Cold Acclimation in Populations of Pinus contorta from the Northern Rocky Mountains

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Abstract
Freezing tests were conducted to follow cold acclimation in seedlings representing 30 populations of P. contorta from the northern Rocky Mountains. For each of 12 dates from Aug.-Nov., leaves from 2-yr-old seedlings growing in a common environment were frozen at 4 test temperatures. Injury from freezing was scored primarily by tissue discoloration. Hardiness of populations developed in a slow and uniform pattern. Mean differences in the hardiness of populations were readily detected throughout acclimation, and the relative ranking of populations for hardiness remained essentially constant. Elevation and geographic region of the seed origin accounted for 78% of the variance in hardiness among populations.