Saturday, November 28, 2009

Book Review: American Chestnut

American Chestnut: The Life, Death, and Rebirth of a Perfect Tree
Susan Freinkel

(Find it in our widget at right under food nonfiction!)

In light of some of the chestnut recipes featured recently on this blog, it only seemed right to read a book about the sad fate of the American chestnut tree and the improbable but exciting efforts to bring it back.

You may not know the story of what happened to the American chestnut tree, especially if you’re in your 20s – because the tree has been for all intents and purposes extinct in the wild for your entire lifetime. How would we know to miss something that has never been there? Well, back in the day chestnut trees used to comprise a huge amount of the deciduous forest from Maine all the way down to Georgia, across the eastern seaboard and west to Ohio. The trees were particularly important in Appalachia, where they provided a free source of animal feed for impoverished farm families. In fact, there used to be an interesting east coast chestnut economy: many poor mountain families would gather chestnuts each fall and winter after big storms and take them to the general stores which used to serve as the centers of Appalachian commerce. There they’d be paid in little metal tokens which would serve as store credit for shoes, sugar, and other things the families could not make on their own – each store used these credits like its own mini-currency. From there, the general store owners would bring the loads of chestnuts to dealers at train stations; even the train conductor on these trips would get a cut, which was often his best pay for the whole year. The huge chestnut haul would finally be shipped to cities like Philadelphia and our very own New York City, and distributed to street vendors – before the blight, street carts roasting chestnuts were a classic scene and aroma on cold early winter New York City nights.

But in 1904, in the park which today has become the Bronx Zoo, a forester first discovered the fungus known as the chestnut blight – Cryphonectria parasitica. C. parasitica, unbeknownst to anyone, had taken advantage of increased international commerce by hitching a ride in from Asia, where it attacks Japanese and Chinese chestnuts. Those related species carry a high degree of immunity to the fungus and therefore usually survive infection. Not so for the American chestnut tree: this fungus creeps under its bark and eventually chokes off the flow of its sap, killing the tree within a couple years. Only some of the root system remains intact, and it sends up new shoots for several years more in an effort to regenerate. However, in a disturbingly Sisyphean manner, every time those shoots start to get big enough to be a viable sapling, the fungus attacks again and suffocates them. If you take a hike in eastern forests you may well see the little shoots of these frustrated American chestnuts, but you are extremely unlikely ever to see an adult tree. By midcentury, the blight had killed about three to four BILLION American chestnut trees, basically eliminating them from the wild but for some miraculous old survivors.

Susan Freinkel’s American Chestnut tells this story, and goes on to chronicle the various 20th-century efforts to save the chestnut from its blight. The first third of this book reads roughly like a disaster movie, with the blight creeping down the coastline despite all efforts of frantic state governments to save this valuable tree. (Ironically, many of them made it worse by chopping down vast swaths of chestnut forest in an effort to quarantine the fungus or to get maximum value out of the chestnut lumber before the trees were attacked.) The next third is more of a detective novel – chronicling how various scientists and enthusiasts, from the start of the pandemic to today, have come up with ideas as to how to save the chestnut.

One idea is called “hypovirulence,” and basically consists of introducing a parasite upon the parasite. Yes, this has a disturbing give-a-mouse-a-cookie quality – but it turns out there actually is a virus that weakens C. parasitica (as Frienkel says, it’s like the fungus catching a cold), which can give an individual American chestnut a fighting chance. Unfortunately, the chestnut as it previously existed almost always isn’t strong enough to ultimately fight off the virus even where hypovirulence is employed.

Freinkel also devotes a chapter to efforts to genetically engineer a blight-resistant American chestnut. The resources haven’t been devoted to this that have been brought to bear on, say, creating Monsanto’s “roundup-ready” crop monstrosities, but a couple researchers have tried to add foreign genes to the chestnut to help it resist the blight. (Research still hasn’t revealed which genes give the Chinese and Japanese chestnuts their immunity.) So far, it hasn’t worked out so well; Freinkel deals with this subject evenhandedly, and expresses justifiable concern about things like adding antimicrobial frog-skin genes to an edible plant. (Believe it or not, that was actually one idea.)

But the majority of this section concerns efforts to breed blight-resistant chestnuts, both by crossing the rare surviving American chestnuts with each other and – the most promising method – by “backcrossing” American chestnuts with their resistant Chinese cousins. Basically, this means making an American x Chinese match, and then crossing the result with other American trees over and over and over, selecting the best offspring that still have good resistance, until you have a tree that is almost entirely genetically American but isn’t susceptible to the blight. The American Chestnut Foundation took this approach. Of course, trees grow slowly, so the timescale for doing a project like this was many decades – far longer than one individual researcher’s career. That’s part of what makes the story of the chestnut a good book and an interesting exploration of environmental tragedy, the power of human nostalgia, and faith in science to ultimately put things right.

But what makes this book stand out to me is not just the compelling story, but the author’s thoughtfulness about the ultimate consequences of releasing a new, blight-resistant “backcrossed” American-ish chestnut tree into the wild once we do have one. What does environmental restoration really mean? After all, we can’t actually recreate the forests that existed back before the blight (which were filled with passenger pigeons – oops – and not yet devastated by coal mining). Is it meaningful to create our best approximation? Are we kidding ourselves to think that’s even possible? Does it just make us feel better about the next time we make a huge environmental mess, because we presume we can just clean it up later? Freinkel comes down on the side of restoration, but you can see why it’s best to be cautious where we have insufficient scientific knowledge to really know the consequences of our environmental tinkering.

This book was written in 2006, so the story ends right at the cusp of developing a truly resistant, mostly-American chestnut tree – and I’m happy to say that since then, the news has been good. Check out this Times article from September on the first efforts to reintroduce a brand new blight-resistant tree:

For what it’s worth, since this IS a food blog: real American chestnuts are apparently a little smaller and therefore harder to peel than Chinese ones, but they are sweeter, with a carroty taste. I like the hybrids we can buy at the market today, but I still hope that someday I can try a real American chestnut.

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