Shoot Elongation Patterns of Loblolly Pine Families Selected for Contrasting Growth Potential

Abstract

Abstract Ten half-sib families of loblolly pine chosen to represent a wide range of size in 8-year-old field trials, exhibited different shoot elongation patterns during their second year in retrospective seedling trials. In all but two families, the different patterns of annual shoot elongation were consistent in irrigated and nonirrigated treatments. Two families that ranked high for growth rate in the 8-year-old field trials also had greater annual shoot growth in the seedling trial without irrigation, but performed poorer than expected when well watered. The different patterns in annual height increment arose as a consequence of changes in the relative contributions of numbers of stem units, the average shoot length per stem unit, and the percentage of trees elongating. However, total annual height increment produced during the second year was a better predictor of the size of half-siblings after 8 years in field trials than any of the components of shoot growth. Families with greater size after 8 years in field trials had longer annual leaders in the seedling trial, but for varying reasons. Some were longer primarily because they had more stem units, while others had average numbers of stem units but greater-than-average stem unit lengths. The percentage of trees elongating near the end of the season was of little or no importance in determining the relative ranks of families within each of two geographic populations studied, but contributed to the differences between the two populations. For. Sci. 36(3):641-656.