Todd Esque, an ecologist with the USGS Western Ecological Research Center, says that although cheatgrass is not a big problem in the Mojave, other exotic species such as red brome are spreading fire through native communities that often have few evolved defenses against such disturbances. Esque and others are conducting detailed studies to better understand how increased fire size and frequency can affect desert ecosystems, and how native plants and animals can be protected. "We're trying to take a holistic view of the fire-weed cycle," says Esque. "We're looking at how fire changes nutrients in the soil, which changes the plants that are there, and in turn how animals respond to this dramatic change in habitat."
One of Esque's USGS collaborators, Dr. Matt Brooks, has studied recent historical changes in fire incidence and fire effects in the Mojave. Brooks says that while it is difficult to reconstruct long-term fire histories in desert systems, records from federal land management agencies do show an increase in Mojave Desert fires over the past two decades. Expanding human use of desert lands may be behind some of the increase, but Brooks says the pattern holds even in remote areas where fires are almost all lightning-caused.
"The increase in fires seems to be due to the alien annual grasses," Brooks says. These grasses often build up during years of heavy rainfall and, unlike many native annuals, their dry stalks may remain rooted in the ground for many years after they die, providing a lasting fuel source.
Brooks and others have also found that native Mojave Desert plants are often particularly vulnerable to fire. Although some species do resprout after burning if the fire intensity is not too high
Contact: Catherine Haecker
United States Geological Survey