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We're back with ALL THINGS CONSIDERED from NPR News. I'm Guy Raz.
At the U.N. Climate Change Conference earlier this month, one of the few areas of agreement was on protecting forests as a way to curb global warming.
Trees store carbon dioxide. And the U.N. estimates that cutting them down accounts for about 20 percent of the annual rise in global warming.
NPR's Elizabeth Shogren reports that warmer weather is making it difficult for some forests to survive, especially forests around Yellowstone National Park.
ELIZABETH SHOGREN: If you want to see how quickly tiny beetles are devouring Yellowstone's majestic whitebark forests, you have to ski uphill, way uphill. The trees only grow above 8,500 feet.
Dr. JESSE LOGAN (Entomologist): And really snug it down as hard as you can. You don't want snow getting under that front if you can help it.
SHOGREN: Entomologist Jesse Logan sticks what are called skins to the bottom of his skis. They look like skinny strips of carpet, and they help you ski uphill. For centuries, the peaks where whitebark live have been too frigid for mountain pine beetles. But more than a decade ago, Logan predicted that with global warming, these tiny ravenous beetles would start to thrive here.
At the time, other insect experts were skeptical. But in recent years, winter cold snaps haven't been nearly as brutal as usual. Logan looks up at the slopes speckled with skeletons of dead trees and says the massacre is happening faster than even he expected.
Dr. LOGAN: It's the sort of time in your life when you hope to hell you're absolutely dead wrong, and it comes to be you weren't right enough. And now I wonder if my grandchild will ever have the experience of being in whitebark.
SHOGREN: After hours of climbing, Logan stops at a 40-foot pine tree that looks like it has a bad case of pimples.
Dr. LOGAN: Each one of these is a point of attack by a pair of mountain pine beetles. This is a dead tree even though it's green. So I'll start to just carefully chip away the bark.
SHOGREN: The bark peels away easily.
Dr. LOGAN: And it's loaded with both adults and larvae. So if we take a look, you see these little translucent guys.
SHOGREN: Those are immature beetles that will grow up and attack other trees. It's not just mild winters that help the beetles multiply like crazy. Warmer summers mean the bugs are completing entire life cycles in one season.
Mr. WALLY MACFARLANE (Geographer): It's not that we just happened to come across a tree that had been hit.
SHOGREN: Geographer Wally Macfarlane is in the tree well with Logan, thigh deep in snow. He says he saw just how voracious those beetles are during 10 flights in a small plane over the Northern Rockies. On most of the region's high peaks, he saw large stands of trees, the wrong color.
Mr. MACFARLANE: As you look down at them, instead of green, you see red.
SHOGREN: When whitebarks die, they turn red first. Then, when the needles fall off, they turn gray. He says that in just a few years, beetles have ravaged more than half of the region's whitebark forests.
Their toll includes beloved landscapes in the Grand Tetons and Yellowstone, and crucial feeding grounds for one of America's most charismatic animals.
(Soundbite of woodpecker)
SHOGREN: In a nearby stand of whitebark, the woodpeckers are busy with all the dead trees. But for other wildlife, the fast die off is life-changing, especially for grizzly bears. If this were early autumn, they'd be keeping us company up here.
Dr. LANCE CRAIGHEAD (Biologist): Well, they'd be wandering around digging up catches of whitebark pine cones.
SHOGREN: Biologist Lance Craighead says before Yellowstone grizzlies' hibernate, they gobble up as many cones as they can. They're after the nutritious seeds inside.
Dr. CRAIGHEAD: They're just like pinenuts. Bears love them.
SHOGREN: Biologists know what happens when grizzlies don't get their favorite fall treat: They produce fewer cubs, and they spend more time at lower elevations.
Dr. CRAIGHEAD: Before long, they'll come up and there won't be any whitebark pine and then they've got to find something else.
SHOGREN: So where will they go?
Dr. CRAIGHEAD: They'll go down to Cooke City and try to get a burger at a Miner bar.
(Soundbite of laughter)
Dr. CRAIGHEAD: Well, maybe the dumpster. A lot of them will probably go down near people and get into trouble.
SHOGREN: Craighead says the threat to bears is so great that the government should protect them as much as possible. For decades, Yellowstone grizzlies were on the endangered species list. Three years ago, the federal Fish and Wildlife Service declared them recovered and took them off. Last year, a federal judge ordered them back on. His concerns were global warming and the loss of whitebark pine cones.
But not everyone is so gloomy about the bears' prospects. U.S. Geological Survey biologist Chuck Schwartz thinks grizzlies probably will be okay even without pine cones.
Dr. CHUCK SCHWARTZ (Biologist, United States Geological Survey): They're very adaptable at what they eat. In years without whitebark, grizzly bears eat a lot more root crops, and they eat a lot more meat.
SHOGREN: And Schwartz says it's also too early to give up on whitebarks completely because the beetles don't attack the young trees.
(Soundbite of woodpecker)
SHOGREN: But Entomologist Jesse Logan argues that young trees can't do what mature trees do. Not only do their seeds feed animals, their broad canopies shade the snow so it stays around longer. That makes streams cool enough for trout and keeps the rivers flowing.
Dr. LOGAN: So they're tremendously important for things we value like wildlife and, of course, water.
SHOGREN: What can be done to prevent them from dying?
Dr. LOGAN: Long pause. There's not any silver bullet, like a pesticide or something we can apply. That's just not going to happen. What we can do is begin to address seriously the issue of climate change. That's what's really causing this.
SHOGREN: That's no easy task. And the beetles are making it even harder. As the trees they've killed decay, they release the carbon dioxide that they've been storing into the atmosphere. That adds to the global warming problem.
Given all this, the federal government is considering putting whitebark on the endangered species list. But at least for now, we can enjoy what might be a fleeting pleasure.
One of our skiing partners zooms past us going downhill. We rip off our skins and follow, weaving our way through the tree's wide canopies. There's no better back-country skiing than a whitebark forest.
Unidentified Man: Whoa, Lance, watch out for that tree.
(Soundbite of laughter)
SHOGREN: Elizabeth Shogren, NPR News.
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