Many Americans alive today know that there is an American chestnut tree, but few know that it was once a keystone tree species on the East Coast of the United States from Georgia to Maine. According to a recent article in the Natural Lands magazine, this “Sequoia of the East” was well known and prized for its incredible properties: rot resistance, straight graining, fast growth and regrowth after being cut down, nutritious and prolific nuts for human and animal consumption, and all types of general ecology services. Its history as a strong native tree in the United States dates back some 40 million years.
Then came 1904. Like so many other similar tragedies in the native plant world, a parasitic fungus hitchhiked to the eastern U.S. on a type of chestnut tree native to East Asia. The fungus, Cryphonctria parasitica, gradually destroyed four billion American chestnut trees over about a 40 year period. Some old trees remain alive in scattered pockets and some trees regrow from root systems of the former trees to a short height of up to 15 feet before dying back again. Occasionally, the tree grows barely big enough to produce a seed, a pure heirloom seedling may grow, but then the tree succumbs to the fungus.
During and after the decline of the species there were many attempts to just keep raising seedlings and planting them with the hopes of a comeback somehow, regardless of the fungus. These effects were almost completely ineffective. By the 1960s, the American chestnut was considered “effectively extinct.”
In 1983 the American Chestnut Foundation (TACF) was established with the goal of developing a tree that had all the traits of the heirloom tree yet also resist the Asian fungus. Disease resistance was now considered key, since more was known that the fungus was here for the long term, spread far and wide by water, wind and insects. But, how to accomplish this goal?
The TACF program is based on the science of backcrossing, a very tedious hybridization process. Over 30 years has been devoted to cross breeding the Chinese chestnut, which is resistant to the fungus, with the heirloom American Chestnut tree from cultivation. Over and over again, the seeds of the hybrid have been planted and grown into new cultivars. By selective breeding methods, fungus resistance is encouraged while the closest possible traits of the original American chestnut tree are maintained. The goal is to make this hybrid indistinguishable from the heirloom tree in almost every way.
There is also an effort underway to take tissue from existing American chestnut trees that have somehow survived the fungus, and to graft that tissue into new heirloom American chestnut rootstock that has been carefully cultivated. This results in a pure strain, with apparent resistance to the virus. This line of thinking is based on historical evidence that somehow a tree species may adapt or that some individuals may have a latent genetic ability to come back after a very substantial loss of population such as this. An example is cited that hemlock trees went extinct or nearly extinct about 5,000 years ago, but then reappeared a few centuries later. One of the ways this was studied was by examining preserved layers of pollen in a North American lake bed.
Since the American chestnut trees vanished, other species have taken their places and other conditions have changed. So, the U.S. Forest Service is looking into a few things that will also factor into its reintroduction success or failure:
· Site quality: how important is it to chestnut blight resistance?
· Deer browsing: what is the impact of a high occurrence of deer browse on these trees?
· Prescribed fire: What will the response be of the American chestnut trees to being burned intentionally as part of regular forest management?
· Timber harvesting: What type of timber harvest methodology will be best suited for their success, use by humans, and regrowth scenarios?
There are many unknowns about the reintegration of the American chestnut tree into a contemporary forest scene as compared to what existed more than a century ago. But many people believe that the fungus can be overcome. In fact, many scientists and foresters believe that the general hardiness of this tree may be very much needed as temperatures rise due to a changing climate. It may be time for the American chestnut to make its comeback!
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