DMC - History - Antarctic Forests Reveal Ancient Trees

November 5, 2004

260-million-year-old leaf

A quarter-billion years ago, forested islands flashed with autumnal hues near the South Pole - a polar scene unlike any today, researchers say.

Geologists have discovered in Antarctica the remains of three ancient deciduous forests complete with fossils of fallen leafs scattered around the tree trunks. The clusters of petrified tree stumps were found upright in the original living positions they held during the Permian period.

Some stumps were even poking up through the snowfield in the Beardmore Glacier area, said geologist Molly Miller of Vanderbilt University.

"These were not scrubby little things," Miller said. "These were big trees."

Some are estimated to have attained heights of 80 feet (24.6 meters), based on their trunk diameter.

250-million-year-old tree bark

Miller, Tim Cully and graduate student Nichole Knepprath came upon the three stands of the lost forests in December 2003. Knepprath will be presenting their discovery on Sunday at the meeting of the Geological Society of America in Denver.

Unlike any trees today, the long-extinct Glossopteris trees lived in stands as thick as almost a thousand per acre just 20 or 25 degrees from the South Pole, a latitude at which they received no sunlight for half the year.

As for what they looked like, Glossopteris tapered upwards like a Christmas tree. Instead of needles, they had large, broad lance-shaped leaves that fell to the ground at the end of summer. It's unknown if the leaves turned colors, said Miller, but it seems likely.

"These are early, early deciduous trees," said Miller.

They lived at a time when the Antarctic climate was much warmer - although the trees still had to survive an extreme light regime of low sunlight half the year and darkness the other half.

"We don't have any modern analogues to these polar forests," said paleobotanist David Cantrill, curator at the Swedish Museum of Natural History in Stockholm.

The fossilized tree rings in the Glossopteris trees reveal that they grew steadily each summer and abruptly stopped for winter, as if a switch had been thrown.

"They probably reacted to light (rather than temperature) to switch off," said Cantrill.

Modern deciduous trees slow down and then stop growing when cold weather moves in.

Although fossil trees from the Permian have been found before in Antarctica, this is the first time whole stands of trees have been discovered, said Cantrill. With stands, researchers can now measure the spacing and calculate sizes of the trees to glean information about how much sunlight and energy was available - valuable and rare clues to the Permian climate.