Shoot Growth Patterns of Young Loblolly Pine
Abstract
Most shoot elongation on Pinus taeda L. seedlings and saplings near Durham. North Carolina. was supplied by the lirst growth Ilush, which began about April 1 and ended in mid-May 1967. New growth per shoot declined with distance from the tree top. All leaders had three flushes and half had four. Variation in internode growth was dependent upon growth rate, not length of growth period, which was remarkably uniform among all sampled shoots. Day-to-day shoot growth during the first lush was highly variable. During a 17-day period that accounted for 42 percent of total elongation of the first flush, degree-hour heat sums above 50°F and solar radiation in langleys per day accounted for 93 percent of the variation in total daily growth and 76 percent of the variation in diurnal growth. The effect of temperature was positive. and solar radiation negative. Heat sums alone accounted for 94 percent of the variation in nocturnal growth. The threshold temperature for shoot growth was about 40°F at night, and averaged 50°F during the day. The apparent threshold temperature for diurnal growth increased with increasing intensity oE solar radiation. Growth per unit or hear above threshold temperatures was almost the same during the day as at night.