Greetings on
the day before Thanksgiving. A friend
(retired forester) sent me this short video on the miracle of Yellowstone
National Park. Old news but interesting nonetheless. It appears to be quite controversial as I
found that some scientists claim the video gives the wolves way too much
credit. I provided a news release below
so you can read up on it. I couldn’t
help but think how this might apply to deer and vegetation dynamics in
Pennsylvania. Enjoy it and have a safe holiday.
By John
Hollenhorst
Published:
Aug. 25, 2016
YELLOWSTONE
NATIONAL PARK, Montana — A casual visitor might not notice big changes at
Yellowstone National Park in the years since wolves were reintroduced in 1995.
The scenery
is still fabulous and soul-stirring. The bison — or buffalo — still roam and the
antelope play. The steaming hot springs are still cooking and the geysers still
deliver faithfully to thousands of visitors every day.
But if
visitors were to follow veteran park biologist Doug Smith into a thicket of
willows alongside certain streams, change might literally slap them in the
face. And it may be thanks to wolves.
"This
has been explosive or dramatic willow growth in here and, to a degree, aspen as
well," Smith said as he plowed through a dense tangle of branches. Twenty
years ago the willows were just a few inches high, he said, "and now
they're, well, almost twice as high as I am."
The
possibility that wolves are at the heart of the change has fueled a number of
scientific studies and, as almost anything about wolves typically does, it has
provoked significant controversy.
Are wolves
responsible for a "miracle" that "changed the rivers" of
Yellowstone? That provocative claim in a YouTube video that's been widely seen
over the past two years has ignited excitement about the impact wolves have had
in the 20 years since park biologists brought back the hungry predators.
It's a
fascinating and controversial scientific issue, entirely separate from the
political battles that have raged around wolves. Ranchers, environmentalists
and others have long fought over what the wolves destroy: wildlife and
livestock.
The alleged
"miracle" is that wolves have had the opposite effect on some species
of plants and animals, encouraging biological diversity and abundance.
Willows and aspens
Some
scientists say the explosive growth of willows and aspens in some areas of
Yellowstone is a clear example of a trophic cascade, a sequence of ecosystem
effects triggered by top predators like wolves that ultimately trickle down to
other players in the environment.
"How do
carnivores — wolves and cougars and bears — impact plants? They don't eat
plants," Smith said, quickly answering his own question. "They do it
indirectly, by impacting the animals that eat plants. In this case, it's
elk."
Herds of elk
are a photographer's favorite and a tourist delight in Yellowstone.
"Those
animals are cute," said a young tourist as she and her mother watched
several elk munching plants alongside Yellowstone's scenic Madison River.
But a
generation ago, there were so many elk that they were a sort of biological
blitzkrieg, doing heavy damage to their own habitat. Twenty years ago there
were about 20,000 elk in northern Yellowstone, munching up vast amounts of
willows and aspens. Since then, elk numbers have been cut down by about
three-fourths.
"That
decline in elk reduced elk eating willows and these willows have just shot up,
exploded," Smith said.
That's where
the controversial YouTube video comes in. Titled "How Wolves Change
Rivers," the 2014 video is narrated by British writer George Monbiot. It
gives wolves credit for profound ecological changes.
"As
soon as the wolves arrived, even though they were few in number, they started
to have the most remarkable effects," Monbiot says in the video."
The video
has been viewed 25 million times in the past two years. It describes dramatic
improvement of habitat for a host of creatures. "Rabbits and mice began to
rise," the video says, "which meant more hawks, more weasels, more
foxes, more badgers."
As the video
climaxes, it says, "The wolves changed the behavior of the rivers. They
began to meander less. There was less erosion. Their channels narrowed. More
pools formed." That helped stabilize river banks and fix the rivers in
their courses, the video contends, "So the wolves, small in number,
transformed not just the ecosystem of the Yellowstone National Park, this huge
area of land, but also its physical geography."
Not so fast
Wildlife
ecologist Dan MacNulty of Utah State University takes issue with the video's
sweeping statements. "It's an exaggeration," he said. MacNulty has
been studying Yellowstone wolves, and what they eat, for 20 years and believes
their powers are often overestimated.
"They're
not supernatural predators, and people get that impression from films," he
said.
He believes
both wolf lovers and haters exaggerate their impact. "So basically, you
have two different views that are wrong for the same reason."
Wolves have
definitely played a role in reducing the elk population, MacNulty said, but
it's an open scientific question how big a role other predators played.
"Cougar
numbers have increased, grizzly numbers have increased," he said, arguing
that those other predators may be partly responsible for the decline of elk.
MacNulty also notes that Montana permitted more aggressive elk hunting by
sportsmen since the mid-1990s. On top of that, elk numbers may have been
reduced by a changing weather pattern, noting drought could drive down the elk
population.
Smith agrees
wolves shouldn't get sole credit. But he appreciates the YouTube video for
bringing a complex topic to the public.
"The
video that shows 'Wolves Change Rivers' is a little bit far-flung," Smith
said. "You have to put a lot of imaginative and creative pieces together,
but there is a pearl of truth to it."
The
controversial video seems partly based on the work of professors William Ripple
and Robert Beschta from Oregon State University, and they stand by the main
theme.
"We
have observed changes in streams. … We expect changes in the courses of rivers
to occur, as plant communities improve following the return of wolves,"
Bescheta said in email to KSL and the Deseret News.
Of course,
most of the land area of Yellowstone is not covered by small, meandering creeks
lined with aspens and willows. The changes to those species apply only to a
small percentage of the land. But that doesn't mean the changes are
inconsequential.
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"These
are what we call biodiversity hot spots," Smith said. "These areas
provide a lot of habitat for other plants and animals. And this has impacted a
lot of animals. That has an outsize effect on the entire area."
Some stream-side
areas have not recovered in recent years, possibly because some locations don't
get enough water.
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