Effects of height-growth selection on wood density in black spruce in New Brunswick, Canada
Height growth was the main selection criterion for the early-stage black spruce (Picea mariana [Mill.] BSP) breeding programmein New Brunswick, which has produced significant increases in volume growth. In this study we investigate howthe height-growth selection influences growth traits and wood density. Two genetic tests, a realized gain test of large plotsand a progeny test of small plots, were used for this purpose. Wood density was measured using the Resistograph methodon the standing trees. Growth and wood density of the improved seedlots were compared with those of an unimprovedstand checklot. In the progeny test, height-growth selection not only made the improved seedlots taller but also produceda proportional increase in DBH growth relative to the checklot. In the realized gain test, height-growth selection didincrease height, but did not produce a corresponding increase in DBH growth. Effects of height-growth selection on wooddensity varied with tests: the improved seedlot produced a greater although statistically non-significant decline in wooddensity in the progeny test; this reduction was at a much lesser extent or even non-existent in the realized gain test. Overall,results suggest that the improved growth from early stage improvement activities might not substantially and negativelyaffect wood density in plantation forestry and the predicted reduction in wood density in genetic tests of small plotsmight be inflated. Key words: Resistograph, realized gain test, progeny test, tree improvement