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Word of the Week: Burl
April 15, 2020 by Haya Aldoori

Welcome to Word of the Week! Stay tuned for a new word each Friday to amp up your nature vocabulary!

Photo by Toronto Botanical Garden

Burl [burl] (noun): An abnormal rounded knotty growth on the exterior of a tree.

Beauty can always be found in the abnormal and a perfect example of this in nature is the tree burl! Often found on tree trunks, branches, and at the root crown, burls have a way of making you stop in your tracks and admire them.

A burl will form when bud growth cells develop in an abnormal way. As these dormant cells start dividing in many directions, they end up creating a rounded shape rather than forming the tree limb, which they originally had intended to grow.

The bark on the burl begins to look more coarse than the rest of the tree, and inside, the grain is twisted and more compact, which results in the production of a harder wood. Every once in a while, a dormant bud will become active, and you’ll notice a sprout from the burl itself!

The tree undergoing some form of stress is understood to be what stimulates the abnormal development of the bud growth cells. Some of these stressors might include bacteria, fungi, viruses, mechanical wounds, fire damage or a combination of factors.

You might be pleased to learn that, although a stressor is what stimulated this abnormal growth, a tree that has formed burls is not living in a harmed way and as such, removing the burl is not something that is necessary. In fact, trying to remove the burl can, more often that not, be more harmful than helpful to the tree!

It is important to note that a burl is quite different from a gall! Galls form along twigs and leaves, while burls develop on trunks, major branches, and at the root crown. Since burls are a part of the tree itself, the growth of the burl will occur at the same rate as the tree. Galls will kind of just grow at their own pace.

In High Park, we often notice burls that have formed on the willow trees that live by the waters.

Keep an eye out for tree burls on your next visit to High Park!

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