American chestnut

The American chestnut is a tree species that was once one of the most common in the northeastern United States. However, it is functionally extinct today. The American chestnut was a large nut-bearing tree that grew in forests as far north as Maine and as far south as Georgia. The American chestnut was a keystone species in the Northeast. It was also an important species for humans, and many Americans were devastated when between three and five billion chestnut trees died over the course of only forty years. Scientists have attempted to revive the American chestnut species by developing a tree that resists the chestnut blight that killed nearly all the old American chestnut trees.

Background

The American chestnut grew throughout Appalachia and beyond in North America. It was a keystone species, which means it was a species upon which many other species relied. American chestnut trees were an important food source for many animals, as chestnuts fell by the millions throughout forests in the eastern United States. Native birds, including the now-extinct carrier pigeon, squirrels, bears, and hogs all relied on the nuts for food. The American chestnut also provided important nectar to bees in North America, as mature trees produced many white flowers in the spring.

The American chestnut was also useful to humans. People collected and ate the nuts, which can be milled into flour, boiled, or roasted. Many people in Appalachia collected the nuts and sold them to earn money. People also used the wood of the American chestnut to build furniture, musical instruments, fences, and buildings. The straight grain of the wood made it easy to split, making it a favorite for kindling wood. Chestnut wood was also used outdoors because it is highly rot resistant. Chestnut wood is resistant to rot because it is high in tannic acid. People cut down American chestnut trees, stripped the bark from the wood, and sent the bark to tanneries, which used the tannic acid in the bark to the tan animal hides.

American chestnuts also grew extremely fast. These trees grew more quickly than other trees in North American forests, and each tree could live for four to five hundred years. Furthermore, when an American chestnut tree was cut down, the root system sent up numerous saplings in the tree’s place. A few of those saplings would often grow into mature trees.

The American chestnut was such a dominant species that it became an important part of American popular culture. For example, the famous first line from “The Christmas Song” that goes “Chestnuts roasting on an open fire” most likely refers to nuts from American chestnut trees. Furthermore, the famous American poet Robert Frost wrote a short poem specifically about the devastation of the chestnut blight.

Overview

The American chestnut grew in North America for forty million years until European colonizers arrived. After Europeans arrived, they began importing plant and animal species from other countries, bringing with them fungi and microbes that had never before been introduced to North America. In 1904, the fungus Cryphonectria parasitica traveled to the United States on trees that Americans bought from other countries. The fungus causes chestnut blight, and it found a very susceptible host in the American chestnut. The first trees known to be affected by the blight were at the Bronx Zoo. The fungus traveled, through the wind and on animals, quickly to other stands of American chestnut trees. By 1909, American chestnuts throughout Pennsylvania were dying from the blight, and people cut down entire forests of chestnut trees to try to stop the spread of the disease. Their efforts did not to stop the spread, however.

When the fungus lands on an American chestnut tree, it attaches itself to the bark. The blight causes a canker to form on the side of the tree. The fungus attacks the tree by producing an acid that kills the bark and the rest of the trunk. A different type of fungus inside the soil stops the blight fungus from killing the roots. A tree infected with blight first develops an orange-yellow canker, and quickly the entire tree dies. The blight was so devastating because nearly every American chestnut tree that was infected with the fungus died from the blight. Scientists believe that only a handful of mature American chestnut trees still exist, and many of these are outside the tree’s native range.

The United States Department of Agriculture (USDA) has listed the American chestnut as functionally extinct, but it is not fully extinct. It is only functionally extinct because chestnut blight does not kill the tree’s root system. American chestnut root systems survive in many areas where the large trees once grew. Scientists use those roots and the small saplings that grow up from them in experiments through which they hope to bring back the American chestnut population.

Scientists have attempted to create a type of American chestnut tree that could again survive in North American forests and resist the chestnut blight that killed its predecessors. One way scientists are trying to bring back the American chestnut is through breeding. Scientists are breeding American chestnut with Chinese chestnut trees, which are naturally resistant to chestnut blight. Scientists want to breed the two types of trees and then selectively breed the offspring trees, choosing to breed the trees that have traits that are closest to the original American chestnut. Scientists hope that they can produce a tree that has traits very similar to the American chestnut but also has resistance to chestnut blight.

A second way that scientists are trying to create blight-resistant chestnut is by changing the genetic information in the tree. Scientists are using a process called transgenetics to change genes inside American chestnut trees. Changing a few individual genes could help maintain most of the traits of the original American chestnut while also making the tree resistant to blight. Scientists have inserted genes from wheat plants inside American chestnut trees in the hopes of blocking the blight fungus from producing the acid that kills the trees. Although the research into transgenetics seems promising, scientists will have to crossbreed any trees they produce via transgenetics with wild, original American chestnut trees to help ensure the species has enough genetic diversity to survive in the wild.

In 2022, researchers from the State University of New York College of Environmental Science and Forestry experimented with genetically modified pollen to develop American chestnut trees that are resistant to blight in an effort to repopulate forests with the species. (At the time of the experiments, the Washington Post argued that replenishing only a fraction of the estimated 2 billion tons of lost American chestnut trees would greatly help in reducing atmospheric greenhouse gases.) However, the proposed introduction of genetically modified species into the wild proved controversial, and several agencies, including the US Environmental Protection Agency, debated the potential impact of the program on natural ecosystems.

Other organizations have attempted to develop American chestnut hybrids that can withstand blights. Some of the saplings, which are 94 percent American chestnut and 6 percent Chinese chestnut, grow in Pennyback Park in Northeast Philadelphia, where they are monitored by researchers, including some from the American Chestnut Foundation (TACF). Researchers are concerned that their genetic compatibility may not align as well as they had thought. This means the trees may not have enough resistance to fend off the blight. However, even if the saplings do not survive, as of 2024, TACF remained resolute in its commitment to bring back the majestic trees.

Bibliography

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