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Library program demonstrates the history hidden in tree rings

Sunday, August 12, 2007

Trees of the same species growing in the same region will create similar patterns of growth rings.

Slices from a spruce tree planted in 1939 were stacked against the Hirsch Community Room wall of the Cape Girardeau Public Library on Saturday for a presentation and hands-on workshop by Cape Girardeau resident Steve Lowes. The slices, referred to as "tree cookies," were more than a foot in diameter and came from a tree cut down in Lowes' yard.

Lowes' educational project with his granddaughter, 7-year-old Gwynn Rice, blossomed into a library program when they shared their findings with library staff after having dated the tree by its rings. The two marked the family history onto the wood, corresponding dates with rings.

A shiny three-foot tree cookie sat on an easel at the front of the room, illuminated by a brass light for ease in detecting the red markings, representing 10-year increments. It was provided for the presentation by Missouri Department of Conservation Forestry Regional supervisor Joe Garvey. Lowes explained that the sliver of oak had been polyurethaned, making the rings easily visible. Working with raw cookies, the class had magnifying glasses to better detect the rings.

Although slivers of the tree that had been cut down were no longer living, Lowes explained that by using increment bores, tree drillings of about a pencil's width, scientists can study the patterns of the rings from old trees without killing them.

Robert Jones, 3, and Stephen Jones, 6, of Cape Girardeau both attended the presentation. Stephen had the activity all figured out.

"First we will write down its name and then we're also going to write down all my family. We can do it on both sides." He'd watched his dad cut down a tree limb before but had never seen a slice of tree like the one in front of him.

Their mom, Meri Jones, a homeschool teacher, came to the program because she believes in offering a variety of learning opportunities to her children.

Ample space was provided for marking family history onto the tree cookies program participants received. Saplings from the tree that had been cut were available to take home.

Lowes geared the program toward all ages, with hands-on instruction that deciphered individual cookies. Linda Dedert pointed out that her cookie had two rings at the center. Several explanations were offered from other participants and Lowes, who believed it was a damaged spot.

"Knots are usually an indication of a branch but can also indicate an infection from insects," Lowes said.

Dedert, a regular library patron from Cape Girardeau, said she attended the program because she was "here at the library."

"They're real inventive when it owes to bringing in new programs," she said. "The main thing I learned was how the limb showed up visually on the tree cookie."

Dendrochronologists extract history from trees. Dating the tree by ring width, whether it is wide or compressed, will indicate climate at that time in history. If the weather was rich in sunlight and rain, the rings will appear thick and well-defined. A drought will result in small rings that are close together. Frost rings, appearing crushed together, result from harsh, cold conditions.

Along with ring chronology, matching the ring data with other existing legends, written manuscripts and scientific research will make a best guess as to how old the tree is, especially for trees that are extremely old. Lowes said an example of the best-guess technique where tree rings have helped estimate a date is the eruption of Mt. Etna in Sicily in 42 B.C. The volcano's expulsion of sulfurous gas caused the sun to grow pale for many weeks, resulting in a temperature drop recorded by frost rings for four years.

Lowes also explained that trees of the same species growing in the same region will create similar patterns of growth rings. By matching the growth ring patterns in living trees to the patterns in older trees or timbers from historic houses, scientists can count back in time and create a tree-ring timeline, centuries long, that can be used to date wooden objects. He said tree rings may be able to tell the future by the rapid growth in bristle cone pines growing faster and that studies suggest the trees are reacting to the increase of carbon dioxide in the atmosphere.

cpagano@semissourian.com

335-6611, extension 133


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