Genetic and Cultural Effects on Stem Taper and Bark Thickness in Loblolly Pine (Pinus taeda L.)

Abstract

Total inside-bark volume is the most important selection criterion for productivity in tree breeding programs in the Southeastern U.S. Tree breeding programs typically estimate total inside-bark volume based on diameter at breast height (D) and total height (H) without accounting for stem taper or bark thickness. A genotype by cultural treatment study with weed control and fertilization treatments was measured in the 13th growing season. Twenty-five open-pollinated first- and second-generation loblolly pine (Pinus taeda L.) families were destructively sampled to measure diameters and bark thickness along the stem and to make a direct determination of total inside- and outside-bark volume.

Selection for volume using a combined-variable (D*D*H) equation was found to be highly effective for making volume gains; although, overall estimates of total inside-bark volume using a combined-variable equation from Warner and Goebel (1963) were less accurate than those from destructive sampling. Precision could be improved by adding further terms to the prediction model, such as bark thickness and form quotients; however, these additional measurements could not explain all of the imprecision. Genetic components for both stem taper and bark thickness were estimated. These two factors had a small effect on volume estimates due to the high correlation between estimated and measured total inside-bark volumes. There was a positive genetic correlation between bark thickness and D that indicates that selection for larger D will produce individuals with thicker bark and may eventually affect total inside-bark volume estimates.