Shawnee New-Star Sunday October 1st 2017 Becky Emerson Carlberg You've seen them.   While hiking through the woods or driving down the road, this tree catches your attention.   Something crazy is growing on the trunk, at its base or along a branch; an impressively large weird lump, covered in bark.   Your imagination kicks in and you [...]

Shawnee New-Star Sunday October 1st 2017

Burls on Cottonwood

Becky Emerson Carlberg

You've seen them.   While hiking through the woods or driving down the road, this tree catches your attention.   Something crazy is growing on the trunk, at its base or along a branch; an impressively large weird lump, covered in bark.   Your imagination kicks in and you think 'that looks like a dog face.' Your rational brain then takes over and you realize this is not normal could it be contagious?  Out comes the phone, a few pictures are taken and you leave.

You just encountered a burl, or burr if in the United Kingdom. The trunk or branch is rather deformed; exciting for some, intimidating for others.   Burls can be humongous or tiny.   They probably began life as a gall, those large round marble sized smooth beige-colored balls that fall off oak trees in late summer.   Galls are the result of interactions between the tree and the tiny wasp that laid a miniscule egg on the tree branch or leaf.   The tree deposits layers of tissue around the egg which hatches into one larva that eats until it pupates into an itty bitty wasp.   The wasp emerges and the gall eventually drops to the ground where you step on it and nearly break your neck.   In woody twigs it may take a gall wasp over 2 years before it is ready to face the world.   Other than unsightly, these little wasps do little harm to the trees.

My Black-Eyed Susan patch began having galls form on the stems.   Usually only two or three within the group, but definitely an insect had found just the right host for its eggs.   The wild blackberry began exhibiting swollen lumps on a few woody vines and the culprit could be Crown Gall.   Crown Gall is caused by the bacterium (the newer updated Rhizobium radiobacter or the older more commonly known scientific name Agrobacterium tumefaciens) that has cleverly weaseled its way into the plant through a wound or cut, which usually happens at the crown of the plant.   The crown is where the stems join the roots, or in trees, the place branches sprout from the trunk.   Once inside the plant, the bacteria operates from its safe house and discharges tumor-inducing plasmids (Ti plasmids) charged with DNA determined to take over certain plant processes.   In the case of trees, the plasmids direct production of special amino acids and growth regulators that form the burl.

Each burl is unique, different and usually covered in bark.   When sliced open, the wood grain is curved and twisted into fascinating designs within the burl.   The burl wood grows faster and is actually softer than the surrounding wood, but the conducting tissues that move food and water inside the burl are still functioning.   Although the burl began as a gall, not always would there be an insect responsible.   Genetics, fungi, bacteria or viruses transmitted by insects may be at play.   Healthy trees use a host of defenses to protect themselves against invasion since they can't run away or visit the doctor. Having their genes manipulated to form burls is amazing but scary.

Burls at the Wildlife Expo

In managed forests, burls are cut out and left for the termites. Professional woodturners scoff at this and say burls often reach deep into the tree and this type of cutting damages the tree's health.   The specialty woodworkers love burls for their beauty and salability.       Different species of trees produce various patterns such as eyes, flames, curls and spalted, a condition when the wood is colored by the action of fungi.   Maple, ash, cherry and walnut burls often have eye patterns, while mulberry, birch and sweetgum burls have swirls.   Burl wood is used for inlays, veneers, box lids, handles and turned products.

The fascinating cottonwood on the ground in Horsethief Canyon outside Perkins was basically an assembly of hundreds of burls with a little bit of normal tree here and there.   Cottonwoods seem quite adept in forming burls which are turned into expensive burl bowls. That makes sense.   Burl means forest or cup bearer. The day I decided to search for a tree with a burl was rainy.  After taking pictures of everything but a burl, the umbrella was left on the porch to drip dry.   An hour later I brought the brolly inside and propped it against the closet door.   Cleo the cat took an immediate interest in the waterproof parasol.   I bent closer to see what she saw.   A brilliant yellow very fuzzy caterpillar was making its way from one rib to another.   Outside the caterpillar, umbrella and I went, to the cottonwood where it happily crawled onto the tree.

The colorful American Dagger moth caterpillars feast on the leaves of oaks, maples and cottonwoods.   This juvenile lemon yellow member of the Owlet moth family will eventually turn into a gray moth with forewings decorated in tiny eye-like designs.  The moth will join others as invaluable pollinators that live in the eastern part of North America.   If you have the insane idea to pick up the caterpillar and pet it, be aware the groups of long dark hairs embedded within the yellow bristles at the tail end can break off and penetrate your skin.   If you are a sensitive type person, an itchy rash may result.

American Dagger Moth caterpillar

I stared at my cottonwood as the flashy caterpillar disappeared from sight. That tree barely survived Tornado Bob.   Half the tree was blown away and the rest was rocked back and forth, breaking up the sidewalk to the house, yet it remained standing as did our house.   The cottonwood has somewhat recovered, its trunk straight but no bulging burls.   Not to worry.   While at the Wildlife Expo last weekend, I noticed by the bird feeding station that some of their post oaks had bark-covered lumps of various sizes. Do they not realize they could be sitting on a collector's gold mine many years from now when the trees reach maturity?   Post oaks can live 250 years.