilsen and the interviewer was John Nielson. The interview was titled Autumn Leaves: Pretty or Poisonous? What surprised me was Nilsen, while discussing allelopathic qualities of colorful autumn leaves, which he studies at Virginia Tech, stated But it may be the tree that was the master of this strategy is one that?s not even around anymore. It was called the American chestnut, and it was wiped out by an exotic fungus in the early 1900?s. Nilsen says the leaves that fell from chestnut trees were exceptionally potent, which is partly why they once completely dominated the forest in southern Appalachia.

Recently, I received a transcript of the interview and tracked down Dr. Nilsen, Professor of Biology at Virginia Tech. Note there are several errors with names in the transcript; Erik Nilsen is listed as Eric Nilsson and the college is listed as Virginia State. I emailed Nilsen to get clarification on several statements. He was kind enough to clarify those statements and to send me a paper [Elsevier Abstract] (which if you e-mail me, I can forward the copy) titled ?American chestnut as an allelopath in the southern Appalachias.? I am not allowed to distribute the transcript but you can listen to it or obtain a copy of the transcript at the NPR website. Instructions are provided below.

Several interesting findings in the paper:

  • Chestnut?s ability to suppress germination of eastern hemlock and anecdotal evidence of hemlock?s ability to exclude chestnut suggests a dynamic competitive relationship between two important southern Appalachian tree species.
  • American chestnut leaves produce allelopathic chemicals that inhibited the germination of lettuce, rosebay rhododendron, and eastern hemlock seeds and the radicle growth of lettuce and rosebay rhododendron in a germination chamber study
  • These results suggest that allelopathy could have been a mechanism whereby American chestnut was able to control competition from both tree and shrub species in pre-blight southern Appalachian forests.
  • The fact that both American chestnut and eastern hemlock exhibit allelopathic properties may explain their rare association in pre-blight forests.
  • The rapid expansion of rosebay rhododendron during much of the 20th century may be attributed, at least in part, to the loss of the allelopathic properties of American chestnut leaves.

To listen to the interview,