That 90%
of a tree root system can be found
in the top 18 inches of soil. That's why
doing any construction, even light construction, near a tree can
be extremely hazardous to its health.
When a tree grows, it grows from the top and
the sides. A branch emerging from the trunk at a point three feet from the ground
when the tree is five feet tall will still be three feet from the ground when
the tree is 40 feet tall.