Trees sometimes develop unusual growths known as burls, which often spark curiosity due to their distinctive appearance. This article explores what burls are, how they form, their impact on tree health, and their unique value in woodworking.
Defining a Burl and Its Appearance
A tree burl is an abnormal, rounded outgrowth found on a tree’s trunk, branches, or roots. These growths are characterized by their gnarled, distorted, and often bulbous shape. They vary in size from small bumps to massive formations, always presenting an irregular, lumpy exterior.
Burls are covered by the tree’s bark, but their unique internal wood grain becomes evident when cut open. This grain is highly complex, featuring intricate swirls, knots, and “eyes” that differ dramatically from the typical straight grain of surrounding wood. This internal chaos makes burl wood distinctive and visually appealing.
How Burls Form
Burl formation is a tree’s response to stress, injury, or infection. Several factors contribute to these abnormal growths. Physical damage to the bark or cambium layer, such as from pruning wounds or impacts, can trigger burl development.
Infections play a significant role, with fungi, bacteria, and viruses often disrupting the tree’s growth hormones. For instance, the Agrobacterium tumefaciens bacterium causes crown gall, leading to burl formation by stimulating abnormal cell growth. Insect infestations also contribute to this stress response.
Environmental stressors like drought, extreme temperatures, or certain soil conditions can induce burl growth. Burls can also arise from the uncontrolled growth of dormant buds, where undeveloped tissues proliferate abnormally instead of forming typical branches. Genetic predisposition can also make certain tree species, such as maples, oaks, and redwoods, more prone to developing burls.
Burls and Tree Health
Despite their unusual appearance, burls are not harmful to a tree’s health and do not signal a disease requiring intervention. A burl represents a tree’s defense mechanism, forming a protective callus over a wound or area of stress. The dense, contorted wood within a burl helps to compartmentalize injuries and prevent the spread of decay or pests.
While burls are abnormal growths, they do not compromise the tree’s structural integrity. Attempting to remove a burl can be more detrimental to the tree than leaving it intact, as it creates a large, open wound that increases the tree’s vulnerability to further infection or pest infestation. Therefore, it is advisable to allow burls to remain on the tree.
The Value of Burl Wood
Burl wood is highly prized in woodworking due to its unique aesthetic qualities. The chaotic grain patterns, intricate swirls, and characteristic “eyes” found within burl wood result from disorganized cell growth. This distinctive figure is unmatched by regular wood grain, making each piece of burl wood unique.
Artisans and woodworkers seek out burl wood for creating decorative items, furniture veneers, and artistic sculptures. Its rarity, combined with the challenges of harvesting and processing the dense, interlocked grain, contributes to its high value. Burl wood is known for its stability and resistance to warping or splitting, which makes it suitable for detailed craftsmanship and turning projects.