Using silvicultural management and genetic selection to assist in the restoration of American chestnut to the northeastern U.S.
American chestnut (Castanea dentata) was once a prized forest products species throughout the eastern United States. Introduced chestnut blight removed American chestnut as an overstory tree by about 1950. Current restoration efforts include the hybridization of American chestnut with blight-resistant Chinese chestnut (Castenea mollissima) followed by repeated backcrosses of resistant offspring with American chestnut. An important consideration for restoration at the northern limits of American chestnut’s range is the inclusion of germplasm that provides for growth and survival in colder environments. We have shown that American chestnuts (both pure and backcross stock) are vulnerable to shoot freezing injury and experience winter dieback. In order to elucidate sources best suited for regeneration in the North, we established a progeny planting in Leicester, VT in 2009 that includes 13 American chestnut sources from across the species’ historical range (NC to ME). This planting also included three silvicultural treatments: open, partial and closed canopy. Seedlings were planted in a replicated design and annual measurements of height and diameter growth and shoot winter injury were conducted. In addition we assessed shoot cold tolerance in our laboratory in January, February and March of 2014.
In each year, trees in the open canopy treatment have been significantly taller than trees in the closed canopy with the partial canopy trees closer in height to the closed canopy trees. Partial canopy trees have been close to, but significantly taller than trees in the closed canopy in all but the first year of growth. After six years of growth in the field, open canopy trees averaged over 3 m in height while partial and closed canopy trees averaged 0.75 m and 0.25 m, respectively. Open canopy trees had significantly greater shoot winter injury than partial and closed canopy trees for the first two winters, while in the subsequent three winters closed canopy trees had the greatest winter injury followed by partial canopy trees and open canopy trees. Results from the laboratory shoot cold tolerance assessments will be completed and presented. Our findings indicate that American chestnut grows best in the open and that there are seed source differences in growth. There may also be winter injury differences related to silvicultural treatment with open grown trees suffering the most winter injury in the first two years and the least winter injury in the subsequent three years.