Study with about 26,400 sequoias in 19 California groves indicates that controlled burns reduced the risk of death by 77% and may have preserved approximately 1,900 trees during extreme fires.
Giant sequoias exposed to controlled burns in the previous ten years were nearly four times more likely to survive the 2020 and 2021 fires in California’s Sierra Nevada, according to a study by the University of California, Davis.
Controlled burns reduced the risk of death by 77%
The research, published in the journal Nature Communications, analyzed the effects of the Castle Fire, which occurred in 2020, and the KNP Complex, recorded in 2021. The two fires hit giant sequoia groves and killed thousands of these trees.
The results show that controlled burns carried out during the previous decade reduced the probability of sequoia death by approximately 77%. In treated areas, the chance of survival was about four times higher.
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The comparison was made between trees located in areas subjected to fire management and nearby sequoias situated in untreated portions of the same groves.
Computer simulations indicated that the burns conducted before the major fires prevented the death of approximately 1,900 giant sequoias.
The researchers also estimated that another 3,900 trees could have survived if all the sequoias present in the affected groves had received similar treatment.
“Controlled burns are effective in reducing the mortality of giant sequoias, even in today’s extreme wildfires,” said lead author Dan Dixon.
Dixon was a postdoctoral researcher at UC Davis and worked in Professor Yufang Jin’s lab when the study was conducted.
“If the goal is to protect giant sequoias, controlled fire is an essential tool available to managers,” added the researcher.
Study evaluated about 26,400 sequoias in 19 groves
Scientists from UC Davis, the United States Geological Survey, and the Sequoia and Kings Canyon National Parks participated in the research.
The team evaluated approximately 26,400 giant sequoias distributed across 19 groves affected by the Castle Fire and the KNP Complex.
To examine the conditions existing before the fires and estimate subsequent damage, the researchers combined different remote sensing data.
One of the resources used was airborne lidar, a technology that employs laser pulses to measure the forest structure. The analysis also incorporated high-resolution images captured by PlanetScope satellites.
This combination allowed for the assessment of fuel conditions before the fire’s passage and related these characteristics to the survival of the trees.
According to Yufang Jin, the union between high-resolution remote sensing and a rigorous statistical framework revealed information about controlled burns that go beyond the reach of traditional reports or field surveys.
Decades of management created different conditions among the groves
Sequoia and Kings Canyon National Parks have maintained since the 1960s one of the most extensive controlled burn programs in the United States, according to the study.
This work has created, over the decades, groves with very different fire histories. Some areas had recently received controlled burns, while others remained without fires for more than 100 years.
In places without fire, dead wood, shrubs, and other combustible materials accumulated. The contrast between the areas provided scientists with an opportunity to measure the effects of previous management during extreme fires.
Controlled burns reduce the amount of available fuel in the forest. With less accumulated material, the study indicates that the groves may show lower mortality when reached by a large-scale fire.
“This study is timely, considering the history of fire suppression in these forests and the increasing pace and scale of fuel thinning in the state in recent years,” declared Jin.
Millennial trees are also vulnerable to extreme fire
Giant sequoias are among the largest and longest-living organisms on the planet. A single tree can weigh the equivalent of 15 blue whales and remain alive for over 3,000 years.
In nature, these trees grow only on the western slopes of the Sierra Nevada in California. They evolved in a landscape marked by periodic low-intensity fires.
Their thick bark and high canopies offer protection. Smaller fires also remove vegetation, recycle nutrients, and help create favorable conditions for the growth of new sequoias.
These characteristics made adult sequoias considered by many people to be practically immune to fire. The perception changed after the 2020 and 2021 seasons, when entire groves were affected.
“The trees live for so long and have already experienced so much climate variation, differences in wildfires, droughts, they’ve seen it all,” stated Dixon. “Having so many dead in just two years was unprecedented.”
The study points out that sequoias remain resistant to common fires but can die when exposed to sufficiently intense flames.
According to the research, climate change is increasing the frequency and severity of disturbances affecting primary forests, including droughts and extreme fires. In this scenario, controlled burns appear as an available tool to reduce the vulnerability of the groves.
