Trees May Dry Up With Global Warming
Warming global temperatures could cause massive tree die-offs. That's the gloomy conclusion of a new study by scientists at the University of Arizona.
The study addressed a fairly basic question: Do warmer temperatures make trees more susceptible to drought?
It might seem surprising that scientists don't already know the answer to that question. But biologist David Breshears of the University of Arizona says there's a lot that scientists don't know about trees. "Like, what does it take to kill a tree, and do warmer temperatures matter in terms of killing trees?" he says.
To study the effect of heat on the drought tolerance of trees, Breshears and his colleagues decided to do an experiment. They uprooted 20 mature pinyon pine trees from a ranch near Ojitos Frios, N.M., and shipped them approximately 600 miles to Biosphere 2 in the Arizona desert outside Tucson.
Biosphere 2 was originally built to prove that humans could live in a closed, self-contained ecosystem. But the project ran into problems, and now the facility is basically a giant greenhouse with different climate zones inside.
Henry Adams, who worked with Breshears on the study, says they put the trees into two areas: one where conditions resembled those in New Mexico, and the other with a temperature of about 8 degrees Fahrenheit warmer.
Then, they stopped watering half of the trees in both of those spaces.
"What we saw was that trees in the warmer area died 30 percent faster on average than trees in the ambient area," says Adams.
These finding appear in the current issue of the journal Proceedings of the National Academy of Sciences.
Breshears says these results spell trouble for trees if predictions about global warming come to pass.
"If what we see for this pinyon pine species also applies to other widespread tree species," says Breshears, "then there's potential that we could have a lot of die-off in a lot of places."
Although the results don't come as a major surprise, Phil van Mantgem says it's one thing to suspect something, and another to demonstrate it scientifically. Van Mantgem is a research ecologist with the U.S. Geological Survey's Western Ecological Research Center in Arcata, Calif.
"It was important to do this sort of work to demonstrate that this does occur in biological systems," he says.
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ROBERT SIEGEL, host:
If you're so inclined, this might be a good time to hug a tree. As NPR's Joe Palca reports, new research suggests that global warming could cause massive tree die-offs in the future.
JOE PALCA: There's a lot of fairly basic stuff that scientists don't really know about trees.
Professor DAVID BRESHEARS (Natural Resources, University of Arizona): Like, what does it take to kill a tree, and do warmer temperatures matter in terms of killing trees?
PALCA: David Breshears spends a lot of time studying trees. He's at the University of Arizona in Tucson. About a decade ago, he got involved in a project that looked at tree die-offs following drought. He compared the number of trees that died in a 1950s drought that hit the Colorado, Arizona, New Mexico area with a drought that struck a similar area in 2000. More trees appeared to die in 2000, even though the droughts lasted about the same time. That led Breshears to wonder.
Prof. BRESHEARS: Is warmer temperature on top of drought going to be a problem for us in terms of really triggering a lot more mortality than we've had in the past?
PALCA: So he and some colleagues decided to do an experiment. They uprooted 20 mature pinyon pine trees from a ranch near Ojitos Frios in New Mexico and trucked them approximately 600 miles to Biosphere 2 in the Arizona desert outside Tucson.
Biosphere 2 was originally built to prove that humans could live in a closed, self-contained ecosystem. But the project ran into problems, and now the facility is basically a giant greenhouse with different climate zones inside.
Breshears' colleague Henry Adams says they put the trees into two areas.
Mr. HENRY ADAMS (Ecologist, University of Arizona): We made one area as cool as possible.
PALCA: So that it resembled the cooler climate of the trees' native New Mexico. The others were put in another area that was about eight degrees warmer.
Mr. ADAMS: What we did is stop watering half of the trees in both of those spaces.
PALCA: And then they waited.
Mr. ADAMS: What we saw was that trees in the warmer area died 30 percent faster on average than trees in the ambient temperature area.
PALCA: In other words, the warmer temperatures made the trees significantly more vulnerable to drought. Adams reports these findings in the current issue of the journal PNAS.
Dave Breshears says these results spell trouble for trees if the expected global warming comes to pass.
Prof. BRESHEARS: If lots of areas have warmer conditions and periodic drought, if what we see for this pinyon pine species also applies to other widespread tree species, then there's potential that we could have a lot of die-off in a lot of places.
PALCA: Although the results don't come as a major surprise, Phil van Mantgem says it's one thing to suspect something and another to demonstrate it scientifically. He's a research ecologist with the U.S. Geological Surveys Western Ecological Research Center in Arcata, California.
Dr. PHIL VAN MANTGEM (Research Ecologist, Western Ecological Research Center, United States Geological Survey): It was important to do this sort of work just to demonstrate that this, in fact, does occur in biological systems.
PALCA: The new study represents a kind of scientific revival for Biosphere 2. Earlier this decade, it was basically abandoned as a research facility, but in 2007, the University of Arizona took it over. Travis Huxman is now the director. He says Biosphere 2 offers scientists a chance to do experiments on a scale that begins to resemble the great outdoors, rather than a laboratory bench.
Dr. TRAVIS HUXMAN (Director, Biosphere 2): It's a $250-million facility, and it's been sitting in our backyard for some time, and we feel an obligation to try to figure out, you know, something to do with it.
PALCA: Huxman says stay tuned, there's more to come.
Joe Palca, NPR News, Washington. Transcript provided by NPR, Copyright National Public Radio.
