Population variation in growth and 15-year-old shoot elongation along geographic and climatic gradients in black spruce in Alberta

Twenty black spruce (Picea mariana (Mill.) BSP) populations from Alberta were tested at one trial to study the variation of shoot elongation at ages of 15 years, height growth at 10 and 15 years, and breast-height diameter (DBH) at 14 years. Significant difference among populations was found for all of the growth traits and some of the shoot elongation traits investigated. Population means for shoot elongation and cumulative growth traits of significant difference were further regressed against the geographic coordinates and climates of seed origins to study patterns of genetic variation in relation to geography and climate. Both linear and quadratic regressions were investigated, but the one with better fit (lower P and standard error) was chosen and further analyzed. Geographic and climatic gradients explained 20%–62.9% of the population variation in regressions that were statistically significant. Shoot elongation and cumulative growth traits were closely related to frost-free periods, but diverged in their relationships to geographic and all other climatic variables considered. While shoot elongation was associated exclusively with latitude, longitude, day length, and negative temperature variables, growth traits were associated with elevation and positive temperature and moisture variables. Climate factors were more effective than geographic coordinates in describing differentiation in shoot elongation and growth traits. The most effective factors in predicting growth traits were mean annual precipitation and summer moisture index of the seed origin.