Variation, heritability, and gain in open-pollinated progeny plantations of Virginia Pine (Pinus virginiana Mill.)

The objectives of this study were to evaluate the genetic and environmental sources of variation in height, diameter, and volume per tree. Ten-year data from open-pollinated progeny of random trees from 12 natural stands in Tennessee and Kentucky were analyzed. The data were measurements of individual progeny from 128 half-sib families outplanted at three locations in Tennessee. Individual location analyses indicated that variance components for each source of variation, expressed as a percent of the total variation, were relatively similar from location to location. However, the family-within-stand (S²F̳/S̳) variance component was consistently lower at the Camp York location, probably due to the site heterogeneity evident at this location. Generally, the variance components in the combined location analyses are similar in magnitude to those in the individual analyses. Direct comparisons between the two types of analyses are not strictly valid since the combined analyses are based on different niombers of stands and families-within-stand than those of the individual location analyses. The two levels of genotype x environment interactions, location by stand and location by family-within-stands accounted for only a small amount of the phenotypic variation; the sum of the interaction components accounted for less than 1.5 percent of the phenotypic variance. When compared with two- and five-year estimates, ten-year heritability estimates were smaller at Camp York and the Highland Rim locations, and were the same or larger at the Ames Plantation location. Heritability estimates derived from the combined location analyses were in close agreement with the average of estimates derived from the three individual locations; average heritability estimates from the individual location analyses were within a standard error of the heritability estimates from the combined location analyses. Expected gains were computed on the basis of a hypothetical roguing of each plantation using three selection schemes. Gains from a three-stage system, which include stand, family-within-stands, and within-family selection, ranged from 16.1 to 22.4 percent over mean unselected stem volume. Gains from two-stage selection provided the largest gain in stem volume at all locations. Gains ranged from 22.3 to 30.6 percent over mean unselected stem volume. Mass selection resulted in gains ranging from 6.1 to 10.3 percent. Two of the plantations, Ames Plantation and Camp York, were actually rogued using the two-stage selection system. Expected gains above the mean unselected population were 29.9 percent at Ames Plantation and 18.0 percent at Camp York.