Scientists are scratching their heads over strange patterns cropping up on moss-covered logs in parks in the region.

Biologists first discovered symmetrical, bulls-eye patterned bare patches on liverworts, a plant closely related to moss, growing on fallen pine trees in the Great Smoky Mountains National Park last winter.

While biologists first thought snails were to blame, a closer look showed a lack of zigzag patterns, which would have suggested snail feeding patterns.

Other scientists have speculated millipedes may be to blame, but tests remain inconclusive.

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A few weeks ago a biologist from the U.S. Geological Survey found similar growths on cliff faces — not pine logs — in the Big South Fork National River and Recreation Area on the Kentucky-Tennessee border northwest of Knoxville.

Similar patterns, resembling miniature crop circles etched into the soft green liverworts, have been observed in arctic regions of Greenland and Canada, but never as far south as the Smokies, which straddle the North Carolina-Tennessee border.

Chuck Parker, the government scientist who found the patterns in Big South Fork, said finding the growths outside the Smokies and on a surface other than pine trees is particularly interesting.

"There's a real fascination here," Parker said. "I'd love to figure it out."

Another group of scientists first spotted the circular formations in the Smokies while attempting to document all living things in the park.