What is a burl?

What is a burl?

Have you ever seen one of those wart-like growths on the side of a tree?

Big Oak Burl in Belmont, MA

Once upon a time, one of two things happened.

Injury: Look at the trees along your street where the branches were cut off.  If the trimming happened last year there will only be slight bulges at the fringe of where the branch was originally.  If the trimming happened decades ago, a bulging protective coating may wrap over where the branch originally was.  Maybe injury happened when the water in the tree froze during that week of -30ºF temperatures last year? Maybe one tree collided with another when it fell during a wind storm?  Maybe a cowboy wrapped some barb wire around the trunk? The story of a tree is journaled in its structure, and the layering of these bulges catalog its entire life, recording the waves and wiggles as it struggled to overcome.

Personally, I don’t classify the growth from injury as a burl, but wikipedia disagrees.

Infection: This is the growth that entrances me.  Bacteria and viruses are everywhere, and sometimes, maybe resulting from an injury or just the remnants of a hungry woodpecker, a sprinkling of these invaders enter the inner part of the tree. An eruption of erratic growth results. These are the bulbous wart-like growths you might see hanging off the side of a tree, and if you pull off the bark you often see ’pins’ which look like the sharpened tip of a pencil.  More dense or larger pins suggests you’ve really found something with a visually compelling story to tell.

slab cut cherry burl

The trick with working with burl is the unknown.  Each cut or sanding step might reveal a bark inclusion or void that requires you to revamp the entire piece. It might also reveal even greater complex beauty.   

A tree records every cut and bump as part of its physical structure, healing but never forgetting. I admire this.  This is also why I feel incredible pressure to portray the tree’s story as beautifully but honestly as my abilities allow — burled trees led adventurous lives. 

Historically, burl wood was used to construct the furniture of kings and queens, and you likely know someone that has an heirloom furniture piece incorporating burl. Given its incredible beauty, why don’t you see more of it? 

Burls are rare.  If you spend the day walking in the forest, you will likely find one, and to my continued surprise, where there is one burl there are often 10 nearby. Burls are an added stress to a tree, so while small 8” diameter burls are proportionally common, finding a 36” diameter burl is like finding a unicorn. If that massive burl is not rotten, then you’re witnessing Bigfoot riding a unicorn.  Sorry, I digress.

The second reason you hardly ever see furniture or works of art using burls is much more sad — lumber mills don’t want them. All lumber processed by a commercial-scale lumber mill must pass grade, meaning a limited number of knots, no bark inclusions, and limited usable sections of the tree’s wood. In this demented world where plantation grown pine passes grade while a rough cut oak boad will not, a board containing a burl causes an immediate failure. This rebounds back to the loggers, who are taught early-on to cut out the burls from any log and let them lay.

I hope this insight helps you smile in understanding next time you see one.

root burl with the boys

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