Upland oak (Quercus spp.) forests of the central hardwood region and southern Appalachians are failing to regenerate in the absence of disturbances like fire that clear the understory and increase light. Because of the ecological and economic importance of oaks as mast producers and premier hardwoods, managers are increasingly implementing prescribed fire across the region in an attempt to reduce competition from shade-tolerant, fire-intolerant competitors (i.e., mesophytes) and improve growing conditions for regenerating oaks. To better understand how fire impacts upland oak seed germination, seedling establishment, and seedling growth, we implemented several studies at Spirit Hill Farm in northern Mississippi and Bernheim Arboretum and Research Forest in western Kentucky that manipulated the burn regime by varying fuel loads, burn season, and burn frequency, either singly or in combination.
Results/Conclusions
In northern Mississippi, we found that an early December burn after acorn drop caused ~ 55 and 40% reduction in white oak (Q. alba) and Shumard oak (Q. shumardii) acorn germination rates, respectively, under normal fuel loads, but that doubling and tripling fuel loads killed most acorns, likely because of the higher temperatures reached in these fires. However, acorns of both species that germinated post-fire exhibited similar growth (both height and basal diameter) compared to unburned controls. Greater post-burn success of Shumard oak may relate to their heavy seed coats (hence providing greater protection from the heat of fire) and seed dormancy and stratification requirements, which do not occur in white oaks. These findings suggest that while acorns are susceptible to fire-driven mortality, that many can survive a low-intensity fire and grow similarly to unburned acorns. In both northern Mississippi and western Kentucky, single dormant season (March) burns failed to improve oak seedling stature relative to co-occurring competitors like winged elm (Ulmus alata) and red maple (Acer rubrum). Multiple (2-3) dormant season burns in western Kentucky improved the annual growth of oak seedlings, but their competitors exhibited similar growth increases, leading to no competitive advantage for oaks. Overall, single and multiple dormant season burns appeared to have no positive impacts on oak seedling growth relative to their competitors, suggesting the need to expand the burn window to encompass growing season fires or implement other silvicultural practices (e.g., thinning and/or herbicide application) to increase oak establishment and growth into the canopy.