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Format:
Print
Author:
Saielli, Thomas McNeill
Dept./Program:
Natural Resources
Year:
2011
Degree:
MS
Abstract:
Approximately 100 years ago, American chestnut (Castanea dentata (Marsh.). Borkh.) was rapidly removed as an overstory tree by the fungal pathogen Cryphonectria parasitica (chestnut blight). Over the years multiple efforts ofrestoration have been attempted. Currently, the most effective method involves the hybridization of American chestnut with the highly blight resistant Chinese chestnut (Castanea mollissima Blume). However, preliminary evidence suggests that backcross material may not have the cold hardiness needed for restoration in the north. Two factors that can significantly influence cold tolerance are genetics and the environment (e.g., cold exposure ofplant tissues). Also, the cold tolerance of nuts is of concern because reproductive tissues are particularly sensitive to freezing damage.
Thus, in an effort to contribute to the successful restoration of American chestnut in the north, the focus of this research was to analyze the cold tolerance of American chestnut through 1) the comprehensive evaluation of nut cold tolerance for a range of American and Chinese chestnut nuts, and red oak (Quercus rubra L.) acorns for comparison, and 2) by studying the first-year growth and shoot winter injury of a range of American Chinese chestnut, and red oak seedlings under three silvicultural treatments (open, partial-and closed canopies) in the Green Mountain National Forest (GMNF). Differences in canopy cover among silvicultural treatments were measured using hemispherical photography. Differences in winter air temperature lows associated with silvicultural treatments were also assessed.
We examined American chestnut sources by region -north, central and southern portions of the species' range (nut cold tolerance experiments only) and by temperature zone (warm, moderate or cold) that differentiated sources based on winter low temperatures in the areas where they originated (both experiments).
Nuts of Chinese chestnut were significantly less cold-tolerant than either American chestnut nuts or red oak acorns, which were indistinguishable. Among American chestnut sources, nuts from the southern region were significantly less cold tolerant than nuts from the northern region, with nuts from the central region being intermediate. Significant differences among sources were also identified within each region. Nuts from warm and moderate temperature zones exhibited similar levels ofcold tolerance, but were significantly less cold-tolerant than nuts from the cold temperature zone.
There were significant differences among sources within the warm and moderate temperature zones, but not within the cold temperature zone. The seedlings at GMNF grown under open canopies exhibited greater growth than seedlings grown under partial and closed canopies (which were indistinguishable), but also experienced increased shoot winter injury. Chinese chestnut seedlings had significantly greater growth, but also experienced greater winter injury than American chestnut and red oak seedlings. Among American chestnut sources, seedlings from sources from warmer low-elevation, southern and central locations grew more, but experienced greater winter injury than seedlings from sources from the colder north.
We believe that the temperature zone index may provide a reliable guide for assessing the tradeoffs between growth and vulnerability to winter shoot injury, as well as nut cold tolerance, and could help to identify those sources that best bridge tradeoffs in cold tolerance and growth. Our results also suggest that both silvicultural treatment and genetic selection can greatly influence growth and winter injury of American chestnut at the northern limit of its range.