Abstract
BackgroundDespite the widespread use of prescribed fire throughout much of the southeastern USA, temporal considerations of fire behavior and its effects often remain unclear. Opportunities to burn within prescriptive meteorological windows vary seasonally and along biogeographical gradients, particularly in mountainous terrain where topography can alter fire behavior. Managers often seek to expand the number of burn days available to accomplish their management objectives, such as hazardous fuel reduction, control of less desired vegetation, and wildlife habitat establishment and maintenance. For this study, we compared prescribed burns conducted in the dormant and early growing seasons in the southern Appalachian Mountains to evaluate how burn outcomes may be affected by environmental factors related to season of burn. The early growing season was defined as the narrow phenological window between bud break and full leaf-out. Proportion of plot area burned, surface fuel consumption, and time-integrated thermocouple heating were quantified and evaluated to determine potential relationships with fuel moisture and topographic and meteorological variables.ResultsOur results suggested that both time-integrated thermocouple heating and its variability were greater in early growing season burns than in dormant season burns. These differences were noted even though fuel consumption did not vary by season of burn. The variability of litter consumption and woody fuelbed height reduction were greater in dormant season burns than in early growing season burns. Warmer air temperatures and lower fuel moisture, interacting with topography, likely contributed to these seasonal differences and resulted in more burn coverage in early growing season burns than in dormant season burns.ConclusionsDormant season and early growing season burns in southern Appalachian forests consumed similar amounts of fuel where fire spread. Notwithstanding, warmer conditions in early growing season burns are likely to result in fire spread to parts of the landscape left unburnt in dormant season burns. We conclude that early growing season burns may offer a viable option for furthering the pace and scale of prescribed fire to achieve management objectives.
Highlights
Despite the widespread use of prescribed fire throughout much of the southeastern USA, temporal considerations of fire behavior and its effects often remain unclear
These results suggest that seasonal variability of prescribed fire behavior in southern Appalachian forests before complete overstory leaf-out may be influenced by solar radiation and fuel moisture more so than other environmental conditions that remained similar between seasons
Early growing season burns had a greater degree and variability of time-integrated heating induced by fire than did dormant season burns, influenced by warmer and drier burn day conditions
Summary
Despite the widespread use of prescribed fire throughout much of the southeastern USA, temporal considerations of fire behavior and its effects often remain unclear. Opportunities to burn within prescriptive meteorological windows vary seasonally and along biogeographical gradients, in mountainous terrain where topography can alter fire behavior. We compared prescribed burns conducted in the dormant and early growing seasons in the southern Appalachian Mountains to evaluate how burn outcomes may be affected by environmental factors related to season of burn. Wildland fire extent in largely deciduous forests of the southern Appalachians today is inversely related to vegetation greenness (Haines et al 1975; Norman et al 2019), with most area burned either in late winter (dormant season) and spring before complete leaf expansion (early growing season) or in the fall following leaf abscission (Schroeder and Buck 1970). Fire seasonality is further confounded in mountainous topography with less predictable fire behavior due to more heterogeneous temperature and moisture conditions across the landscape (Stambaugh and Guyette 2008; Lesser and Fridley 2016)
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