Fire Behavior and Fire Effects on Eastern Redcedar in Hardwood Leaf-Litter Fires

Abstract

Treatment of stands of hardwoods in the cross timbers of the central United States with tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-dimethylurea) can significantly decrease canopy cover of hardwoods. However, at the rate used for hardwood control, tebuthiuron does not control eastern redcedar (Juniperus virginiana L.). Our objective was to determine the potential of using fires in the hardwood leaf litter, either before or after tebuthiuron, for controlling eastern redcedar. To do this, we compared fuelbed characteristics, fire behavior, and fire effects on eastern redcedar in naturally occurring hardwood leaf litter with those augmented by leaves dropped following a single application of tebuthiuron. Studies were conducted in 1988, 1989, and 1991 on a cross timbers site dominated by an overstory of post oak (Quercus stellata Wangenh.) and blackjack oak (Q. marilandica Muenchh.) and with eastern redcedar in the understory. Factors evaluated included herbicide treatment (tebuthiuron or no herbicide) and burning season (late summer or winter). Tebuthiuron at 2.2 kg a.i. Ha^-1 was applied to plots (25 X 25 m) in March of the study years. In late summer, tebuthiuron-treated plots contained almost twice the 1-hr fuel loading as untreated plots. Fuel depth on untreated plots in late summer was about half that of other herbicide treatments and burning date combinations. Fuel loading on plots burned in winter was not affected by tebuthiuron treatment, and no differences in fuel consumption were detected among any treatments. Moisture content of 1-hr fuels on plots burned in winter was more than twice that of 1-hr fuels on plots burned in late summer. Fire intensity was low with all bums, and no differences in fire behavior were detected among any treatments. Crown scorch of 75% or greater on small eastern redcedar trees was considered a successful burn, and this resulted on all but the late summer-no tebuthiuron treatment. The natural log of fireline intensity explained about 47% (P<0.0006)) of the variation in fire success, and ambient air temperature explained an additional 19% (P<0.0468). Although tebuthiuron treatments effectively augmented leaf-litter fuel load by late-summer and provided a suitable fuelbed for burning, crown scorch and tree kill were not greatly improved by burning in late summer as compared to winter. We conclude that understory eastern redcedar can be controlled successfully by burning leaf-litter fuelbeds in either late fall or winter after natural leaf-fall from hardwood trees or in late summer, fall, or winter following a spring application of tebuthiuron for control of overstory hardwoods.