RETROSPECTIVE SHOOT GROWTH ANALYSIS FOR 3 SEED SOURCES OF LOBLOLLY-PINE

Height growth by year and by individual cycle on the terminal shoot was reconstructed from stem analysis for 45 loblolly pine (Pinus taeda L.) trees that were 35 years old. Sample trees represented three seed sources (Clark County, AR; Livingston Parish, LA; and Onslow County, NC), each of which had been planted at three installations (Arkadelphia, AR; Poplarville, MS; and New Bern, NC) located in the general geographic area where one of the seed sources had been collected. Stem analysis was facilitated by the development of a staining technique that enhanced recognition of the boundaries between individual height-growth cycles and between years. Both annual height growth and number of cycles produced varied with tree age, seed source, and installation. Number of cycles produced per year ranged from two to seven; maximum annual production of cycles per seed source was achieved between ages 3 and 10 years. Even between ages 30 and 35, trees still exhibited polycyclic behavior, producing two to five cycles annually. Annual height growth was greatest between ages 4 and 15; height growth declined with age more rapidly than annual number of cycles. The relationship at each installation between cumulative height and cumulative number of cycles showed that the tallest seed source (Onslow in all cases) was the one that had produced the greatest number of cycles. Shorter trees at the poorest site resulted from lower numbers of cycles produced and, particularly after the production of 50 to 65 cycles, shorter mean cycle length. For all three seed sources, mean height was greatest at the installation where the trees produced the most cycles. Height-growth curves for two of the installations crossed, demonstrating differences in height-growth patterns related to site characteristics.