From sprouts to split
March 23, 2010
Have you seen the split oak tree on Highway 49 near Pekolee Drive?
This tree has prompted a lot of questions since it came apart in a storm this winter.
Many oak trees are stump sprouts, growing off an old stump and root system of an oak tree that fell over, was cut down or burned in a fire. A good clue you’re looking at a stump sprout is there are multiple trunks coming from the base. From sprouts to split is the life of a stump sprout tree, and that is what happened to the tree you see there.
After the tree is reduced to a stump and roots, stored energy is used to grow sprouts and the tree is reborn. These new sprouts grow out of the newest outer layer of wood. The inner part of the stump and much of the root system dies of starvation due to lack of flow of nutrients.
The dead tissue then begins the inevitable natural recycling process of decay. The new sprouts grow vigorously and compete with each other for light, as well as attachment to the stump and roots. As the sprouts begin to produce energy, new roots start to grow from the surface and the ends of the remaining root system.
Over the years, a few of the sprouts become dominant and out-compete the others. The few remaining trunks continue to compete, often growing tall and skinny, with branches only on one side, and leaning away from each other.
Eventually, as the trunks grow in diameter each year, they cover the old stump and begin to press against each other. This bark-against-bark pressure kills the tissue in an ever increasing area between the trunks, called included bark.
As the trunks continue to grow up against each other, the wood at the point of connection only grows on the outside, leading to an increasingly asymmetrical and weak attachment between the trunks and the roots. Eventually, as this problem grows, the tree will split and the cycle will repeat itself.
What you can do for a stump sprout tree
When the sprouts are young, you can prune to improve the structure of the tree.
Pick one or a few sprouts that are best attached and vigorous to favor. Remove or reduce (cut back to a side branch) the remaining sprouts to give room to the favored ones.
This is best accomplished with a few prunings over the first 10 years. Never remove more than 25 percent of the live portion at one time.
Once the tree has formed trunks, it is better to reduce a trunk, and then remove it a few years later, once the rest of the tree has filled the space. With a little training when young, sprouts can grow up with better-attached trunks.
Once the trunks are big enough to require a chain saw for removal, the size of the cut in relationship to the rest of the tree must be considered. Large dominant trunks that form a significant part of the trees canopy should not be removed, as this will undermine the strength of the attachment of the remaining trunks.
Only small, declining or dead trunks should be removed at this point. Pruning of limbs off trunks by raising, thinning and reduction is still an option to improve the trees structure by favoring fewer, better attached trunks.
When the tree’s trunks have grown large enough to have formed included bark between them, avoid removing trunks. Pruning limbs can still improve tree structure and reduce the chances of failure.
At this point, if your goal is to preserve the tree, or if tree failure poses a hazard to people or property, then consider a cable system to reduce the chances of failure.
Fortunately, most people’s sprouts are somewhere in the middle of life. With proper care, you might be able to avoid splitting or at least put it off until the future.
Aero Acton is owner of Leaf it To Me Tree Service. He can be reached at (530) 477-9822 or e-mail firstname.lastname@example.org.