INTERSPECIFIC COMPETITION IN YOUNG LOBLOLLY PINE PLANTATIONS ON THE VIRGINIA PIEDMONT

An experiment was conducted in plantations of three ages (0, 1, and 2 years old) on three tracts in the Virginia Piedmont, to investigate the growth response of young loblolly pines (Pinus taeda L.) to different amounts of release from competing vegetation. Eight chemical release treatments involved the removal of all, two-thirds, one-third, or none of the hardwood stems in combination with either total or no herbaceous weed control.;Growth and yield models were developed on both the stand-level, with stand average and diameter distribution models, and on the individual-tree level, with empirical and modified Chapman-Richards equations. The inclusion of competition variables in stand average models containing the normal stand attributes significantly increased the explanation of variation in pine growth and yield. The best models explained 93% of the stand volume three years after treatment and 90% of the three year relative volume growth. A parameters recovery method of diameter distribution modeling performed slightly better than the parameter prediction method, but both were improved with the addition of interspecific competition variables, and gave comparable results to similar studies in older stands. Competition indices also significantly contributed to individual tree models. Distance-independent measures performed better than distance-dependent indices, and models based on the Chapman-Richards equation performed slightly better than empirically-derived regression equations. The best empirical regression equation had an R('2) of 0.82.;Results after three growing seasons showed a significant increase in pine diameter and volume growth with competition control. Three year volume growth ranged from 292 to 758 cm('3) for the youngest age, 1274 to 2555 cm('3) for the seedlings released before the second season, and 2911 to 4451 cm('3) for the oldest seedlings. Treatments including herbaceous weed control resulted in better growth than the same treatments without herbaceous weed control. The best response, obtained with the two-thirds woody plus herbaceous control treatment, resulted in a 100% increase in volume growth over the treatment without control in seedlings treated at the beginning of their second growing season in the field, a 93% increase in one-year-old seedlings, and a 53% increase in the growth of three-year-old seedlings.