Even for the wretched coyotes, so ingloriously dethroned, life in the harsh new kingdom of the wolf came with its rewards. It came with the spoils of war. Though the stomach of a wolf could hold twenty pounds of meat, there were seldom enough stomachs in a pack to finish off a seven-hundred-pound elk, let alone a bison bull at twice the mass. Leftovers soon became the lucrative new way of life in Yellowstone.
Coyotes only began to enumerate the beneficiaries. They and red foxes, American crows and bald eagles, black bears and grizzly bears, Clark’s nut-crackers, gray jays, magpies, golden eagles and turkey vultures, and record gatherings of common ravens—all of them, plus fifty-seven varieties of beetle, were to be found making a good living on wolf leftovers. The carcass, with its attendant crowds of professional bone-pickers and carrion gourmands, had become the most conspicuous billboard celebrating the wolves’ return.
The Ecology of Fear
The wolves had brought to Yellowstone a perpetual windfall of carrion, a never-ending scavenger’s ball. But from where Bob Beschta was standing, there in 1996 on the broken banks of the Lamar, it seemed a bit premature to celebrate the reawakening of an ecosystem whose arteries were coming undone. Beschta was a river man, and the Lamar by his measure was going downhill in a bad way. Back at Corvallis, he gave a seminar to his colleagues on what he’d seen in his first visit to the Northern Range of Yellowstone. He exhibited the shorn willows and aging cottonwoods, the missing cohort of seedlings and saplings that by all means ought to have been growing flush along its rivers. He reviewed the prevailing hypotheses, the idea that a changing climate was somehow to blame; that wildfire, with its cleansing, restorative powers, had been suppressed for too long. He rejected these in favor of the least popular hypothesis in the park: that too many decades of too many elk in Yellowstone were pinching the blood supply of the park’s biological diversity. When Beschta mentioned to his colleagues that aspen—whose forests ranked second only to riparian ecosystems as the lynchpin of biological diversity in the arid West—was also on the wane in Yellowstone, his colleague Bill Ripple sat up.
What the river was to Beschta, the aspen was to Ripple. As an amateur photographer, he particularly courted the aspen for “those cryptic yellows and golds and orange of the fall leaves, against that low autumn sun angle, and that backdrop of blue sky.” As a landscape ecologist, he knew the aspen as one of the premier magnets of wildlife in the western mountains—forage of herbivores, shaded refuge of wildflowers, food and lodging of birds. Yellowstone should be the last place to be losing its aspen, thought Ripple, and the first place a scientist like himself should be asking why. Ripple turned to his graduate student Eric Larsen and said, “What do you say we go out there and solve this mystery?” As Ripple and Larsen began reconnoitering their new study area, their interviews took them south of Yellowstone, to the adjoining Grand Teton National Park. As the two walked into the visitor center, there hanging high on the wall was a poster portraying the subject of the day—a grove of aspens, with their creamy trunks rising from a fresh bed of snow. Standing right of center, staring forth with piercing amber eyes, was a big gray wolf.
Ripple again turned to his protégé Larsen, asking, “What about wolves protecting aspen?”
It was just a thought, an aside perhaps magnified now through the romantic haze of hindsight. And the wolf staring from the aspen, truth be told, had been mechanically inserted there by the artist’s own hand. But either way, that poster would come to hang in Ripple’s office. Over the following year, that image of the guardian wolf hovered in the mind, as the two scientists toiled through the legwork of backtracking the aspen’s downfall.
Digging through the archives, Ripple and Larsen uncovered photos and aspen surveys dating to the early 1920s. They backed them with two summers in the field, aging live aspens where they stood. Once back in Oregon, they reconstructed a century’s history of aspen in Yellowstone. Larsen then tallied the results and walked them into Ripple’s office.
At first there was nothing but old news and dead-end leads: Indeed the aspens of the Northern Range had all but ceased reproducing after the 1920s. And nothing in the park’s climate record or fire history suggested anything magical about that date. The elk, for their part, had been there all along, but only since the 1920s had their browsing brought Yellowstone’s aspen to its knees.
And then, from out of the shapeless thicket of data, sprang an unmistakable figure. The 1920s, the last years of the Yellowstone aspen, were the last years of wolves in Yellowstone.
The hypothesis rapidly assembled itself. Aspen were dying not from any apparent lack of fire or rain but from a preponderance of elk, by way of too few wolves. In the wolves’ absence, elk had begun eating nearly every unprotected shoot in the park. From where Ripple and Larsen stood, the aspen’s demise was a food-chain reaction, a trickle-down demise tracing missing wolves to freeloading elk to missing aspen—in the ecological lexicon coined by Robert T. Paine, a trophic cascade.
In publishing their inaugural paper on Yellowstone’s aspen demise, Ripple and Larsen recognized their wolf cascade as heavy on conjecture, a hypothesis woven out of aspen cores and old photos, eighty-year-old anecdotes and ecological theory. As senior investigator and upstart Yellowstone outsider, Ripple said he realized he was “going out on a limb—on tree rings, as it were.” Yet the soft-spoken visitor from Oregon offered no apologies to the resident competition, whose fire- and climate-based theories had creaked for too long on far more rickety foundations. To Ripple’s mind, the importance of aspen to the biological diversity of the West, and the appearance of wolves maintaining them, was a story too compelling to bury until proven beyond all doubt.
A year later, he and Larsen were back, this time with a meatier paper that had two top Yellowstone biologists added to the byline and a title leaving little doubt of their convictions: “Trophic Cascades Among Wolves, Elk, and Aspen on Yellowstone’s Northern Range.” Yes, agreed the authors, including Douglas Smith, leader of the wolf reintroduction program, aspen were indeed sprouting taller in certain streamsides and wet meadows, which happened to lie in the most heavily trafficked wolf territories of the Northern Range.
Only time would answer whether the suspected wolf effect would be enough to allow the few aberrant sprouts to become Yellowstone’s first new aspen forest in eighty years. But Ripple wasn’t waiting. In the summer of 2001, he rented a cabin just outside the park’s northern boundary. He thought he might do a little photography, maybe some writing. Inevitably he ended up doing little but contemplating a landscape newly infused with the presence of wolf. For the next five weeks Ripple traveled up and down the valley of the Lamar, “just watching and looking and feeling it,” he said, his search image now tuned to the willow shrubs that intermittently poked their stems above the stream banks, never forgetting that this was now something more than a particularly famous stretch of Rocky Mountain floodplain. This was now the territorial heart of the Druid Peak wolf pack.
With every trip through the valley, he found himself gravitating to the point where Soda Butte Creek fed into the Lamar River. There at the confluence, he was struck by the valley’s most incongruent flush of greenery, of willow thickets towering twelve feet above bared banks. Somehow or other, the elk had ignored these particular patches.
Or—it occurred to Ripple as he sat gazing down from the overlook—what if the elk had more purposefully avoided this place? What if this point of land, in the eyes of an elk, was a death trap? What if the fertilizer ultimately responsible for these blossoming banks was a healthy dose of fear?
Ripple sent a message to his Oregon colleague Bob Beschta to come have a look, to listen to an idea he couldn’t contain. Beschta, who’d been simmering on a low boil since his dispiriting visit in 1996, immediately set out. As he was driving up through the valley toward his meeting with Ripple, he came around the corner to the Soda Butte Creek confluence, to the scene of Ripple’s amazement. There, where five years earlier Beschta himself had vowed to do so
mething about the deplorable barrenness of the riverbank, were newborn thickets of willow.
Beschta spent the rest of the day being chaperoned through the Northern Range, visiting all the resurgent patches that Ripple had scouted in his retreat. Notice where they’re growing, Ripple pointed out. Islands and gravel bars, steep banks and gullies—one could easily imagine the hazards posed to a fleeing elk. These curious little sanctuaries of willow were quite possibly the work of the wolf.
Beschta was slow to swallow the pill. “My feeling was, yeah, wolves are in the system, but what are they gonna do?” he said. “They can’t eat enough elk to make a difference. All I could see was elk numbers. Thousands and thousands of elk. And if there are a few wolves in the system, what could they do?”
But there was no easily dismissing the willows, sprouting so conspicuously where elk—it could now be imagined—perhaps feared to browse. That summer, Beschta undertook his own study in the Lamar Valley, this time focusing on cottonwood trees. Cottonwoods, together with willow, formed the mainstays of the broad-leafed forest that typically cloaked the streams and rivers of the American West. And cottonwood, like aspen and willow in the Lamar Valley, had become scarce to the point of widespread concern. As Ripple had done with aspen, Beschta repeated with the cottonwoods of the Lamar. He counted tree rings, looked through old photos. The youngest cottonwoods of the Lamar were sixty years old. He checked for causes. Changes in weather, shifts in the stream channel, floods, and fires—none bore a pattern that could explain the missing generations. There was only one variable that Beschta could detect that coincided with the end of the cottonwood’s line, and it had happened early in the century. “Holy smokes,” exclaimed Beschta. “It’s a wolf story.”
In 2003, Ripple and Beschta went to press with their first Yellowstone collaboration, delving more deeply into the beginnings of the willow’s and cottonwood’s recovery and honing their case for fear as a dominant force. Introducing their “terrain fear factor,” they suggested there were natural incongruities on the land that had kept the elk from dallying too long, which in turn had spared the saplings. There were gullies and terraces, islands and fingers of land jutting in the stream. These were the same places where the willows and cottonwoods had finally begun to show signs of recovery—places that an elk in a land of wolves did not want to be caught dead.
Fear so neatly answered the question of why thirty years of sporadic gunning by park rangers had not accomplished what a half decade and a hundred wolves apparently had. A few sporadic weeks of rifle fire left the riverside unguarded the rest of the year. But for elk in a neighborhood patrolled full time by wolves, every minute lounging in the river bottom involved a gamble of lethal stakes. It wasn’t so much a change in elk numbers as it was a change in elk attitude.
The streamside forests, in modest little spurts, were reawakening, thanks to what appeared to be a healthy dose of fear. In one of the greening tributaries of the Lamar, a beaver colony had set up shop, bringing along its busy waterborne commerce of wildlife. It was the first beaver colony in many years on the Northern Range, and the first of nine more to come within the wolf’s first decade back. It was as if a seventy-year winter had finally broken, giving way to springtime in Yellowstone.
Ripple and Beschta followed with a stream of reports, each building on the last, emboldened by the ever escaping willows of Yellowstone, and but-tressed by a swelling literature of top-predator ecology. Fellow biologists from as far afield as Russia were reporting similar cascades triggered in the absence of top predators. Next door in Grand Teton National Park, where the wolf and grizzly and hunting human had been missing for many years, the moose densities had quintupled, and their gnawings had left the park with a battered riparian forest missing several of its native nesting songbirds—songbirds that soon returned as the first wolf packs ventured down from Yellowstone. Farther up the Rocky Mountain chain, from the Canadian national park of Banff came a report of willows, aspen, beavers, and songbirds more commonly frequenting areas more heavily stocked with wolves. From Jasper National Park, near Banff, came news suggesting the recovering wolves there were coinciding with a twenty-foot spurt of fresh aspens.
Ecologists and evolutionists since Darwin have recognized predation as one of the fundamental drivers of the diversity of life, a reaper of the weak, mother of invention, inspiration of poets. Wrote Robinson Jeffers,
What but the wolf’s tooth whittled so fine
The fleet limbs of the antelope?
But death by fang only began to gauge the power of the predator’s bite. The fear of those fangs had become an evolutionary force unto itself. An animal might survive a few failures at finding food or a mate, but as the behavioral ecologists Steven Lima and Lawrence Dill so wryly observed, “Few failures, however, are as unforgiving as the failure to avoid a predator: being killed greatly decreases future fitness.”
The fear could be seen in the heron, fishing under the cover of dusk in anticipation of raptors by day; in the kangaroo rat, the deer mouse, the fruit bat—night foragers by nature—shunning moonlit evenings for fear of owls and fellow nocturnal predators; in salamanders and dragonflies, sparrows, marmots, and antelope, all shying away from richer feeding grounds for fear of predators lurking there.
Fear had even been detected in the psyche of the grasshopper. In a famous experiment conducted in a field in northeastern Connecticut, grasshoppers caged with enemy spiders ate less grass and lived fewer days. No big surprise there, except that the researchers had diabolically glued the spiders’ fangs together, rendering them harmless. Without delivering a single bite, the spiders had triggered a trophic cascade.
Such was the ecology of fear that Ripple and Beschta believed they saw reviving the groves of Yellowstone. A herd of elk in the open could be a formidable quarry. But a gangly ungulate clambering through a streamside log-jam, or floundering up a cutbank coated in ice, was an animal more likely to be rendered as meat. Ripple and Beschta would stand on sites where aspen were growing, look around, imagine what an elk might be thinking, and ask, “What is it that would make me feel uncomfortable here?”
“It’s kind of like being a hiker in bear country in Alaska,” said Beschta. “If you’re in bear country, you very quickly find yourself walking across a landscape of fear. You get these sensitivities when you walk into willow bushes. It makes a world of difference. In open terrain I see bears half a mile away, and it’s not a big deal. But when I start getting close to shrubs or start coming up over a sharp rise, man, I can tell you the hairs on the back of your neck go up, because you’re not aware of what’s coming over that ridge.”
Yellowstone’s newly instated ecology of fear was an intuitive, irresistible story. Wildlife magazines and major dailies across the country ran the alluring saga of the wolf as ecological archangel, sending ripples through the food web, restoring a pulse to Yellowstone’s moribund valley of the Lamar.
The science was so sexy—for some, too sexy by half. It was one thing to suggest spiders guarding grass in a square meter of Connecticut pasture, and yet another to link wolves to willows in a two-million-acre ecosystem called Yellowstone. There were grumblings among the park’s biologists that Ripple and Beschta had jumped the gun, had gone off too fast with their risk-based hypotheses. There were nonbelievers in the wolf’s almighty ecological powers.
And so, with each new paper, Ripple and Beschta would dutifully reexamine the competing hypotheses, with boring predictability. “We were hard-pressed to find any climate signature that would even come close to trying to explain why willows would fall apart like they did in the Lamar Valley, all at the same time, and then start to grow again the last decade,” said Beschta. “And to credit a large flood with creating the necessary conditions for willows to reproduce is almost ludicrous. All you had to do was put a fence around them and willows did just fine. Same with aspens. Put a fence around them and they do fine. I think to hang everything on a large flood is just ignoring the fact that every place anybody pu
t up an exclosure, woody browse species did just fine. The inability of aspen, willow, and cottonwoods to grow above the browse level of elk for many decades, and now their journey to recovery, is all coincident with one fact: the removal of wolves, and now the recovery of wolves.”
Yet the murmurs persisted. All of which was perfectly understandable, if not quite entirely on scientific terms. “Yellowstone is the oldest park in the world, and there are people who have been around here thirty, forty years,” explained Doug Smith, lead wolf biologist and diplomatic park service employee. “They know an incredible amount of the park, a great deal of detail. So whenever you suggest an overarching paradigm, they find some detail that doesn’t fit. They reject the new paradigm.
“Then some people,” continued Smith, “I guess, are just ideologically opposed to the idea that this could be going on.”
For some, there were just too many variables involved in Yellowstone’s transformation to bet a professional reputation on the single, sexiest one. There was drought, there were water tables fluctuating, growing seasons lengthening. The elk herd itself was in flux, its numbers falling steadily since before the wolves arrived. (A fact that Ripple and Beschta themselves eventually came to incorporate into their wolf-centric hypothesis for Yellowstone’s botanical resurgence.) On top of all was nearly a decade of mild winters and subpar snowpacks to consider, allowing elk the luxury of foraging the grassy hillsides all season long, of never being driven by starvation to the stream bottoms where the emergency rations of willow lay exposed. At the end of his presentations, Smith would often hear a familiar challenge: Just give me one hard winter, and if the willows make it through, I’ll be a believer in the wolf hypothesis.
Where the Wild Things Were Page 17