Impact of nursery management practices on heritability estimates and frequency distributions of first-order lateral roots of loblolly pine.
Frequency distribution and heritability of first-order later root (FOLR) numbers in 1-0 seedlings were followed for 5 years for 115 different half-sib seedlots from the Georgia Forestry Commission's Arrowhead and Baldwin Seed Orchards. In 1986 and 1987, seedlings were permitted unrestricted growth under management conditions similar to those practiced in most forest tree nurseries in the Southern United States. Seedlings were placed in four different classes based on the number of FOLR with proximal diameters above a threshold value. These classes were 0-3, 4-5, 6-7, and greater than or equal to 8 FOLR. In 1988, 1989, and 1990, management practices were altered to restrict height growth by 30 to 40 percent for each of four FOLR groupings. The associated reduction in seedling sizes had very little affect on either FOLR family mean heritability estimates or the assumption of truncated normality for FOLR data. Restricting growth did reduce FOLR proximal diameters, but in each data set the seedlings in the FOLR group with the fewest FOLR (0-3 in 1986 and 87, 0-2 in subsequent years) were always significantly smaller than those in the other groups. Not only were seedlings in this first FOLR group of smaller size, they also had unfavorable traits: succulent stems, preponderance of primary nedles, and poorly developed or absent terminal buds.