A burl results from a tree undergoing some form of stress. It may be caused by an injury, virus or fungus. Most burls grow beneath the ground, attached to the roots as a type of malignancy that is generally not discovered until the tree dies or falls over.
Burls are caused by fungi, insects or bacteria and create interesting wood textures on the inside of the growth. Burls do not kill trees and can usually be removed without harming the tree

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