Global warming stalks Yosemite - small creatures moving uphill
Retracing the steps of a meticulous early 20th century biologist,
researchers find that some of the park’s tiniest residents have moved a
startling distance uphill
- Michelle Nijhuis
Sunday, November 27, 2005
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Biologist Joseph Grinnell was a world-class researcher, but he wasn't
always the most pleasant of traveling companions. "We'd be sitting in
camp, and we'd both be skinning," recalled naturalist Ward Russell, who
spent years helping Grinnell trap, skin and otherwise document the
wildlife of California. "Pretty soon, he'd throw a rat over to me, and
he'd say, 'Here, Russell, finish this one up,' and he'd just ... pick up
his notebook, and start writing."
Despite his dubious camp etiquette, Grinnell's devoted record-keeping led
to one of the most famous datasets in modern biology. During their travels
throughout California between 1904 and the late 1930s, Grinnell and his
colleagues snared or shot more than 20,000 mammal, bird, reptile and
amphibian specimens, took about 2,000 photographs, and filled 13,000
journal pages with erratic penmanship and beautifully detailed
observations. Their portrait of the natural diversity of California
remains unmatched in its scope and depth.
Grinnell, the founding director of the Museum of Vertebrate Zoology at UC
Berkeley, was by all accounts a dedicated, methodical researcher. His
field journal, which he kept until just five days before his death in
1939, numbered more than 3,000 pages. He helped build the museum's store
of animal skins and skeletons, an international collection now ranging
from a hippo skull the size of an easy chair to shrew skeletons no larger
than a thumb. His theories about species and their habitats are still
taught in college biology courses.
Yet in 1910, Grinnell predicted that the real value of his and his
colleagues' painstaking fieldwork would not "be realized until the lapse
of many years, possibly a century." Change was clearly part of the natural
world, he wrote. But he also saw "vastly more conspicuous" transformations
of the environment in the speedy deforestation, cultivation and irrigation
of the West. He believed that in the future, scientists would return to
some of his more than 700 study sites, and use his findings to chart these
That future is now. Though several researchers have mined the Grinnell
data during the past nine decades, no one has ever attempted a broad
resurvey of the sites. Now, researchers at the Museum of Vertebrate
Zoology, inspired by Grinnell's writings, hope to revisit about a third of
the California sites by the museum's centennial in 2008. With funding from
the U.S. Geological Survey and the Yosemite Fund, a nonprofit organization
that supports research in the park, biologists began in 2003 to study 40
sites along Grinnell's "Yosemite Transect."
Just as Grinnell foresaw, his data provide evidence of conspicuous change
in the natural world. But even the prescient Joseph Grinnell didn't count
on global warming.
During a driving rainstorm in mid-August, near the head of a long, gently
sloping glacial valley called Lyell Canyon, the soggy modern-day Grinnell
team takes temporary shelter in camp. Berkeley professor James Patton, his
wife, Carol, and U.S. Geological Survey wildlife biologist Les Chow have
spent much of the summer here, among the toothy granite peaks of Yosemite
National Park, following the very precise footsteps of Joseph Grinnell and
Each day, they check long rows of mammal traps, hiking through alpine
meadows and up rocky slopes. Patton skins a few unlucky specimens with a
small pair of scissors, then records his findings and observations using
the exacting Grinnell method. Patton even stores his trays of animal skins
in the same scuffed crates once used by Grinnell and his colleagues; the
wooden boxes, originally designed to carry cans of lard, have survived a
century of nearly constant use.
For Patton, who has spent his career studying small mammals throughout the
Americas, the project is also a journey into his scientific heritage.
Grinnell and his colleagues often wrote down their musings about the
natural world, and Patton sometimes dips into their journals during his
days in the field. Their voluminous notebook entries, with their
imperfections, their detours, and their moments of clarity, exude the
excitement of discovery.
"To be at the same spot, the same rock outcrop, and to be able to read
what they were seeing and thinking ..." Patton shakes his head. "The only
reason we have this opportunity is that Grinnell was fanatic about what he
Field science has changed a bit since the days of Grinnell. In the Lyell
Canyon camp, the researchers eat rehydrated dinners out of foil packets
instead of cooking on an open fire, and eschew worsted wool in favor of
Some researchers store their field journals on Palm Pilots, instead of in
the traditional lined loose-leaf notebooks. And while Grinnell used stacks
of "museum specials," a sort of burly mousetrap, to break the backs of
tens of thousands of small mammals, Patton and his crew now trap their
subjects alive in slim aluminum boxes, often releasing them unhurt.
But the most significant difference between the old and new Grinnell
expeditions lies inside the traps. When Patton first visited Lyell Canyon
in 2003, he opened one of his aluminum boxes to find a small mouse with
remarkably large ears. "I thought, 'What the heck is this thing doing
here?' " says Patton. "I was dumbfounded." Its huge ears immediately
introduced it as a piñon mouse, which, as its name suggests, is a familiar
resident of the lower-elevation piñon pine forests of the Sierra Nevada.
On the east side of the Sierra, Grinnell and his assistants only saw piñon
mice below 7,000 feet, a finding confirmed by other researchers throughout
the central part of the range. Patton's group found numerous mice
frolicking in the talus slopes of Lyell Canyon, 10,200 feet above sea
level and about eight miles from the nearest Grinnell sighting. The
distance was too great to be the work of just a few wandering individuals;
it was clear to Patton that the range of the piñon mouse, and its habitat,
were far different now than in 1915.
"They're common, and they're easily identified," says Patton. "If they had
been up here before, (Grinnell and his compatriots) would have seen them."
The new Yosemite crew has uncovered more changes. Four other small mammals
have expanded their turf in the park, increasing the upper limits of their
ranges by an average of 2,000 vertical feet.
The alpine chipmunk, two high-elevation ground squirrels -- including the
Belding's ground squirrel, known as the "picket pin" for its
ramrod-straight alarm posture -- and a small relative of the rabbit called
the pika have retracted their haunts uphill, drawing in the lower edge of
their ranges by an average of 1,700 vertical feet. At least two species of
small mammals, a chipmunk and a wood rat, have dramatically shrunk the
overall size of their ranges, and are now extremely rare in the park.
Ornithologist Andrew Rush, who recently revisited the Grinnell sites in
Yosemite, also saw and heard some surprises. In Lyell Canyon alone, he
recorded 17 bird species not mentioned by the Grinnell team, many of them
riparian and wetland species more familiar at lower elevations. Some of
these species, such as the blue-winged teal and the mallard, were even
breeding in the canyon's high-elevation meadows.
The Grinnell survey and resurvey represent just two snapshots in time, and
what happened in the intervening years is largely unknown. But studies of
particular species in the area help fill in the gaps, and confirm that
neither Grinnell nor his modern followers witnessed a fleeting anomaly.
So what's going on in Yosemite? Fire suppression, with its transforming
effects on habitat, has certainly played a part in the rearrangements of
wildlife at lower elevations. It may also explain why a couple of small
mammal species moved downhill in the park, defying the overall trend. Yet
in alpine areas such as Lyell Canyon, Grinnell photographs from 1915 show
that forests and meadows looked almost the same as they do today.
There is little question, however, that the entire park is warmer than it
was during Grinnell's time. Snow is melting earlier in the spring, and
Lyell Glacier, like other glaciers throughout the Sierra, is disappearing.
Researchers at Portland State University in Oregon found, using another
series of historical photographs, that the surface area of the western
lobe of Lyell has shrunk 30 percent since 1883, and the eastern lobe has
contracted 70 percent.
Weather records from Yosemite Valley show a 9 degree Fahrenheit increase
in mean minimum temperatures over the past century. Though weather data
from higher elevations are spotty, Museum of Vertebrate Zoology researcher
Robert Hijmans estimates that mean minimum temperatures throughout the
central Sierra rose 5 degrees Fahrenheit over the last 100 years.
The vast majority of scientists say humans have a lot to do with such
changes, which are now observed around the world. They say the rising
concentration of carbon dioxide and other greenhouse gases in our
atmosphere -- due in large part to cars, coal-fired power plants and other
human inventions -- bears significant blame for the planet's warming
In high, relatively undisturbed places such as Lyell Canyon, these rising
temperatures -- and their various effects on the landscape -- are the most
dramatic changes in the environment over the past century, and they are
the most obvious explanation for the shifting alpine wildlife of Yosemite.
For some species, it appears, just a few degrees' difference in
temperature makes home uncomfortable and previously inhospitable habitat
more welcoming. "For the pika, the alpine chipmunk and the Belding's
ground squirrel, I don't know what else to link it to, other than climate
change," says Patton.
Back at the Museum of Vertebrate Zoology, museum director Craig Moritz
agrees. "This is a work in progress," he cautions, "but my gut feeling is
that we've got a whopping climate change signature."
Thus the legacy of Joseph Grinnell survives, informing a new world.
"Grinnell was one of those classic early ecologists that snobby
scientists, toward the end of the 20th century, would dismiss as
'descriptive,' " says Raphael Sagarin, a researcher at UCLA who uses
historical datasets to study the effects of climate change. "Now we are
seeing how important good descriptions of nature really are."
The results of the Grinnell resurvey reflect a much larger pattern, one
already documented by legions of scientists. Camille Parmesan, a biologist
at the University of Texas at Austin, estimates that researchers have now
collected good data on the effects of climate change on more than 1,500
animal and plant species worldwide. Half those species have clearly
shifted upward or northward in recent decades, and two-thirds are breeding
earlier in the year. Only a handful are moving to warmer climates, or
Stanford University biologist Terry Root, who reviewed the existing
research in a 2003 paper in the journal Nature, reported that a consistent
"fingerprint" of global warming is now perceptible on species "ranging
from mollusks to mammals and from grasses to trees."
Scientists warn that even if we could quit adding greenhouse gases to the
atmosphere tomorrow, the planet would continue to warm up. Researchers at
the National Center for Atmospheric Research in Boulder, Colo., call it
the "climate change commitment." What we've already pumped into the
atmosphere will cause global air temperatures and sea levels to rise,
slowly but significantly, over the next several centuries. Every day of
new emissions commits us to yet more warming, and deeper waters.
The Intergovernmental Panel on Climate Change, considered the global
scientific authority on the subject, foresees that between 1990 and 2100,
Earth's average surface temperature will increase by between 2.5 and 10.4
degrees Fahrenheit. "The projected rate of warming," the panel concluded
in its most recent report, "is much larger than the observed changes
during the 20th century, and is very likely to be without precedent during
at least the last 10,000 years."
Yosemite National Park, like all national parks, is supposed to muffle
these and other "vastly more conspicuous" transformations wrought by
humans, to use Joseph Grinnell's expression. "It would seem to me that
national parks should comprise pieces of the country in which natural
conditions are left altogether undisturbed by man," Grinnell wrote to
Yosemite Superintendent W.B. Lewis in 1920. Yet the Grinnell resurvey team
has found that when it comes to global warming, Yosemite is no refuge.
"Places like Yosemite mean so much to so many people," Patton reflects.
"People think we've preserved this piece of the environment, but we
haven't. The high-elevation species, those that seem to be retracting
upwards, have no place to go -- so when they go, they're gone, and they're
never coming back."
Michelle Nijhuis writes for High Country News, based in Paonia, Colo.,
where a longer version of this article appeared. Contact us at
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