Vegetation dynamics vary across topographic and fire severity gradients following prescribed burning in Great Smoky Mountains National Park

摘要

Fire exclusion in the United States over the last century has had major impacts on forest ecosystems and landscapes. Out of a desire to reverse or mitigate the impacts of fire exclusion, some managers conduct prescribed fires meant to mimic the historic ecological role of fire and restore ecosystem properties. In the Southern Appalachians, fire exclusion in pine- and oak-dominated xeric ridge forests has allowed fire-sensitive hardwood species to establish, filling in the canopy and creating shady, moist conditions that are unfavorable for reproduction of fire-dependent pines and oaks, Managers of natural areas use prescribed fire to restore pine and oak dominance, promote pine and oak regeneration, and reduce stand densities. Here, we use multivariate analysis of monitoring data collected before and after 21 fires over 16 years in fire-suppressed xeric pine-oak forests in the Great Smoky Mountains National Park to assess how community composition and structure change after prescribed fire, to what degree changes after fire persist over time, and how the impacts of prescribed fire vary with fire severity and site environment. Fire consistently reduces stand density and shifts plots towards lower shrub cover and higher herbaceous cover. On the other hand, compositional shifts, i.e. changes in relative abundances of species, were highly variable in both magnitude and direction. Fire severity, measured as total fuel reduction and litter and duff reduction, was important for predicting the magnitude of change after fire. The magnitude of fire effects also varied with elevation, likely reflecting variation in local moisture conditions. Our results indicate that while fires do reduce stand density, they have not yet been successful in consistently restoring pine and oak dominance in the canopy. Restoring pine- and oak-dominance in xeric ridge forests in the Southern Appalachians will thus require extended management focus with flexible, adaptive, long-term planning and continued monitoring and research. (C) 2016 Elsevier B.V. All rights reserved.