Patterns of genetic variation in mountain hemlock (Tsuga mertensiana (Bong.) Carr.) with respect to height growth and frost hardiness

Genetic structure (variance among and within populations) and geographic pa ttern of variations in growth and frost hardiness of mountain hemlock (Tsug a mertensiana (Bong.) Carr.) populations from coastal British Columbia (BC) were examined, Populations fell into two main groups - south coast (16 sou rces) and north coast (two sources). Height growth of greenhouse grown seed lings was measured during the first growing season on a weekly basis wherea s frost hardiness and branch water content were evaluated during the fall a t monthly intervals. Significant differences among the populations were fou nd in maximum instantaneous growth rate, height at the end of the growing s eason and in October and November frost hardiness. There were no difference s in date of maximum growth rate, branch water content and September frost hardiness. Most of the genetic variance was found within populations: 77% f or height, maximum growth rate and November frost hardiness and 87% for Oct ober frost hardiness. Geographic trends were identified using multiple line ar regression and canonical correlation analyses based on population means and latitude, longitude and elevation of the population origin. The une cn distribution of sources limited the extrapolation, but some general trends appeared. Maximum instantaneous growth rates increased with latitude, eleva tion and decreased with longitude (R-2 = 0.64) and consequently were negati vely correlated with the length of the growing season in the seed collectio n sites. Both populations from the north coast developed frost hardiness ea rlier than any population from the south coast. The relationship between cl imate coldness and growth rates has potential implications for seed transfe r guidelines. Due to their higher growth rates, plants from higher altitude s may accomplish the same amount of growth within a shorter period compared to plants from lower altitudes when both are transferred north. Results of the frost hardiness tests indicate that seed transfer along the British Co lumbia coast of more than 3 northward will considerably increase chances of frost damage in plantations. (C) 2001 Elsevier Science B.V. All rights res erved.