DESTINATION SCIENCE: YELLOWSTONE NATIONAL PARK, USA
Just after midnight on June 25, 1972, a man named Harry Eugene Walker, 24, was eaten by a bear at Yellowstone National Park. A ranger who saw the remains just before dawn said Walker looked as if he were sleeping, except that his midsection was missing.
It was not an isolated incident. Between 1950 and 1974, 1,060 people were injured by bears in Yellowstone, a symptom of an ecosystem out of balance. Easily available human foods and garbage caused bears to live too close to people, and they were not the only animals in Yellowstone with worrisome eating habits. For decades the world’s oldest national park suffered from managerial missteps that altered what ecologists call trophic relationships—those of soil to plant, plant to plant eater, and plant eater to carnivore.
Today’s Yellowstone is a much different place, but it takes some tips from experts to see how it has been changing. On a warm afternoon, William Ripple, an ecologist from Oregon State University, and I meet former Yellowstone superintendent Mike Finley near the steaming pools of Mammoth Hot Springs, five miles south of Gardiner, Montana. Instead of joining the families of tourists trooping up through the springs’ white travertine terraces, we head toward the Lamar Valley, where a lesser-known drama is unfolding.
Yellowstone was created in 1872 to protect its geyser basins, Finley explains as he drives. But the 2-million-acre park put the government in the wildlife business, and unfortunately scientific wildlife management did not begin until more than half a century later. No detailed records exist of the area’s animal population and feeding behavior at the time the park was established.
Early rangers fed elk and bison as one would feed cattle and began killing wolves. By 1926, following a federal directive, the last wolves had been eliminated. Then elk overpopulated the park, eating through grass, brush, and any part of a tree they could reach. So in 1934 the rangers began shooting them, too; records show that in 1962 alone, 4,619 were killed. In 1967 public distaste forced the Park Service to quit. But the park did not recover.
Meanwhile, open-fill garbage dumps became feeding grounds for generations of grizzlies. Black bears learned to beg from tourists along roadsides or take what they could get from campsites. Rangers put out natural fires, altering vegetation. Aspen forests were declining, and willows along creeks were eaten down, some to the point of disappearing altogether.
In the 1990s park science hit its stride. Dumps were closed and bears were weaned off human food. Natural fires were allowed to burn sometimes. And then, in a momentous act by Department of Interior agencies, wolves were reintroduced.
Finley—a formidable man in a khaki shirt, jeans, hiking boots, and a floppy hat—has returned to Yellowstone to witness the effects of these changes since he left the park in 2001. He pulls the car over at an unmarked turnout next to the bridge across the Lamar River. Up the hill to our right is Crystal Creek Bench, where he and his fellow rangers set the first six wolves free in 1995.
Ripple, an affable outdoorsman in his midfifties, is particularly interested in the rebirth of the aspens; it is the result, he contends, of the wolves’ effect on elk and the elk’s on plants—a domino effect that Ripple, his research partner Robert Beschta, and others in the field call a trophic cascade.
A quarter mile up Crystal Creek through the sagebrush, Finley starts beaming. “There they are!” he says. To our left are mature aspens, their snow-white trunks and leaves quivering in the slightest breath of wind. Beneath them is the cause of Finley’s excitement, a thicket of new aspens 10 to 15 feet tall. “This is amazing,” he exclaims, wading in to grasp one of the saplings. “When I was here these were all knee-high. They’d grow and get eaten off, grow and get eaten off. Look at them now!”
On another day, farther up the road with Ripple, the Lamar Valley opens up before us: a great green plain ringed with mountains and dotted with bison and elk. Ripple points out the brown buildings of the Buffalo Ranch. “That’s where they raised bison like cattle in the early days,” he tells me.
We stop at a roadside display with the title “An American Eden.” The display features a picture of the valley in front of us. There is a noticeable absence of small trees—big, old cottonwoods can be seen, some of them fallen, but no little ones growing up to replace them. “That’s what Bob [Beschta] noticed when he first came here, along with the river,” says Ripple, who has been studying the valley for 14 years. Many areas along the Lamar lack streamside willows and other woody plants because they were stripped away by elk and other herbivores, he explains. Without the plants’ stabilizing roots, the river cut away its banks, washing away topsoil that took centuries to build.
Back in the car and up the road, Ripple points to a thicket of young trees and brush on a hillside to our left. You have to look closely to see the fence around it, installed by other researchers. “That exclosure shows what this place would look like without grazing by elk and other plant eaters,” he says. On our side, the ground is still virtually bare except for sagebrush.
Plants are not coming back everywhere yet, and elk are more numerous now than when the rangers stopped shooting them in 1967, Ripple says. “So?” I ask. Ripple points up the road and grins.
We stop at the Lamar River’s junction with Soda Butte Creek, and Ripple takes out a photograph of the same place a decade ago. The transformation is remarkable. In front of us are tall stands of willow; in Ripple’s photo the same willows are clumps of sticks, eaten off close to the ground. But why has regrowth happened here and not up the road at American Eden or outside the exclosure? I ask Ripple. He wondered about that too, he says. In 2001 he came up with a hypothesis he calls “the ecology of fear,” which is now supported by his later research. “See all those channels, bluffs, and so on?” he asks, gesturing. “It’s like a corral. If I were an elk, this is the last place I would be when the wolves arrive.”
I look out across the river. An American Eden? Perhaps redemption is possible. Somewhere out there, wolves are doing their work. In 2009 the park had more than 3 million visitors, and no one was injured by a bear. Maybe we’re learning.
NEXT: OTHER SPECTACULAR PARKS AND WILDERNESS AREAS