San Antonio Natural Area Parks
News & Articles

HOME

Wood Burls
Peggy Spring
Education Coordinator

Burl Tree
Photo by Don Pylant, 2007

The lumpy, abnormal swelling on the tree in this picture is commonly known as a burl. Burls are formed when tree cells divide and grow excessively and unevenly. “The uncontrolled growth of tissue in a burl leaves a hemispherical bump on the tree without typical growth rings and wood structure.” (1)

The precise cause of burls is unknown. The following quotes contain some of the theorized causes. “ They may be the result of injuries, burns or continued irritation of some sort. In most cases the cause in not fully understood.” (2) “A burl is a wart-like, deformed growth on the trunk or root and sometimes even the branches of a tree, caused by an injury to, or and infection in the tree just under the bark, or the existence of an unformed bud (or cluster of buds) which has all the genetic material necessary to grow a full branch, or even a whole tree, but which for some reason did not grow properly.” (3) Whatever the cause, the tree is left with an unusual, eye-catching bump.

the tree just under the bark, or the existence of an unformed bud (or cluster of buds) which has all the genetic material necessary to grow a full branch, or even a whole tree, but which for some reason did not grow properly.” (3) Whatever the cause, the tree is left with an unusual, eye-catching bump.

(Burl) growth follows the contour of the original deformity, producing all manner of twists, swirls and knots in the wood fiber. Usually, this results in wood that has a spectacular pattern that can be used to great effect in woodworking, and sometimes it is also accompanied by the creation in the burl of dormant buds which create "eyes" that make the burl even more spectacular when worked.” (3)

Years ago, burls were considered a nuisance to sawmills as they made cutting of logs difficult. The timber cutters removed the burls from the logs and left them to rot on the forest floor. Now they are sought after for their spectacular grain pattern and natural beauty.

Burl Tree
Burl on Live Oak

Take a look at the trees in your neighborhood or park or Natural Area. You may be surprised how many burls you find now that you know what those lumpy things are. They’re part of what makes each organism unique and they contribute to the amazing diversity of the natural world!

1. 2. 3.

References
Urban Forestry Newsletter. Summer 2005.
Burls. University of Saskatcheewan Extension
Burls. Author unknown.

 

Peggy Spring is the Natural Areas' Education Coordinator for the City of San Antonio Parks and Recreation Department.


design by woodland company | sponsored by Friends of Friedrich Park