358 ■ CHAPTER 20 Communities of Organisms
ECOLOGY
R
obert Beschta will always remember
the day he visited Yellowstone National
Park’s Lamar Valley in 1996. Beschta,
a hydrologist, was there to observe the Lamar
River, which winds through the valley’s lush
lowland of grass and sage (Figure 20.1). But on
that day, as he walked toward the waterway, he
noticed something odd: all around the valley,
there were not many trees. The few tall, white
aspens he saw looked haggard, their bark eaten
away. And there were no young saplings to
be seen.
Beschta had studied forestry and rivers for
decades and knew what a healthy valley was
supposed to look like. This was not it. Beschta
approached the river and observed that its
banks were also devoid of trees. The leafy green
cottonwoods and wide willows that had once
arched gracefully from the riverbank over the
water were absent. And with no tree roots to
hold the soil in place, the riverbanks themselveswere jagged and eroding. “I was dumbstruck,”
recalls Beschta. Something unprecedented was
happening in Yellowstone.
Beschta returned to Oregon State Univer-
sity (OSU), where he worked, and described his
observations in a seminar. He showed pictures
of aspens with their bark stripped away and
empty riverbanks where saplings should have
been growing. In the audience, William Ripple
sat up a little straighter. Also a scientist at OSU,
Ripple studied forest ecology. He was particu-
larly interested in aspen trees, which grow as
tall as 70 feet and live up to 150 years. From
what Beschta was saying, aspens were no
longer growing in Yellowstone. Ripple wanted
to know why.
“It was a scientific mystery as to what was the
cause of the decline,” he recalls. In that moment,
listening to Beschta, Ripple knew exactly what
his next research project would be: to document
the extent of the aspen decline and determine
why it was occurring.
Within a year, Ripple and one of his gradu-
ate students, Eric Larsen, traveled to the Lamar
Valley. There, they drilled small holes into the
centers of aspens and removed from each a plug
of wood about the diameter of a pencil. Then
they counted the growth rings in each plug—one
for every year the tree has been in existence—to
determine the age of the tree. They found that
most of the aspens had begun to grow prior
to 1920. After 1920, almost no new trees had
begun growing.
“We started scratching our heads at that
point,” says Ripple. He, Beschta, and Larsen
began to brainstorm reasons why the trees
might have stopped regenerating. They looked
for environmental changes in the 1920s that
could have done it: a fire that killed off saplings,
or a change in climate that reduced the trees’
ability to reproduce. But nothing lined up—until
an ordinary moment gave Ripple an extraordi-
nary idea.
Standing in a gift shop in Grand Teton
National Park, just south of Yellowstone, Ripple
looked up at a poster on the wall. It featured a
grove of tall, white aspen trees in the winter.
In the middle of the trees, its paws covered in
snow, stood a large gray wolf. “That was an ‘aha’
moment,” says Ripple. “I thought, ‘Maybe the
wolf protects the aspen.’ ”ROBERT BESCHTA
Robert Beschta is a professor emeritus at
Oregon State University. He studies water
processes in forest and rangeland ecosystems.Figure 20.1
The Lamar River flows through Yellowstone National Park