by Bernd Heinrich
December 20, 2013
Source: The New York Times Opinion Pages
THIS Christmas season, I am roasting chestnuts by the fire. American chestnuts, to be exact. These nuts, once widespread, were almost wiped out by a fungal blight. For a century, most of the chestnuts we eat, like the sweet Castanea sativa variety, have been imported from Europe and Asia.
And yet, I have been enjoying American chestnuts for several years now, harvested from some trees that are now part of my forest of 600 acres in western Maine. I planted four seedlings in the spring of 1982. Beyond all my expectations, the trees thrived, and some are now 35 feet tall. I never would have imagined such success; it was a Hail Mary shot in the dark to see if they might grow in the forest where they were once so common.
The American chestnut was once considered the “king of the eastern forest.” It was a dominant species from Maine to Mississippi, accounting for 25 to 30 percent of the hardwoods, with trees capable of growing to a hundred feet in height and almost 16 feet in diameter. Then in the late 1800s nuts of a similar tree were imported from Asia, and some spores of Cryphonectria parasitica, a fungus that produces oxalic acid, which poisons and kills the tree, were inadvertently introduced as well. The Asian trees were immune to it, but the American trees were not. The fungus was discovered in the Bronx in 1904 and by 1950, it had done most of its damage. An estimated four billion trees were swept from our forests within a half century, and the American chestnut essentially disappeared.
Fewer than a hundred were left in its former range, along with scattered survivors elsewhere in the country. I had purchased my seedlings from a breeder in Michigan, but have no way for knowing for sure whether they are the genuine article, Castanea dentata, or whether they were at some point interbred with an Asian chestnut to give them resistance to the blight. My hopes for these seedlings were not high. The chestnut blight fungus can also live in northern red oaks, though it does not kill them. These oaks are common in my woods, and there is some evidence that American chestnuts planted near northern oaks will catch the fungus and die. And plenty of the other trees in my forest show signs of fungal infections.
And yet, the chestnuts grew. They reached reproductive maturity and produced seeds, and those seeds have now been “planted” throughout the forest. In my small corner of western Maine, the American chestnut is now promising to again become a significant component of the ecosystem.
I share my chestnuts with the blue jays, who carry off the surplus, up to three at a time. They store them by shoving them under leaves or into the ground to eat later, often losing track of their caches and inadvertently becoming tree planters. On my last count in October, with the help of forestry students from the University of Vermont, we located 149 separate plantings (many with several seedlings in each), some a half mile or so away from the parent trees. Young chestnut trees, the offspring of my four seedlings, are now spread over 200 acres of surrounding forest.
My trees seem to have some blight resistance, which could mean they were selected for those traits; some of the old trees did have the ability to avoid the blight.
Since the 1980s, researchers have worked to select chestnuts for resistance to the blight, slowly and methodically crossing and back crossing, testing and measuring the trees’ response to exposure. That’s traditional tree breeding.
But meanwhile, researchers at SUNY’s College of Environmental Science and Forestry have been trying to create a better chestnut tree by inserting into it a gene derived from wheat, one that would enhance the tree’s resistance to the chestnut fungal blight. This attempt has been promoted as the solution to the chestnut extinction, presumably by introducing this new tree into the wild to populate our forests. Last year, 10 of these genetically modified trees were planted in the Bronx, at the site associated with the outbreak of the epidemic.
How will those trees evolve over time with their altered genome? Will they crowd out the remaining natural chestnuts? The consequences of genetic engineering can be unpredictable — genes behave and are expressed in complex ways.
Yes, I would love to see the American chestnut restored to our forests. But do we need to alter the chestnut’s genome — the code of life that has evolved over millenniums? I don’t think so, and I worry that the feel-good campaign in the Bronx could be a Trojan horse that may seduce the public into accepting other genetically engineered trees — like the eucalyptus currently being tested across the southeastern United States to satisfy an expanding industrial demand for pulp and biofuels.
It is possible to bring back the American chestnut to the forests where it belongs without genetic engineering. In the meantime, I’ll be roasting my own homegrown chestnuts in the peace of my cabin in the Maine woods. It is a sacred act for me. If the trees were wheat-gene tweaked freaks, I don’t believe I would have much appetite for their nuts.
Bernd Heinrich is an emeritus biology professor at the University of Vermont and the author of “Life Everlasting: The Animal Way of Death.”