Herbicides have been added to silvicultural treatments involving fire for nearly 50 years and, for some objectives, can even substitute for a prescribed burn. Herbicides and/or fire create changes in the effects of silvicultural treatments at individual plant, forest community, and ecosystem levels. The interactions between herbicides and fire can be additive, synergistic, or antagonistic. When used properly, the addition of herbicides to prescribed burns for site preparation usually results in hotter burns, consuming more organic matter and debris, and in greater control of existing woody plants. Combined improperly, herbicides can be ineffective at controlling regrowth, can cause excessive erosion and loss of soil productivity, and can create new vegetation management problems. The physiology and phenology of herbicide activity in target plants, as determined by the characteristics of herbicide chemistry, dictate the interactions that are possible. The reaction of the plant community to the characteristics of the burn, as well as the objectives of the burn, determines whether herbicides can be a viable substitute for fire. © 2000, Tall Timbers Research, Inc. Abstract reproduced by permission.