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Letter From California

The Ancient Ecology of Fire

Lessons emerge from the ways in which North American hunter-gatherers managed the landscape around them

Monday, August 14, 2017

Letter From California Wildfire

 

The Quiroste Valley on California’s central coast lies sheltered from the wind that blows in from the Pacific not two miles distant. Coniferous pine and redwood trees stand along the valley’s rim and sweep down into the lowland where they compete with thickets of poison oak, buckeye, and coyote brush. This overgrown valley of some 200 acres was once the home of the Quiroste, a people who would not recognize their traditional lands today. When a Spanish expedition first visited the Quiroste’s village in 1769, the valley was full of meadows, hazel groves, and stretches of burned earth. The expedition chaplain, Juan Crespi, noted in his diary that the Quiroste hunter-gatherers were careful managers of the landscape. He wrote that they regularly burned the meadowlands “for a better yield of the grass seeds that they eat.”

 

On public lands today, vegetation often goes unmanaged and, as a result, becomes the tinder that fuels wildfires. Nearly 7,000 blazes ravaged California in 2016 alone. But for the Quiroste, fire was a powerful tool. They used it to manage a number of food resources, not just grass seeds. And by regularly setting controlled fires, the Quiroste also kept themselves safe from catastrophic wildfires, which feed on dense undergrowth. Recently, a group of archaeologists, ecologists, and members of a local Native American tribe set out to understand the history of this practice in the Quiroste Valley, now part of Año Nuevo State Park. “We had a lot of questions we wanted answers to,” says University of California, Berkeley, archaeologist Kent Lightfoot, one of the project’s directors. “First and foremost we wanted to know if we could even identify the general pattern of human-made fires in the archaeological record. Then, if so, we wanted to know when they started, how widespread the practice was, and what its impact on the local ecosystem was.” Identifying fires from the ancient past is difficult enough, but differentiating natural ones caused by lightning strikes from those deliberately set posed a serious problem for the researchers. Underlying the challenge was the fact that some scholars have argued that prescribed burns might not have been as widespread in the ancient past as they had become when the Spanish first arrived in California.

 

As a first step, the team studied how ecosystems on the central California coast have reacted to fires caused by lightning in the recent past. Ecosystems similar to the Quiroste Valley take about 100 years to fully recover from a fire. The first plants to regrow are grasses and herbaceous plants. But grasslands are disturbance-dependent communities, meaning they can only persist with regular grazing, tillage, or burning that removes encroaching woody plants. Given no further disturbance, grasses don’t last long, and within about 20 to 30 years most of the grassland is choked out by coyote brush and poison oak scrublands. Within a century, the vegetation reaches a mature stage, with most areas covered by scrublands and mixed conifer forests, and once again the landscape becomes fuel for wildfires.

 

This fire ecology research suggests that anthropogenic, or human-made, fires would create a landscape dominated by open, prairie-like vegetation, while those fires occurring naturally would result in a landscape of shrubs and conifer forests, such as the one in the present-day Quiroste Valley. Using these expectations about natural fire cycles and the succession of plant species, the team hypothesized that they could differentiate between the general pattern of anthropogenic fires and that of natural ones in the archaeological record. “If people frequently burned the landscape in the past,” says Lightfoot, “we would expect to find archaeobotanical and faunal remains that reflect widespread grasslands and fire-adapted trees.”

 

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