Early gains from planting large-diameter seedlings and intensive management are additive for loblolly pine

A seedling size/intensive management study with Pinus taeda L. was establis hed in 1993 on two sites in the Coastal Plain of Georgia and South Carolina . Each site contained a 2 x 2 split-plot study involving two seedling sizes and two levels of establishment intensity. Ideotype "B'' seedlings average d 5.0 mm in diameter (at the root collar) and were 43 cm tall. Ideotype ``A '' seedlings averaged 8.5 mm in diameter and were 50 cm tall. ``Standard'' establishment practices included herbicides (hexazinone and sulfometuron) a nd fertilizer (DAP) applied during the first year. The ``intensive'' manage ment involved two herbicide applications during the first year and two duri ng the second year, fertilizer during the first and third years, and insect icide applications during the first two years (for control of tip moth, Rhy acionia frustrana Comstock). Intensive management did not affect survival b ut planting larger seedlings increased survival slightly on one site. Howev er, treatments affected early growth at both sites. On both sites, fourth-y ear plot-volumes were increased with greater establishment intensity and la rger seedlings but there was no interaction between stock size and establis hment intensity. Early growth gains were greatest when both intensive manag ement and larger seedlings were combined. Depending on site, this combinati on resulted in 21% to 51% more volume (at age 4) than the next best treatme nt (standard seedlings with intensive management).