Prescribed fire effects on structure in uneven-aged stands of loblolly and shortleaf pines

Key words Structure was assessed in uneven-aged stands of loblolly (Pinus taeda) and shortleaf pine (P. echinata) that were subjected to prescribed winter burns on cycles of 0, 3, 6, and 9 years. Vegetation assessments were made in late summer of 1990, 10 years after a single hardwood control treatment (basal injection of nonpine woody plants >2.5 cm in ground-line diameter with TordorP 101 R); 1 year after the fourth 3-year burn cycle; 4 years after the second 6-year burn cycle; and 1 year after the second g-year burn cycle. Compared to unburned controls, prescribed burning tended to increase (P < 0.008) percent ground cover from graminoids and composites. For understory woody plants that were >l m tall but ~2.5 cm diameter breast height (dbh), American beautyberry (Callicarpa americana) had the greatest percent ground cover on burned and unburned plots. Horizontal cover between 0-and 3-m height tended to average less (P I 0.002) with more frequent prescribed burning and with shorter time since burning. There were no burn treatment differences in density (P = 0.199, p = 0.853) or basal area (P = 0.477, fi = 0.898) for sapling-size stems (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 other treatments. In forest management, timing, intensity, and frequency of prescribed burns are not only critical to successful stand establishment and development, but they also indirectly impact wildlife by changing food and cover (Davis 1959, Wade and Lunsford 1989). Fire can be used to enhance the establishment of herbaceous vegetation and stimulate resprouting in forest stands by top-killing woody species. However, little is known about the effects of fire on structure in uneven-aged stands of loblolly (Pinus tuedu) and shot-deaf pine (P. e&in&u). In response to public concerns about the ecological consequences of even-aged management, some national forests in the southeastern United States have dramatically increased planned acreages under uneven-aged management by using single-tree and group-selection cutting (U.S. Dep. Agric. For. Serv. 1990). In the selection system, some trees are harvested regularly as individuals or in groups, with total volume cut at any 1 time being roughly equal to the growth that has occurred since the last harvest (Reynolds et al. 1984, Baker et al. 1996). Uneven-aged management has also been recommended for private nonindustrial forest landowners (Baker and Murphy 1982). In the southeastern United States, nearly …