The U.S. Forest Service Upland Hardwood Ecology and Management Research Work Unit (RWU 4157) has been conducting American chestnut research since 1995. The primary goal of the chestnut research program is to develop prescriptions that forestry field managers can implement to restore this species. Our American chestnut research is forestry focused, and we do not conduct research on breeding for blight resistance. Primary questions we hope to answer are:
- How can we develop high-quality nursery seedlings for planting?
- Is it best to plant chestnut seedlings in open-conditions (clearcuts, low residual tree shelterwoods) or under shaded conditions that will be opened up in a few years (high residual tree shelterwoods)?
- How will the seedlings compete on a range of sites that vary in quality and disturbance history?
- Will the advanced breeding material behave similarly to a pure American chestnut while maintaining blight-resistance?
What Happened to the American Chestnut?
Decimated by an exotic fungus known as the chestnut blight ( Cryphonectria parasitica Murr. Barr), when the blight was introduced into North America in the latter part of the 19th century. American chestnut was a keystone species in the eastern hardwood forests, and its demise has altered forest ecosystems by reducing species diversity, reducing availability of hard mast, and changed soil and litter dynamics. The loss of the American chestnut as a mature component in eastern forests has resulted in large-scale shifts in species composition, particularly on upland well-drained stands where the species was most competitive. Because the chestnut blight affects only the above-ground portion of the tree, the species has managed to exist as short-lived stump and root sprouts, which will occasionally live long enough to flower and bear fruit.
What's Being Done to Restore the American Chestnut?
Restoration of American chestnut to eastern forests depends on the development of blight-resistant seedlings. The Forest Service does not conduct breeding research, but supports efforts of The American Chestnut Foundation (TACF), a private non-profit organization whose goal is to produce blight-resistant chestnut trees through a back-cross breeding program involving the blight-resistant Chinese chestnut ( Castanea mollissima Blume). The TACF breeding program's end product is essentially an American chestnut with blight resistance from Chinese chestnut. The final breeding generation produced in the TACF's program will be the third intercross of the third backcross generation (BC 3 F 3 ). Seedlings from this generation will be 15/16 American chestnut with stable blight resistance.
Chestnut restoration does not end with development of a blight-resistant tree, but also requires a prescription for how and where to plant trees once available. To date, planning for American chestnut restoration has emphasized producing a blight-resistant tree, and only limited attention and resources have been specifically given to test procedures needed for successful establishment and growth of resistant seedlings. The U.S. Forest Service signed a Memorandum of Understanding with The American Chestnut Foundation in 2004, which designates the Forest Service as the ‘most favored recipient' of the TACF's chestnut material, and the resulting seedlings are to be incorporated into management activities on National Forest System (NFS) lands.
The Upland Hardwood Ecology and Management Research Work Unit is conducting research to develop prescriptions that managers can use for planting blight-resistant American chestnut seedlings, once they become available. This research is being led by Dr. Stacy Clark. Dr. Clark uses material from TACF and works with partners from The University of Tennessee's Tree Improvement Program and the Southern Region of the National Forest System to conduct her research.
Making History: The First Plantings
Field testing of seedlings from the final generation (BC 3 F 3 ) of the American Chestnut Foundation's (TACF) breeding program will be established on three National Forests in the Southern Region (Region 8) in the winter of 2009. The first BC 3 F 3 nut collection by the TACF occurred in 2007, with adequate numbers (550 nuts) available for field planting. These chestnuts were transferred to the Southern Region of the National Forest System and in turn given to Dr. Stacy Clark of the Southern Research Station's Upland Hardwood Ecology and Management Research Work Unit for experimental testing. Dr. Clark is working in cooperation with Dr. Scott Schlarbaum, Director of the University of Tennessee's Tree Improvement Program and the Southern Region to implement these test plantings. These experiments will be the first testing of the TACF's BC3F3 generation in field conditions.
As part of the test plantings, a study was also established to determine if size of the chestnut affects seedling development in the nursery. This is a question of interest to nursery managers, because size of other seed, including acorns, has been found to affect seedling development. BC 3 F 3 chestnuts along with chestnuts from all phases of the breeding program (pure American, Chinese chestnut, BC 1 F 3, and BC 2 F 3) were sown at the Georgia Forestry Commission's Flint River Nursery in January 2008. The chestnuts from each seed lot were first divided into ‘Large' and ‘Small' size classes to test if chestnut size affects seedling development. The seedlings will be lifted in early 2009 to establish experimental plantings on three National Forests in the Southern Region. Prior to planting, each site will be tested for presence of Phytophthora cinnamomi an exotic fungus that will kill chestnut seedlings by attacking the root system of the tree. P. cinnamomi testing is being conducted in assistance with Bill Jones with U.S. Forest Service, State and Private Forestry. Each planting will consist of approximately 400 trees, including 150 seedlings from the BC 3 F 3 generation.
Early surveys of 2008 nut crops indicate that adequate experimental material will also be available for 2010 test plantings. Dr. Clark and Dr. Schlarbaum will oversee testing of seedling performance in ‘real-world' forest conditions, and results will guide the TACF in making selections of superior families in their breeding program. The test plantings can be used as education and demonstration sites for local citizen groups and professional organizations to illustrate how forest management can be used in the restoration of a native species.