Freeze Testing and Field Mortality of Pinus sylvestris (L.) in Northern Sweden

Six short-term freezing experiments were carried out on 24 one-year-old single-tree open pollinated families of Pinus sylvestris (L.) representing four populations in northerly Sweden (latitude 62 degrees 10'N to 66 degrees 50'N). Two experiments were conducted in a climate chamber, two in a greenhouse and two outdoors. For freeze testing the plants were exposed to -10 degrees C for three hours in a freezing chamber. A freezing experiment in a climate chamber of 28 one-year-old full-sib families (half diallel with two parents from each population) was also carried out. The results were related to the mortality of the same open pollinated families over the first 18 years in the field. The ranking of the populations was the same in all six freezing experiments as in the field. Significant differences in frost resistance between one-year-old open pollinated families were found within all populations except the most northern one. The correlations within populations between frost resistance and field mortality varied considerably between populations and freezing experiments. The results from the two greenhouse experiments showed the best correlations with the cumulative field mortality after 18 years. The freezing test of the 28 full-sib families resulted in the same mutual ranking, according to the general combining ability of parents within populations, as was obtained from the freezing tests of single tree families.