Wednesday, July 18, 2007

Growing Knees

More than any other year, the Bald Cypress knees at the Audubon Center at the Francis Beidler Forest are growing! Visitors often come in and ask what is gnawing or rubbing on the spikes in the swamp.

The spikes are projections from the cypress trees' roots called knees. Nobody knows for sure what they do, but the theory that appears to be most accurate is that the knees help anchor the large Bald Cypress trees as they grow in the often saturated soil. If the soil could be scraped away, one would see intertwined all the horizontally-growing roots from all the various species of trees. The cypress knees grow vertically from the cypress roots through the horizontal tangle of roots. If one takes note of fallen cypress trees in the swamp, one would see that the trunk often breaks near the ground, but all of the roots remain below the soil. This is not the case for trees (pines and hardwoods) that grow on higher, drier sites.

Back to the growing! The knees in the image appear worn and orange on the top. Although beavers have appeared this year and chewed their share of young cypress trees (see image), the knees have not been attacked by beavers. The Bald Cypress bark is naturally orangish in color. Unless bark has been stripped from the trunk by the wind or nest-building animals, it appears a dirty gray due to exposure to the elements. Therefore, the knees in the images are showing orange because they are growing and not because an animal is gnawing or rubbing on them. Knees usually grow to a height comparable to the average depth of the water (deeper water, taller knees). We're not sure why so many knees are growing this year.

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