Sunday, June 17, 2012

American Chestnut Trees

Here's something you don't see every day...

American chestnut (Castanea dentata) leaves. American Chestnut tree!  My parents are growing American Chestnuts (Castanea dentata) on their property to help bring this great American tree species back to prominence.  Mom learned about the American Chestnut and wanted to get involved, and Dad was game to help Mom put in the work needed to plant and protect these trees as they try to survive.  They are both pleased with their American Chestnuts.

Dad with an American Chestnut on Father's Day.
Eastern forests in the United States were once dominated by this tree species.   If you think about how prevalent oak trees are in the Eastern forests of this country, it gives you a sense of the size of the American Chestnut's niche.  Its nuts provided great quantities of seriously delicious food for people, deer, bears, squirrels and many other animals.  It is a fast-growing member of the oak plant family (Fagaceae), and its wood is strong and particularly resistant to decay, so it was an extremely useful lumber-producing tree.

Why am I speaking in the past tense?  Because this tree species is now mostly gone due to the chestnut blight.  Chestnut blight (Cryphonectria parasitica) is a fungal disease that evolved in Asia and was accidentally brought to the U. S. in the late 1800's, probably on furniture, lumber or nuts.  Chinese Chestnut trees evolved with the disease, so they are resistant to it, but our trees were not resistant, and they succumbed to the disease as quickly as Native Americans died from European diseases introduced by the first European settlers of this land.  The disease was discovered in 1904, and by 1950, almost all the American chestnut trees were dead, with only small shrubby root sprouts left surviving.

Chestnut catkins (flowers).  The narrow ones have only male flowers, the upper one has some pollinated female flowers, which will produce nuts.
Several organizations, including the American Chestnut Foundation, are trying to breed blight-resistant chestnuts and repopulate our forests with this missing foundation species.  Chestnut-lovers are using existing trees to search for blight resistance.  They are also breeding Chinese Chestnut trees with American chestnut trees, eliminating those that don't survive the blight, and crossing the offspring back with American Chestnuts to result in trees that are mostly American but with the Chinese blight-resistance genes.  Right now, there exist trees that are 98% American with 2% Chinese genes.  These mostly American Chestnuts are responding well to blight exposure.  Nothing against Chinese Chestnut trees - they are great, but they're adapted to Chinese ecosystems.  Chestnut-lovers and ecologists want to maintain both species - with the American Chestnut trees back in the ecosystems here.  In the mean time, many people have planted Chinese or European Chestnuts in their yards in order to have some chestnuts to eat in the fall. 

Chestnut catkins with pollinated female flowers that have become burs, and male flowers above them.
Chestnuts have either all male flowers or male and female flowers.  Mom and Dad obtained dozens of chestnuts from the American Chestnut Foundation so they would have many trees and guarantee that they could have cross-pollination between the trees.  Chestnuts cannot self-pollinate.  This time of year,  pollinated female flowers are enlarging into burs.  Burs are spiky fruits that contain chestnut seeds.  In the fall, the seeds will be mature, the fruits will crack open, and the whole bur will fall to the ground.  As soon as the burs crack open, the seeds are mature and ready to overwinter and grow into new trees or to be eaten.

There are a few remaining adult American Chestnuts in North America.  Many of the surviving ones are outside the former range for American Chestnut trees, so the blight hasn't spread easily to them.  Also, there are different climactic conditions outside our chestnut's normal range, which cause the blight fungus to be weaker, or hypovirulent.  Mom and Dad's chestnut trees are outside the normal range, so they may survive longer than other American Chestnuts.  Of the original seeds they planted, about half remain.  Their trees probably didn't die due to blight, but to non-ideal climactic conditions.  Blight tends to affect teenage trees, and these trees are younger.  It is likely that all my parents' trees will eventually die, unfortunately.  Still, they may have a resistant tree, and their trees help maintain living tissue, help educate people about the trees, and help scientists learn more about what these trees need to survive.  With so many people working to solve this ecological tragedy, it appears likely that American Chestnuts will eventually recover.  I'm so proud of my parents for helping the American Chestnut!


  1. Good to see some dedicated souls are making the effort. It is amazing how many people are working to bring back the chestnut. So many of the people who remember the Chestnut are beginning to die. My aunt in Tennessee regales in the stories, but she is the only one of that generation who grew up in Southern Appalachia and who reemembers.

  2. For the past 3-4 years we have been trying to get 10 small seedlings from TACF to grow on our property in SW PA. We have one healthy original chestnut stump sprout nearby so we know the range is good. Our seedlings have died each 18 months or so and had to be replaced. Only two currently survive. We are tempted to go with Chinese replacements since the newest generation of the improved mix are not yet available. But we don't want the rigidly spiny husks littering our property.

  3. Hey Gary, Thanks for your comment, and glad to see you're trying to get the chestnuts growing. Congratulations on having two survive! Given that many seedlings die when any tree is planted from seed, this does not sound unusual. Did you take care of them or let them fend for themselves? If you let them fend for themselves, you can assume they do well in your environment. If you don't want husks, I would recommend against a Chinese chestnut. All chestnuts have spiny husks, and if you aren't enjoying the nuts or helping the American chestnut recover, it seems like you would like another tree better. Good luck!

    Lorna at Biological Thinking

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