California’s giant sequoias are pillars of living history. Climate change may kill them

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• Amna Nawaz:

  California's giant sequoias can live for thousands of years, but scientists say they have rarely seen the kind of intense fire that have swept the state in recent years.

  The KNP Complex Fire is just 11 percent contained and is burning across nearly 50,000 acres, including treasured groves in Sequoia and Kings Canyon National Parks. And another fire is blazing in Sequoia National Forest to the South.

  The national parks are closed to visitors, but special correspondent Cat Wise got a firsthand look on a recent media tour with officials.

  Christy Brigham, Sequoia and Kings Canyon National Parks: We're standing up on the slope, and the fire came from below, and those are the conditions that, if the weather had been bad, would have generated running crown fire, and could have carried the flames up into the canopy of these trees.

• Cat Wise:

  At the smoke-filled entrance to Giant Forest in Sequoia National Park, the proud sentries known as the Four Guardsmen still keep their watch.

• Christy Brigham:

  They're probably 2,000 to 3,000 years old. These trees have survived hundreds of previous wildfires.

• Cat Wise:

  Scientists like Christy Brigham feared the ancient trees wouldn't survive the KNP Complex Fire, which has been burning dangerously close to the trees for weeks.

  Fire crews wrapped the bases of the Guardsmen in a flame-retardant foil to protect them. And Brigham says longer-term efforts of prescribed burning, where crews set controlled fires to help thin the forest and clear debris, helped save these national treasures from destruction.

  This is a place of majestic giants. These trees are some of the oldest and largest living organisms on the planet. And, today, the air is thick with smoke from fires all around us.

  While some areas of the park have had prescribed burns for the last six decades, others are a tinderbox.

• Christy Brigham:

  This area was at risk because of how dense this forest is. Those branches are 100 feet off the ground. But in this new kind of fire, you can get crown fire into a crown that high.

• Cat Wise:

  A new kind of fire, with greater intensity and higher flames than Brigham says the mighty trees have had to withstand.

• Christy Brigham:

  What we're seeing is 100-foot flame lengths, what's called running crown fire, where the fire gets into the crown and moves from crown to crown, instead of on the ground, and that is crazy.

• Cat Wise:

  Farther into the park, we come upon the crown jewel of the sequoias, General Sherman, thought to be the largest tree in the world.

  So, Christy, General Sherman is still standing.

• Christy Brigham:

  Thank goodness.

• Cat Wise:

  His massive 36-foot base is also wrapped in the foil.

• Man:

  It's not just aluminum foil. It's got that fiberglass backing.

• Cat Wise:

  While General Sherman remains safe, fires have been burning in several other sequoia groves in the park, and staff haven't been able to reach those areas yet.

• Christy Brigham:

  The wrapping that we saw today and the raking, those are all things we never had to do because we did not have high-severity fire.

• Cat Wise:

  It's an alarming trend.

• Christy Brigham:

  We really are seeing impacts of climate change that these parks and models did not predict until 2050 or 2080 at the earliest. And they are happening now.

  The drought that California had 2012 through 2016, it was incredibly severe in the Southern Sierra, where we are right now, killed 5.8 million trees. That many dead trees really changes fire behavior. And that's what we're seeing.

• Cat Wise:

  Those impacts are coming at an unnaturally fast pace.

• Christy Brigham:

  We cannot have huge swathes of land converting from forests to shrubs overnight. The plants and animals can't adjust to that. Things we care about, clean air, clean water, they will be detrimentally affected, they will be negatively affected by those rapid, large-scale, abrupt changes.

• Cat Wise:

  Last year's Castle Fire killed 10 to 14 percent of the entire population of giant sequoias, which only grow in California's Sierra Nevada Mountains.

• Christy Brigham:

  When we got the drone footage, the helicopter footage, we all cried. We had never, ever seen anything like that.

  And when we finally hiked out there in the spring and saw it in person, people were hopeful, like, oh, maybe it won't be as bad as it looked from the helicopter. And we hiked out there eight miles, no trail. And it's devastated, black dirt, almost no seedlings, entire sequoias turned to sticks.

  That is what can happen if we do not prepare beforehand.

• Cat Wise:

  A year later, two sequoias are still burning from the Castle Fire.

• Christy Brigham:

  We used our helicopter. We dumped water on them. They're still burning. And if unless we get a heavy winter, a regular winter that really dumps snow, cools them down, gets the wood fully saturated, I don't know when they're going to stop burning. That is climate change.

• Cat Wise:

  Mark Morales has been overseeing efforts to fight this year's KNP Complex Fire. He says the decades of prescribed burning in the park are paying off. But the sheer number of wildfires that have burned across the West this year means resources are limited.

• Mark Morales, Southern Area Blue Incident Management Team:

  We're trying to figure out where we can go put lines, what resource is needed, whether it's a bulldozer, a hand crew, an engine crew.

  And so, if you don't have those resources available, you have to decide, where can we go? So you may not be able to put people in the highest-priority areas.

• Cat Wise:

  Given the challenges, Morales is proud of his crew's progress battling the fire. But he says the relentless pace takes its toll.

• Mark Morales:

  They have been at this for an extremely long time. And so they're at the — not even at the end of a very long season.

  So, cumulative fatigue is an issue for all of the leadership on those crews that they have to constantly assess. It's been a tough season.

• Cat Wise:

  And they aren't yet out of the woods.

• Robert York, Berkeley Forests:

  After a fire, it regenerates and then it grows very fast.

• Cat Wise:

  In a sequoia grove used by U.C. Berkeley for research that hasn't burned in 100 years, Robert York points out the potential for the kind of destructive fire that happens when too much fuel piles up on the forest floor.

• Robert York:

  When I look at this forest, what I'm thinking about is, oh, there hasn't been a fire here in a long time. And, therefore, there hasn't been a fire that could essentially clean out all of the logs and the sticks that are on the ground.

  I also think about how difficult it might be to have a good fire at this point, because there's so much fuel. That's going to create more intensity for when a fire does occur.

  This is an area that was burned with a prescribed fire in 2012.

• Cat Wise:

  It's a paradox: Bad fires that burn too hot and too high can be lethal for sequoias, but the trees do need some fire to release seeds from their cones. And the years-long Western drought and hotter temperatures are threatening the viability of those seeds.

• Robert York:

  So, if we continue to have hot and dry springs, even if we do get dispersal of seeds, if they don't have adequate soil moisture, they're not going to survive, and there's going to be failures of giant sequoia seedlings.

• Cat Wise:

  So, York is looking at ways to do more prescribed burning and even plant new sequoias.

• Robert York:

  They're a strong species in many ways. And it gives me hope that they're going to persist under some pretty variable conditions in the future. But I also think that they will probably need some help. I know that they will need some help.

• Cat Wise:

  Christy Brigham agrees that the ancient sequoias will struggle to survive without some help.

• Christy Brigham:

  The action has to happen before the wildfire comes. And the problem is, when it's not burning, people don't feel the urgency.

  We need to do the prescribed burning and the restorative thinning before the fire gets there.

• Cat Wise:

  Out of the ashes she hopes will rise a new sense of urgency to protect these pillars of living history.

• Christy Brigham:

  We do think of them as being immortal, and that is one of the things we love about them. They're like superheroes, right? Nothing can kill them. They live forever. They have been here 2,000 years.

  But they are being killed. They're being killed by actions that we have taken, by climate change. Two thousand years of living history. I mean, they're ancient beings. And they're dying before our very eyes. And what really gets to me is that we're not acting fast enough.

• Cat Wise:

  A reminder that even some of the world's most resilient organisms can be casualties of climate change.

  For the "PBS NewsHour," I'm Cat Wise in Sequoia National Park.