Comparison of short term low, moderate, and high severity fire impacts to aquatic and terrestrial ecosystem components of a southern USA mixed pine/hardwood forest

Abstract

Historically fire was an important natural disturbance shaping the structure and composition of pine-dominated forests in the southern United States. Longstanding fire suppression policies have resulted in structural and compositional changes, notably accumulation of heavy fuel loads and reduction in vegetation species diversity. Primary goals of forest management through prescribed burning include fuel load reduction and mimicking ecosystem impacts of historically natural wildfires. In addition to the influences of fire frequency and season, the influence of fire severity on ecosystem responses is currently of interest. In this study we sought to quantify the impacts of low, moderate, and high severity fires, and their interaction with prior forest management practices, to several aquatic and terrestrial ecosystem components of a southern U.S. mixed pine/hardwood forest using a before–after, control-impact (BACI) approach. The ecosystem components we assessed were water quality, community composition of aquatic arthropods (wildfire impacts only), forest structure characteristics, community composition of understory vegetation, and community composition of ground-dwelling arthropods. We found that increasing fire severity increased aquatic nutrient levels and productivity, but the magnitude of effects increased with severity. Low and moderate severity fires had weak effects on forest structure characteristics, community composition of understory vegetation, and community composition of ground-dwelling arthropods in the initial years following burns. In contrast, high severity fires dramatically reduced fine and large fuel loads, increased diversity of understory vegetation, and influenced community composition of ground-dwelling arthropods. Further, wildfire severity was reduced in areas with a prior moderate severity prescribed burn, but not in areas with a prior low severity prescribed burn. Our results provide quantitative evidence for the role of fire severity as a primary factor influencing responses of ecosystems to fire, and indicate that forest management practices influence the impact of high severity fires on ecosystems.