You will often hear the virtues of proper tree planting depth. Trees that are planted to deep will often fail to thrive, appear stunted and not grow. However, this is not always the case. Many instances when a tree is planted to deep will have no outward signs of stress. How do you know if your tree is planted to deep? It will look like a telephone pole sticking out of the ground.
What I am drawing your attention to is called a root flare or buttress. This is a transition zone between root and stem tissue. Plant tissue above the flare is not designed to be buried in the ground. When buried it will be a continuous source of stress which over time will reduce the vigor of the tree and predispose it to other issues and could be a point of failure.
June 16th the Omaha Metro area was pounded by tornadoes and straight-line winds. Many trees that had all the outward appearances of being healthy failed to stand up to the wind. I was out and about taking pictures that Friday night and time and time again I kept seeing trees that were planted to deep snapped off at ground level. When a tree is planted to deep it is unable to stand up to some of our extreme environmental conditions.
Not every case of failure was due to improper planting. Even trees that were properly planted were still pushed out of the ground but they did not snap at the base. If you need to replace a tree after the storm take a few minutes to make sure that it isn’t planted to deep. Check out this diagram and article from the Nebraska Forest Service on how to properly plant trees: http://nfs.unl.edu/tree-planting
Planting depth makes all the difference on the success of a tree.