The oral tradition has helped scientists to reconstruct the 3,000-year history of California’s vast tropical rain forest. The results suggest that parts of the forest are more dense than ever, and are at risk of massive veld fires1. Research is part of a growing effort to integrate Indigenous knowledge with other scientific data in order to improve understanding of ecosystem histories.Wildfires are a major threat to California forests. Clarke Knight, a palaeo-ecosystem scientist at the US Geological Survey in Menlo Park, California, and his colleagues want to understand how Indigenous communities helped shape the forest by controlling this danger in the Klamath Mountains in the western part of the region. In particular, they have learned the use of Indigenous peoples in cultural heating – small, controlled fires that keep biomass low and reduce the risk of widespread burns.
Indigenous peoples use fire
“When I was a child, my grandmother used to burn down the house,” said Rod Mendes, a firefighter for the Yurok Tribe, whose family is part of the Karuk Tribe in northern California. The Karuk and Yurok tribes have called the Klamath Mountains home for thousands of years. “She kept the place clean. Indigenous people are probably doing some of the first fireworks in history, ”said Mendes.Understanding how indigenous peoples use fire is essential to forest management in order to reduce the risk of veld fires, Knight said. “We need to listen to the Aborigines and learn and understand why they treated it the way they treated the land,” Mendes added.
To create a map of the region’s forest history, the team based on historical accounts and interviews from members of the Karuk, Yurok and Hoopa Valley Tribe compiled by other research author Frank Lake, a naturalist of US Forest Service research in Arcata, California. , and descendants of Karuk, as part of his 2007 PhD thesis. These accounts describe national fire and land use. For example, members light small fires to keep the tracks clean; this also reduced vegetation, preventing the spread of veld fires from lightning strikes. Larger fires, called scattering fires, were used to improve the appearance, hunting, and nut-harvest conditions in the forest. The effects of fire on plants lasted for decades.
Analyzing the sediment cores
Knight said it was important to work with the nations because of their knowledge of the region. The Karuk Resources Advisory Board has approved the research proposal before it begins. “In a way, it removes the colonial model of the existing education system that does not fully integrate indigenous history,” Lake said.Researchers are also analyzing the sediment cores collected near two of the highest peaks in the Klamath Mountains, which are traditionally important to the nations. Pollen layers in the cores were used to measure approximately the density of trees in the area at different times, and modeling helped the day of the cores to be able to measure how the density changed.
The team also measured the coals in layers of cores, which helped to identify the volatility of the fire rate in the area. Burning scars on tree trunks pointed to specific fire events between 1700 and 1900. Because stump rings act as a biological calendar for their environment, researchers were able to compare fire times with the information associated with dense vegetation. They then put together how the overcrowding evolved with fire incidents. Although the methods used could not directly confirm the fires of the nations, the patterns suggest when this could happen, Knight said. For example, an increase in the number of burns during cool and wet seasons, when fires caused by lightning were almost uncommon, suggested human influence.
By gathering a lot of evidence, Knight and his team showed that the density of trees in the Klamath mountain range began to increase as the area became colonized, because European immigrants prevented the Indigenous people from burning the culture. In the twentieth century, complete firefighting became a common practice, and fires of any kind were extinguished or banned – although controlled temperatures are currently used in forest management. The team reports that in some areas, overcrowding is more than thousands of years old, thanks to firefighting.
Healthy forest
The dense jungle is not really healthy, Knight said. Douglas firs (Pseudotsugamenziesii), native to low-lying Klamath forests, are fire-resistant and prone to catastrophic wildfires. “The idea that we should let nature take its place is not supported by this work,” he said. He added that one of the strengths of the research was the many lines of evidence that showed that the Indigenous burning of the past helped to control the overgrowth of trees.
Fire biologist Jeffrey Kane at California State Polytechnic University Humboldt in Arcata says the findings of the growing tree density are not surprising. He has made similar observations in the Klamath region. He says: “There are more trees than there were just 120 years ago.Dominick DellaSala, a senior scientist at the Wild Heritage forestry organization Talent, Oregon, points out that the effects of tree overgrowth cannot be applied to the entire Klamath region, due to the limited list of lake research data.Knight, however, says that the results can be transferred to other similar low-lying areas with similar plant species.
Palaeoecology studies are increasingly incorporating Indigenous knowledge – but there is still a long way to go, says geologist MichelaMariani at the University of Nottingham, in the UK. In Australia, Mariani also found that tree populations began to increase after the British colonies disrupted cultural burns. “It is very important that we now include the Aborigines in the fire control negotiations and continue,” Mariani said. “They have a deep knowledge of the world we do not have.”Incorporating Indigenous words into research is also important in removing colonies from conventional scientific methods, emphasizes Lake. “It is a form of justice for those Indigenous people who have long been marginalized, discriminated against and disenfranchised,” he said.
Source Journal Reference: Jude Coleman. Indigenous knowledge reveals history of fire-prone California forest, Nature News (2022), doi: https://doi.org/10.1038/d41586-022-01232-x
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