Burls are usually a rounded lump or protrusion located on the stem, branch, and, on rare occasion, the roots of trees. They are dense. These outgrowths can range in size from small to large and can have a rather unique look to each one.
While they may look cancerous to the tree, burls are benign and are a response growth to outside stresses.
When trees are stressed, they create chemicals that encourage unusual cell growth which form burls. These chemicals cause multiplied cells to divide and form small fibers that all grow in different directions. This gives burls a unique appearance and makes the wood very strong.
Burls can be very hard to break with the contorted grain. One of the main benefits that they offer to trees that produce them.
Stress that causes burls varies. It can be injury or attack from fungus, bacteria, or virus.
Burls rarely cause harm to a tree though. Usually, they are a solution to stress. If the current state of your tree causes discomfort, reach out to an ISA-Certified Arborist.
Identification
Burls can occur on any tree, but some species develop them more than others. Including maples, oaks, elms, and willows.
A burl’s wood grain will be wavy, curly, or have a bird’s-eye effect both in the burl and affecting the immediate surrounding wood. A bird’s eye is the result of an aborted adventitious bud.
Adventitious buds are abnormal buds that grow in areas of a plant that don’t have meristem tissue. Which is responsible for the primary growth of the plant. These buds help replace plant parts they grow on. Epicormic sprouting on trees start from adventitious buds.
Similar irregularities in the tree like incipient cankers and galls may contain bark rot, twig knots, and even boring-insect damage.
Wood
Some avid woodworkers love to work with burls due to their unique structures. When it comes to lumber values burls are not as highly sought.
For veneer logs, burls are not sought after but they do not stand out more than the standard defect.
For factory logs, if the burl can be identified correctly it is technically not a degrader. However, in factory setting all features that look like burl gets categorized as such.
For construction logs, the disturbance in the grain caused by the burl degrades the value of the log.
Article source and photo credit: Texas A&M Forest Service
