Performance of American Chestnut (Castanea dentata) and its hybrids on reclaimed mine sites in unglaciated Ohio

Background/Question/Methods

American Chestnut (Castanea dentata) once accounted for a large portion of the Eastern Deciduous Forest overstory until the introduction of Chestnut blight (Cryphonectria parasitica). The American Chestnut Foundation has bred a putatively blight-resistant Chinese-American hybrid for reintroduction. Chestnut has been proposed as a candidate species for reclamation of previously mined lands, especially those being reclaimed with the newly developed Forestry Reclamation Approach--early studies have shown promising results. This study compared the performance of chestnut under field conditions at a reclaimed strip mine in eastern Ohio. Seeds (660) were planted on a two-year-old reclaimed mine site in March 2008. The seeds were pure American, pure Chinese, and three intermediate hybrid genetic lines. The seeds were planted in 132 experimental blocks, each containing one individual of each genetic type. Survival and growth in height over three growing seasons was monitored. Leaves were collected at the end of the 2011 growing season to compare morphological differences (e.g., pubescence, thickness, and stomatal density) that were expected to vary among lines but also may have ecological significance under the conditions found on reclaimed mine sites (i.e., low moisture, high light).

Results/Conclusions

Pure American seedlings had significantly lower survival rates compared with hybrid and pure Chinese seedlings (Cox proportional hazard ratio = 36.16, df = 4, P < 0.01) over the four years of the study. Survival rates of the hybrids were intermediate between parent lines. Annual growth rates differed significantly among genetic lines and years, but showed no overly clear trends by genotype. Measured leaf morphological characters (SLA, pubescence, stomatal density) exhibited significant variation among genetic lines, and may have had an effect on survival. Consideration of these differences may be important for selection consideration to ensure the best possible phenotype for specific site types as the American chestnut restoration program moves forward.