Hot Spot

Tom Van Devender can wrap his head around climate change better than
most folks.

Back in the 1970s, the paleo-climatologist helped publish a pivotal
study on Pleistocene packrat middens in Arizona’s Lower Grand Canyon
region. It turns out the ancient dens precisely traced shifting climes
over thousands of years.

“They’re almost like museum collections as you go through time,”
says Van Devender, a longtime Arizona-Sonora Desert Museum scientist
who now works with the Sky Island Alliance. The wide variety of plant
material left in the rodents’ droppings provided a priceless record of
how area vegetation had changed along with the climate.

“You could tell what the rainfall distribution was like, because you
would find 90 percent winter and spring annuals (plants), and only a
few summer annuals,” Van Devender says. “There was really a lot of
resolution.”

What that resolution told him was that, as the flora around them
changed with the environment, the packrats were able to adjust their
diet accordingly. Other animal remains found in the middens,
particularly those of reptiles, likewise revealed their broad ability
to adjust to—or at least survive—drastic changes in
temperature and rainfall.

Still, Van Devender is particularly cautious about using data from
the past to help predict the future. What he will say is this: He
doesn’t expect global warming to prompt mass extinction. Nor does he
expect a batch of new species to emerge from changing habitats. But he
doesn’t downplay the impacts of global warming, either.

“I believe there will be massive changes in geographic ranges and
elevational ranges,” he says, “with some readjustment of biological
communities. And things are happening faster than at any other time in
the recent past.”

It’s the unprecedented speed of that change—average global
temperatures have jumped nearly two degrees since the 1880s—that
makes impacts on wildlife so difficult to predict.

Researchers with the Intergovernmental Panel on Climate Change have
estimated that Arizona’s average temperature could rise by nearly seven
degrees over this century. That’s easily enough to disrupt ecosystems
through rainfall fluctuation, reduced mountain snow packs and severe
droughts. In other words, we could see the same transformations Van
Devender glimpsed in those packrat middens, but in one century rather
than many.

How that will affect Arizona’s wildlife is among the many unanswered
questions. The state is now home to a remarkable variety of animals,
including more than 100 species of reptiles and nearly 500 types of
birds—and each could be impacted in widely differing ways.
According to the National Wildlife Federation, riparian habitat
critical to birds such as the endangered Southwestern willow flycatcher
will almost certainly decline, as will streams hosting fish such as the
Apache trout.

In addition, Tucson’s Center for Biological Diversity has undertaken
a “350 Reasons” campaign, which cites at least 350 species expected to
go extinct if atmospheric carbon dioxide—the main culprit in
global warming—isn’t reduced to 350 parts per million, down from
the current 387 parts per million.

In Arizona, that list includes the Chiricahua leopard frog, once
found in 400 wetlands and streams, but now existing in fewer than 80.
It also includes the desert nesting bald eagle, which lives in
increasingly shrinking riparian habitat, with nestlings particularly
vulnerable to hot temperatures.

If you think this potential loss won’t have any impact on your own
existence, Scotty Johnson believes you might want to think again.
“These aren’t just species on the brink of extinction,” says Johnson,
who works for Defenders of Wildlife in Tucson. “This is also a huge
part of Arizona’s economy.”

He says that outdoor recreation in Arizona is a $2 billion dollar
industry, “and any impact to that needs to be averted.”

But gauging the impact—both on wildlife and related
tourism—is still a work in progress. Among those hoping to
understand possible changes is Cecil Schwalbe, a UA ecologist who also
works for the U.S. Geographical Survey’s Sonoran Desert Research
Station. Schwalbe is part of a team that recently won a $1.7 million
grant from the agency’s National Climate Change and Wildlife Science
Center to study the issue.

They’ll begin by looking at vegetation changes, says Schwalbe. “Then
we’ll try to weave into that the particular species of animals that may
be affected, so that we can know how they’ll react. Then we can plan
our management strategies better.”

Schwalbe says that studying the impacts on animals is much trickier
than studying the impacts on plants. “The animals are a little more
plastic in that they can usually move through two or three biotic
communities. They can live in desert grasslands and move up to oak
woodlands or down into Sonoran Desert scrub. Conceptually, it makes
sense. But getting the data together to prove your point is not so
simple.”

To gauge specific effects in Southern Arizona, Schwalbe’s team is
conferring with the Sky Island Alliance and Pima County. “The county,
with its Sonoran Desert Conservation Plan, is really into monitoring
(wildlife), so we’re trying to pick their brains as well,” he says.

Van Devender’s insights—drawn from those packrat
middens—will also play a part. According to Schwalbe, they reveal
that many animals can adjust to habitat changes—albeit not
happily. For instance, “the vegetation changed at one site,” he says,
“and where it’s now creosote and bursage, in the past, it was cool
enough for piñon and juniper.”

Surprisingly, the reptiles found in those same middens remained
constant over time. “Which tells us that, in areas without an elevation
variant—where they can just follow things upslope—they’re
kind of trapped,” Schwalbe says. “But even though that may not be their
preferred habitat, they can hang on and survive.”

Schwalbe credits Van Devender’s work for pushing biologists to
question their own habitat assumptions. “Tom’s work was very valuable
in forcing us to think out of the box, and say, ‘What in the hell were
these animals doing when, in piñon-juniper, they were still able
to survive?’

“The (reptiles) didn’t really like it when it was that cold,” says
Schwalbe. “But they didn’t really have any choice.”

Still, under even the most optimistic projections, there will be
losers. A poster child could be the alpine tundra around the San
Francisco Peaks, north of Flagstaff.

“That is a doomed ecosystem under this scenario,” says Schwalbe,
“because that biome is already at the top of the mountain, and as it
gets warmer, it will just die.”

This article appears in Nov 19-25, 2009.