Blue Ridge Naturalist: Consequences

A tick waits patiently on a grass stalk with its front legs out, ready to grab onto any large mammal passing by. Photo: Marlene A. Condon.

Thought experiments can be extremely useful when making decisions about how to manage the natural world. They can allow us to confidently predict a future outcome within specified parameters by employing knowledge of current, similar situations. 

For example, we know that one of the reasons the deer population exploded in the eastern United States over the past few decades was because the main predators (wolves, cougars) of these hoofed mammals were driven to extinction by humans in this part of the country. We also know that tick numbers increased as a result, along with Lyme Disease. 

By employing this knowledge, we can work through a thought experiment to predict what will happen when the efforts to bring back the American Chestnut (Castanea dentata) have reached fruition. It may make us rethink whether this effort is as good an idea as it might seem.

The American Chestnut, ecologically, culturally, and commercially significant, was infected by an Asian fungus first noticed around the beginning of the 20th century. Within 50 years, chestnut trees from Ontario, Canada (the northern edge of the species’ range) to its southernmost distribution in the eastern United States were virtually gone—the consequence of people’s interest in acquiring exotic plant species, some of which carry pathogens our native plants have no ability to coexist with.

Many organizations and scientists have since worked hard to breed a resistant American Chestnut. For decades, researchers have been crossbreeding a naturally resistant Asian species of chestnut with the American species in the hopes of creating a plant with the American Chestnut qualities that made it so valuable. However, it takes years for these trees to reach sexual maturity, making the entire process very slow, and no trees have been bred of extremely high resistance to the fungus.

But scientists have a new “trick” for improving resistance. American researchers are hoping to bring the American Chestnut back as a genetically modified organism, abbreviated as GMO, a term you may be familiar with. Many food crops are now GMOs, a tinkering with nature that some folks think is great, but which others have concerns about—and with good reason. “Transgenic” organisms (those with the genes of a totally different species within them) could possibly alter the genetic blueprint for others of their kind in the wild, with unknown consequences. Once the genie is out of the bottle, there is no putting it back in.

People tend to dismiss such concerns when they want something, and people want to bring back the American Chestnut. Researchers from the State University of New York’s College of Environmental Science and Forestry have engineered highly blight-resistant saplings by splicing a gene from wheat into the tree’s genome. Wheat and other grasses carry a naturally occurring gene that produces an enzyme that lessens the effects of oxalic acid, the main “weapon” of the fungus infecting our native chestnut.

It may take two to four years for the researchers to obtain permission from U.S. and Canadian regulators to distribute their GMO. If they are successful, their trees would be the first genetically modified organisms released into the wild for the purposes of reintroducing an endangered species. Recent tests have shown their genetically modified trees match or surpass the resistance of Asian trees to the fungus.

However, there will be consequences to bringing back the American Chestnut that people have not considered. Although many folks fall easily into the trap of believing that there couldn’t possibly be anything wrong with trying to restore the natural world to a former state, there can be plenty to be concerned about, especially in this case.

Today’s world is not the world of more than a century ago. When the chestnut dominated the forest canopy, it fed billions of Passenger Pigeons (Ectopistes migratorius) with the copious amounts of nuts it produced annually.

According to an 1813 account written by the renowned painter and naturalist, John James Audubon, “The air was literally filled with Pigeons…The light of noon-day was obscured as by an eclipse…” At the end of that day, these now-extinct birds were still flying by in the same numbers—their flight continuing throughout that night and into the next day and the next!

But thanks to humans, the population of Passenger Pigeons went from billions to just one within a hundred years of Mr. Audubon’s experience. A victim of overhunting and deforestation, their numbers dwindled until only Martha, a solitary female in a cage at the Cincinnati Zoo, was left (she died on September 1, 1914).

Fred Paillet, a University of Arkansas geoscientist, wonders whether it’s possible for the chestnut to someday be viewed as “invasive”, a problem, he writes, that he “would gladly live with.” [Winter 2010 issue of American Forests magazine] But he obviously hadn’t thought through that sentiment. 

Without the huge numbers of Passenger Pigeons that had coexisted with the American Chestnut, what will become of the superabundance of nuts that every mature chestnut tree will drop every year? They will be eaten by birds (such as jays, crows, and turkeys) and bears, increasing their numbers and making these animals a nuisance when they more frequently cross paths with people who will want more of them killed.

Deer and numerous kinds of rodents will increase in number, but the numbers of snakes (including venomous species) that could limit mouse populations may not increase, thanks to the overabundance of people who are living just about everywhere already, many of whom believe that the only good snake is a dead one. (Put this comment into a search box online and you might be horrified, as I was, to see the videos showing pointless cruel treatment of snakes.)

When folks refuse to coexist with these reptiles, snake populations do not keep pace with rodent populations, leading to a superabundance of mice and the ticks dependent upon them for a part of their life cycle. The ticks can reach adulthood and easily increase in number, thanks to the chestnut-fattened-up deer whose numbers will be virtually unlimited because people refuse to live with the predators that should be here. The associated diseases that ticks carry will then infect many more people than currently occurs.

The reality is that, in the 21st century and beyond, a world teeming with the imposing American Chestnut would be a world all out of whack and upsetting to people. Although it’s easy to fall for the allure of feeling virtuous by trying to recreate the natural world as it once was, that is an impossibility. You should be careful what you wish for, at least if you haven’t first considered the consequences. 


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