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A Charismatic Extinction and an Irreversible Loss - February 4, 2018

Few who delve into the annals of American biological history have not lamented over the loss of the American Chestnut (Castanae dentata). For 40 million years these stately trees ran the gamut of the Appalachians, veritable monuments to nature’s bounty. The American Chestnut was a bonafide Jack-of-all-trades, supporting a major timber industry, a thriving nut-crop economy, and even the American leather industry (as the main source of tannins for leather tanning). But in 1904 the Asian chestnut blight (Cryphonectria parasitica) was first discovered on chestnut trees in the Bronx Zoo. In less than 40 years the fungal blight spread through the chestnut’s full range, killing almost every mature chestnut tree in the United States.

By 1950, the USDA declared the American Chestnut functionally extinct. Today, out of an original 4 billion, less than a few thousand American Chestnuts remain. But each year that number steadily rises, thanks to a few important factors:

First and foremost, the American Chestnut never really went “extinct”. Chestnut blight kills the tree, but the roots remain alive, putting out shoots year after year that catch the blight and die before reaching maturity. Millions of these living stumps dot eastern forests, waiting for a chance to try again next year. These chestnuts-in-waiting provide the much-needed genetic material for selective breeding programs that will eventually produce blight-resistant trees.

Second, and most importantly, people care.

A lot.

Maybe it’s because of the historic economic importance and ubiquity of the tree, maybe it’s because of its tall, stoic charisma, or maybe people just prefer to fight a winning battle, whatever the reason the plight of the American Chestnut has enough moral support and monetary backing to rival the panda, the elephant, and all the sea turtles combined. Truly, the American Chestnut is the world’s most charismatic extinction.

And that’s a great thing: to see the American Chestnut return to the forests of Appalachia would be an undeniable win, and it’s something our children will likely see. We could point at those revenant saplings and proudly proclaim “We did it! We fixed our mistake!” and environmentalists could go home feeling good about themselves for a change.

But we must remind ourselves extinction does not happen in a vacuum. In the 40 years of drastic American Chestnut decline, more was lost that just trees: three species of moth went extinct without the chestnuts to complete their life cycle.

And that’s real, honest-to-goodness extinct. Not charismatically extinct like those lucky chestnuts. Three entire species of animal, with their unique and complex genetic information, gone for good, with names that you’ve almost certainly never heard of before:

Argyresthia castaneela, the Chestnut Ermine, whose caterpillars ate the underbark of the American Chestnut

Coleophora leucochrysella, the Chestnut Casebearer, whose caterpillars wove little cases out of chestnut leaves

Zimmermannia phleophaga, the Phelophagan Chestnut Moth, whose larvae lived under the bark of the American Chestnut, and who probably unwittingly caused their own extinction by helping spread the blight from tree to tree

All gone for good.

This phenomenon is known as coextinction, in which organisms solely dependent on one species go down with the ship. In Science, September 2004, Koh et al. estimated that 6,300 species not currently recognized as endangered would go “coextinct” along with their endangered counterparts. Like the chestnut moths, these organisms put all their eggs in a basket that might suddenly disappear.

But the biggest issue facing these at-risk organisms is the challenge of studying them. Almost all these creatures are small, specialized on an organism that is already hard to find, and painfully uncharismatic; many of them are host-specific parasites like mites, fleas, or flatworms. Unlike the American Chestnut, people just don’t care. After all, if you didn’t care about the cute, captivating Carribean Monk Seal going extinct, you certainly didn’t shed a tear for Halarachne americana, the tiny nostril-mite that disappeared along with it.

This is a fundamental problem with the reporting of endangered species to begin with; the IUCN Redlist is severely lacking when it comes to small and uncharismatic organisms. Biologist Robert Dunn describes endangered insect species as the “Neglected Majority”; of the thousands of modern insect extinctions that have occurred, only 70 have been documented. The same goes for studied coextinctions; only a handful have been successfully recognized.

The one silver lining of coextinction is that protection of charismatic organisms casts indirect protection on their less than alluring affiliates. But the unfortunate truth is that humanity knows very little about earth’s littlest members when compared to its largest, and this lack of contextual information makes study more challenging. Even the list of insects that vanished with the chestnut is likely incomplete; many chestnut-specific beetles and wasps may also be extinct, but without further comprehensive study we just don’t know.

The extinction of any organism, big or small, is a loss of irreplaceable proportion. It is a loss of biodiversity; that safety net of genetic variety that allows for ecological adaptation and change. It is a loss of unique evolutionary history never to be replicated. Above all, it is a loss that we are almost certainly responsible for in our beneficial, but ill-informed, shaping of the natural world.

In the case of the American Chestnut, we should take great pride in its eventual return. But we shouldn’t forget the web of life that was irreparably damaged with its demise. Bringing the chestnut back won’t bring those moths back, and it won’t restore the ecosystem to what it once was.

Whatever does grow from the stumps of the old guard will be something entirely new, albeit no less charismatic.

 

Simons is a seasonal scientist with the Maryland Coastal Bays Program. 



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