Woody and herbaceous competition effects on stand dynamics and growth of 13-year-old natural, precommercially thinned loblolly and shortleaf pines

Stand dynamics of naturally regenerated, even-aged, loblolly pines (Pinus taeda L.) and shortleaf pines (P. echinata Mill.) were examined on the Upper Coastal Plain of southeastern Arkansas, U.S.A., following four levels of competition control. Treatments included a check (Ck) with no competition control, woody control (WC), herbaceous control (HC), and total control (TC) of nonpine vegetation. After pines became established from natural seeding, herbicides were used to control herbaceous plants for four consecutive years and woody plants for five consecutive years. At age five, 1235 crop pines/ha were retained and all noncrop pines >1.5 m tall were precommercially hand thinned. Although 93% of crop pines on Ck plots were judged free-to-grow 13 years after establishment, crop pines on vegetation control plots were larger (P less than or equal to 0.001) in mean diameter at breast height, total height, and volume per tree. From age 5 through 13 years, crop pine diameter growth increased on WC plots and decreased on HC plots because of hardwood competition in the latter treatment. At age 13, mean pine volume production was 48% greater (P < 0.01) on plots that received competition control than on Ck plots (160 m(3).ha(-1)); TC resulted in 31% more (P < 0.01) volume (282 m(3).ha(-1)) than the mean of WC and HC plots; and there was no difference (P = 0.15) between the latter two treatments.