Have you ever wondered what those odd looking growths are on tree trunks or branches? If you are a wood turner you may already know and probably keep your eye out for them when you are driving or walking through the woods.
The burl tree. “Burl” is just one word for the abnormal growths protruding from all over the above tree. So how are these formed? Burls are made from abnormal proliferation of xylem production by the vascular cambium, or tree hyperplasia. Yeah. Cambium is the layer of actively dividing cells–they make the growth rings for each growing season–and it lies in between the xylem, or wood tissues, and phloem tissues. If the cambium cells divide more rapidly for a longer period of time in a highly localized area it creates this big lump sticking out of the tree. Viruses, bacterium, or fungus can be the root cause of the disruption that leads to over dividing cambium cells. Basically, a burl is a prettier, tree version of a wort.
Now, what makes the pattern of a burl really interesting (according to people with much more understanding of plant pathogens than myself) is the irregular orientation of the dividing cells. This means nothing if you have never seen the inside of a burl:
This is exquisite. The coloring. The pattern. The unique character. Two burls are never the same. Like snowflakes. Now you see the draw for wood turners? It doesn’t need to be turned into anything more than a simply shaped bowl and it looks amazing. To see something so simple and even ugly from the outside and watch a beautiful pattern unfold as the wood is gently carved away…it’s a therapy.
Don’t go cutting burls off trees though, unless the tree is already down. First, it can open the tree up to disease and decay–it is not the same as cutting off a branch. Tree branches grow differently than burls, and with them comes a kind of protection which makes branch trimming okay. Depending on the vigor of the tree, cutting off a burl could be a death sentence. Poor tree. Second, if you want to use the burl for wood turning it is best to cut at least 6″ of trunk above and below the burl. This will help keep the burl from drying out too quickly and can even add more character as colors change while it dries.
Gall or tumor are other words to describe the abnormal growths. Many plant galls are created by insects or mites. These are the little ‘bumps’ or round growths on the undersides of leaves and plant stems. Gall and burl can be used interchangeably, but gall is usually used to describe the insect induced growths on non-bark material (leaves and green stems). I don’t really care for tumor because it implies negativity. These growths don’t really harm the tree or plant. Galls are little habitats for the baby insects (larvae) that live inside them; burls are highly sought after, unique wood pieces. Whatever you want to call them (maybe you have a fun, made-up name too), don’t be alarmed if you find these in different shapes and sizes on the trees and plants in your yard.