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Thursday, October 20, 2016

My Tree Trunk Is Dying from the Inside to the Outside

Q. What’s wrong with my tree? The tree trunk is dying from the inside to the outside.

A. The vast majority of trees are dead in the center of their trunk as they get older. This dead interior gets larger and larger as the tree gets older.The dead inside of the tree is covered by a thin layer that is living. This living thin layer is constantly getting bigger and bigger in diameter. To the inside of this thin layer, the dead wood is left behind. This occupies the vast majority of the center of the tree.
Living part of the tree on the outside of the trunk growing over the dead inner portion of the tree
            The only living part of the tree is a cylinder of living wood just below the bark. The living cylinder of wood can heal itself. The center part of the tree, which is dead, cannot. If this cylinder of living wood is damaged and the dead center of trunk is exposed, it can become infected. About 90% of the time this infection cannot spread to the living cylinder of the tree.This is because these infections only feed off of dead wood, not living tissue.

The only living portion of this tree trunk is the green cylinder close to the bark
            The dead interior of the tree rots. The living cylinder stays healthy. The dead center rots away leaving the center of the tree hollow. A tree like this can live for decades with the center of the tree gone or rotted. But the strength of the tree is compromised. It is more likely to be damaged during heavy winds that cause "shearing" damage. Hollow cylinders have good "compressive strength", but poor "shear strength",
Here is the trunk of a Chinaberry tree. It has been damaged enough to expose the dead inside of the tree.
            Normally, we don't pay much attention if the center of the tree is rotting. We get concerned when the living cylinder becomes infected. From the pictures you sent, it looks like the dead interior is under attack. To me, this appears to be normal for a tree which has its center rotting out.

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