A. Benowicz et al., Patterns of genetic variation in mountain hemlock (Tsuga mertensiana (Bong.) Carr.) with respect to height growth and frost hardiness, FOREST ECOL, 154(1-2), 2001, pp. 23-33
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.