Previously prescribed burns help limit spread of fire threatening Yosemite’s oldest Sequoias

By Heather Waldman

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    YOSEMITE NATIONAL PARK, California (KCRA) — As the Washburn Fire continues to burn, firefighters and conservationists are focused on protecting some of the oldest trees in the state of California.

The fire has been threatening the Mariposa Grove of Giant Sequoia trees on the southern edge of Yosemite National Park. The grove is home to about 500 mature Sequoia trees, each at least 500 years old.

For anyone that’s seen a Sequoia in person, it’s a wonder to behold. The oldest trees have been growing for the past 2,000 to 3,000 years and can be as wide as 30 feet.

Interestingly, Giant Sequoias have adapted over the millennia to naturally withstand and even thrive in wildfires.

Anthony Ambrose has studied these large redwoods extensively, first at UC Berkeley and now with his new nonprofit group The Marmot Society which focuses on forest research and conservation. He said, “Fire at low-to-moderate severity helps open the tree’s cones to release seeds from the mature trees.”

He said it also clears out the understory and reduces fire fuels. But while low-intensity fires are beneficial, more recent intense fires can be devastating.

A century-long lapse in controlled burns has allowed forests to become much denser with younger vegetation.

Meanwhile, climate change is leading to increasingly warmer conditions and drier fuels near the ground.

Both of those things have combined to create a situation in which ladder fuels can easily turn a low-intensity brush fire into an extremely hot blaze that reaches the canopies of Giant Sequoia trees.

“That is actually killing Giant Sequoias in conditions that normally they would be able to survive,” Ambrose said.

According to the National Park Service, during the past six years, six different wildfires have combined to burn about 85% of the acreage of Sequoia groves. The NPS anticipates that 20% of the world’s giant Sequoia population, which only grows in California, could be lost to wildfires in the next three to five years.

But Ambrose said the current situation at Mariposa Grove with the Washburn Fire can serve as an example of hope.

“The Yosemite National Park has a really good long history of implementing prescribed fire in that grove and so the conditions within that grove are actually pretty good,” Ambrose said.

That prescribed fire program has helped to eliminate some of those previously mentioned ladder fuels and given firefighters a better chance to protect the trees even if flames do enter the grove.

“That really highlights the importance of investing in proactive prescribed fire in these areas not only in giant sequoia forests, but other Sierra forests as well,” Ambrose said.

Even though Sequoias have adapted to prosper through the fire, if the eldest trees are lost in a major fire, they’re gone as far as humans are concerned.

“These two, 3,000-year-old giant monarch sequoia trees are irreplaceable on any meaningful human time scale and once they’re gone, they’re gone,” Ambrose said.

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