Recent USGS studies have shown that nonnative annual grasses in the genera
Bromus and Schismus now dominate most plant communities in the
Mojave Desert. Unlike most native annual plants, which specialize in
particular microhabitats, these grasses grow in many different situations
and can create continuous fuel beds across the landscape, filling in the
plant-free space that once separated and protected native perennials from
fire. And unlike native annuals, which crumble and blow away soon after they
die, dried remains of the nonnative grasses stay rooted in highly flammable
dense stands for years after they die. They ignite easily and carry fire
rapidly and unbrokenly across the landscape.
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Many native annuals can survive fires by remaining dormant as seeds in the
soil, but they may not successfully compete with the nonnative annual grasses,
which dominate postfire landscapes. Wildlife is killed by fire, and those
animals that survive may be adversely affected by changes in the structure of
their habitat. The invasion of nonnative annual grasses and the increased
frequency of fires are changing the face of the Mojave Desert.
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Because nonnative plants are difficult to control, preventing their initial
establishment may be the best approach to managing them. Based on the limited
information currently available, it appears that all wildfires should continue
to be suppressed in desertscrub habitats. Studies are in progress by USGS
scientists to further evaluate the effects of fire and develop postfire
restoration techniques that minimize the dominance of nonnative annual
grasses in the Mojave Desert.
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