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POSTED: Sunday, Jul. 12, 2009

WWU researcher turns to ancient bristlecone pines for clues on climate change

Andy Bunn will walk through a starkly beautiful landscape in September, where twisted and ancient bristlecone pines grow from a dry, rocky land scoured by high winds and blanketed in snow much of the year.

The Bellingham scientist's aim during those 10 days in Great Basin National Park in Nevada will be to extract small core samplings from as many as 100 trees. The diameter of a pencil, the cores will be taken to his lab at Western Washington University's Huxley College of the Environment.

At Huxley, the pieces of trees with a lifespan of thousands of years will be examined under a microscope, their rings studied and counted to gain a sense of how the climate has changed in the past - before people had an impact - in the hopes of understanding what climate change could mean for the future.

Bunn is working with undergraduate students from WWU and paleoclimatologists from the University of Arizona, home of The Laboratory of Tree-Ring Research. His research is funded by a $50,000 grant from the National Science Foundation.

The work focuses on bristlecone pines perched about 11,000 feet up in three remote areas - the White Mountains near the California-Nevada border, Great Basin National Park, and the Ruby Mountains in Nevada.

Why bristlecone pines? Because they are considered to be the world's longest-lived organisms and, as such, they could be a bridge into the past.

"Individual trees can live for about 5,000 years," Bunn said. "And then even after the tree dies, the environment they live in it's so cold and it's so dry that they don't rot. The husks of them, the dead stems, stay on the landscape for thousands of years."

And it's how the trees grow, in good years and bad, that provide clues to past climate patterns.

"What we're trying to do is use these trees as thermometers and rain gauges going back to a time when there weren't thermometers and rain gauges," said Bunn, noting that existing climate data go back just 100 years.

An environmental scientist with interest in paleoecology, Bunn studies how landscapes have changed over time, including tree-line forests and how they moved up and down slopes over decades and centuries as the climate changes. A tree-line forest is the place where trees stop growing on a mountainside and tundra starts.

"What controls that threshold? We know it relates to temperature, that at some point it just gets too cold for trees to grow any higher," he said.

That's where the tree rings of the ancient bristlecones come in.

Counting the rings makes it possible for researchers to determine a tree's age. Examining width and variations in the rings over time gives scientists an idea of what kind of stress the trees might have been under.

Ring width, for an example, is an indicator of a tree's health. When it's a good growing season, more of a tree's energy goes into producing wood for the ring. A poor growing season - temperatures too cold, precipitation too low - means a much narrower ring.

"The question that's asked is a thousand years ago, trees were growing at higher elevations than they are now," he said. "We know that the tree line is limited by temperature. What does that mean about what the temperatures were like a thousand years ago?"

His study also focuses on climate patterns prior to human activity, such as the use of fossil fuels that release heat-trapping carbon dioxide and other greenhouse gases into the atmosphere.

"One of the things that I'm interested in is how much did the climate vary on its own before we were doing that? Were there periods of warm growth independent of human activity? That gives us a good idea of how much the climate system can vary all by itself without us pushing it," Bunn said.

The study is in its last year. Once the data has been analyzed, it will be released to the wider scientific community.

Initial findings show that the growth of bristlecone pines in the last 50 years "is greater than at any time in the last thousand years, probably the last 2,000 years."

"What that tells us is that the environment is different now than it has been at any time in the past," Bunn said.

And so scientists are trying to figure out what caused that growth. Was it a change in temperature, which Bunn said seemed to be the primary factor? Was it changes in precipitation? Is the greater amount of carbon dioxide in the air helping the trees, fertilizing their growth in a way?

Finding the cause is no easy feat.

"The trees can't tell us why they're growing faster," he said.

The data that's gathered by Bunn and his students will be poured into an ocean of information that other scientists are gathering through a multitude of studies.

"No one study can weave together every aspect of how climate change works and sum it up in one neat little package," he said. "Our studies will give an idea of how climate has varied over the last several thousand years."

Gathering that baseline of how the climate has varied by itself is critical going forward.

"Many different lines of evidence are playing into our understanding of how humans have a role in controlling climate," he said. "It all rests on our understanding of the physics of the climate system and that carbon dioxide is a heat-trapping gas. We've known that for well over 100 years."

But the actual mechanism of how the climate system works and how much carbon dioxide will change the Earth's temperature, that's outside the scope of his study and a question for atmospheric physicists and atmospheric chemists, he explained.

His work will give an idea of what climate patterns emerged in the past.

"We have to understand the world can change very quickly all by itself, without us helping it along," he said. "Now, we're looking at rapid climate change in the American West, where there are tens of millions of people living."

NOTE: Andy Bunn is the Western Washington University assistant professor who is studying bristlecone pines. His name was incorrect in earlier versions of this story.

LEARN MORE

Additional information about the bristlecone pine and the research of Andy Bunn, assistant professor in Western Washington University's Huxley College of the Environment, is available online at:

• myweb.facstaff.wwu.edu/bunna to learn more about Bunn and his research.

• pbs.org, type "bristlecone pine" into the search window.

• ltrr.arizona.edu for The Laboratory of Tree-Ring Research at The University of Arizona.

• fs.fed.us/r5/inyo for Inyo National Forest, which is home to the Bristlecone Pine Forest high up on the White Mountains.

• nps.gov/grba to learn about the bristlecone pines in Great Basin National Park in Nevada, where Bunn will go in September.

• thepolarisproject.org for The Polaris Project, which aims to study the effects of global warming on the Siberian Arctic and educate the public about them. Bunn is one of the principal investigators.