Have you ever wondered about tree tumors?

Introducing the new
“Have you ever wondered?” segment.

In the summer of 2015, I found myself on a long drive after finishing a 32 day hike on the Appalachian trail. I met a ton of hikers on the trail who found inspiration in Bill Bryson‘s A Walk in the Woods and I wanted to know what it was all about–I downloaded the audio book to accompany me on my drive.

Image result for a walk in the woods book

Bill Bryson‘s book is incredible for a number of reasons. Bill is funny, relatable, and his writing is easy to follow (I could go on and on in praise of his book). He also did this thing. When I was on the trail, I kept wondering about all the things in the woods. I kept asking questions like, “who put these rocks here,” “what’s up with these mushrooms?” “what kind of trees grow like that?!?” Bill Bryson finished his hike on the Appalachian Trail, went home, researched all the things I wanted to know about and wrote them down in a book. Thanks to Bill Bryson, I had all the answers I wanted!

Of course, more than two years later, I’ve forgotten all the things. SO! We’re instituting the “Have you ever wondered?” segment to the H54H blog. Selfishly, this will force me to learn some of the things I want to know, AND you might learn something new!

Tree Tumors=Tree Burls

I’m always wondering about the tumor like growths on the trunks of trees. Almost every hike in the woods is paired with a sighting or two of a tree like this:

20171028_155139_HDR (1)

I often call these tree tumors, “tree cancer.” I just assume that the goiter like growth is a bad thing! That’s where our minds go right? It’s different so it must be bad.

I took to the internet and I found just enough information for our needs.

What are they?

What I have been calling “tree tumors” or “tree cancer” are most commonly called “burls.” Sometimes a tree will have one very large burl, but other times, several small goiters will appear in succession along a large branch or tree trunk.

What’s the cause?

Basically, no one knows. They do have some hunches: it could be caused by environmental stress, a bug infestation, and/or a bacterial, fungal or viral infection. One source says that that “a burl is a result of hyperplasia, a great proliferation of xylem by the vascular cambium.” This combined with “disordered orientation” creates the burls.


The short explanation: A specific part of the tree is producing cells more rapidly than other parts of the tree in an irregular fashion. And therefore…burls.

The longer explanation: From what I understand, the xylem transports water up through the tree. The xylem is what creates the “lines” we use to count the age of a tree.  Between the xylem and the phloem (which transports nutrients rather than water) is a thin wall of cells called the vascular cambium. The vascular cambium is the source of cell growth for the xylem and the phloem–when it goes into overproduction of cells that contribute to the xylem, the tree experiences localized, rapid growth. NOW, the cells are dividing rapidly, but they are also dividing irregularly, which is what creates the twisty nature of many burls.

**There is more to it than this, but I’m good with keeping it simple. Hopefully you are too. If not! Check the resources.**

Are they harmful?

Evidence says no? That seems impossible to me, but apparently burls are a common irregularity. The only complaint I heard is from people wanting to use the trees for timber. As of right now, control strategies have not been cultivated or implemented because they’re just not necessary.

Burl Bandits!

Something to know is that wood working artists LOVE the irregular patterns found in burls. Since the cells split irregularly, the wood’s typically straight lines curve, twist, knot and feather in unusual, visually appealing patterns. People kill for these burls! They are prized possessions and can be sold for a ton of money!

That being said, there are a couple of problems:

  1. Damage in Removal: Burls may not cause a threat to the tree, but when they are removed, it creates a wound. If the tree’s immune system is strong, it will often heal over time. Unfortunately, the wound often gets infected and causes the tree to die. Humans barely ever use nature for self-serving purposes, so it’s probably no big deal to steal a couple burls from a couple of trees…..
  2. Actual Burl Bandits: This part makes me laugh a little. Many tree wardens experience “burl theft” in their area of jurisdiction. Apparently this happens a lot? In 2012, a park in North Carolina lost two burls from an old sugar maple that could have been sold for ~$120,000.

Someone should tell convenience store robbers
that they’re in the wrong business. 

I do love the artistic representation of tree burls in the world, but I think I’m on the side of the trees on this one. I guess if you’re in search of a burl for your artwork, make sure to get permission from the land owner. Stealing is bad and maybe nature isn’t here just for our own personal agenda. In addition, when removing large burls from ancient trees, consider the impact removal could have.

Have you ever wondered about tree tumors??
Whelp, wonder no more!

Sincerely yours,

The Mitteneers


  1. Burls for kids! Wonderopolis: “What is a Burl?”
  2. USDA Forest Service: “The Biology of Burls
  3. Boston Globe: The Tree Lover’s Interest
  4. USDA Forest Service: “Burls, Galls, and Tumors”



  1. A new word for me also with meaning of the word. Now I have to do is to find a way to use the word.
    I was taught by Saint Joseph religious, one of the sisters would say, “ when you learn a new word, use it in sentences 10 times and you can call the word yours. “
    Thank you, for adding to my vocabulary.

Leave a Reply