Climate change altering America's national parks

YOSEMITE NATIONAL PARK - Towering above the other trees in the Mariposa Grove, the Grizzly Giant stands like an adult among toddlers. Twenty-five feet across and almost 20 stories high, the estimated 3,000-year-old sequoia seems invincible.

But the iconic evergreens - and the beloved park around them - are facing a fierce and unrelenting adversary: climate change.

National Park Service forest ecologist Garrett Dickman bears witness to the struggle. A 22-year drought. Ferocious fires. Vanishing glaciers. Invasive species. Hotter summers and shorter winters.

Walking through the sequoia grove, one of three located in the national park visited by 3.3 million people last year, Dickman points out tree after tree killed by insects, thirst, or both.

"Sugar pine, ponderosa pine, white fir, giant sequoia. All dead," he said. "Millions of trees have died within the park's boundaries."

The nation's national parks are places so awe-inspiring they were meant to be forever preserved, "unimpaired" for future generations.

That's no longer possible. Last year the park service published a landmark document laying out the harsh realities of global warming. In most of the nation's parks, much will change, not everything can be saved and some things will be lost forever. The report outlines how park officials must plan in earnest for "unprecedented" future conditions.

Such conditions are already visible at Yosemite. Rhapsodized by naturalist John Muir more than 150 years ago as "God's first temples," the park he helped create has long been a place that deeply touches those who visit.

But the grandchildren of this year's visitors will see a different park from the one that beckons today.

Dan Porter, The Nature Conservancy's California forest program director, first worked at Yosemite in 1996 as part of a children's program.

"Back then, the thought that it could be irreparably changed didn't even cross our minds," he said. "Seeing what is happening there tells us there is no place on Earth that is safe anymore from the impacts of our unsustainable way of living."

'A species shift'

On a blazing August day, Dickman stood at Yosemite's Wawona Point, nearly 3,000 feet above the valley floor, surveying the forest far below. In the past five years, the area has been devoured by flames: the Railroad fire in 2017, the Ferguson fire in 2018 and the Washburn fire in 2022. All were high-intensity fires that charred large patches of forest.

Fires, a critical part of this ecosystem, now burn so hot that instead of being beneficial, clearing dead brush and sparking new tree growth, they leave only scorched earth. What regrows may no longer be a woodland. In the past 80 years, the climate has become warmer, drier and suited for an entirely different landscape.

"We're seeing a species shift," he said, pointing toward the chaparral and brushland emerging from the seared ground. "In a few areas, what's coming back isn't forest at all, it's cheatgrass."

As the composition of the forest changes, no one knows what that will mean for the animals, birds and insects that have evolved to inhabit it.

"Even five years ago, we thought whitebark pine was doing great and now we're seeing it die in large patches," Dickman said, shaking his head. "Just this year, for the first time, I'm seeing Douglas fir being killed by insects and woodpeckers at large scale."

The southern edge of the Douglas fir's range, he says, is "moving north before our eyes."

After decades of hiking the park's trails, there are some places Carl Casey, 67, can no longer bear to return to.

"There's … so many dead trees," he said. "Devastating."

Trees react to change

Giant sequoia evolved to drop seeds after fires when leaf litter on the ground has been burned and competing vegetation creates gaps in the tree canopy to bring in sunlight.

But last summer, some of the largest giant sequoias in Mariposa Grove released their seeds not during a fire but during a heat wave.

"We've never seen this before," said Anthony Ambrose, executive director of the Ancient Forest Society, a nonprofit forest research and outreach organization that works with the park service. He has spent years working in the grove and was disturbed by what he saw.

The seeds, which should have fallen on mineral-rich soil cleared by fire, instead fell in leaf litter on the forest floor. When summer came, the mulch couldn't hold enough moisture to support them.

"When we went back this spring, there were literally billions of seeds on the ground that had dried up and died because the conditions weren't appropriate for them to germinate," Ambrose said.

Scientists aren't sure why the seeds fell without the trigger of a fire. It happened during a drought and an intense heat wave as smoke from fires miles away filled the grove.

Perhaps some combination of all three confused the trees.

"Things are changing in the ecosystem. We're still trying to understand," Ambrose said.

Lumber as dry as kindling

Yosemite also is in the throes of a 22-year megadrought, worse than any since the year 800 A.D.

Although droughts have always come and gone in the West, it's also getting hotter. Temperatures are on average 1.6 degrees warmer than they were in 1895. The average minimum nighttime temperature is now 7.6 degrees warmer than it was in 1915.

Less snow and rain has turned trees into tinder. Dickman has tested branches with fuel moisture levels of 8%.

"As a comparison, the kiln-dried lumber you buy at the lumber store has a moisture content of 8% to 14%," he said.

Studies show that 1,200 years ago, Yosemite went through an intense drought and some giant sequoias died during high-severity fires.

"The record of losing giant sequoias (to environmental causes) doesn't start up again until the 1980s," Dickman said.

Last year, the nation's giant sequoia managers added up all remaining trees. To their horror, the number of the threatened redwoods, harvested almost to extinction in the 1800s, had decreased significantly.

"We tallied it all up and we'd lost 20% of them in just two years," Dickman said.

The megadrought is part of a one-two punch that's hurting the park's woodlands in ways even casual visitors can see.

Water-stressed trees are easy to spot because they look like they've had a bad haircut. Dickman can stand in one place, turn in a circle and point out dozens. Under drought conditions, the trees drop needles, through which they lose water, to protect themselves.

Sometimes there's so little water the trees simply can't pump it all the way to their crowns. "Then their top dies off," Dickman explained.

Some trees send out a new top, or a lower branch will crook upward and become the tree's new trunk. "Others," he said, "just die."

Damage from insects

The drought also is making trees more susceptible to bark beetles. Though the insects are native to the region, an almost three-month increase in frost-free days means the beetles can reproduce more.

Under normal circumstances, they only attack diseased or damaged trees, digging through the bark to eat the nutrient-rich wood underneath and lay their eggs.

Healthy, well-watered, trees fight off the beetles by trapping them in sticky pitch and pushing them out through the bark - a process known as "pitching the bugs out," Dickman said.

"The trees can fight back," he said. "Giant sequoia pitch especially is really gnarly; it's bitter and awful."

But water-stressed trees can't create enough pitch to expel the beetles. When that happens, the beetles multiply, sometimes killing a tree within six months. Between 2010 to 2019, the Forest Service estimates more than 163 million trees in California's forests were killed, mostly by bark beetles.

The beetles can't get through the thick bark at a tree's base. Instead, they attack at the tree's top, where the bark is thin and there is less pitch.

Dickman pointed to tree after tree, topped with brown, dead needles. "They die from the top down," he said.

Paul Wagner, 70, of Napa, California, has been coming to the park for 52 years.

"It used to be people wanted to know how bad the mosquitoes are. Now they ask if there's going to be any water in the creeks," he said.

It's worth the fight

Larry Orman, 73, is a conservation advocate who started his career as a whitewater rafting guide on the Tuolumne River in the 1970s. He founded the Greenbelt Alliance, a California conservation nonprofit, and spent 19 years as director of the GreenInfo Network, which creates maps to aid conservation groups.

"Remember, there's a lot about Yosemite that nobody's going to change except for a meteor," he said.

The park's geology and its awe-inspiring formations will endure. There's a reason the Tunnel View Overlook, with its first, breathtaking view of the valley and its soaring granite guardians, El Capitan, Bridalveil Fall and Half Dome, draws as many as 7,000 visitors a day.

The park and its ecosystem will be different as climate change shifts its ecology, and it won't be Orman's park anymore, but it's going to be someone's, he said.

And whatever that is will still be worth fighting to save.

That's what keeps Dickman motivated, no matter how many dead trees he has to tag for removal.

"It's fully worth doing everything we can to protect this place," he said. "How could you not?"

DMU Timestamp: February 20, 2024 23:51

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