Jonathan is going to make tables and wall art out of the slabs and remaining section. He knew in advance that artists use burls, but wasn't sure what exactly they are. So I received a request from him to post information about burls.
A burl is is a tree growth in which the grain has grown in a deformed manner. Burls are found in the form of a rounded outgrowths on tree trunks, branches, or roots.
A burl can develop when a tree undergoes stress such as an injury, virus or fungus. Most burls grow beneath the ground and are caused by insect or mold infestation. When burls form on roots, they appear as a type of malignancy that is generally not discovered until the tree dies or falls over. Such burls sometimes appear as groups of bulbous protrusions connected by a system of rope-like roots. Almost all burl wood is covered by bark, even if it is underground.
One of the largest burls ever discovered was found in Vancouver Island, Canada. Engineers were surveying a timber track for future logging roads when they found the burl on a 35 year old spruce tree. The tree was 271 feet tall and six feet in diameter at the height that the burl was cut. The burl, which weighed 44,947 pounds (22 tons) had a circumference of 45 feet. Because the burl was caused by various pathogens that attached the tree, a layer of fiberglass was molded over the burl to protect it from further decay.
Burls yield a very peculiar and highly intricate wood, prized for its beauty and rarity. It is sought after by furniture makers, artists, and wood sculptors. Although burls are well sought after, their wood is very hard to work with hand tools. However, this "wild grain" makes burl wood extremely dense and resistant to splitting, which made it valued for bowls, mallets, mauls, furniture, clocks, and wooden pegs.
Because of the value of burls, ancient redwoods in National Parks in Western United States have recently been poached by thieves for their burls, including at Redwood National and State Parks. Poachers often cut off the burls from the sides of the trunks using chainsaws, which exposes the tree to infection and disease, or fell the entire tree to steal burls higher up.
Another nice burl is shown below, It is also a spruce burl that measures 50 inches high, 40 inches wide, and 42 inches deep.
Only a very small percentage of trees produce burls. Some species are more vulnerable. Plus, multiple trees in a particular area may have burls since they are likely to be attacked by the same pathogen.
A burl bowl...
Just because a tree has a burl does not mean that the tree is not healthy. In fact, many of these trees can go on to live for decades. In some cases, new trees can sprout out of burls. When this happens, the offshoots can grow large enough to cause significant stress to the tree, which can cause damage or even kill the "parent" tree.
Roger Griffith, from http://commons.wikimedia.org/wiki/File:Burr_section_on_Larch.JPG
Dar-Ape from http://commons.wikimedia.org/wiki/File:Tree_with_many_burls_%28Olympic_National_Park,_Washington,_May_2008%29.jpg
DoggerelBlogger from http://en.wikipedia.org/wiki/File:Doggerel_bowl.jpg