wolf introduction has had numerous unexpected effects as well. The
animals' impact on the flora and fauna in the park has been profound.
Indeed, the breadth of change has been so far-reaching that researchers
from around the country have come to study the alterations. "Wolves are
shaping what you see here," says Douglas W. Smith, leader of the
Yellowstone Wolf Project. "In 30 years, when you drive through the park,
it will look very different."
|YOUNG WOLF By
midsummer, pups are mature enough to leave the den and join their
parents in socializing with other wolves. |
The Ecology of Fear
Ripple, for one, is hoping for more
trees. "I like aspen trees," he remarks over coffee in a cozy log
restaurant near a cabin just outside Yellowstone where he stays during
field research. "I am
passionate about them." Among other things, he explains, they are
biodiversity hot spots in the West, home to a variety of songbirds. When
he heard in 1997 that aspen trees were on the decline in Yellowstone and
no one knew why, he was drawn to the park to try to solve the mystery.
Ripple points to some black-and-white photographs taken of the same
spot in the Lamar Valley more than 50 years apart. "You can see that young
aspen and willow were abundant in the early 1900s. By the 1930s the trees
had stopped regenerating, and there are no young ones.
"I had a lightbulb," he continues. He took core samples from 98 aspen
trees and discovered that only two had begun to grow after the
1920s--around the time the last substantial populations of wolves were
killed or driven off. And these two were in places that elk would be
hesitant to frequent for fear of being attacked by predators. Ripple found
big trees and tiny trees but nothing in between, because nothing new grew
from the 1930s to the 1990s. It was the first concrete evidence of a "wolf
|The wolf-effect theory holds that wolves kept elk
numbers at a level that prevented them from gobbling up every tree or
willow that poked its head aboveground. When the wolves were
extirpated in the park as a menace, elk numbers soared, and the hordes
consumed the vegetation, denuding the Lamar Valley and driving out
many other species. Without young trees on the range, beavers, for
example, had little or no food, and indeed they had been absent since
at least the 1950s. Without beaver dams and the ponds they create,
fewer succulents could survive, and these plants are a critical food
for grizzly bears when they emerge from hibernation.
After the wolves' reintroduction in 1995 and 1996, they began to
increase their numbers fairly rapidly, and researchers began to see
not only a drop in the population of elk but a change in elk behavior.
The tall, elegant mahogany-colored animals spent less time in river
bottoms and more time in places where they could keep an eye out for
predatory wolves. If the wolf-effect hypothesis is correct, and wolves
are greatly reducing elk numbers, the vegetation should be coming back
for the first time in seven decades.
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|Hiking along the purling Lamar River, not far from a
den of one of the wolf packs, Ripple walks by a small rise and parts a
dense green curtain of booth willows to make a point. There on the
ground lie the bleached skull, ribs and spine of an elk. And all
around, the willows are much taller than Ripple, some more than three
meters high. Ripple and his colleague Robert L. Beschta, a forester at
Oregon State University, have indeed found trees and willows
rebounding in Yellowstone as wolf numbers have climbed--but that is
only part of the change occurring in the park.
Trees are coming back most dramatically in places where a browsing
elk doesn't have a 360-degree view; these willows, for example, sit
below a rise that blocks the animals' view. A look at the plants shows
they have not been browsed at all in several years. Elk don't feel
safe here, Ripple contends, because they can't see what is going on
all around and are nervous about spending time in this vicinity. Just
50 meters away, however, where the terrain is level and wide open and
the elk enjoy a panoramic view, the willows are less than a meter tall
and have been browsed much more heavily over the past three years.
"It's the ecology of fear," Ripple says.
|ELK COW WITH CALF is
alert for wolves in the vicinity. Since wolves have been
reintroduced into Yellowstone, many more calves are lost each
spring to predation, and the overall elk population is roughly
half what it was just before the wolves returned.
The Long Reach of the Wolf
Other changes accompany the regrowth of vegetation taking place along
the Lamar. Just upstream is a small beaver dam, one of three--the
first dams documented on the river in 50 years. Slough Creek, a
tributary of the Lamar, has six dams. Both Ripple and Smith believe
that because of the regrowth, beavers have something to eat again.
"Their food caches are full of willow," Smith says. And other changes
are in the offing. As more woody vegetation grows along the Lamar, it
will stabilize the banks and stop some erosion. More vegetation,
Ripple predicts, will also shade and cool the stream. It means, too,
more woody debris in the Lamar, which will slow the river, cause water
to pool, and improve the trout habitat, leading to more and bigger
Although the scientific focus so far has been on vegetation, the
wolf seems to have an incredibly long reach into other parts of the
Yellowstone food web as well. One of its most dramatic effects has
been on coyotes. For three years before the reintroduction of wolves,
Robert Crabtree, now chief scientist at the Yellowstone Ecological
Research Center, a nonprofit organization based in Bozeman, Mont., and
his wife, Jennifer Sheldon, who are both canid biologists, gathered
baseline data on the park. Coyotes, they have found, have sacrificed a
great deal to make room for the much larger wolves.
The number of coyotes in the park is down 50 percent and in core
wolf areas has dropped 90 percent. Male coyotes are smaller than they
were before the wolves arrived, perhaps, Crabtree says, because "the
larger ones were more aggressive and challenged the wolves and lost."
With fewer coyotes, their prey--voles, mice and other rodents--have
exploded in number. That has benefited red fox and raptors. But red
fox prey on songbirds as well, and more foxes could mean a greater
toll on birds.
|Wolves have also thrown the doors to the
Yellowstone meat market wide open. Rarely do grizzly bears or
cougars attack full-grown elk, although they eat calves or feed on
the winter-killed carcasses. Wolves, on the other hand, pull down
big ones all the time. After they eat their fill, they wander
away, meat drunk, to sleep it off, or they get pushed off the kill
by a grizzly. The presence of wolves has meant that much more meat
is available on the ground. All manner of scavengers make a living
on these carcasses, and an increase in numbers of everything from
grizzly bears to magpies reflects these newfound riches. The
largest number of ravens on a wolf kill ever recorded (135) was
here. "We see bald eagles, golden eagles, coyotes, ravens and
magpies on every kill that's made," Smith says. "I don't know what
they did before wolves showed up."
But are wolves really the engine driving these changes? Most
scientists think so. Smith says that "wolves are to Yellowstone
what water is to the Everglades"--the primary force shaping the
ecosystem. In Banff National Park in Canada, scientists have
documented changes brought by wolves that returned on their own in
the 1980s: willows reappeared, the diversity and abundance of
songbirds doubled. Now researchers are coming to Yellowstone to
tease out some of the first evidence of the impact that wolves are
having on areas near the riverbanks; at least six projects are
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|Some researchers, however, are agnostic about the
effects of the wolf. Crabtree, for example, says that yes, willows
are rebounding and imaging data show the regrowth dramatically.
But a strong correlation between the return of wolves and the new
growth is far from demonstrated. "Claiming wolves are responsible
verges on bad science," he states. "The ecosystem in Yellowstone
is a multicausal interactive system, and there's never a single
cause. Even a predominant cause is rare. At the same time the wolf
numbers were coming back, there was flooding along the river, and
the climate is a lot warmer. Wolves probably have a role, but it
is confounded by those factors. It will take 20 years or more
before we know definitively."
|VEGETATION in the
park is rebounding because of decreasing numbers of elk. These
mature cottonwood trees are now reinforced by seedlings and
saplings that, without the overabundant elk, can grow to
Duncan Patten is a research ecologist who served on a National
Academy of Sciences study of Yellowstone published in 2002.
Yellowstone has not had a hard winter since wolves reached high
levels, he observes, and elk may not have needed to resort to
trees for food: "When winters are hard, elk take a lot of chances
to put something in their belly. Give me two hard winters in a
row, and I'll buy the argument."
The debate over the wolves' influence on the elk is fanning a
long-standing argument over the proper way to manage Yellowstone's
elk. At one time the park service also believed elk were too
numerous and in the 1960s sent rangers to trap and shoot them by
the thousands in a program called "direct reduction." By the end
of the decade the total number of elk was down to an estimated
4,000. Public outcry ended the shooting, and in the 1970s the park
service adopted a policy of natural regulation in wilderness parks
such as Yellowstone, a management philosophy that would lift the
heavy hand of humans and manage the parks as "vignettes of
primitive America." Ever since, the elk numbers have climbed.
For decades now, critics, including the state of Montana, have
denounced the National Park Service for allowing so many elk to
crowd the vast stretch of native grasses. Letting nature take its
course in what is a decidedly unnatural situation is folly, the
critics argue. Few elk would spend the winter at such a high
altitude, they add, if the animals could migrate onto the plains.
Instead hunting pressure in the surrounding area compresses them
into the park.
Some researchers assert that the return of vegetation along the
riverbanks--brought on by a reduction in the number of
elk--undermines the long-running contention of the park service
that Yellowstone's elk population is within natural limits. But
Smith defends the park's view and suggests that there are other
ways to look at the situation. Elk numbers are going to fluctuate
wildly over time, he says, and although numbers might have been,
and still are, high, "they're within natural limits over the long
|Countering this defense, Alston Chase, author of
the 1986 book Playing God in Yellowstone, which was harshly
critical of the policy of natural regulation, says for the park
service to make such an argument is absurd. He found little
evidence of large elk populations on the Yellowstone Plateau in
the past. Between 1872 and 1920, he points out, the park was
established, poaching was stamped out, the Native Americans were
evicted, and the U.S. Biological Survey was killing wolves. That
is when elk numbers started to soar--and it was a wholly unnatural
Unwitting Restoration Biologists
Although the jury is still deliberating the effects of wolves,
early evidence strongly suggests that the canids are unwitting
restoration biologists. By simply doing what they do--mainly
preying on elk--they are visiting great changes on the Yellowstone
ecosystem. Many of the changes are positive for those things
humans value, and for experts to accomplish some of these same
goals would be hugely expensive.
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|Wolves have brought other lessons with them. They
dramatically illustrate the balance that top-of-the-food-chain
predators maintain, underscoring what is missing in much of the
country where predators have been eliminated. They are a parable
for the unintended and unknown effects of how one action surges
through an ecosystem. More important, the Yellowstone wolves are
bringing into focus hazy ideas of how ecosystems work in a way
that has never been so meticulously documented. Just as the
actions of the wolf echo through Yellowstone, they will
reverberate into the future as they help to increase the
understanding of natural systems.
JIM ROBBINS is a freelance journalist based in Helena, Mont.,
who writes about the changing American West for the New York
Times and other publications.
|MORE TO EXPLORE:
Yellowstone after Wolves. Douglas W. Smith, Rolf O.
Peterson and Douglas B. Houston in BioScience, Vol. 54, No.
4, pages 330–340; April 2003. Available at
konstanza.ingentaselect.com/ vl=4060996/cl=73/nw=1/ rpsv/cw/aibs/00063568/v53n4/s8/p330
|Yellowstone Wolves in the Wild. James C.
Halfpenny. Riverbend Publishing, 2003.
|Yellowstone National Park Wolf Information is at
www.nps.gov/yell/nature/animals/wolf/wolfup.html and www.ypf.org