In upland oak forests of the eastern United States, anthropogenic fire exclusion is thought to be a major cause of increased dominance of fire-sensitive species and simultaneous oak regeneration failure. Forests will likely become less flammable as fire-sensitive species (i.e. mesophytes) become more common, which may create cooler, moister understories through a hypothesized feedback loop known as mesophication. In this study, we examine how gradually shifting forest composition from oak to mesophyte dominance affects forest flammability. To determine the role of increasing contributions of mesophyte leaf litter to forest flammability, we measured leaf litter and fuel bed traits that likely drive flammability and flammability metrics (flame height, burn temperature, rate of spread, and fuel combustion) after plot-level experimental burns using leaf litter from post oak (Quercus stellata) and southern red oak (Q. falcata) and three hypothesized mesophytes, hickory (Carya spp.), sweetgum (Liquidambar styraciflua), and winged elm (Ulmus alata).
Results/Conclusions
Preliminary results show that on average, oaks had 52% thicker and 44% larger leaves than mesophytes. In addition, oaks exhibited a 66% lower surface area to volume ratio and an 83% lower specific leaf area than mesophytes. Southern red oak leaves and sweetgum had a significantly higher degree of lobing and curling than other mesophytes and post oak. These differences in leaf characteristics are linked to differences in burning time, temperature, flame height, and rate of spread and indicate lower flammability as the contribution of mesophyte litter to the fuel bed is increased. Determining the impacts of mesophyte dominance on fuel bed flammability will allow us to better understand future impacts of mesophication and inform options for managing upland oak forests through the use of prescribed fire.