VEGETATION CONTROL AND SITE PREPARATION AFFECT PATTERNS OF SHOOT ELONGATION FOR 3-YEAR-OLD LOBLOLLY-PINE

Effects of vegetation control and site preparation on the magnitude, morphology, and phenology of loblolly pine (Pinus taeda L.) height growth were investigated duing the third growing season following planting in the Piedmont of North Carolina. Biweekly measurements were made of shoot elongation (by flush) throughout the growing season on a subsample of trees within three replicated plots receiving a factorial combination of site preparation (chop versus shear, pile, disk) and weed control (none, partial control with herbicide, and complete control by hand weeding) treatments. Cumulative height growth on the most intensively treated plots was twice that found on the chopped-only plots, with weed control having a more pronounced positive effect than intensive site preparation. Superior height growth resulted principally from greater length per flush but also from an increased number of flushes. Trees on plots where vegetation was controlled averaged between four and five flushes compared with trees on chopped-only plots, which averaged three flushes. As growth rate of one flush slowed, growth rate of the subsequent flush accelerated, resulting in a rather uniform elongation rate for the shoot apex throughout most of the growing season. Treatment effects on the seasonal distribution of growth and on growing season length were minimal. Thus, intensive culture influenced shoot growth rates and morphology, but not phenology. Apparently the effect of intensive culture was to improve the availability of limited environmental resources and, consequently, to increase growth rate throughout the growing season.