The girdling root

This photo shows a tree root that is growing above ground and is wrapping around the base of a tree. This is not a normal occurrence for trees. Usually a tree will grow a girdling root or roots after improper planting by humans.

When planting a small sapling. it is necessary to dig the hole wide enough and deep enough to comfortably accept the root system. The rootball should be untangled just before planting. Sometimes a girdling root will grow because the tree was planted too deep and dirt or mulch was filled in around the lower trunk. A new root can grow out of the buried trunk and be unable to grow downward because of tree roots already there. This new root can grow around the trunk and cause a strangulation effect shortening the life of the tree.

In this case the tree is a large cottonwood tree I guess to be about 70 years old.