Altitudinal variation in freezing resistance ofAbies sachalinensisin central mountainous areas in Hokkaido was investigated. Freezing resistance of winter buds of the open-pollinated progenies from 51 mother trees and ramets from 80 clones, growing at different altitudes, was assessed. Freezing resistance increased with increasing altitude from about 300 to 1200ensp;m. The increase in freezing resistance was always accompanied by a decrease in the variance. These results suggest that natural selection has operated under influence of winter temperature gradients to bring about the hardiness related to altitudinal occurrence.
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