Researchers at Michigan Technological University and Harvard have had a unique opportunity to study a 10,000-year-old buried forest, preserved virtually intact in sand and water.
Their findings were published today (February 21) in the Journal of Ecology. The spruce forest, preserved through a highly unusual set of circumstances at the end of the last Ice Age, was discovered by accident in a sand pit located in Michigan's Upper Peninsula. Besides its uncanny state of preservation, it's also extraordinary in its resemblance to certain modern forests.
"The processes have transcended time," said Dr. Kurt Pregitzer, the principal investigator and a professor in Michigan Tech's School of Forestry and Wood Products. "It looks like a typical white-spruce forest you could find today near Hudson Bay, where the tree line is advancing north. . . . We believe that the spruce trees that grew on this site were the first trees to colonize the sediment created by the retreating glacier."
While the spruce needles had fallen to what was once the forest floor, most of the trees were upright and intact, including bark and twigs. Mosses, spruce cones, and pollen were preserved on the ground below. Trees ranged from 5 centimeters to 50 centimeters (about 2 to 19 inches) in diameter, and the tallest ones topped 9 meters, about 30 feet. The oldest trees were about 145 years old when they died.
"Most of what we know about changes in forests has come from studies of fossil pollen, buried in ponds and lakes," Pregitzer said. "It's unique to find an entire forest standing, so you can see everything."
The buried forest has particular relevance today, said Dr. Patrick Martin, an associate professor in Michigan Tech's Department of Social Sciences. "The forest was growing at a time when climates were warming, and many believe that's what's happening now," he said. "It was also the time when people first came to this part of the world, so it gives us a snapshot of what the local environment was like then." Paleoindian artifacts, probably dating from the same era, have been found within a few miles of the buried forest.
Dr. Theodore Bornhorst, chair of Michigan Tech's Department of Geological Engineering and Sciences, described how the forest came to be preserved.
"It takes a real unusual set of circumstances," he said. ณThe trees were probably killed in standing water. Then they were quickly but gently buried many yards deep in sand carried in small streams running off a nearby melting glacier.
"If you saw those trees standing there, you'd say oh my gosh," Bornhorst added. "The trees still have little limblets, only 1 millimeter in diameter. The preservation rate is really astounding."
The scientists collected 140 tree cross-sections and studied an additional 70 trees at the 5-acre site. Because the forest was discovered below the water table, researchers had to do their work in a few days' time, while water was held back temporarily by dikes and pumps. After the scientists completed their study, the area was allowed to reflood.
The study was made possible by a grant from the National Science Foundation. In addition to Pregitzer, Martin, and Bornhorst, the article's co-authors are Drs. Glenn Mroz, David Reed, and Peter Laks and Shannon Brown of Michigan Tech; Dr. David Foster of Harvard; Dr. Jason McLachelan, formerly of Harvard and now of Duke University; and Douglas Stokke, formerly of Michigan Tech and now of Iowa State University.
The Journal of Ecology is one of the journals published by the British Ecological Society, http:// www.demon.co.uk/bes
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