The Oregon State University publication Fire Resistant Plants for Home Landscapes includes a landscape plan for making a home more fire resistant, as well as numerous pictures and information about fire-resistant plants. It notes dry mulch is a fire hazard unless it is kept damp, which is difficult to do in these drought times. A combination of wood bark mulch surrounded by decorative rock is less flammable than wood bark mulch alone.

Another idea is to use a fire-resistant ground cover instead of bark and rock, and several are listed in the publication, including drought-tolerant ones. A well-irrigated lawn around your home would serve the same purpose, but you are looking to conserve water.

You want to keep any mulch away from the trunks of the trees as the mulch could harbor insects and pathogens that can infest the trees. The shade of the trees as well as their water needs will keep down any weeds.