Genetic variation in height and volume of loblolly pine open-pollinated families during canopy closure

Heritabilities and age-age genetic correlations for heights and volumes were estimated for 12 open-pollinated families of loblolly pine planted in 100-tree plots on a lower coastal plain site in North Carolina from age 4 to 11 years. Families differed significantly in cumulative height for all ages, but no family effects were present for diameter at breast height. Family differences in individual tree volume were not present until after age 8 and in stand volume after age 10. Heritabilities showed the same pattern over ages, having the highest family and individual heritabilities for height (h(F)(2)=0.65 to 0.84, h(F)(2)=0.15 to 0.27), moderate to none far tree volume (h(F)(2)=0.43 to 0.61, h(I)(2)=0.06 to 0.05) and stand volume (h(F)(2)=0.32 to 0.53. Genetic correlations between early height and height at II years were high (around 0.95) and did not change from age 4 to 10, Similar high correlations were Found for height and tree Volume (0.9) and height and stand volume (>0.95). The stability in rank among families and high correlation suggests that selection for height would be efficient at age 4. The increased difference in volume production between families with time even after canopy closure indicated that Families differed in the efficiency by which they utilized the site's resources for stemwood growth. A superior family will maintain a higher growth rate even after the stand has closed. This could be due to higher light interception and/or more stemwood produced per unit light intercepted.