It was the first time I’d ever heard real wolves in the wild, having listened for their voices all my life. Hearing wolves in Yellowstone, I remembered the Celtic melody “Winter Wolf,” with its rich, woven harmonies:
High above the timberline
Call and echo
Watching, waiting
“For nearly sixty years there has been an unnatural silence in Yellowstone, the absence of this sound that would have been heard here every day for thousands of years,” McIntyre said softly. “This year that silence is broken.”
At last the Crystal Creek pack loped off into the forest, pups prancing with their tails held high. What adventure awaited them? A hunt? A nap? More play? As we gathered our gear to descend back to the warmth and predictability of our lodges, McIntyre reminded us that wolves devote much of their daily lives to play. Then he took me aside and asked me to follow him back to his parked truck. From under a well-worn tarp he pulled out a full wolf skin and handed it to me carefully.
“I carry this with me for show-and-tell when I give educational talks to schoolkids,” he said with a smile. “Children always want to touch the wolf skin and feel this rich, winter fur. It’s like something of the wolf is still here.”
I held the surprisingly heavy wolf skin, running my fingers through the silver-gray fur of the thick tail.
“Here,” McIntyre said quietly, “this is how it should be worn.” He draped the massive wolf’s head over mine, stretched the long skin down my back like a cape, and then tucked the forelegs around me.
The thick pelt embraced me with its warmth, its responsibility. McIntyre laid a hand lightly on the wolf skin over my shoulder.
“The wolf needs storytellers,” he said.
6. TROPHIC CASCADES: A NOT-SO-SIMPLE STORY
Science is not only built upon always evolving research; it is also based upon theories that are continually updated and increasingly complex. The trophic cascades theory is one such continuing story. In the years before wolves were reintroduced to Yellowstone and during the two decades of their gradual return, different scenarios kept playing out in ecosystems.
Scenario One: Wilderness Areas Without Wolves
On the eroded riverbank a large gathering of elk rarely glances around in fear. Nonchalantly they nibble new-grown willow and cottonwood right down to the roots. The sparse trees get little chance to grow tall, so beaver can’t find enough wood for their river dams. Silted and awash in loose soil, rivers flow slower, offering habitat for fewer native fish, frogs, and amphibians. Deer stroll unchecked through valleys, grazing so greedily because they are starving as their populations are exploding past sustainability. In rain forests fern prairies smother the earthen floor, strangling the healthy underbrush and nurse logs.
In my home state of Washington the ancient Hoh Forest still seems magnificent, but the old-growth trees, rivers, and animals have suffered much since the last wolf was killed in 1920. “We think this ecosystem is unraveling in the absence of wolves,” Oregon State University ecologist William Ripple warned in 2009. The Mount Olympus National Monument was created in 1909 by President Theodore Roosevelt to conserve an elk population of about three to five thousand animals. But without wolves to control elk populations, the Hoh Rain Forest within Mount Olympus is now “totally out of whack.” Another OSU researcher, Robert Beschta, points out that after wolves were eliminated from the forest, few seedlings made it “past the knee-high stage,” and in one area “not a single new cottonwood survived the ravenous elk in the last half-century.” He warned that “the degradation we’re seeing in the park is profound. It’s catastrophic.” Where once flowed mighty rivers dense with trees for shade, fertile with underbrush and logs to spawn the Northwest’s iconic salmon, there are now sadly diminished waterways with slip-sliding-away banks.
Scenario Two: Wilderness Reclaimed by Wolves
Exposed again to a top predator, elk and deer retreat from river banks and meadows. These prey animals are wary of the wolf eyes that track them from hillsides or hide behind now-thriving underbrush. Without the rapacious bite and strip of elk, new cottonwood saplings, willows, hemlock, and maples sprout up. The green, vegetable world again flourishes to renew forests and securely root river banks. Beavers, those essential “ecosystem engineers,” find wood to build their nourishing dams; these watery woodpiles create cool eddies and pools for ducks, fish, and reptiles. Weasels and foxes feast on what was left of the prey the wolves left behind. Butterflies skitter and sway across nourishing meadows now bright with wildflowers and pollen. Bears discover more delicious berries in the surging bushes. Songbirds alight and sing in thriving trees where they can again make their nests. Because wolves keep the coyotes from overbreeding, there are multitudes more mice and rabbits. Mile-high in the sky, soaring hawks and eagles no longer glide past the degraded forest; instead, they spy the squiggling ground prey and decide to build their nests here in stalwart trees. Ravens flock back. Rivers return to life.
Since the reintroduction of wild wolves to Yellowstone and beyond, this new story of how wolves enhance and help nourish a whole ecosystem has been told again and again. As it turns out, wolves are perhaps the best wildlife and habitat managers of all. After twenty years of wolf recovery in Yellowstone and elsewhere, the wild lands where wolves returned have changed dramatically. “The whole ecosystem re-sorted itself after those wolf populations got large enough,” said David Graber, the regional chief scientist for the National Park Service.
Scientists call the benefit of restoring top predators the trophic cascade effect. University of Washington ecologist Robert T. Paine was the first to coin the terms “trophic cascades” and “keystone species.” When wolves limit their prey’s grazing and behavior, this opens their shared habitat to more richness and diversity. Conservation biologist Cristina Eisenberg of Oregon State University describes a trophic cascade as a dynamic waterfall that flows through the entire food web once keystone species such as wolves are restored. “Trophic cascades are an ecosystem writ large upon aquatic and terrestrial landscapes,” she writes in The Wolf’s Tooth: Keystone Predators, Trophic Cascades, and Biodiversity. Wolves and other top predators can help restore our wild lands into “landscapes of hope.”
This trophic cascade concept has deep roots in the green world hypothesis first proposed in 1960—that top predators help keep the world verdant and healthy. It also draws from cutting-edge research on how keystone species such as wolves help bring stability to degraded ecosystems by regenerating healthy soil, vegetation, and even cleaner water. “Wolves nurture the entire ecosystem,” Eisenberg explains. “If we eradicate wolves or lower their numbers, the whole system will grow impoverished and collapse.”
Eisenberg is part of the vanguard of researchers documenting why wolves matter so much to healthy ecosystems. Eisenberg’s research and writing have revolutionized the way we see wolves. I first met her in 2008 when we taught together at Iowa State’s symposium “Wildness, Wilderness, and the Creative Imagination.” Flying into Iowa in February, I barely beat a blizzard and spent a lot of time freezing. But the heavy snow meant that Cristina and I, along with the other writers—including the late Irish author Patricia Monaghan, cofounder of Black Earth Institute with Michael McDermott, and Iowa poet laureate/memoirist, Mary Swander—enjoyed a lot of time stranded inside cozy cabins. We gathered close around Amish rock-hewn fireplaces coaxed to burn high with perfectly dried and seasoned wood. Surrounded by such inspiring writers, we told stories—mostly about wild animals—during the snowbound night.
Slender with thick, dark hair down to her shoulders and an engaging, open face, Cristina’s Mexican heritage also shows in her gracious and welcoming manner. Cristina told me about her grandfather, who both won and later lost his vast ranch in remote Chihuahua near the Sierra Madre Occidental. This was near the same Sonoran border wilderness where Aldo Leopold studied wolves in the 1930s. Cristina’s father spent his summers working the ranch with the cattle and hunting wild game to feed the cow
boys. In his saddlebag he carried his favorite wild animal stories by Ernest Thompson Seton. Although he was ordered to kill any wolves he spotted, Cristina’s father noted that the wolves didn’t bother the cattle and were never aggressive toward him.
In The Wolf’s Tooth Cristina would later write about her father and how he never could bring himself to shoot a wolf because they “always seemed to be moving through the herd on their way to someplace else.… And there was something about them, their eyes, in the way they carried themselves, that compelled him to let them go peacefully.” Her father “realized that his direct experiences with wolves did not resemble my grandfather’s nor the ranch hand’s, so he kept them to himself.”
Cristina’s story made me wonder how many other ranchers observe wolves simply moving benignly through cattle territory on their way to kill their preferred prey of elk and deer. Wolves are actually responsible for very little livestock predation—many more livestock are killed by disease, coyotes, dogs, bears, and mountain lions than wolves. And in the case of wolf predation, livestock producers can receive compensation for their losses. If these statistics were more commonly known and if more ranchers like Cristina’s father told their stories about wolves, more accurate information might replace the stereotype of the vicious wolf devastating cattle.
As Cristina and I spoke by the fire I asked her how she first chose to study wolves or whether they had simply called her to this work. I’ve noticed that many wolf researchers have a first-contact story about wolves, an encounter that initiates them into their lifelong studies of what many cultures consider the most spiritual animal. Cristina had such a story and also said that her science is a form of service.
As we talked I often felt that I was in the hands of not only an expert scientist but also a fine storyteller. “My husband and daughters and I moved to Montana in the early 1990s, when wolves had reintroduced themselves naturally, migrating down from Canada,” Cristina began. “Our Montana cabin was remote, really wild country. The land bordered the Bob Marshall and Great Bear Wildernesses. It was like having millions of acres of wilderness for a backyard. One night I heard a sound that was both primal and totally familiar. Wolves howling. I ran to the window to listen… and those wild voices were comforting, like ‘Welcome home.’”
Local rangers and researchers had assured Cristina that there were no wolves left anywhere around. But if there were wolves, there were very few and just now returning. Her family hadn’t moved to Montana to study wolves. “They were just another animal to me,” she explained. “But then everything changed.”
One summer morning Cristina and her daughters were weeding their garden. It abutted three acres of lush mountain meadow. Often they’d watch elk standing around for hours, nibbling the nutrient-rich grasses and trees. “We didn’t realize that there was something really wrong with that picture of elk fearlessly grazing, standing around like lawn ornaments,” she laughed. “I wasn’t an ecologist then. The land taught me about ecology.”
Suddenly the nearby forest exploded with sound—a lean deer lunging and racing, her legs stretched out like a terrified thoroughbred horse. On her flying hooves were two wolves, one big black wolf and one smaller gray wolf. “The deer ran right toward us, as if for protection,” Cristina said. “Came within twenty feet of our garden and then veered off to the other side of the meadow. Disappeared into the forest. We were in total shock. Never seen anything like that. We just stood there in the garden until one of my kids said, ‘Let’s go track them!’”
Cristina had taught her children how to recognize the tracks of grizzly bears and cougars to protect themselves when hiking and playing around their remote wilderness cabin. These skills meant they never felt threatened by predators. “So we tracked the wolf chasing that deer,” Cristina continued, her voice quickening. “We could smell the wolves—a beautiful, earthy scent. And we noticed the grass was springing up already after the imprint of hooves and paws. We even tracked exactly when the gray wolf turned back to look at us following her. That slight shift in her shoulder changed her gait, and we saw the change in her tracks. I had to wonder: How many times had this wolf hunt gone on around our cabin and we’d just never even noticed?”
“So what happened next?” I asked.
“The wolves had left shreds of fur in the bushes as they loped past. I took the fur in a little plastic baggie to the Forest Service guy. He said, ‘Oh, lady, that’s fur from big dogs.’”
Although the Forest Service ranger dismissed her field sample, Tom Meier with the Wolf Project was very curious to see her evidence. Had wolves really recolonized themselves to their former Montana territory? “Tom looked at the fur for a really long time. Then he turned to me and smiled. ‘Want to track them for me?’ he asked.”
That was the beginning of Cristina Eisenberg’s research, work that led her to become one of the top wolf specialists in the world. “After our first sighting of wolves that summer,” Cristina concludes, “we noticed that our meadow completely changed. Within three years the meadow was deeply filled in with shrubs and trees. We’d always counted birds for Cornell University. Now all these new warblers showed up, the kind who only live in the thick understory of young, thriving forests. That’s how I got into studying trophic cascades.”
As for the black and the gray wolves she first saw, Cristina says, “They turned out to be the breeding male and female. Two or three years later they came by with their pups. It was as if they were introducing their family to our family,” Cristina said.
Cristina would also study “the ecology of fear” in the relationship between apex predators, like wolves and grizzlies, and their prey. When predators are missing from an ecosystem, their prey can overpopulate, like the elk and deer in Yellowstone. According to Cristina, “fear is an essential and very healthy force in nature. We—including humans—coevolved as species that lived in a landscape of fear. This kept us in check and enabled a form of equilibrium in the natural world. Take that fear away, and we are removing wildness, part of what makes us humans and an important part of what makes the world function… like those elk in our meadow, complacently mowing down the shrubs and saplings.”
OVER THE YEARS I kept up a lively correspondence with Cristina about wolf issues. It was to her I turned in the winter of 2016 to help me understand when some new research on trophic cascades surfaced that needed her clear thinking.
With any widespread theory like trophic cascades, there will be debate. Science is always revising and adding nuances to its theories. A few researchers recently argued that wolves are not the only factor reducing elk and deer populations and restoring Yellowstone’s degraded ecosystem. Field biologist Arthur Middleton claims that “wolves have made less of a difference than previously expected.” Willow and aspen haven’t recovered as much as some claimed, he says. “A few patches of Yellowstone’s trees do appear to have benefited from elk declines,” he admits. “But wolves are not the only cause of those declines. Human hunting, growing bear numbers and severe drought have also reduced elk populations.” Rather than being the single cause of elk populations dropping in Yellowstone, they are one among several important influences, Middleton concludes. He urges scientists and conservationists to focus on “pragmatic efforts that help people learn how to live with large carnivores. In the long run, we will conserve ecosystems not only with simple fixes, like reintroducing species, but by seeking ways to mitigate the conflicts that originally caused their loss.”
Another article in Nature also questions any overly simplistic interpretation of how wolves and trophic cascades affect complex ecosystems. It finds that “the more-complicated story of how beavers and changes in hydrology” might be even more important than wolves to help willows recover: “Restoring an ecologically complete ecosystem in Yellowstone requires the return of willows—and with them beaver. There’s a clear threshold for ecosystem recovery. Willow stands must be more than 6 feet tall, the scientists found. That height is important.… Then willows are beyond
the reach of browsing elk, and can serve as seed sources for new young willows.”
A 2010 study of Yellowstone aspen by the Wyoming Cooperative Fish and Wildlife Research Unit concluded that “the major influence on the trees is the size of the elk population, rather than elk behavior in response to wolves. And though wolves influence elk numbers, many other factors play a part”—like grizzly bears, drought, and elk migrating out of the park in winter.
Cristina echoes this Nature article, adding, “We’ve been trained as a culture for generations that there is a simple solution to everything. When we introduced wolves to Yellowstone there were noticeable impacts ecologically within three to four years. Elk suddenly had to be wary instead of standing around overgrazing. Conservation organizations, myself included, thought, ‘What a great story. Makes perfect sense.’”
But more research led to more complexity in understanding not only how wolves change their habitat and the behavior of other animals but also how factors like climate change and, especially, drought affect the ecosystem. “Climate change reduced frost-free days by 33 percent in the park,” Cristina explains. “This increased the growth of willows, which then created dryer stress for aspen in Yellowstone’s Lamar Valley. Added to that, the aspen hadn’t burned since the park’s 1988 fires. So fire was another big factor in understanding Yellowstone. It’s really an ecological mosaic.”
Researchers noted that in some areas of Yellowstone, like river banks, aspen flourished, growing in healthy thickets. Meanwhile on the Lamar Valley floor, aspen trees were struggling. Further studies of elk populations revealed even more complexity: climate change affected the elk’s food source. “Heat in the spring determines how elk survive the winter,” Cristina says. “In May and early June the grasses sprout up and are at the peak of their nutrient-rich protein. That’s right before the elk give birth, so this protein-rich grass is essential in healthy birth rates. If the grass is not at its nutritional peak because of climate change, elk births and survival rates go down.”
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