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Circling roots can mean unstable trees
Roots that circle next to or near the trunk were associated with numerous fallen trees.
The pine in the photo that fell on the building was planted many years ago. One huge root circled the trunk causing a trunk constriction. This inhibited the root system and root flare from developing properly on this side of the tree and appeared to cause decay in the center of the trunk.
This large pine above crushed the roof when it fell. Examination of the root system revealed a huge girdling root.
The root caused a large indentation in the trunk at the base of the tree. It also prohibited the root system from properly developing on this side of the tree.
I have seen this type of decay occur on other trees with circling roots. Trees with circling roots often blow over in the direction away from the circling root. The young elm in this street tree planting formed a circling root in the nursery container before it was planted. Sometimes trees become stressed from circling roots.
This American elm leaned badly following the hurricane. Examination of the root system showed that there was a one inch diameter circling root close to the trunk. This root formed in the nursery container before the tree was planted. The root should have been cut at planting so new roots would grow straight out away from the trunk to help stabilize the tree.
