This study examined changes in individual tree height and diameter at breast height and stand-level gross total volume over time, comparing plantation-grown jack pine (Pinus banksiana) and black spruce (Picea mariana) to wildfireorigin, mixed conifer stands. Mensurational data were collected from fixed-area plots in 32 plantations (15 jack pine; 17 black spruce; age 6–64 y) and 21 fire-origin conifer-dominated stands (jack pine/black spruce mixtures; age 4–91 y). Using a generalized three-parameter modified-Weibull function, we described relationships for individual tree and standlevel measures of growth and age for managed and natural origin stands, separately, and then compared the functions to assess growth pattern differences between managed and natural stands. Both the black spruce and jack pine plantations consistently outperformed the natural stands based on all measured individual and stand-level parameters, and significantly lowered the age to operability of the trees. For example, the modeled gross total volume at age 50 resulted in “improved” volumes over the natural stands of 35% and 50% for plantation-grown jack pine and black spruce, respectively. The results from this study suggest that establishing and maintaining desired species at moderate and relatively uniform densities on productive boreal sites can significantly increase yields and shorten the age to operability by nearly 15 y.