American Chestnut Cooperators’ Foundation History and Progress
The American Chestnut Cooperator's Foundation's work began in the 1960s, the roots of our heirloom, grassroots program. Our founders identified and studied original large chestnut blight survivors, natural blight resistance and ecology of American chestnuts in the forest. The ACCF breeding program began using original large standing blight survivors that showed varying levels of resistance. Decades of selective breeding yielded our orchards full of American chestnuts with improved resistance levels.
ACCF was officially established in 1986 to form the network of Cooperators dedicated to continuing pursuance of a research-based restoration program that serves this grand, native species. ACCF Cooperators, spread throughout the entire native range of the American chestnut, grow nuts from our breeding orchards in Blacksburg, VA and/or make donations to fund ACCF work. Since our founding, Cooperators have planted hundreds of thousands of nuts and seedlings.
ACCF all-American intercrosses accumulate resistance exclusively from American chestnuts which show natural blight resistance. Our integrated management approach combines ideal sites managed for American chestnut (control of competing hardwoods), grafting for blight resistance and the manipulation of a naturally occurring biological control (hypovirulence of Cryphonectria parasitica in cankers). By making intercrosses among resistant American chestnuts from many locations, we have improved levels of blight resistance producing American chestnuts that can compete in the forest.
True to nature, there are always new factors introduced to our field of interest, including setbacks and challenges, which as scientists and stewards of native ecology, we embrace and integrate into our program. With belief in the inherent strength of the American chestnut, the ACCF continues in its goal of restoring the American chestnut as a pure, significant species to its native range. This is only accomplished by keeping a long-term perspective, continuing our work with patience and dedication, and through the continued efforts of our Cooperators.
History of the American Chestnut
American chestnut (Castanea dentata) is a broadleaf deciduous tree found in multiple eastern forest types. Its native range spans the east coast from Canada and Maine down to Mississippi and Georgia, and spreads west as far as Michigan and Missouri. Before 1900, American chestnut was a dominant canopy species throughout this range; approximately 3.5 billion canopy trees made up nearly one quarter of eastern forests. American chestnuts were commonly over one hundred feet tall with trunks five to seven feet in diameter, they were the tallest and most bountiful member of the forest community. A dependable yearly crop of nuts provided food for wild birds, squirrels, turkeys, deer, and bears and cash for mountain families. The durable, straight-grained wood was used for telephone poles, houses, barns, furniture, paneling and fences. Today much of the rail fencing along the Blue Ridge Parkway is chestnut.
In 1904, chestnut blight (Cryphonectria parasitica), an aggressive fungal pathogen was introduced to the US via nursery stock imported to New York. The blight quickly spread throughout the entire chestnut range. Human reaction included encouragement from several different entities to fell chestnuts in efforts to delay spread of blight, remove snags, and harvest the wood. This action, in combination with the blight, effectively removed American chestnut from eastern forest canopies. As a result, American chestnut has been reduced to far less significance, occupying a different niche as an understory species. Remaining chestnuts survive mostly as sprouts from the root systems of the original giants.
American Chestnut and Blight Resistance
All chestnut species (European and Asian included) can and will be infected by the blight fungus if they are exposed. Within all chestnut species, individuals vary in their blight resistance levels. Thus, some American chestnuts are susceptible to the blight, and some are resistant. Resistance does not mean immunity to the blight, but a healthy reaction to its presence. Trees have a natural defense system that includes identification of threats and a signaling response to compartmentalize those threats, preventing spread into transport systems.
Chestnuts that are susceptible to the blight, or at least to the more lethal strains of the blight fungus, either do not recognize the fungus in time, or cannot isolate the infection quickly enough. Thus, cankers on susceptible chestnuts reach the cambium and ultimately girdle the tree, cutting off its resource transport, eventually killing it.
American chestnuts with resistance also become infected but recognize the blight fungus quickly and effectively initiate the protective response in time to stop it from reaching the cambium. (A similar example would be a healthy tree that is hit by a mower that responds by signaling resources to form wound wood to seal off the damaged section of trunk in order to prevent the spread of disease or pathogens through the wound into the cambium.)
Cankers on resistant trees are referred to as "superficial" and are contained in the outer bark, preventing the fungus from reaching the tree's transport system. Superficial cankers themselves will not kill the trees. These cankers may not look pretty to a first-time observer, however, for those who regularly inspect cankers on American chestnuts, they are exciting to see. "That's a good-looking canker" is a frequently heard description in evaluation of ACCF chestnuts.
Factors besides resistance that affect American chestnuts' response to a blight infection are size, overall health and environment. Health and environment contribute to a tree's ability to effectively carry out responses. Reacting to stressors such as too much shade, competition for resources, exposure to extreme temperatures, and lack of water availability can limit and/or exhaust a tree's energy reserves. If a chestnut (resistant or not) recognizes a blight infection but does not have sufficient energy to carry out protective responses, it may not be able to compartmentalize the fungus. The size of a tree can also affect its ability to compartmentalize a threat. Small trees dedicate majority of their energy to growth, in order to secure more energy in the future, leaving less energy stores available to address a threat. Another factor relevant to response to blight response in a small diameter chestnut is the short distance a fungus needs to travel to reach the cambium. Thus, smaller chestnuts are more susceptible regardless of their resistance level.
The American chestnut species is not rare or extinct. Existing healthy root systems continue to sprout prolifically throughout eastern forests. The species is stuck in the understory for now, waiting for its comeback. Chestnuts growing in ideal environments continue using resources from original root systems, some growing into quite impressive trees. If given advantage, these American chestnuts have potential to once again fill forest canopy space. We contribute to the American chestnut's advantage by breeding chestnuts with improved resistance levels that can be competitive in natural forest settings.