Do any of your trees have knobby, wooden lumps? Those are called burls, and you might wonder whether they can harm your tree. The good news is that burls are usually harmless, and can sometimes actually be helpful! The team at Monster Tree Service of South Charlotte is here to answer the question: “What causes a burl on a tree?”
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What Are Tree Burls?
Burls are characteristic knobby wooden lumps that can grow on tree trunks and branches. They typically have a swollen, rounded appearance and a craggy bark pattern. Knobs can grow on pretty much any type of tree, but they are most common in poplars, elms, oaks, and cherries.
What Causes Tree Burls?
What causes a burl on a tree? The short answer is, we don’t really know! We know that burls form because of abnormal cell development in trees, but we haven’t pinpointed a root cause (pun intended). Experts theorize that trees might grow burls in response to hormonal imbalances, genetic mutations, or as a stress response, but the jury is still out. Scientists are still working out the exact cellular mechanisms that cause burl formation.
Are Burls Harmful?
If you see any tree burls, don’t panic. Burls are usually harmless and should not negatively affect your tree's health or development. In fact, burls can sometimes be beneficial as they tend to form over exposed vascular tissue, protecting the tree from fungal infection or insect damage. For example, burls can form over exposed parts of trees after tree pruning. You can think of them as analogous to scars on the human body.
Should I Remove Tree Burls?
Generally, we discourage tree burl removal. They don’t harm the tree, and removing burls can leave exposed tissue that’s at risk of infection and physical injury. You might think burls are unsightly, but they do more good than harm. Many arborists consider the presence of burls as a sign of a healthy tree that can protect itself.
Tree Burls Are NOT Burr Knots
Many confuse burls with burr knots, but they are not the same. Burr knots are masses of young roots that can start growing on branches or trunks. Unlike burls, which are basically normal wood in a weird shape, burr knots are immature root tissue that is susceptible to damage. Burr knots can be harmful to trees as they affect branch development and can also become infected, so you should remove them. Burr knots are extremely common on apple trees, but any tree can grow them.