Indigenous knowledge reveals the story of California’s fire-prone forest

Indigenous knowledge reveals the story of California’s fire-prone forest

Forest and brush are on fire in the Lower Klamath National Wildlife Refuge, winter 2020.

Controlled fires can be used to reduce the risk of wildfires.Credit: David Hoffmann/Alamy

Native oral histories have helped scientists reconstruct a 3,000-year-old history of a great fire-prone forest in California. Findings suggest parts of the forest are denser than ever and at risk of severe wildfires1. The research is part of a growing effort to combine indigenous knowledge with other scientific data to improve understanding of the history of ecosystems.

Wildfires pose a significant threat to California’s forests. Clarke Knight, a paleoecosystem specialist at the US Geological Survey in Menlo Park, California, and her colleagues wanted to understand how indigenous communities have helped shape the forest by managing this risk in the lush western Klamath Mountains. Specifically, they studied Indigenous peoples’ use of cultural burning – small, controlled fires that keep biomass low and reduce the risk of more widespread burning. The results are published in the Proceedings of the National Academy of Sciences.

“When I was little, my grandmother was burning around the house,” says Rod Mendes, fire chief for the Yurok Tribe Fire Department, whose family is part of the Karuk tribe in Northern California. The Karuk and Yurok tribes have inhabited the Klamath Mountains for thousands of years. “She was just keeping the place clean. Native people probably carried out some of the earliest prescribed burning operations in history,” Mendes says.

Understanding how indigenous tribes used fire is key to managing forests to reduce wildfire risk, Knight says. “We need to listen to the Aboriginal people and learn and understand why they managed the landscape the way they did,” adds Mendes.

Collaboration for corroboration

To map the forest history of the area, the team relied on historical accounts and oral histories of Karuk, Yurok and Hoopa Valley tribesmen collected by study co-author Frank Lake, a U.S. Forest Service research ecologist in Arcata, California, and a descendant of Karuk, as part of his doctoral dissertation in 2007. These accounts described fire and tribal land use. For example, members lit small fires to clear trails; it also reduced the amount of vegetation, preventing the expansion of forest fires caused by lightning. Larger fires, called broadcast burns, were used to improve visibility, hunting, and nut harvesting conditions in the forest. The effects of the fire on the vegetation lasted for decades.

Knight says it was important to work with the tribes given their knowledge of the area. The Karuk Resource Advisory Board approved a study proposal before it began. “In a way, it decolonizes the existing academic model that hasn’t been very inclusive of Indigenous histories,” says Lake.

The researchers also analyzed sediment cores taken near two low-lying lakes in the Klamath Mountains that are culturally important to the tribes. Pollen layers in the cores were used to infer the approximate density of trees in the area at various times, and modeling helped date the cores so they could estimate how that density changed.

The team also measured the charcoal in the layers of the cores, which helped map fluctuations in the amount of fire in the region. The burn scars on the tree stumps indicated specific instances of fire between 1700 and 1900. Because the tree rings of the stumps serve as an ecological calendar, the researchers were able to compare the fire periods with the corresponding tree density data. trees. They then reconstructed how this density fluctuated with the incidence of fires. Although these empirical methods could not specifically confirm that the fires were started by the tribes, models have suggested when this was more likely, Knight says. For example, increased burns during cool, wet periods, when lightning-caused fires were likely less frequent, suggested human influence.

Combining multiple lines of evidence, Knight and his team show that tree density in this area of ​​the Klamath Mountains began to increase as the area was settled, in part because European settlers prevented indigenous peoples from practicing cultural burning. . In the 20th century, total fire suppression became standard management practice, and fires of all kinds were extinguished or prevented – although controlled burns are currently used in forest management. The team reports that in some areas, tree density is higher than it has been for thousands of years, in part due to fire suppression.

healthy forest

A dense forest is not necessarily healthy, says Knight. Douglas firs, which dominate the forests of the Klamath Lowlands, are less fire resistant and more prone to catastrophic wildfires. “This idea that we should just let nature take its course is just not supported by this work,” she says. She adds that one of the strengths of the study is the multiple lines of evidence showing that past aboriginal burning helped manage tree density.

Fire ecologist Jeffrey Kane of California State Polytechnic University Humboldt in Arcata says the study’s findings on increased tree density aren’t surprising. He made similar observations in the Klamath region. “There are a lot more trees than just 120 years ago,” he says.

Dominick DellaSala, chief scientist for the forest conservation organization Wild Heritage in Talent, Oregon, points out that the results suggesting record tree densities cannot be applied to the entire Klamath region, due to the limited scope of the lakeside study data.

Knight, however, says the results can be extrapolated to other similar low-lying lake sites that have similar vegetation types.

More indigenous voices

Studies of paleoecology are increasingly incorporating indigenous knowledge, but there is still a long way to go, says physical geographer Michela Mariani of the University of Nottingham, UK. In Australia, Mariani also found that tree density began to increase after British colonization hampered cultural burning. “It is very important that we now include indigenous peoples in the discussion on fire management,” says Mariani. “They have a deeper knowledge of the landscape that we just don’t have.”

Including Indigenous voices in research is also crucial to decolonizing conventional scientific methods, Lake points out. It “becomes a form of justice for Indigenous peoples who have long been excluded, marginalized and unrecognized,” he says.

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