Have returning wolves really saved Yellowstone?

Researchers fear that some damage can’t be undone.

 

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Wolves were reintroduced into Yellowstone in the 1990s, giving researchers the chance to study the predators’ effects on the ecosystem, such as providing food for scavengers, after a long absence.
Dan Hartman

Some come for the geysers and grizzlies, but I’ve traveled hundreds of miles to  Yellowstone National Park simply to stand in the drainage of Elk Creek, stooped over a stunted willow bush. Tan branches, tinged with red, just reach my thighs, and narrow pale-green leaves blend into the wheat-like stalks of timothy grass and smooth brome filling this humdrum meadow.

Nearby, David Cooper, a Colorado State University ecologist, inspects one willow like a doctor examining a patient. The diagnosis isn’t good. “This plant has obviously got a lot of problems,” Cooper says. “It’s just stuck.” This willow could be 30 years old and should be 12 feet tall, but it looks as if I could uproot it with one swift jerk. It’s a clue to the mystery that drew me to the park: Have wolves saved Yellowstone?

National Geographic, Scientific American, countless newspaper articles, documentaries, even a TED talk, have all marveled at the transformation wrought by the re-introduction of wolves to Yellowstone in the mid-1990s. The story goes like this: After a 70-year absence, returning wolves put elk on the run, depleting their numbers and scattering the remainder. Freed from relentless browsing, the region bloomed with fresh vegetation, inviting songbirds, beaver and other animals. Wolves were bringing Eden back from the brink.

It’s a lovely tale, but researchers like Cooper warn that the reality is more complicated. For him and fellow Colorado State professor Tom Hobbs, Elk Creek is key to understanding north Yellowstone’s ecosystem, and to telling a truer story, one of an older, more vibrant landscape that may already be lost, perhaps irrevocably.

Cooper, who is stocky and has a trim white beard, has spent his career as a plant ecologist, tracing water and its role in Western landscapes from the Sonoran Desert to the Rocky Mountains. Hobbs, lanky and loquacious, specializes in mathematically modeling how large mammals shape ecosystems. In 2000, the duo came to Elk Creek, drawn by talk of intriguing changes rippling through the ecosystem as wolf packs grew. They wondered what was happening in the smaller streams that lace the area, particularly to the willows that are the linchpin to their health.

“It’s not like the wolves came in and everything has readjusted to normal,” Cooper says. “Some sites may recover more quickly, others may never recover.”

Much of north Yellowstone falls away from the park’s high central plateau in a series of broad valleys, steep canyons and rolling sagebrush hillsides. Its lower elevation and drier climate make it a winter haven for elk. In the wolves’ absence, plants like willow and aspen declined, as expanding elk herds browsed on them in winter.

On a hot summer day, there’s little sign of elk in the creek named after them. Cooper lets go of his stubby willow branch, strides down to the stream and points to a wall of dirt carved away by the water, revealing layers of fine-grained gray and brown sediment, the traces of vanished ponds. Less than a century ago, we would have been underwater. “This was a pond environment for thousands of years,” Cooper says. “This whole valley was just full of beaver dams.”

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Researchers Tom Hobbs, left, and David Cooper examine a willow stunted by elk browsing in Yellowstone.
Warren Cornwall

In fact, in the early 1920s, a naturalist named Edward Warren spent two summers here, photographing and cataloguing beaver colonies near the Yellowstone River. On Elk Creek’s North Fork, Warren counted 17 dams, the largest a 350-foot-long bulwark worthy of a medieval castle. In all, he guessed there were more than 200 beaver in the streams he surveyed. Back then, the concern was that too many beaver, with too few predators, were devouring too many plants. Today, in those same places, there are no beavers at all.

Populations of the flat-tailed rodents naturally ebb and flow in a creek. Nature’s engineers, the beavers gnaw down aspen and willow, move on to other places when they’re gone, then return when new plants grow in the soft, moist soil created by the abandoned dams. As we walk downstream, Cooper and Hobbs explain that the loss of wolves appears to have short-circuited this natural cycle in places like Elk Creek. Exploding elk numbers destroyed the willow and aspen, driving the beaver away. Over time, the creek eroded into a steep-banked gully, lowering the water table. A wet meadow became a dry valley, inhospitable to plants like willow, even after wolves returned and elk numbers fell. 

This became clear in experiments the two have run at Elk Creek and several other streams. They built dams in the creeks to simulate beaver and fenced off patches of willow to keep elk out. In most cases, the willows only rebounded when they were fenced off and grew near the dams, where the ground was moist. In other words, without the dams, it didn’t matter about the elk — or the wolves that might have chased them.

Cooper thinks Elk Creek and similar streams have undergone such profound changes that recovery might require the return of both the wolf and the beaver. But it’s not that simple, either. “Until there’s enough  willow that the beavers can come back, it’s going to be stuck,” he says. “So the question is, what’s it going to take for the engineers to come back?”

For Doug Smith, the head of Yellowstone’s wolf reintroduction program and the park’s main beaver biologist, Elk Creek is a sobering reminder that some of the damage wrought in the wolves’ absence might never be repaired — that Eden may never fully return. “This has changed to a site that can’t go back,” he says later, when I take him to the creek. “There’s no water.”

But there is another story unfolding elsewhere, he says: Go to the West Fork of Blacktail Deer Creek.

If Elk Creek is Exhibit A for the wolf skeptics, Blacktail Deer Creek, just nine miles to the west, is a shining example for wolf champions. Slightly bigger than Elk Creek, it’s hidden in a forest of willows, which sway in the breeze like seaweed in the tide. Over the last 13 years, Robert Beschta, an Oregon State University hydrologist, and his colleague, ecologist William Ripple, have used this creek to document what they see as a wolf-driven revival of north Yellowstone.

Before the predator’s return, Blacktail Deer’s willows looked much like those in Elk Creek. But by 2003, a growth spurt had begun: The tallest willows were roughly six feet longer than in 1997. As these tallest plants grew, the number chomped by animals fell from 100 percent to 55 percent or less. In the last few years, beaver have begun making summer forays into the creek. “Come back in 15 years and ask the question, ‘Where are the beaver?’ and I bet you they’re going to be everywhere,” Beschta tells me.

I drive Cooper to Blacktail Deer Creek. We walk a mile up its West Fork, through sagebrush punctuated by fledgling aspen groves. This section of stream has witnessed some of the most dramatic growth. “If you’re wondering why the plants here look so different,” Cooper says, “we’re wondering that, too.”

Were these willows simply more resilient when the elk reigned, and therefore poised to rebound? Or was the ground here simply wetter? What lessons do this creek and Elk Creek hold for the broader region?

For Smith, the conclusion seems to hinge partly on where scientists decide to look. After two decades at the park, he’s convinced he sees real improvements in some larger streams and rivers. And he credits wolves for playing an important part. “Elk are key, but so are site characteristics,” he says. “You need both.”

Yet Yellowstone is a massive ecosystem, and we don’t know everything about it. Some of its watersheds could be blossoming out of sight, even as others languish, never to return. Yellowstone is recovering. And Yellowstone is stuck. There is more than one Yellowstone, and more than one story it can tell us.

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