Influence of Precommercial Thinning and Fertilization on Total Stem Volume and Lower Stem Form of Loblolly Pine

Abstract

Abstract Two cultural treatments were applied in an overstocked loblolly pine (Pinus taeda L.)plantation (2,900 trees/ha after eight growing seasons): precommercial thinning (Yes or No) to 747 trees/ha after the eighth growing season and broadcast fertilization (Yes or No) with diammonium phosphate (150 kg/ha of P and 135 kg/ha of N) early in the ninth growing season. Total height and diameter at breast height (dbh) measurements were taken periodically through the 14th growing season. Fertilization increased tree volume more than thinning in the 9th through 10th growing seasons, but thinning was most effective by the 13th growing season. Over the 6-year period, thinning was the most effective cultural practice: check, 110 dm3; fertilized only, 135 dm3; thinned only, 165 dm3; and thinned and fertilized, 220 dm3/loblolly pine tree. After the 14th growing season, the first 5 m of bole was divided into five sections beginning at a 15-cm stump height: 15–30, 30–60, 60–125, 125–250, and 250–500 cm, and the volume for each section was calculated. Outside-bark volume per section increased consistently with thinning and fertilization; therefore, cultural practices did not change stem form in the lower bole. South. J. Appl. For. 29(4):215–220.