Longitudinal differences in Scots pine frost hardiness

The autumn frost hardiness of Scots pine (Pinus sylvestris L.) populations from Scandinavia (57degrees28'-68degrees54' N, 13degrees00'-27degrees-00' E) and the Komi Republic in Russia (61degrees30'-64degrees20' N, 49degrees10'-54degrees50' E), and open pollinated families from a population in Komi (61degrees43'N, 51degrees07'E) were examined in artificial freezing tests with one-year-old seedlings. The aims were to estimate genetic variation in hardiness between families of Russian origin and to compare populations of Russian (continental) and Scandinavian (maritime) origins. The longitudinal distance between the Scandinavian and Russian seed sources was associated with a significant difference in climatic conditions. At latitude 63degreesN the degree of continentality (the difference between July and January monthly mean temperatures) was 23.7degreesC for longitude 15degreesE in Sweden and 35.2degreesC for longitude 54degreesE in Komi. The narrow-sense heritability of frost hardiness calculated for the Russian families was 0.22. This indicates relatively high genetic control of the trait, of similar magnitude as earlier shown for populations of Scandinavian origin. Both Scandinavian and Russian populations showed a strong clinal variation in frost hardiness, northern populations being the hardiest. In addition, Russian populations were more frost hardy than Scandinavian ones from corresponding latitudes and attained the same level of hardiness as Scandinavian populations from 4.1degrees latitude further north. The results indicate that the longitude or continentality of the origins of Scots pine populations is associated with adaptive pressures that have significant effects on hardiness and are distinct from photoperiodic effects. When enriching breeding or production populations by including populations from remote origins it is essential to recognize not only latitudinal origin, but also longitudinal origin or temperature regime, in order to match material to the planned utilization areas.