Season of burn effects on vegetation structure and composition in oak-dominated Appalachian hardwood forests

Abstract

Previous research indicates that low-intensity single or multiple prescribed burns in oak-dominated upland hardwood forest do not substantially change stand structure or species composition of the arborescent regeneration layer, leading managers and ecologists to suggest that burns during the growing-season may better achieve restoration goals. We examined season of burn effects on dry-mesic oak-hickory forests in the southern Appalachian Mountains, North Carolina. Treatments included: (1) control (CON); (2) dormant-season burn (DSB), and (3) growing-season burn (GSB). Prior to burning and again after three growing seasons post-burn, we inventoried the forest overstory (stems ≥ 25 cm dbh), subcanopy (stems ≥ 5 and <25 cm dbh), sapling (stems ≥ 1.2 m and < 5 cm dbh), and seedling (stems < 1.2 m) strata. We found no effect of prescribed fire, regardless of burn season, on stem density or basal area of the overstory and subcanopy strata, leaving the light environment in the forest understory relatively unchanged. In general, treatment effects on the sapling and seedling layers were limited to the mesophytic species group, where seedling density post-burn was greater in GSB than both CON and DSB and sapling density post-burn was lower than pre-burn in DSB and GSB. Mortality of individually-tagged seedlings three growing seasons post-burn did not differ among treatments for the red oak, white oak, red maple, mesophytic, and pyrophilic species groups, and averaged 29.0, 28.5, 31.8, 29.3, and 25%, respectively. This study provides support for the notion that a single fire in a closed-canopy oak-hickory forest has little effect on forest structure or regeneration composition, regardless of the burn season. Prescribed fires should be repeated in subsequent years to assess whether the effects of burn season are amplified under a periodic burning regime.