Response of southern Appalachian table mountain pine ( Pinus pungens) and pitch pine ( P. rigida) stands to prescribed burning

Abstract

Southern Appalachian table mountain pine ( Pinus pungens) and pitch pine ( P. rigida) forests require disturbance for regeneration. Lightning-ignited fires and cultural burning practices provided the disturbance that prehistorically and historically maintained these forests. Burning essentially ceased on public lands in the early twentieth century when fire suppression became the primary fire management initiative of federal land managers. The last five to six decades of forest succession in the absence of fire have allowed chestnut oak ( Quercus prinus), scarlet oak ( Q. coccinea), and red maple ( Acer rubrum) to dominate both midstory and understory strata and to become poised to invade table mountain pine and pitch pine canopies. This study examined first-year responses of three 60–80-year-old southern Appalachian table mountain pine and pitch pine stands to prescribed fire. Prior to burning, mean canopy (woody stems ≥2.5 cm DBH), understory (all shrubs and saplings <2.5 cm DBH), and ground layer (all vascular species ≤1 m in height) species richness values ranged 6–8 species/0.02 ha, 2–3 species/0.01 ha, and 1–3 species/m 2, respectively. Mean pre-burn basal area ranged from 23 to 32 m 2/ha for the three stands. Canopy and understory densities averaged 1500–1900 and 70–120 stems/ha, respectively. Mean pre-burn ground layer cover ranged from 28 to 77% per metre square. There were no pine seedlings present in the pre-burn ground layer. On all sites, burning top-killed some overstory and midstory fire-intolerant species such as sassafras ( Sassafras albidum), red maple, and white pine ( Pinus strobus). Numerous sprouts of these species appeared in the post-burn understory and ground layers. Canopy species richness was significantly lower (45%) whereas understory and ground layer species richness were significantly higher (two times pre-burn values) following most burns. All three burns significantly reduced canopy basal area (20–30%), canopy density (50–70%), and ground layer cover (40–70%) but increased understory density (two times pre-burn values). Table mountain pine (8000 seedlings/ha) and pitch pine regeneration (15 000 seedlings/ha) was observed following two of these burns but the seedlings were not likely to survive due to shading and competition from overstory, midstory, and understory strata. Future burns to restore similar stands must open the forest canopy, reduce accumulated litter and duff layers, and expose regenerative basal buds of hardwoods to lethal temperatures in order to lessen post-burn sprouting. Prescribed burns that do not accomplish these goals may further encourage succession towards hardwood-dominated stands as sprouts of understory hardwoods grow into midstory and overstory strata.