These lower elevation ecosystems experienced unprecedented fire frequency in the last century, with fire returning to the same area every 10 to 20 years, altering the ecology of the landscape.
"In Southern California, lower elevation ecosystems have burned more frequently than ever before. I think it's partly climate, but also people starting fires during bad conditions," Keeley said. Bad conditions include extended droughts and dry fall days when the Santa Ana winds blow through the canyons.
In high elevation conifer forests, spring temperatures and drought are strongly correlated with fire, and Keeley thinks climate change and management choices are likely playing a role in current trends. But in the hotter, drier valleys and foothills cloaked in grass, oak, and chaparral, human behavior dominates. Through arson or accident, in southern California, over 95% of fires are started by people, according to Cal Fire.
"Climate change is certainly important on some landscapes. But at lower elevation, we should not be thinking just about climate change," said Keeley. "We should be thinking about all global change." Land use change and population growth create more opportunities for fires to start.
The high frequency of fire has instigated a persistent switch from chaparral to grass in some areas. Frequent fire favors quick germination and spread of forbs and grasses. Most grasslands in California are not native.
Since the more recent arrival of immigrants from Europe and Asia, several o
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Ecological Society of America