No. While bare ground would certainly provide an effective fire-defensible space, it is not necessary and looks bad. Bare ground may also cause soil to erode. Many homes have yards that are both effective defensible spaces and attractive landscapes with little or no bare ground. Most professionals consider the 30 feet closest to a structure the most critical area to consider for fire hazards, and likely more distance if the structure is on a slope.
See Firescaping - Landscape Design for Wildfire Defensible/Survivable Space and Selecting Firewise Plants for ideas about managing space around your home.