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BURNS, Ore. - Questions about global warming keep rolling through our national psyche like tumbleweeds. Now scientists at a remote research station on the high desert of eastern Oregon say some of the answers are out on the range.

Rangelands, including grasslands, cover about half of the Earth's land area and account for a third of all plant life. But we don't know much about how they fit into the global climate change puzzle, says Tony Svejcar, a scientist at the Eastern Oregon Agricultural Research Center here.

Oregon State University and the U.S. Department of Agriculture's Agricultural Research Service operate the isolated research center.

"The role of oceans and forests in the global carbon cycle has been studied, but rangelands have received relatively little attention," said Svecjar. "Scientists have been unable to account for a substantial amount of the earth's carbon. Rangelands (including grasslands) may hold the key."

You probably know the global warming scenario: Humans and other animals produce carbon dioxide, plant life consumes it, and the balance of this exchange equation apparently is changing.

There seems to be an increasing amount of carbon dioxide in the atmosphere due in part to an increasing world population that burns fossil fuels. Researchers don't know exactly what this means in terms of long-term climate change but many believe our atmosphere is warming.

There also are suggestions that the world's climate may change as a result of increasing C02 whether there is significant warming or not. The timing of precipitation is one of the climate factors that could change.

About 35 miles west of the little ranching community of Burns, Svejcar and other scientists are taking part in a national attempt to learn more about the rangeland-carbon dioxide relationship and about how precipitation timing affects plant life on rangelands.

Their experiments involve space-age instrumentation and sheds that look kind of like picnic pavilions.

A device called "the Bowen ratio-energy balance unit" looks sophisticated with its digital readout and solar power panels. But it makes a fairly simple, though precise, measurement.

"It measures the difference between the carbon dioxide content of the air at two different levels - one just above the plants and the other about three feet above the canopy (of rangeland plants)," explained ARS scientist Raymond Angell.

"It can detect concentration changes as small as one part per million," Angell said. "This, in turn, can tell us whether CO2 is being drawn into the plant life or being released into the atmosphere. There are 11 more of these devices spread around the western rangelands at other ARS facilities, where they cumulatively collect about 12 megabytes of data per week."

Angell notes that this large-scale measurement is supplemented by small-scale, one-meter plastic chambers that can be placed over individual plants. Together, they present a picture of rangeland carbon cycling.

On the low-tech end of the spectrum are the five sheds that resemble picnic shelters. They are open on the sides and fitted with sprinklers.

Svejcar said that one of the theories about global climate change is that climate fluctuations are becoming more pronounced.

"The climate in the high desert has always been extremely variable," he said. "This area has an annual average rainfall of 11.5 inches. But in 1993 we recorded a record high of 21.6, and the very next year recorded a record low of 5.6 inches."

A historical blip or the beginning of a trend?

"What we may see in the future is not necessarily a reduction in rainfall but altered rainfall patterns," Svejcar speculated. "Rainfall patterns have shifted in the past and no doubt will in the future."

He explained that the five 20- by 40-meter sheds simulate different precipitation patterns. Each shed has three different rainfall environments, one with more rain in winter, one with more in spring and the third representing an average distribution based on rainfall records.

"As a control, we're tracking an uncovered plot just outside the shed," said Svejcar.

The experiment measures plant growth, distribution and diversity under these different rainfall conditions. OSU range scientist Rick Miller is leading the study of plant composition, such as increases and decreases in grasses and shrubs under various conditions. "We're also looking at plant physiology - for example, how different conditions affect photosynthesis," said Miller.

"We know this experiment isn't perfect," said Svejcar. "The roofing on the sheds reduces the amount of sunlight that reaches the plants by 40 percent, and we have to devise strategies for keeping rabbits from eating plots that are green when adjacent rangeland is dry and brown. But we're hoping to run the experiment for a minimum of five years.

"Forests certainly receive the lion's share of public attention," he said, "but the arid lands may also be critical to the global climate picture. These experiments may help give us a better idea of just how critical they are."