Relationships between prescribed burning and wildfire occurrence and intensity in pine-hardwood forests in north Mississippi, USA

Using Geographic Information Systems and US Forest Service data, we examined relationships between prescribed burning (from 1979 to 2000) and the incidence, size, and intensity of wildfires (from 1995 to 2000) in a landscape containing formerly fire-suppressed, closed-canopy hardwood and pine-hardwood forests. Results of hazard (failure) analyses did not show an increased likelihood of large, small, or intense wildfires with an increase in the number of years since the last prescribed fire. Wildfires of various sizes and intensities were more likely to occur in years with lower than average precipitation, regardless of when these areas were last burned. Calculations of expected lightning-fire potential based on weather patterns predicted a peak in lightning-started fires in the early to late summer. Lightning fires were rare, however, and wildfire activity was greatest in the spring and fall. We hypothesize that the ineffectiveness of prescribed burning in reducing wildfire hazard and the low incidence of wildfires in the midsummer in north Mississippi are both artifacts of fire suppression in the past, which converted open oak-pine woodlands with persistent pyrogenic surface fuels that accumulated over time to closed-canopy forests that lack such fuels. We suggest that open canopies and grass-based surface fuels must first be restored before prescribed burning will achieve most desirable management goals in this region, including hazard reduction and ecological restoration of natural fire regimes.