Some burl info from Highlander 71:
"For those who don't know where a burl comes from, sometimes when a tree gets wounded or infected, its genetic material is disrupted, causing a deformation in the way the fibres grow. If you think of the way a tree normally grows, you can picture the fibres like strings of yarn, mostly long, straight, and parallel, whereas the fibres within a burl are more like a ball of yarn, all tightly wrapped around each other. A burl is not a sign of a dead tree, but rather a healthy and growing tree, as you can see by the specimen in this park."