Short-term effects of prescribed fire on mixed oak forests in the southern Appalachians: vegetation response
We examined vegetation responses to prescribed fire on three mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each of the study sites was within a sub-watershed that drained a first order stream. Our objectives were to: 1) evaluate overstory mortality following prescribed fire treatments; and 2) assess changes in composition, abundance, and diversity of overstory (stems = 5.0 cm dbh), understory (stems < 5.0 cm dbh, = 0.5 m height), and herbaceous layer (woody stems < 0.5 m height and all herbaceous plants) vegetation in mixed-oak ecosystems. Each site included a burned and unburned area (control). Before the prescribed fire treatments were applied, we established permanent plots (10 × 20 m) in the prescribed burn areas (12 plots in AL, 12 plots in RB, and 10 plots in RM) and adjacent unburned areas (5 plots in AL, 6 plots in RB, and 4 plots in RM), for a total of 49 plots. Within the plots, we sampled vegetation before and after the prescribed burns. All of the prescribed fires were low to moderate intensity; i.e., they had moderate flame temperatures and low flame heights. After the prescribed fires, overstory mortality was low for all sites, and there were no significant differences between mortality in burned areas and that in unburned areas. Understory density was lower on the burned than the unburned plots the first (t = -5.26, P < 0.0001) and second (t = -3.85, P = 0.0020) growing seasons after burning. There was either an increase (AL, RB) or no change (RM) in herbaceous layer cover depending on the site and no significant change in species diversity after burning for any site. Thus, we found no negative effects of prescribed fire on herbaceous flora.