Time trends in genetic control of height growth in ponderosa pine

Height growth in ponderosa pine plantation with 71 families in 7 elevational zone sources was analyzed at ages 3, 5, 7, 8, 12, 20, 25, and 29. Height growth varied by seed source zone and by family within zone. Zonal variances were well established at an early age, and the differences were maintained with minor variations through the study period. Family variances were smaller than zonal and environmental variances, the differences were not well correlated between the earlier and later phases, and the correlations were sometimes negative. Three observed growth phases, related to ecological dominance and competition, affected the levels of variance attributable to genetics and environment.