Wednesday, October 30, 2013

Forest Restoration Setback

In 2003, our organization expanded a forest restoration project originally begun in 1990.  In the expanded planting of 200 trees, we included a dozen pure American chestnuts (Castanea dentata) that we obtained from a nursery in Oregon.  The Oregon nursery said it believed its seedlings were resistant to the chestnut blight fungus (Cryphonectria parasitica), a pathogen introduced into the United States in the 1920s via imported Chinese chestnut trees.

For those who don't know the story of chestnut blight, the fungus quickly spread from the point of introduction (New York City) throughout the eastern United States.  By the time the pandemic had subsided, one quarter of all trees in the eastern deciduous forest had died, and what had been a major component of the forest became, for all intents and purposes, ecologically extinct in only a few decades.  (Not all chestnut trees died outright; the roots of some of the trees remain alive and continue to produce sprouts.  Once the sprouts reach about 20 feet in height, they are attacked by the fungus again [the fungus remains in the environment] and die back to the ground.  Some saplings even survive long enough to flower and set seed.)

With regard to our planting, the chestnuts have grown tall and beautiful over the last decade; perhaps, I hoped, they really were resistant to the fungus as the nursery suggested.  Then, two weeks ago while on a walk, I noticed that one of the trees had a wound located right a the top of the tree shelter we use to protect all trees from deer damage.  Maybe the tree shelter had rubbed the bark and caused the wound...  But, you probably already know where this is going.  On closer inspection and upon comparison with references, the wound turned out to be a canker caused by the blight fungus.  In fact, there are tiny tell-tale red fungal fruiting bodies on the bark surrounding the canker as well, visible above the canker if you look closely at the image accompanying this post.

I contacted the American Chestnut Foundation (which is trying to develop a resistant chestnut strain) to determine if I should destroy the tree to prevent or delay the fungus from spreading to the other chestnuts.  The Foundation's representative told me that my story was all too familiar and that destroying the tree would only delay spreading the fungus by a very short time.  Better, the person said, would be to let nature takes it course and, hopefully, the roots will re-sprout once the above-ground portion of the tree dies back.


packrat said...

I'd not heard the chestnut blight story, Scott. Too sad. Your recent discovery doesn't bode well for your trees, but, perhaps, some of the batch you got from Oregon will prove to be resistant. One can always hope.

Mark P said...

Oh, man, what a bummer.

Scott said...

mark: My reaction exactly.

Scott said...

Packrat: I now think that the Oregon-raised trees might have been believed to be resistant because Oregon is not in the native range of American chestnut. Someone probably planted a chestnut in Oregon many yeas ago, it thrived and produced many nuts, but there wasn't a critical mass of American chestnut trees there to carry the blight. The Oregon tree probably wasn't resistant at all, was just planted far enough away of the epicenter of the blight to escape infection. We can hope that the remainder of its cohort here in my preserve will do better, but I suspect they'll succumb, too.

robin andrea said...

That really is a bummer.

Scott said...

Totally, Robin Andrea!

John "By Stargoose And Hanglands" said...

I admire a man who can use the word "setback" when he really wants to use something much stronger. Although I'd not heard of Chestnut Blight all the elements of the story are familiar as we've had something similar with English Elms, Ash and our Horse Chestnut trees. One can only hope that resistant strains are eventually found.

Scott said...

John: You're right, but the American chestnut die-off occurred before I was even born. I'm sure that if I had been around when one-quarter of the trees had died, I would have been much more distressed.

American elms experienced a similar die-off when another fungus was introduced into the United States; we call it Dutch elm disease, but I'm not sure if the fungus originated in The Netherlands or not. American elms had been planted very widely as shade trees, and nearly all (that were not treated annually by arborists) died. Horticulturists have developed several new resistant strains of American elms (one is called the "Liberty" elm), and they're being planted again; in fact, we have planted about 10 of them in our preserve.

Our White Ashes (one of the most common trees in my preserve) are under attack by a syndrome called "ash yellows" that kills the trees over a period of a few years. But even more problematic is an introduced insect, the emerald ash borer, that was introduced from eastern Asia to the central United States in wooden shipping pallets; where the borer has spread, every single ash tree (not treated annually by an arborist) has been killed. So, if the ash yellows leave any ash trees living in my preserve, the borer will get them within the next few years.

We have a few Horse Chestnut trees here, and they seem to be doing fine. Horse Chestnuts are an insignificant component of our woodlands; they're usually planted ornamentally here.

All very discouraging.