Fire is critical for persistence of native plant species in pine forests and savannas of the southeastern United States. Differences in fire behavior associated with season of fire and ignition technique may be important for predicting the response of plant communities. We conducted a study to determine how season and ignition pattern of prescribed fires affect fire behavior. We hypothesized that head fires and growing season fires would have greater fire behavior measurements, including fireline intensity and maximum temperatures. We established research plots in a native upland shortleaf pine (Pinus echinata) forest in northern Florida managed with single tree selection timber thinning and burned on a 2 year fire return interval. Plots were assigned treatments of either dormant or early growing season fires, and one of two ignition types, head fire or backing fire. At three points within each plot, flame length was measured and temperature recorded, and three pre and post burn fuel samples were collected to determine fuel moisture, fuel loads, and calculate fuel consumption. Weather conditions were also measured during fires. We performed two-way ANOVA tests to determine how fire intensity, temperature, residence time, and fuel consumption differ in response to season and ignition treatment combinations.
Results/Conclusions
Fire season had the greatest effect on measures of fire behavior and fuel consumption. Fireline intensity, residence time, and fuel consumption were greater in dormant season compared to early growing season fires. Fireline intensity was also greater for head fires compared to backing fires. Fuel consumption and the flaming and smoldering residence times did not differ between head fire and backing fire treatments and maximum fire temperature was not different for season or ignition treatments. Fire behavior measurements from early growing season fires did not support our prediction of greater fire behavior, possibly due to the conditions under which these prescribed fires were conducted. Live herbaceous fuel moisture and relative humidity were greater for the early growing season treatments and these variables can reduce fireline intensity. Results suggest that season of fire may influence plant responses that relate to fire intensity and residence time, two variables are known to be important in predicting plant mortality. The seasonal differences in fireline intensity and residence time may also influence the resprouting vigor of hardwood species, and seed germination and flowering of species cued by fire effects. In contrast, ignition technique is likely to influence fire effects on vegetation in this community type.