Overview:
By Karen Edgington
Each week, Signal Akron will help you in your gardening adventures with an excerpt from "The Root of It," a monthly newsletter from the Summit County Master Gardeners, Ohio State University Extension.
On a walk through an old-growth forest, a tree lover stopped to admire a stately, old maple. Her admiring glance swept up the broad trunk, but paused at the sight of a large, bark-covered growth on the upper trunk – a burl. What is that foreign-looking growth? Will we lose this tree? What can we treat it with?
While scientists are still working to understand the mechanics, they know that, like galls, burls are the result of a change – or “hijacking” – of the growth cells in the cambium region of the tree, the region where trees grow new xylem (water and mineral transport) and phloem (food transport) cells.
Burls are initiated by bacteria, viruses, insects, or fungi, or perhaps an injury to the tree trunk. The cause can be hard to detect – by the time the burl is formed, the culprit may be long gone. Burls can be compared to a slow-growing, benign tumor in a human. They grow as the tree grows, and can eventually reach several feet in diameter.
While a startling sight, burls are rarely lethal, and for the most part do not affect tree health or longevity. In most cases no intervention is recommended – the wound from their removal puts the tree at much greater risk than the burl itself. Burls can grow on any tree species – cherry, walnut, elm – but OSU Forestry Program Director Kathy Smith notes that she most often sees them on maples and oaks.
Woodworkers approach burls from another perspective, prizing burl wood for its interesting, contorted grain which may include “birds-eye wood” (wood from aborted adventitious buds – buds emerging in an abnormal location).
Local master woodturner, George Raeder, tells us that burls can be tricky to work with, but their swirling wood and voids can create extraordinary wood bowls and other pieces. He notes that you never know what the wood inside a burl will look like until you open it up, making woodworkers cautious about purchasing them. It’s a bit of a gamble: there may be beautiful, patterned grain inside or large voids and marginal wood.
Watching trees grow is one of the sweet rewards that accompany the passing of years. Burls grow with the mother tree, becoming more interesting and distinctive as they age. Observe and enjoy these mysterious structures on your hikes through woods or neighborhoods.
Look Around!