I would like to remove a burl from one of my fir trees. Can I do this without causing harm to the tree?
I was unable to find any information on the incidence of burls (lignotubers) on fir trees (Abies), but I did locate information about redwood (Sequoia sempervirens) burls from a version of The Sempervirens Fund website which is no longer available:
About Redwood Burl
by Chris Brinegar, PhD
“The swollen tissue at the base of some redwood trees is commonly known as a “burl” although scientifically it is referred to as a lignotuber (from the Latin for “woody swelling”). All redwoods have lignotuber tissue but not all have large visible burls. Lignotuber tissue is derived from cells that exist in the tree’s seedling stage and then proliferate near the base of the tree as it ages. Buds form within the woody burl and remain dormant until stimulated to grow by damage to the main trunk (usually by fire or logging). The resulting shoots grow rapidly using carbohydrates stored in the surrounding cells and minerals transported through the parent tree’s root system. Lignotubers can also form their own roots.
Lignotubers are responsible for vegetative (clonal) reproduction common in redwoods. Without this mode of propagation, the redwood forest would appear far different than it does currently. The second and third-growth redwoods in our coastal forests were generated vegetatively after 19th and 20th century logging of the original forests. If redwoods were solely dependent on reproduction from seed, their numbers would only be a small fraction of what we see today.
Most people think of burl as the “sliced redwood” sold in gift shops and roadside stands, but they do not realize that many of these burls were obtained illegally. There is a growing black market for burl with much of it coming from unscrupulous dealers who harvest it from healthy redwoods on protected forestland. In some cases, removing burl can kill a tree or, at the very least, deface it and reduce its reproductive potential.
Burls can be planted under the appropriate conditions to allow the shoots to form roots and then grow into trees, but the typical buyer of a redwood burl places it in water, watches the shoots grow, then disposes of it after the shoots die from lack of nutrients. If you are determined to grow a redwood tree we suggest that you purchase a small seed-derived tree from a reputable nursery rather than trying to grow one from a burl that may have been acquired through questionable methods.”
According to the information here, it seems that by removing a burl, you may risk harming or killing the tree. You might want to contact a certified arborist in your area, and ask them what they recommend. Here is a link to the website of the Pacific Northwest chapter of the International Society of Arboriculture, where you can find lists of certified arborists.