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Ancient Wood Uncovered

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Published on: Jan. 2, 2003

cases, entire oaks were buried so quickly and preserved so thoroughly that the bark is still intact. Streams have not only buried whole trees but also portions of the forest floor. Ancient forest floor litter can be found sandwiched between layers of alluvial deposits. Twigs, leaves, acorn caps, hickory nuts and husks and walnuts are common in the buried litter.

One section of Medicine Creek in Putnam County yielded a fantastic find. Specimens of two coniferous tree genera, spruce (Picea) and fir (Abies), that dated to about 11,200 years before present. Today, boreal forests grow in the northern lake states and Canada, and are composed of species such as white and black spruce, white cedar, balsam fir, and jack pine. Shortly after the last glaciers retreated from the Midwest, boreal forests grew here, too. It is amazing that trees from boreal forests are still present in Missouri, providing stream habitat and structure.

As the glaciers receded further north and temperatures warmed, eastern deciduous hardwoods began to define the composition of Missouri's forests. An oak of the white oak group, carbon-dated to about 13,000 years ago, is the oldest wood we have found at Medicine Creek. The finding suggests that temperate hardwood forest species were commingling with species from boreal forests between 11,000 and 13,000 years ago.

Streams and lakes are the best places to find ancient wood because the low oxygen levels of subterranean and aquatic environments inhibit wood decay. Logs lying on the ground, for example, decay somewhere between nine to 80 times faster than those deeply buried in waterlogged soil or submerged in water. We've found that the density of ancient oak wood is half the density of modern oak after about 6,500 years underground. In contrast, modern oak lying on the forest floor loses half of its density through decay in only 40 years.

The decay processes that act on ancient wood impart unique characteristics that can be used to help identify it. Large logs of some ancient wood, usually more than 8,000 years old, are easily broken and fracture smoothly across the grain. Ancient wood can contain six times more water than wood and often has a sponge-like texture,. The wood is heavy when wet, but after drying out, it is noticeably lighter than modern wood and often falls apart.

Subtle differences between the weathering of ancient and modern wood create, when dry, a distinctive pattern

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