FIRE BEHAVIOR AND FIRE EFFECTS ON EASTERN REDCEDAR IN HARDWOOD LEAF-LITTER FIRES

Treatment of stands of hardwoods in the cross timbers of the central U nited States with tebuthiuron imethylethyl)-1,3,4-thiadiazol-2-yl]-dim ethylurea) can significantly decrease canopy cover of hardwoods. Howev er, at the rate used for hardwood control, tebuthiuron does not contro l eastern redcedar (Juniperus virginiana L.). Our objective was to det ermine the potential of using fires in the hardwood leaf litter, eithe r before or after tebuthiuron, for controlling eastern redcedar. To do this, we compared fuelbed characteristics, fire behavior, and fire ef fects 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 cr oss timbers site dominated by an overstory of post oak (Quercus stella ta Wangenh.) and blackjack oak (e. marilandica Muenchh.) and with east ern redcedar in the understory. Factors evaluated included herbicide t reatment (tebuthiuron or no herbicide) and burning season (late summer or winter). Tebuthiuron at 2.2 kg a.i. ha(-1) was applied to plots (2 5 X 25 m) in March of the study years. In late summer, tebuthiuron-tre ated plots contained almost twice the 1-hr fuel loading as untreated p lots. Fuel depth on untreated plots in late summer was about half that of other herbicide treatments and burning date combinations. Fuel loa ding on plots burned in winter was not affected by tebuthiuron treatme nt, and no differences in fuel consumption were detected among any tre atments. 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. Fir e 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 th is resulted on all but the late summer-no tebuthiuron treatment. The n atural log of fireline intensity explained about 47% (P<0.0006)) of th e 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 suitabl e fuelbed for burning, crown scorch and tree kill were not greatly imp roved by burning in late summer as compared to winter. We conclude tha t understory eastern redcedar can be controlled successfully by burnin g leaf-litter fuelbeds in either late fall or winter after natural lea f-fall from hardwood trees or in late summer, fall, or winter followin g a spring application of tebuthiuron for control of overstory hardwoo ds.