The fight to preserve California's mighty sequoia trees as fire seasons, climate change worsen

The resilience of some of Earth’s timeless towering treasures, the ancient sequoia trees, is being tested by the very thing they rely on to survive: fire.

“Up until just a few years ago, it was just virtually unheard of that fire could actually kill these incredible trees,” said Clayton Jordan, the superintendent of Sequoia and Kings Canyon National Park.

The massive trees, which shoot up hundreds of feet into the sky, date back multiple millennia. But human-caused climate change is fundamentally altering the fabric of the planet’s forests, and with it, experts say, the earth’s sacred sequoia groves.

Sequoia Trees only grow along the western slopes of California’s Sierra Nevada Mountains. Of the roughly 70 groves of the towering trees that exist in the wild, 40 of them live in Sequoia National Park, according to the National Park Service.

One of these groves, the NPS says, includes what’s considered the largest-known single stem tree by volume in the entire world: the General Sherman tree, which is 275 feet tall and over 36 feet wide.

Massive sequoias like the General Sherman are key to the fight against climate change. Altogether, the sequoia groves are among the world's most efficient at sucking up carbon dioxide and converting it to oxygen, according to Christy Brigham, the chief scientist overseeing the sequoias at Sequoia National Park.

“They produce oxygen, they store carbon, they hold the soil in place, they make places for bird nests," Brigham told ABC News.

But last August, even these masters of survival couldn’t hold on as the Castle Fire raged through Sequoia National Park.

“It’s heartbreaking and devastating,” Brigham said.

A report expected to be released later this month details the incredible toll that the Castle Fire had -- it wiped out 10% of the world’s native sequoias, according to Brigham and the National Park Service.

“It's thousands of years of living history that were lost in one fire event that we cannot get back in our lifetime," she said. "It's going to be hundreds of years."

While the Castle Fire began via natural causes, firefighters say part of the reason it charred 273 square miles of the national park was because of mistakes in previous forest management efforts and climate change.

Firefighters had previously worked aggressively to extinguish every single forest fire. But that strategy, along with recent bone-dry conditions year-round, have created a perfect storm for fires to spread. Normally, the smaller fires would go out on their own after burning through the smaller vegetation.

“If you had the absence of fire for a period of time, you [would] have a lot of other trees that are growing up that wouldn't normally be there in a natural healthy forest,” Clayton said.

The unchecked growth gave the flames a ladder to reach the higher up sequoias, providing the fire with more fuel to spread.

“When the fire was burning, we got together and rapidly tried to prioritize all the groves that we thought the fire might get through and talk to the fire team about, 'Can you back burn some of these to protect them,'” Brigham said.

The firefighters' valiant efforts last year weren’t enough. Dozens of trees that had lived since the Middle Ages burned to the ground.

This fire season, firefighters are taking proactive measures to keep Sequoia National Park and its precious sequoias safe.

It may seem counterintuitive, but crews are lighting parts of the forest on fire in an effort to save it.

Prescribed burns help reduce the potential fuel on the forest floor that can turn natural, low-intensity fires into blazing infernos.

“We realized that we really need to take a proactive approach to fire management. We can't just be playing defense anymore," Mike Theune, the fire public information officer at Sequoia National Park, told ABC News.

Along with the smaller fires helping to prevent overgrowth underneath the sequoias, the sequoias also rely on the low-intensity flames to crack open their seeds, allowing them to germinate and grow.

Some officials at Sequoia National Park are gearing up for what they call the fight of their lives -- preserving the towering sequoia for future generations.

“I don't have any plans to leave," Brigham said. "They've been here for 2,000 years. The least I can do is put in a good 10 or 15 [years] on their behalf."

ABC News' Matthew Fuhrman contributed to this report.