Fire and Drought Shaped California: The Human Cause of Recent Wildfires

Fire season in California has sparked again with a vengeance. 

"Big fires today are not outside the range of historical variation in size," said Jon Keeley, one of the researchers, in a news release. In fact, Keeley has researched the history of wildfire across the entirety of California, contrasting history versus contemporary and forested versus non-forested patterns of wildfire incidence. He and his colleagues reviewed records dating to 1910 in order to get a better sense of California's wildfire history.

So what sort of things did they find? It turns out that the chaparral shrublands of southern California and similar sagebrush ecosystems in the Great Basin are not adapted to the frequent fire that's typical of mountain conifer forests. In fact, fires in the lower elevation ecosystems are almost always crown fires, which kill most vegetation. Before humans arrived, they occurred just once every 100 to 130 years. Yet in the past century, fires have increased to every 10 to 20 years.

"In Southern California, lower elevation ecosystems have burned more frequently than ever before," said Keeley. "I think it's partly climate, but also people starting fires during bad conditions."

In fact, it's estimated that about 95 percent of fires in southern California are started by people, whether intentional or accidental. This, in particular, shows how humans are having a major impact on California's ecosystem.

"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."

The findings will be presented at the 99^th Annual Meeting of the Ecological Society of America.