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, m orphology, and phenology of loblolly pine (Pinus taeda L.) height grow th 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 subsam ple of trees within three replicated plots receiving a factorial combi nation of site preparation (chop versus shear, pile, disk) and weed co ntrol (none, partial control with herbicide, and complete control by h and weeding) treatments. Cumulative height growth on the most intensiv ely 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 gre ater length per flush but also from an increased number of flushes. Tr ees on plots where vegetation was controlled averaged between four and five flushes compared with trees on chopped-only plots, which average d three flushes. As growth rate of one flush slowed, growth rate of th e subsequent flush accelerated, resulting in a rather uniform elongati on rate for the shoot apex throughout most of the growing season. Trea tment effects on the seasonal distribution of growth and on growing se ason length were minimal. Thus, intensive culture influenced shoot gro wth rates and morphology, but not phenology. Apparently the effect of intensive culture was to improve the availability of limited environme ntal resources and, consequently, to increase growth rate throughout t he growing season.