PRESCRIBED FIRE EFFECTS ON STRUCTURE IN UNEVEN-AGED STANDS OF LOBLOLLY AND SHORTLEAF PINES

Structure was assessed in uneven-aged stands of loblolly (Pinus taeda) and shortleaf pine (P. echinata) that were subjected to prescribed wi nter burns on cycles of 0, 3, 6, and 9 years. Vegetation assessments w ere made in late summer of 1990, 10 years after a single hardwood cont rol treatment (basal injection of nonpine woody plants >2.5 cm in grou ndline diameter with Tordon(R) 101R); 1 year after the fourth 3-year b urn cycle; 4 years after the second 6-year burn cycle; and 1 year afte r the second 9-year burn cycle. Compared to unburned controls, prescri bed burning tended to increase (P less than or equal to 0.008) percent ground cover from graminoids and composites. For understory woody pla nts that were >1 m tall but <2.5 cm diameter breast height (dbh), Amer ican beautyberry (Callicarpa americana) had the greatest percent groun d cover on burned and unburned plots. Horizontal cover between 0- and 3-m height tended to average less (P less than or equal to 0.002) with more frequent prescribed burning and with shorter time since-burning. There were no burn treatment differences in density (P = 0.199, beta = 0.853) or basal area (P = 0.477, beta = 0.898) for sapling-size stem s (2.5-8.9 cm dbh), but species diversity of saplings was lower (P = 0 .002) on plots prescribe burned at 3-year intervals as compared to oth er treatments.