Steeped in Greenhouse Gas, Pine Trees Deviate

From the air, they look like a cross between unexplained Midwestern crop circles and the megaliths of Stonehenge. But these tall structures loom out of a forest.

Arranged in a loop, the 100-foot-high by 100-foot-wide assemblages are releasing carbon dioxide, a colorless, odorless miasma that wafts through the loblolly pines they encircle.

The 50-foot-tall pines, natives of the Deep South, are subjects in an experiment by scientists at Duke University who are using this engineered micro-climate as a kind of time machine to find out how these trees are likely to react as carbon dioxide builds up in the atmosphere and temperatures climb.

Since 1800, carbon dioxide levels have increased from 280 parts per million (ppm) to 370 ppm, a result of burning fossil fuels such as coal and oil. That level is expected to soar to about 560 ppm by the year 2050.

Carbon dioxide is a potent "greenhouse gas": It traps heat from the sun in the atmosphere, which in turn raises the planet's temperature. Carbon dioxide is also critical to the growth of plants. Without it, they cannot convert sunlight to energy.

The Duke experiment, called FACE (Free-Air Carbon Dioxide Enrichment), is funded by the U.S. Department of Energy and the Forest Service, which are also supporting similar forest projects in Wisconsin and Tennessee. Duke's FACE project, which began in 1996, is the largest and longest-running.

The Duke scientists selected loblollies as their subject because of their fast growth rate and widespread distribution and importance across the region.

Loblolly pines are to the Southeast what sugar maples are to New England or redwoods to California. In the Deep South, the word loblolly means a wet depression in the ground. Early settlers slogging their way through Southern bottomlands called the pines they saw there loblollies.

The loblolly shares the Southern pine ecosystem with the longleaf pine, the red-cockaded woodpecker and the nine-banded armadillo.

"Loblollies have provided us with a major timber resource in the South, served as wind breaks on our farmlands, even graced our homes as Christmas trees," said Ram Oren, director of the Duke project.

Researchers working in the Blackwood division of Duke Forest near Chapel Hill, N.C., the location of the experiment, have found that pines in the carbon dioxide-enriched rings are growing and reproducing much faster than other loblollies.

That, said Oren, is not necessarily good news for the loblollies themselves or the Southern ecosystems of which they are a part.