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.

Saturday, September 15, 2012

Communities of Interest

Last week I was invited to collect fossils for the first time along Scientists’ Cliffs on the western shore of the Chesapeake Bay.  This is a rare treat for fossil hunters who don’t own property here (and don’t kayak) because the only access to the beach from the land side is across private property.

At these cliffs, part of the Calvert Cliffs, the dominant formations are middle Miocene (roughly 16 to 12 million years old).  The fossil material found here is likely to be a bit younger than what I find about 10 miles to the north (a couple of miles below Chesapeake Beach, Maryland) where I usually hunt.  In general, as one moves south down the Bay, the older (lower) formations sink beneath the beach and the younger (upper) formations make up more of the exposed cliffsides.

If I’d done my homework I would have expected to find some fossils here different from my usual suspects.  But, to be honest, I only anticipated a greater abundance of the same, assuming these beaches were not as scoured by collectors as those further north.  (I was wrong about that.)  The beach itself really doesn’t appear dramatically different at first glance, slumping cliffside here seems like slumping cliffside to the north.

But there are some telltale signs that things are actually very different.  For one, the cliffsides here don’t generally reach the heights they do to the north.  Certain familiar layers in the cliffs are dramatically thinner here or no longer even visible.  Yes, indeed, age and distance make a difference.  To the north, many of fossils are eroding out of the older Calvert Formation, while here the younger Choptank Formation plays a much stronger role in creating the community of fossils protruding from fallen blocks of clay and the gray sand on the beach, or swirling in the wash.  In both locations, Calvert and Choptank layers are exposed, so, neither contributes exclusively at one place or the other, but a much greater proportion of the northern cliffs are Calvert, while 10 miles south, the Choptank predominates.  Indeed, most of the Calvert has disappeared.  (Detailed information on the exposure of these formations along the Calvert Cliffs can be found in Stratigraphy of the Calvert, Choptank, and St. Marys Formations (Miocene) in the Chesapeake Bay Area, Maryland and Virginia, by Lauck W. Ward and George W. Andrews, Virginia Museum of Natural History, Memoir Number 9, 2008.)

The picture below captures a small segment of the fossil invertebrate faunal community I found along the Scientists’ Cliffs shore.

The centerpiece of this picture is the mollusk Chesapecten nefrens Ward and Blackwelder.  Though penetrated in places (by predators?  by being battered in the waves?) and marked by barnacles, this is a wonderful specimen because, despite its travails, its perimeter is complete.  To give a frame of reference for the sizes of this and the other fossils in the picture, the C. nefrens measures slightly more than 4.5 inches from top to bottom.  Though C. nefrens is common along the shores of the Calvert Cliffs, this specimen is much larger than any I’ve collected further north.  Harold E. Vokes et al., in Miocene Fossils of Maryland (2nd edition, Maryland Geological Survey, 1999), confirm this size difference between specimens from the Choptank Formation and those from the Calvert.  Further, they observe that Choptank specimens frequently appear with many large barnacles attached to them.  (Though I was guided by Vokes et al., any errors in the identification of this shell and the other specimens in this post are mine alone.  Corrections appreciated.)

At the bottom left in the picture is a small segment of an echinoderm (in this case a “sand dollar”) named Abertella aberti (Conrad).  Vokes et al. describe this animal as common in the Choptank, but typically found broken.  Like a pottery shard, this piece of sand dollar only hints at the grace and complexity of the patterns that adorn the entire surface of the A. aberti.  Below is a close-up of the A. aberti fragment and the drawing of the entire echinoderm that appears in Miocene Fossils of Maryland.

Continuing clockwise are two examples of the mollusk Anadara staminea (Say), not one I’d found in the north, and probably with good reason.  According to Vokes et al., A. staminea is “known only from the Choptank.”

At the upper left is a single example of what I believe is a Balanus concavus Bronn, one of the large barnacles (though this one isn’t particularly impressive) often adorning the shells of C. nefrens.  Barnacles hold a certain fascination for me because, most surprisingly, the animals creating these shells are crustaceans.

Finally, at the lower right corner of the picture, is a damaged example of the gastropod Ecphora tricostata Martin.  I have found these at times up north and so it makes sense that Vokes et al. write that this species is commonly found in the Calvert Formation.  They do note that is rarely discovered in the lower Choptank, so, perhaps the small block of clay in which this specimen was encased came from the Calvert layer still exposed here at Scientists’ Cliffs.

The beach offered me a distinctive community of invertebrates.  There is another distinctive community here.  Well, actually, up above me on the wooded, rolling land that stretches back from the cliff edge.  In the mid 1930s, G. Flippo Gravatt and his wife Annie Gravatt, both scientists with the U.S. Department of Agriculture, purchased 238 acres of land here.  They were on a mission to create “a colony for scientists and professional people of kindred spirit.”  (Shawn White, Scientists’ Cliffs:  An Abbreviated History, April 15, 2009.)  The site held myriad charms for the Gravatts, among them the fossils eroding from the cliffs.  But perhaps more attractive to Flippo Gravatt were the chestnut trees.  He had worked on the pathologies attacking the American chestnut tree and was one of the first scientists to breed these trees.  He “picked the land partly because it boasted a few surviving chestnut trees, and he built his own cabin there from chestnut logs.”  (American Chestnut:  The Life, Death, and Rebirth of a Perfect Tree, by Susan Freinkel, 2007, p. 148.)

In the autumn of 1935, the Gravatts and some colleagues dedicated the site, deciding to name it Scientists’ Cliffs, though that wasn’t the only name attached to it.  According to the history of the colony, Annie Gravatt anointed it “Flippo’s Folly.”  Several cabins were soon built, available initially for rent during the summer.  A more permanent colony emerged quickly with purchases of plots and the cabins.

From the outset it was intended to be a very select community.  Under the constitution and bylaws of the Scientists’ Cliffs Association, incorporated in 1937, only scientists could be members.  According to Susan Freinkel, that meant folks with PhDs.  “Later this was broadened to include all college graduates and then extended to those who had achieved recognized status in their profession without college degrees.”  (Scientists’ Cliffs:  An Abbreviated History.)

Management of the community evolved over time as an increasing number of people came to live here year round and infrastructure and other needs multiplied.  A Community Administrator is now responsible for addressing the quotidian needs of residents.  But the twice annual meetings of the Association, at which issues are discussed and decided, continue, thus ensuring the persistent of “[e]ssentially the atmosphere of a New England town meeting.”  (Scientist’s Cliffs:  An Abbreviated History.)

And then there’s the physical layout of the community, a wonderful mixture of cabins and houses nestled among the trees along winding roads.  Nature still predominates.  Curiously, though, I thought of St. Mary Mead, the home of Agatha Christie's Miss Marple.  No, Scientists' Cliffs is not an idyllic English village in appearance, but I had the same sense of this community as I do when contemplating the map of St. Mary Mead that appears in the Miss Marple mysteries - at its best, it offers a kind of sanctuary.  I suspect, as well, that, regardless of where in the English countryside Christie intended the community of St. Mary Mead to be located (about which there is some debate), fossils would be there, too.

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