We kind of knew that Yellowstone and wolves were more complicated than the “all is well with wolves” idea. Perhaps people went a bit overboard with their “carnivolatry,” but most of us took with several grains of salt..as has been discussed previously at TSW. It’s interesting when folks like the Times discover that there is more than meets the eye to some stories that have been accepted as gospel for some time.
The wolves’ return and predatory dominance was believed to have had a widespread effect known as a trophic cascade, by decreasing grazing and restoring and expanding forests, grasses and other wildlife. It supposedly even changed the course of rivers as streamside vegetation returned.
Yellowstone’s dramatic transformation through the reintroduction of wolves has become a global parable for how to correct out-of-balance ecosystems.
In recent years, however, new research has walked that story back. Yes, stands of aspen and willows are thriving again — in some places. But decades of damage from elk herds’ grazing and trampling so thoroughly changed the landscape that large areas remain scarred and may not recover for a long time, if ever.
Wolf packs, in other words, are not magic bullets for restoring ecosystems.
“I would say it’s exaggerated, greatly exaggerated,” said Thomas Hobbs, a professor of natural resource ecology at Colorado State University and the lead author of a long-term study that adds new fuel to the debate over whether Yellowstone experienced a trophic cascade.
“You could argue a trophic trickle maybe,” said Daniel Stahler, the park’s lead wolf biologist who has studied the phenomenon. “Not a trophic cascade.”
Not only is the park’s recovery far less robust than first thought, but the story as it has been told is more complex, Dr. Hobbs said.
But the legend of the wolves’ influence on the park persists.
A person could ask “if good things happened with more elk killed by wolves, could they have also happened with more elk killed by other predators, including humans?”
Once elk numbers dwindled, willows and aspens returned along rivers and streams and flourished. The beaver, an engineer of ecosystems, reappeared, using the dense new growth of willows for both food and construction materials. Colonies built new dams, creating ponds that enhanced stream habitats for birds, fish, grizzlies and other bears as well as promoting the growth of more willows and spring vegetation.
But wolves were only one piece of a larger picture, argue Dr. Hobbs and other skeptics of a full-blown trophic cascade at Yellowstone. Grizzly bears and humans played a role, too. For eight years after wolves re-entered the park, hunters killed more elk than the wolves did.
“The other members of the predator guild increased, and human harvest outside of the park has been clearly shown to be responsible for the decline in elk numbers the first 10 years after the wolves were introduced,” Dr. Hobbs said.
And wolf-resistant ungulates are growing in numbers..
The changes attributed to the presence of stalking wolves, some research showed, weren’t only the result of fewer elk, but of a change in elk behavior called “the ecology of fear.” Scientists suggested that the big ungulates could no longer safely hang out along river or stream banks and eat everything in sight. They became extremely cautious, hiding in places where they could be vigilant. That allowed a return of vegetation in those places.
Dr. Hobbs and others contend that subsequent research has not borne that theory out.
Another overlooked factor is that around the same time wolves were returning, 129 beavers were reintroduced by the U.S. Forest Service onto streams north of the park. So it wasn’t just wolf predation on elk and the subsequent return of wolves that enabled an increase in beavers, experts say.
Some researchers say the so-called trophic cascade and rebirth of streamside ecosystems would have been far more robust if it weren’t for the park’s growing bison herd. The bison population is at an all-time high — the most recent count last summer found nearly 5,000 animals. Much larger than elk, bison are less likely to be vulnerable to wolves, which numbered 124 this winter.
The park’s bison, some researchers say, are overgrazing and otherwise seriously damaging the ecosystems — allowing the spread of invasive species and trampling and destroying native plants.
Beschta vs. Geremia
“There is a hyperabundant bison population in our first national park,” said Robert Beschta, a professor emeritus of forest ecosystems at Oregon State University who has studied Yellowstone riparian areas for 20 years. He pointed to deteriorating conditions along the Lamar River from bison overgrazing.
“They are hammering it,” Mr. Beschta said. “The Lamar ranks right up there with the worst cattle allotments I’ve seen in the American West. Willows can’t grow. Cottonwoods can’t grow.”
A warmer and drier climate, he said, is making matters worse.
Such opinions, however, are not settled science. Some park experts believe that the presence of thousands of bison enhances park habitats because of something called the Green Wave Hypothesis.
Chris Geremia, a park biologist, is an author of a paper that makes the case that a large numbers of bison can stimulate plant growth by grazing grasses to the length of a suburban lawn. “By creating these grazing lawns bison and other herbivores — grasshoppers, elk — these lawns are sustaining more nutritious food for these animals,” he said.
Dr. Geremia contends that a tiny portion — perhaps one-tenth of one percent — of the park may be devoid of some plants. “The other 99.9 percent of those habitats exists in all different levels of willow, aspen and cottonwood,” he said.
I thought the comments were interesting.. the idea of some is that if bison could just roam freely, everything would be fine. It’s bad western ranchers, and if they were removed, everything would be hunky-dory. Reminds me a bit of previous peoples removed from the landscape with all kinds of good intentions. I didn’t see any comments that a park with 4.5 mill tourists per year (2023) is not really a “natural” place and that Parkies are doing the best they can to find the sweet spot at recreating Indigenous-influenced ecosystems without Indigenous people. Lots of mentions of “balance of nature”, and “what’s the point of the article, no one ever said wolves would solve all the problems caused by humans.”
I do know that I heard much about Yellowstone bison and brucellosis when in carpool in DC with a Lands person in the 1990’s, so the controversy has been going on for awhile.
The heavily grazed landscape is why, critics say, some 4,000 bison, also a record, left Yellowstone for Montana in the winter of 2023-24, when an unusually heavy snow buried forage. Because some bison harbor a disease, called brucellosis, that state officials say could infect cattle, they are not welcome outside the park’s borders. (There are no documented cases of transmission between bison and cattle.)
Montana officials say killing animals that may carry disease as they leave the park is the only way to stem the flow. During a hunt that began in the winter of 2023, Native Americans from tribes around the region took part. All told, hunters killed about 1,085 bison; 88 more were shipped to slaughter and 282 were transferred to tribes. This year, just a few animals have left the park.
The Park Service is expected to release a bison management plan in the coming months. It is considering three options: to allow for 3,500 to 5,000 animals, 3,500 to 6,000, or a more natural population that could reach 7,000.
Richard Keigley, who was a research ecologist for the federal Geological Survey in the 1990s, has become an outspoken critic of the park’s bison management.
“They have created this juggernaut where we’ve got thousands of bison and the public believes this is the way things always were,” he said. “The bison that are there now have destroyed and degraded their primary ranges. People have to realize there’s something wrong in Yellowstone.”
Dr. Keigley said the bison population in the park fluctuated in the early years of the park, with about 229 animals in 1967. It has grown steadily since and peaked last year at 5,900.
Yes, managing wildlife in this world, even in National Parks, can be complex and difficult.
Humorous that the NYT is rediscovering the wolf myth story. I mean this is the third time in their own pages. That Beschta fellow is one of the ones whose trophic cascade “story” was found wanting.
Back when I had an interest in the subject I could hear of a fantastic new finding, follow the link, and after seeing who wrote the paper, I’d already know the conclusions. Wolf folks are pretty much a one trick pony.
Despite all of our education, and high tech methods of communication, if you can get out there and push a story, early enough, and with enough boosters, over time you can make any claptrap the accepted wisdom.