Meet the Giant Sequoia. The Super Tree Built to Withstand Fire.


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The Roman Republic was only two centuries away at the time the Grizzly Giant sprang from the ground in Yosemite National Park. Buddhism would not develop for at most a century. Geoglyphs that made up the Nazca Lines in southern Peru would not be etched until around 200 years after the Grizzly Giant.

At an estimated 2,700 years old (and possibly even older), this giant sequoia is one of the oldest trees in the world—a majestic specimen of a remarkable redwood species that has evolved to withstand the flames that periodically sweep through its environment. Some of these trees, which can grow more than 300 feet tall (about as high as a 30-story building) and dozens of feet wide, are the world’s most massive tree and one of the largest organisms on earth.

Giant sequoias are found only in about 73 groves scattered along the western slopes of California’s Sierra Nevada, from Tahoe National Forest to the Giant Sequoia National Monument northeast of Bakersfield, Calif. President Abraham Lincoln first set aside the Grizzly Giant and the other sequoias of Mariposa Grove as federally protected in 1864, eight years before the designation of the country’s first national park.

General Sherman, a historic sequoia, is viewed by Chief Jon Wallace of Operations Section. He was protected in the park’s structure wrap from flames by Sequoia National Park, in 2021. Numerous groves were protected by firefighters who were trying to stop out-of-control fires. Credit: Gary Kazanjian/AFP via Getty Images

Recent threats to Mariposa Grove have been made by the Washburn Fire. This fire started on July 7th and has ravaged more than 4,000 acres. Alder Creek Grove is another stand of giant sequoias in Giant Sequoia National Monument, which was also scorched by the Castle Fire in 2020. The fate of Mariposa Grove has so far been escaped. Almost all of the trees in the most intense part of the fire perished—This could lead to the loss between 10 and 14 percent of all living giant sequoias. The possibility exists that these massive giants may be followed by more wildfires. This is due to the increasing temperatures and decades of fire suppression which have allowed for fuel to build up.

For more information about these American icons and the conservationists who are working together to preserve them, visit Scientific AmericanPaul Ringgold, chief programme officer at the non-profit Save the Redwoods League, was our interviewee.

[An edited transcript of the interview follows.]

How is it possible for giant sequoias to grow so large?

It’s still a question that hasn’t been completely answered. Like their cousin, we know for certain. Coast redwoodThese trees are very efficient at absorbing water and transferring it high up in the canopy. Their cellular structure seems to be specifically designed to draw water up to great heights. But I think, also, just the resilience that they have—they’ve adapted to be able to survive climate impacts and threats such as droughts and wildfire—has allowed them to continue growing for so much longer than most of the trees they are coexisting with.

Also, the specific adaptations in their bark, which is a natural insulator—that very thick and fibrous bark that can get up to two feet thick in some of the largest trees—it’s a perfect insulator. They’re supertrees. They can withstand fire impacts better than other trees. They have adapted to survive fires, which I believe is what has brought them to where they are today.

What are some other ways they have found to live with fire in their daily lives?

This adaptation also includes the height of your crown and the height of your branches. In the face of natural fires that occur in that environment, you generally don’t have flames reaching up into the canopy.

Their adaptation to fire-adapted environments is what I believe was the key to their survival and adaptation. The giant sequoia cones are serotinous, which means that they don’t open and release seed unless subjected to heat. A ground fire, in a normal setting, would ignite the release of seeds from the cones. It also provides a mineral-soil seedbed to the sequoia. These [seeds] will not do well—and generally don’t survive—if they fall onto a layer of litter on the soil. They just can’t withstand the dryness of the Sierran summer without having that mineral soil that they can start getting down into and reaping the rewards of the moisture that is stored there.

What is the impact of climate change on these trees?

To start with, we’re experiencing these much longer periods of prolonged drought. That has been a major challenge for many reasons. I think the first one is there’s less moisture—and there’s increased competition for that moisture—resulting from the fact that there has not been the natural thinning of trees in these groves. The sequoia have also faced challenges due to drought, regardless of fuels buildup or competition. There have been studies that have shown that the sequoia in some of these really, really serious drought periods during the summer are demonstrating some dieback in their foliage—not enough to kill the tree but enough to demonstrate that the tree is definitely stressed right now. There’s no doubt that even those trees that have withstood drought historically over the past thousands of years are definitely stressed right now as a result of the prolonged drought.

The stress causes more stressors to enter the environment, such as the bark beetle population explosion. What otherwise would be trees that are stress-free and robust and able to withstand some level of insect attack are falling victim to these insects because they’re under so much stress—and because the beetle populations are so much larger.

How can we protect giant sequoias from the more frequent and intense wildfires we’re seeing now?

I think the first thing to keep in mind is that the giant sequoia groves—which represent a very small portion of the Sierran landscape—exist within the broader context of this same challenge around the fuels buildup that exists throughout the Sierra forests. I think that most of the wildfires that we’ve seen started outside the groves. The [Save the Redwoods League]Naturally, the focus is on protecting the Sequoia trees. But this all leads to one of our conclusions, which is that we can’t really accomplish effective protection of the groves by doing work just inside them. We’ve already reduced the level of fuels in some groves. We need to do that not just in the groves themselves but in sort of this buffer area surrounding the groves to make sure that adjacent fire doesn’t carry into the crowns of groves that have been prepared for low-intensity ground fire.

Our biggest problem right now is the incredible fuel buildup on the landscape. This makes it impossible to control wildfires. We saw that just last year—for the first time, We witnessed a fire spreading across the Sierra SummitAnd down into Lake Tahoe. There are unprecedented events that we’re seeing, at least within our history and our memory. The problem is that these fires are so intense that they can burn through large sequoia trees, decimating the habitats of large populations of sequoias.

We also have concerns about type conversion, and the fact that the mortality rate in the sequoias was 100 percent. [hit by some of the recent fires]. So without some active measures to reintroduce seedlings through plantings or reseeding and watering, we’re going to see conversion of what was a sequoia grove to brush fields and other species—because the fire was so hot that not only did it kill the standing trees, but it killed all of the seeds and cones that were ready otherwise to reestablish that population.

Is there anything we could do to help trees in the event of a fire threatening?

Yes. [fire management staffers] did some of that in the Alder Creek Grove when that fire burned, and they’re doing it now in the Mariposa Grove—and that is ground-based sprinkler systems. I think oftentimes people assume that they’re up in the trees, but it really is to keep the floor of the forest moist, which really is effective in reducing the severity of fire as it burns through those areas.

Last year was a good year. [fire managers]we wrapped some larger, named monarchs [the term for the largest individuals in a grove]They wanted to ensure that the buildings were covered with foil insulation. They didn’t do that in Mariposa Grove this year, but they wrapped the buildings there to protect. But what I’ve been hearing is that they’re now concerned that wrapping up the trees in that material may actually have an adverse impact, in the sense of putting foil over a casserole going into the oven, that it may actually reflect some of that heat back into the tree.

The trees were being wrapped when I first saw them. [last year], I was a little bit puzzled, because as far as I know, the threat to old-growth sequoias is not ground fire; it’s crown fire. If you have a fire burning through a grove, and you’re wrapping the trees, you’re basically putting the Band-Aid on the part that doesn’t really need it.

These species are unique in their grandeur and we need to protect them. Even photos can’t convey the magnitude of their size.

It is a must to see the wonders in person to truly experience them. And that’s what I love about the giant sequoias and coast redwoods—that they exist in such different contexts. With the coast redwood forests, you get into these forests, and you can go for miles, and you’re experiencing this consistent pattern on the landscape of these large trees. Whereas the giant sequoia exist in these very remote, oftentimes very secluded groves where you just sort come around a corner and, all of a sudden, there’s a whole other world. It’s a wonderful feeling to be surprised.


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