Air Date: Week of June 9, 2000
Climate change - in the form of warmer, wetter weather - is encouraging European blister rust to infect pine nut trees in Yellowstone. As Jyl Hoyt reports, this could be disastrous for grizzly bears, who rely on pine nuts for food.
CURWOOD: This is Living on Earth. I'm Steve Curwood. In Bonn, Germany, this month, talks continued to revise and refine the Kyoto Protocol to combat climate change. Meanwhile, evidence continues to mount showing that life on Earth is being disrupted by global warming. For example, in Yellowstone National Park, rising temperatures are affecting white bark pine trees, part of the food chain for animals, including endangered grizzly bears. Grizzly bears, it seems, love pine nuts. From member station KBSX in Boise, Idaho, Jyl Hoyt reports.
(Soft voices, clanking)
HOYT: It's just after dawn in Yellowstone's Lamar Valley. There, biologist Lance Craighead adjusts his spotting scope, searching for another glimpse of the mother grizzly and three cubs who just ambled into the trees.
CRAIGHEAD: They were sort of frisky and they were jumping around and exploring, and poking around and looking at different things.
HOYT: Lance Craighead suspects the bears are heading for timber line, looking for food. Grizzlies often raid the white bark pine nuts that red squirrels collect and bury in the fall.
CRAIGHEAD: So way up in the higher areas, like up on that big ridge, there, above those cliffs, you can see some white bark pines. Some years they'll have really big crops of pine nuts, and the pine nuts are probably the most high-energy food available to grizzlies at any time of year. But it's especially important in the fall.
HOYT: Bears must eat enough each fall to get them through hibernation. And if females don't have enough fat, their fertility diminishes. White bark pine nuts can provide up to 40 percent of a bear's fat needs. But white bark pine trees are at risk because of global climate change. The trees need cool temperatures to grow, and warm weather forces them up mountainsides, limiting their range, says Chuck Schwartz, head of the Inter-agency Grizzly Bear Study Team. Higher elevations may be too cold for the white bark pine. And remember, he says, mountains are shaped like cones.
SCHWARTZ: The higher up the cone you get, the closer to the point you get, the smaller the zones will be. So there will be less available acreage for white bark pine.
HOYT: Government scientists like Chuck Schwartz are often at odds with independent biologists when it comes to protection of grizzly bears. But on this point they agree: The climate change can pose a risk to bears. He speculates that climate change may also be creating conditions in and around Yellowstone National Park that encourage the spread of European blister rust, a plant disease carried here inadvertently in 1906 that has already infected forests in the Pacific Northwest.
SCHWARTZ: It impacted the trees significantly, and there are areas now where nearly 98 percent of the white bark, the historic white bark, is gone.
HOYT: Warmer, moister air produces the fog banks that blister rust thrives in. The rust infects and girdles the tree, and it eventually dies. Foresters say blister rust is moving closer to Yellowstone. During the past five years, the number of infected trees has increased by 40 percent in the Gallatin National Forest, just south of the park where grizzlies often forage for food.
HOYT: White bark pine trees protect the bears in two ways. They provide grizzlies with food, plus their remote location shields the animals from humans. But white bark pines don't produce nut crops every year. During unproductive years, grizzlies often head to river bottoms searching for food, into areas where there are people. And that means trouble, says Louisa Wilcox, who heads the Sierra Club Grizzly Bear Ecosystem Project.
WILCOX: Grizzlies walk into these areas, perhaps not meaning to get into trouble, run into dog food on a porch, a bird feeder that's been left out, get a taste of something that's pretty tasty -- and because they have good memories, never forget it. And then within short order become a management problem, in which there is some need to dart and move the bear, or kill the bear altogether.
HOYT: Federal researchers say three times more grizzly bears die during years with no white bark pine nut crops than during years when the nuts are plentiful. With fewer than 400 grizzlies left in Yellowstone, according to several estimates, a modest increase in their deaths could have a serious impact on their population. In the meantime, foresters are developing a rust-resistant strain of the white bark pine. Government officials may plant these saplings if the disease continues its dramatic spread. But it takes 100 years for a tree to produce a usable crop of nuts.
PECK: Did somebody see another bear?
HOYT: Brian Peck of the Sierra Club Bear Project spies another bear through the spotting scope.
PECK: And this is a very dark, almost black grizzly bear. And he's just above the elk. Oh, right in the open now. Ho, ho, ho.
HOYT: People like Brian Peck, who thrill at the sight of grizzly bears and work to protect them, say the key to their preservation is understanding the connectedness of different species.
SCHWARTZ: Human influence can have profound effects on this particular species, and it's kind of an indicator species of the health of wild systems.
HOYT: Chuck Schwartz of the Inter-agency Grizzly Bear Study Team says blister rust is only the latest in a long series of human-caused threats that challenge the health of the wild Yellowstone ecosystem.
PECK: It's walking across, just out for his morning stroll.
HOYT: For Living on Earth, I'm Jyl Hoyt in Yellowstone National Park.
PECK: Oh, he's doing a little digging. There we go. (Laughs)
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