Impacts of repeated wildfire on long-unburned plant communities of the southern Appalachian Mountains

The infrequent occurrence of large wildfires in the southern Appalachian Mountains over the last several decades has offered few opportunities to study their impacts. From 2000 to 2008, five wildfires burned a large portion of the area in and surrounding the Linville Gorge Wilderness in North Carolina. Areas were burned either once or twice. The response of acid cove and thermic oak plant communities (structure, cover, richness, diversity) was measured in 78 vegetation monitoring plots, established in 1992 and remeasured in 2010–11. Fire altered forest structure in both communities, resulting in the mortality of larger trees and increases in the abundance of smaller (<5 cm diameter at breast height (DBH)) stems. Burning twice decreased stem counts for mountain laurel (Kalmia latifolia) in both communities, whereas oaks (Quercus spp.) responded positively to burning twice in the thermic oak community. Table Mountain pine stem counts increased in acid cove and thermic oak communities burned once. Fire appears to promote princesstree (Paulownia tomentosa) invasion. Herbaceous species cover responded positively to fire (once or twice; both communities), with concurrent increases in woody species richness and diversity. Tree species composition in acid cove plots was not affected by burning, although some slight changes occurred in thermic oak plots burned twice.

Fire and the origin of Table Mountain pine – pitch pine communities in the southern Appalachian Mountains, USA

The prevalence of stand-replacing fire in the formation of Table Mountain pine – pitch pine (Pinus pungens Lamb. and Pinus rigida Mill., respectively) communities was investigated with dendrochronological techniques. Nine stands in Georgia, South Carolina, and Tennessee were analyzed for age structure, species recruitment trends, and radial growth patterns to determine whether they had originated as a result of stand-replacing fires. The oldest pines date from the late 1700s or early 1800s. Continuous or frequent episodic pine regeneration from those times to the early to mid 1900s was evident at all sites. During the first half of the 20th century, all sites experienced large surges in pine regeneration. However, no clear evidence of stand-replacing wildfires could be definitively linked to these surges. Rather, the regeneration appeared to have been caused by noncatastrophic surface fires and canopy disturbances occurring together or by the cessation of a frequent fire regime. For the past 25–50 years, there has been little pine regeneration at any of the sites. Restoring the dual disturbance regime of periodic fires and canopy disturbances should help sustain Table Mountain pine – pitch pine communities in southern Appalachian Mountains landscapes.

Wildfire Effects on Forest Floor and Surface Soil in a Table Mountain Pine-Pitch Pine Forest

Wildfire plays a dominant role in creating die environmental and biological conditions necessary for the natural regeneration of mixed Pinus pungens Lamb. (Table Mountain pine)-Pinus rigida Mill. (pitch pine) forests. This study of forest floor and surface soil properties following a mid-July wildfire in these forests in the Shenandoah National Park revealed significant reductions in nutrient contents. Prolific regeneration of the pines occurred following the fire, with over 9,000 seedling/ha tallied in high severity areas, compared with less than 800 seedlings/ha in unburned areas. It is hypothesized that fire degrades site quality and sets back the site succession process so that the pines are better able to compete with invasive, xeric-site deciduous species like oaks and maples. Adjacent, unburned xeric-site oak forests dominate on more moist and fertile sites.

Genetic diversity and structure in Pinuspungens (Table Mountain pine) populations

Pinuspungens Lamb. (Table Mountain pine) occurs in isolated populations from Georgia to Pennsylvania. Estimates were made of the levels of allozyme diversity within and among 20 populations of P. pungens from throughout its range. Pinuspungens has the high levels of genetic diversity typical of conifer species (0.242) and high intrapopulational diversity (0.204). However, P. pungens has twice as much of its diversity among populations (0.135) as the average conifer species. It is argued that the high degree of stand isolation and the opportunity for genetic drift to occur during succession are major factors contributing to the population genetic structure of this species.