Alterations to the fuel bed after single and repeated prescribed fires in an Appalachian hardwood forest

To manage upland oak forests across the central and southern Appalachian mountain and plateau regions, prescribed fire is applied more frequently and across larger areas than in the recent past. The often stated objective is to reduce fuels, but there is a paucity of information on the impacts of repeated burning on fuels, including woody materials and the soil organic layer. These are complex components of forest ecosystems with significant impacts on nutrient and carbon cycling, forest successional dynamics, and soil protection from loss via erosion. Thus, understanding fuel bed response to prescribed fire is essential for predicting future forest function. Using study sites distributed across a range of landscape positions in the Daniel Boone National Forest on the Cumberland Plateau of eastern Kentucky, we examined changes to the fuel bed over six years in response to a single fire (burned once in six years), repeated fire (burned four times in six years), and fire-excluded treatments to determine prescribed fire impacts on fuel loads and mineral soil exposure. Prior to burning, fuel loads were generally similar among landscape positions, although the duff layer was lowest on sub-mesic and greatest on sub-xeric positions. A single fire reduced duff depth by 50%, whereas repeated burning led to depth reductions of > 60%. Repeated burning also significantly increased mineral soil exposure (25%) compared to single burn and fire-excluded (2-4%) treatments, with the greatest effects on sub-mesic and intermediate landscape positions. Repeated burning significantly reduced fine woody (1-h) fuels, but only after three burns, whereas fine fuel mass on sites burned once was similar to those where fire was excluded. There were no statistically significant effects of burning on large woody fuels (100- and 1000-h fuels). Overall, the primary impact of prescribed fire on the fuel bed was to consume the organic horizon and expose mineral soil, which has the potential to reduce fuel continuity for subsequent bums. Fire behavior in this region is driven primarily by fine fuels (litter and duff) and fuel continuity, both of which recover in relatively short periods of one to several years. Reduction of woody fuels is more intractable under a prescribed fire regime.