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What are Knots on a Tree Trunk Called?

Sometimes you see trees with large knots on their trunks or branches that look like deformities. I’ve seen these my whole life and never even considered if they had a name, what caused them, and what it meant for the tree. Let’s take a quick look at these tree knots in this article.

What are knots on a tree trunk called?

These large knots on a tree are known as burls and can range from fairly small and unnoticeable to so huge that they have essentially taken over the tree.

The picture below is of a massive red oak burl on a tree at my house. That thing has grown so huge that it has become a force to be reckoned with, I estimate this tree to be over 200 years old.

The circumference of the base of this oak tree including the burl was over 25 feet! 

About tree burls

Tree burls can be found on a number of different types of trees and range in size from small to very large. A tree with burls in most cases will continue to grow a long healthy life.

What causes burls to grow on trees?

Tree burls are caused when the tree undergoes some type of stress. Whether it is from a virus, mold or fungus, an injury, or insect infestation, it disrupts the trees growth hormones. This disruption in hormones is what causes the abnormal growth to begin that can then take on a life of its own, so to speak, and continue growing.

A burl is a way for the tree to isolate the injury or stressed area so the rest of the tree can continue growing normally.

Do burls kill trees?

While simply having a burl will not directly kill the tree, it can shorten the lifespan and diminish the overall health of the tree. The burl will continue to grow along with the tree and from the looks of my oak tree above, that burl was formed early on in the trees life and has probably been there for a hundred years or longer. That tells me that a tree can still live a very long life even with a giant burl growing out of the base of its trunk.

Does cutting a burl off a tree kill the tree?

Cutting a burl off of a tree poses a big risk to the life of the tree. If you want to harvest a burl from a tree it is best to take down the whole tree as the burl can reach all the way to the center of the tree. If you want to save the tree and not risk killing it in the process then it is best to not attempt it.

Are tree burls worth money?

Burl wood is sought after by furniture makers, and the right type of burl can be worth money. However you won’t get rich off of one, likely a few hundred dollars if you’re lucky.

If it’s a burl like the one on my oak tree then removing it will almost definitely kill the tree and it will have to be removed which can cost a small fortune. Especially if it’s close to a house or is very large.