Restoration of American chestnut: Assessing growth and winter injury of The American Chestnut Foundation’s B3F3 Restoration Chestnut 1.0 in a northern climate
American chestnut (Castanea dentata [Marsh.] Borkh.) was a major component of eastern US forests from Maine to Georgia until it was removed as an overstory species by chestnut blight (caused by the fungal pathogen Cryphonectria parasitica [Murr.] Barr), starting approximately 100 years ago. One approach to achieving blight resistance and restoring the species within its range is through the hybrid breeding of American chestnut with Chinese chestnut (Castanea mollissima Blume) or Japanese chestnut (Castenea crenata Sieb. & Zuc.) followed by backcrosses to American chestnut. Using this approach The American Chestnut Foundation has produced a B3F3 Restoration Chestnut 1.0. The level and consistency of blight resistance of B3F3 stock is currently being evaluated. However, other qualities, including growth and winter injury, need to be assessed for successful restoration efforts across the species’ range. This is particularly important at northern limits where chestnut is exposed to lower winter temperatures.
B3F3 nuts were planted at the Green Mountain National Forest in 2013 establishing the northernmost planting of this stock. In 2014, after two growing seasons, sapling growth and winter injury (percent of shoots killed by winter freezing injury) were assessed to better understand the performance of B3F3s grown in the north.
Average 2-year height of B3F3 saplings was 71.51 cm, with a range in height among seed sources from about 52 to 95 cm. The average percent shoot winter injury for the 2013-14 winter was 20.05%, with a range from about 7% to almost 40%. Despite a sometimes high percentage of winter injury (e.g., near 40 % loss in leader length), some seed sources still reached average overall heights (e.g., ~75 cm) by the end of the second growing season. There were significant (P ≤ 0.05) differences in height and a tendency (P ≤ 0.10) for differences in shoot winter injury among seed sources of B3F3 stock. However, these differences were not associated with American chestnut parental sources or the elevation of these sources. These early results suggest that B3F3 stock has tremendous growth potential despite some inherent vulnerability to shoot winter injury. Indeed, one B3F3 source showed only 9% shoot winter injury, and achieved the second-highest mean height of 80 cm. Ongoing research is assessing 1) year-to-year variability in the balance between winter injury and growth, 2) if seed source differences in growth and injury are consistent over time, and 3) if B3F3 outgrow their vulnerability to shoot winter injury.