Three wildfires in California in the past 15 months killed or mortally wounded thousands of mature giant sequoias, accounting for an estimated 13 to 19 percent of the world’s population of the majestic trees, officials said on Friday.
A National Park Service report estimated that two fires in September, sparked by a lighting storm, caused 2,261 to 3,637 mature giant sequoias — or between 3 to 5 percent of the population of mature giant sequoias — to be killed or so severely burned that they were expected to die within five years. Mature giant sequoias have a diameter of more than four feet.
Giant sequoias, which are found on the western slope of the Sierra Nevada in California, can live thousands of years on their way to dwarfing most everything around them. These trees include iconic national treasures like the General Sherman Tree, which is considered the world’s largest tree, standing at 275 feet tall with a diameter of 36 feet at the base.
The death of the trees in staggering numbers is the product of a “deadly combination” of unnaturally dense forests caused by fire suppression that began about 150 years ago and increasingly intense droughts driven by climate change, Clay Jordan, superintendent of Sequoia and Kings Canyon National Parks, said in an interview on Friday night.
“That becomes a recipe for a catastrophic fire that threatens our sequoia groves, the health of our forests and, at the same time, threatens our communities,” he said. The mortality rates in the sequoias are unprecedented, he said.
KNP Complex, one of the September fires, burned mostly within Sequoia and Kings Canyon National Parks. The other, the Windy fire, burned in the Sequoia National Forest, the National Park Service said.
The Castle fire, which began in August 2020, destroyed 7,500 to 10,600 large sequoias, park officials said, representing an estimated 10 to 14 percent of the entire Sierra Nevada population of large sequoias.
Sequoias evolved to survive, and even thrive, in fires. But the ever-increasing intensity of fires in California has become too much for them.
Experts say the fires that sequoias endured for centuries were mostly low grade. Thick bark and sky-high crowns protected the trees from serious damage. Heat from the flames even helped them reproduce by releasing seeds from their cones.
But now, California’s sequoia groves are dealing with the consequences of fire suppression that has left forests thick with flammable vegetation. Drought and rising temperatures have killed other plants and turned them into kindling.
From 2015 to 2020, two-thirds of the giant sequoia groves across the Sierra Nevada were scorched in wildfires, compared with a quarter in the previous century, according to the National Park Service.
The latest wildfires this year led to fewer tree deaths partly because of emergency actions taken by firefighters, said Christy Brigham, chief of resources management and science for the Sequoia and Kings Canyon parks. This included backfiring operations, breaking and thinning around certain trees, and blanketing some sequoias, like the General Sherman, in protective wrap.
“While these losses are not as stark and large as the Castle fire, they are still significant, unsustainable and are outside the range of historic fire effects on large sequoias,” Dr. Brigham said at a news conference on Friday.
She also said that “climate change is a driving force in what we’re seeing, and we can’t fix climate change by ourselves.”
The fires may have some beneficial effects in areas that burned at low intensity, including fuel reduction, small canopy openings ideal for regeneration, removal of litter and generation of ash — ideal conditions for sequoia seedlings, the park service said.