Monday, September 24, 2012

Hoping for a Chestnut

I went in search of the American chestnut tree, Castanea dentata.  A quest not really so unexpected, given a recent visit to Scientists’ Cliffs on the Chesapeake Bay (see previous post).  The Scientists’ Cliffs community was founded in the mid 1930s by G. Flippo Gravatt and his wife Annie, both Department of Agriculture scientists.  Flippo Gravatt, a plant pathologist, played a role in the government's responses to the blight that ravaged the American chestnut in the first decades of the 20th century, and a few surviving chestnut trees had attracted him to this site on the Bay.

The American chestnut tree was once the dominant species of tree in much of its range along the east coast of the United States.  According to naturalist and conservationist Kelby Ouchley, in the mid 19th century up to half of the trees in the wooded uplands of its range were chestnuts.  (Flora and Fauna of the Civil War:  An Environmental Reference Guide, 2010, Kindle version.)  The picture below, taken at some unknown date in the period between 1891 and 1936, shows a stand of American chestnuts in Big Creek Gap, Tennessee.

(This photograph is from the American Environmental Photographs Collection, carrying AEP image number of AEP-TNP26, Department of Special Collections, University of Chicago Library.  It was downloaded from the Library of Congress.)

In 1785, botanist Humphry Marshall wrote of the American chestnut tree:
This often becomes a large tree, growing to the height of sixty or eighty feet, and to four or five feet in diameter, sending out but few branches, garnished with long spear-shaped leaves, toothed or notched on their edges.  The timber is used much for rails, splitting free and out-lasting most of our Oaks.  The kernel of the nuts are dried and used by some as a substitute for Coffee.  The wood is also burnt into coals for the use of blacksmiths, &c. but not much esteemed for common fuel.
This description appeared on pages 46-47 of Marshall’s magnum opus titled Arbustrum Americanum:  The American Grove, or, An Alphabetical Catalogue of Forest Trees and Shrubs, Natives of the American United States, Arranged According to the Linnean System, a book “recognized as the first botanical treatise written by a native American on American plants, produced in America,”  (Humphry Marshall (1785), American Philosophical Society.)  Marshall gave the American chestnut tree the scientific (Linnean) name Fagus-Castanea dentata, which was shortly changed to Castanea dentata.

(I don’t know the taxonomic reason for the subsequent name change, but the current name without a hyphen seems simpler and cleaner to me.  To name the genus, Marshall joined two Latin words, fagus meaning “beech” and castanea meaning “chestnut.”  Though the chestnut is a member of the beech family and the leaves of the beech (Fagus grandiflora) are somewhat similar to those of a chestnut, there’s no confusing the seed pods or nuts of the two trees.)

In the never ending sequence of subtitles to his work, Marshall noted that for the various genera described therein, it would contain “[s]ome hints of their uses in medicine, dyes, and domestic oeconomy [sic].”  “Hints” was certainly the operative word because his sketch of the American chestnut tree is unduly parsimonious, failing to capture the central role this tree played in 18th and 19th century America, particularly in rural communities throughout the tree’s range.

Of the centrality of the tree in some parts of America, science writer Susan Freinkel, in her engrossing book American Chestnut:  The Life, Death, and Rebirth of a Perfect Tree (2007), writes
A century ago, the American chestnut was one of the country’s most populous and important trees, a soaring tower of wood that ruled the East Coast forests from Georgia to Maine.  Many considered it the “perfect tree,” for chestnut had a value and versatility unmatched by any other hardwood.  And nowhere were those qualities better appreciated than in southern Appalachia, where generations of impoverished mountain farmers had depended on the chestnut for food, lumber, and livelihood.  “Chestnut defined the region,” says Charlotte Ross, a folklorist at Appalachian State University, in North Carolina.  “If ever a region was associated with a tree, then the chestnut was our tree.”  (p. 1-2)
Throughout the tree’s range, rural families turned to chestnuts for sustenance, and left their livestock, particularly their pigs, to roam the forests and feed on the nuts in the forest floor’s mast.  The other flora and the wild fauna that depended upon the chestnut for survival, in turn, also provided food to the people who hunted here.  Many used the chestnut for medicinal purposes, including drinking a tea made from the roots to treat diarrhea. They felled the tree for its rot-resistant wood, built fences, cabins, and furniture from it.  Stands of American chestnuts were safe-guards against an uncertain future.  No wonder many people felt strong emotional ties to these giant, soaring trees.

But, by the first decade of the 20th century, the American chestnut was under deadly assault by a fungus, Cryphonectria parasitica, which possibly hitchhiked into this country with imported Chinese chestnut logs.  Although Asian chestnut trees had evolved to cope with the fungus and keep it in check, American chestnuts had no defense against the invader.  Before mid-century, the American chestnut had been essentially obliterated as an extant species.  A staggering 3.5 to 4 billion trees perished before the efficient onslaught of C. parasitica.

Many people in the generations that grew up with the chestnut and then witnessed its demise grieved for the tree.  Sharpening the sense of loss was the tree’s ability to regenerate from its roots, repeatedly offering false hope until, inevitably, the sprouts succumbed to the fungus.  Freinkel’s book captures this mourning in the poignant recollections of those who experienced the demise of the chestnut first hand.  The photograph below, taken on an unknown date, but presumably in the early decades of the 20th century, shows a woodland wasteland of dead and dying chestnuts on the Skyline Drive in Virginia.  It’s a searing vision of desolation.

(This picture, identified as Catalog B, Higher Plants, 200 2 American Chestnut Tree, Negative No. 6032, carries a reproduction number of HAER VA,70-LURA.V,4—97, and is available from the Library of Congress’ Prints & Photographs Division.)

I can walk through woods today, where once stands of chestnuts dominated the canopy, and, in my ignorance, see nothing missing.  Never knowing what was once there, I do not know what is gone, but an arboreal giant was there and its absence is still being felt, profoundly, in the woodland ecosystem.  Steven Gaines, land manager of the American Chestnut Land Trust (Calvert County, Maryland) has written:
The loss of the American chestnut has disrupted many ecological complexes, many of which are still poorly understood.  The absence of the chestnut as the dominant species in woodlands has left a major niche vacancy throughout its range.  (The American Chestnut:  A Giant Remembered, Watershed Observer, Spring, 2012.)
That vacancy, according to Gaines, has allowed slower growing trees to now dominate the woods, the tulip poplars, oaks, and hickories.  Wildlife has suffered as the nutritional value of mast on the forest floor has diminished markedly with the absence of chestnuts.  The very underbrush has changed because chestnut trees are no longer present to nurture their own seedlings by exuding enzymes that warded off competition.  The consequences are myriad and far reaching.

As the tree was succumbing to the fungus, efforts, misguided or otherwise, were mounted to save it.  Those efforts have changed and evolved, and today several lines of attack are showing some promise of success, some progress in bringing back the American chestnut.  Indeed, these campaigns are fueled these days by renewed optimism.  Freinkel offers an exciting account of these efforts.  Some are also being nicely described in the series of articles by Steven Gaines that appear (or will appear) in the Watershed Observer, the American Chestnut Land Trust’s newsletter.  (In addition to the Spring, 2012 issue (cited earlier), there is an article in the Summer, 2012 about the tree's potential recovery, and another scheduled to come out in the Winter, 2013 issue.)

As best I can reconstruct, there are roughly four approaches into which scientists and lay people are channeling their energies for the renewal of the species.

In the mid 1960s it was discovered that some chestnut trees in Europe seemed to be recovering from the blight because a virus was sapping the fungus’ strength.  As Freinkel puts it, “Incredibly enough, Cryphonectria parasitica had come down with the fungal equivalent of a bad cold.”  (p. 111)  This phenomenon was labeled “hypovirulence” and a concerted effort was undertaken to infect the C. parasitica with this virus to the greatest extent possible.  Not a cure, only a delaying action, and it has proven much more successful in Europe than in the United States where a more complex mix of infecting virus strains has been discovered to be at work.  Still the effort continues.

Not surprisingly, some have turned to bioengineering to identify a gene (or genes) that might convey fungal resistance to the American chestnut tree.  Even as work continues to find or fashion the right genetic combination, the panoply of issues that typically surround any effort to bioengineer an organism has arisen around this approach as well.

And then there’s the breeding of blight resistant chestnuts which has moved down two paths – backcross breeding involving American and Chinese chestnut trees, and breeding focused solely on American survivors of the fungal attack.  In a backcross breeding project, American and Chinese chestnuts are cross pollinated and then the most blight resistant hybrids resulting from that cross are bred back with the American parents (or other American specimens).  This is repeated several times, in each instance selecting the progeny with the greatest blight resistance.  Each backcross reduces the overall contribution of the Chinese trees, increasing the likelihood that all of the desirable American traits (e.g., tall growth) will be retained along with fungal resistance from the initial Chinese breeding partners.  The American Chestnut Foundation is associated principally with backcross breeding.  Products of backcross breeding are now being planted in forests.  Gaines notes that between 8,000 and 12,000 seedlings have been planted in national forests.  “Furthermore, there are currently 350 chestnut breeding orchards in 15 states, containing approximately 150,000 trees under observation associated with this program.”  (Watershed Observer, Summer, 2012 issue.)

Some breeders and groups have focused their cross breeding efforts solely on those American trees that have survived the blight, in hopes of enhancing their resistance.  Successive generations are culled to breed trees with the greatest blight resistance.  Those engaged in this work argue that, if successful, the resulting trees would be 100 percent American chestnut trees, ensuring the continuation of the desirable American traits.  The American Chestnut Cooperators’ Foundation is actively supporting this approach.  Its 2012 newsletter notes that “cooperator” planters reported that, in 2011, over 2,800 of the chestnuts produced by the Foundation’s orchards and previously distributed to these planters were still alive.

I am quite taken by the image of the battle-scarred American chestnut tree standing alone in the woods, battling the fungus to, at least, a draw because of some genetic variant the tree carries.  In theory, it was possible that the fungus might have devastated the American chestnut only to be thwarted, ultimately and naturally, by some genetic oddity (or oddities) in a few surviving stands of trees that would have then fueled the tree’s comeback - evolution at work.  But there’s a particularly sad twist to this part of the story.  The U.S. Forest Service in the 1920s advised landowners to take down all of their chestnuts, diseased or healthy.  Freinkel writes, “The Forest Service, still in its youth, had little experience with forest epidemics; its deadly simple response to the blight was deadly for the species.”  (p. 139.)  And so we decimated the ranks of potential survivors.

Abutting the Scientists’ Cliffs community is land of the American Chestnut Land Trust, an entity which protects over 3,000 acres in Calvert County, Maryland.  I assumed it would be the most appropriate place to begin my quest.  After all, the Trust is named for the so-called “Maryland Champion” chestnut tree which was the largest extant American chestnut in Maryland . . . until it succumbed to the blight and fell in 2006.

I figured my search would start with the site where the tree once stood.  But this was not a romantic gesture, holding up a feeble hope that I would somehow feel the spirit of the fallen “gentle giant” (as the Trust calls it).  No, I had some inside information, I’d been told that, springing from the roots of that tree, were some chestnut sprouts with trunks 5 inches or so in diameter.

A tromp through the Trust’s woods on one of the first cool mornings of late September brought me to Chestnut Trail, a short leg between two longer trails.  I headed northeast in the woods along the trail and quickly reached my goal.  I found a small wooden marker identifying the fallen tree, with its common and scientific names (I fear it misspells the genus name).  A plastic coated, weather worn notice, affixed to the marker, announced the death of the tree.

Behind the marker was what remained of the Maryland Champion.  I stared into the torn, twisted remains of the trunk.

And then I noticed just to my left, two rough-barked trees reaching for the light that came down through the wood’s canopy.  These were chestnut sprouts, robust and tall, perhaps having outgrown the label “sprouts.”

My eyes traced the path one was weaving toward the sun.  Telltale clusters of chestnut leaves shone green above me.  Once more, hope springs for the American chestnut.

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