Effects of genetic selection for growth on frost hardiness in western hemlock

Abstract

Fall and spring frost hardiness was determined from electrolytic leakage of artificially frozen needle segments in 22 full-sib families of western hemlock (Tsuga heterophylla (Raf.) Sarg.) from British Columbia and Washington State representing different levels of genetic gain, and of four provenance materials (stand progenies from the Queen Charlotte Islands, Vancouver Island, and Oregon Cascades, and seed-orchard progenies from the northern Oregon Coast Range). Samples for freeze testing were collected in a 5-year-old trial at Jordan River on southwestern Vancouver Island. Height and date of bud flush were recorded in the field. Genetic gain among the full-sib families was not correlated with fall frost hardiness, but high-yielding families displayed a lower spring frost hardiness and an earlier bud flush than low-yielding families. Both fall and spring frost hardiness increased and height growth decreased with the latitude of provenances. The highest growth, earliest bud flush and lowest fall and spring frost hardiness was demonstrated by the Oregon provenances, while the lowest growth, latest bud flush and highest hardiness was found for the Queen Charlotte Islands provenance.