For tree lovers and woodworkers, there’s beauty in a burl

This undated photo shows a tree with a trunk burl in Rosendale, NY. The fat burl developing on this tree, which does it little or no harm, is valued by woodworkers for its swirling grain. (Lee Reich via AP)

As you glance up into tree limbs, perhaps searching for some sign of spring in a swelling flower bud, your sight might be arrested by fat, rounded growths on the bark.

 

On some trees, these hard, woody outgrowths burls stand out on an otherwise clear trunk like a goiter. On other trees, the whole trunk might be covered with them.

If you’ve never noticed these growths before, don’t be alarmed. These growths cause little or no harm to the tree.

WHAT MAKES A BURL

That said, burls might — just might — indicate that the tree has been under stress. Various All sorts of things have been implicated as the cause of burls. For instance, a burl could grow in response to a limb rubbing against the bark, chewing by insects or some other physical injury. Perhaps the tree experienced or is experiencing environmental stress temperatures too cold or too hot, not enough food or sunlight, for example.

Diseases have also been held responsible for burls. However, no pathogens are found inside burls when they’re cut open. Still, a pathogen could have induced a burl, and then skipped on to other adventures.

We could also blame genetics, because some tree species are more prone to developing burls than others. Redwoods are renowned for their burls, which are often sold as souvenirs.

ODD STEM GROWTH

We do know, though, how burls develop. Along any stem are buds that can elongate to become shoots, and each of these shoots has buds that can become shoots themselves. Obviously, not all buds on a plant stretch out; some remain dormant, at least for a while.

In the case of a burl, instead of dormant buds expanding into straight shoots, they grow inward, twisting and turning under the bark and never emerging as branches.

On the rare occasion when a shoot does elongate from a burl on a mature tree, the shoot usually expires from lack of sufficient light. Interestingly, redwood burls frequently sprout when cut from the tree and placed in a pan of water, almost as if the water reminds the cells that they can be shoots. On a tree, though, cells within a burl generally just keep dividing with no obvious purpose or benefit to the tree.

BEAUTY WITHIN

Benefit to us humans is another story, though. Cut open a burl and instead of straight grain you find waves and swirls of wood, marbled and feathered wood, perhaps some “eyes” staring back at you. Woodworkers lust for burls, especially for turning on a lathe, where the appearance of the swirling tissue need not be constrained within the straight and sharp-edged geometry of sawn lumber. Burls are also frequently sliced into veneer.

The beauty within a burl and theories for what causes them could prompt you to try to induce them on a tree. Yet no one has been able to reliably do so. So burls are harvested from trees on which they naturally formed. Because harvesting a burl can leave a large scar, cut burls only from trees that are being or have been cut down for other purposes.

 

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