Roots rarely grow below four feet although there are numerous cases stating the opposite. The major portion of a tree's root system is in the top few inches of soil. This makes it easier to understand why trees can be easily uplifted during wind storms or other soil disturbances. The main point to take home from this is that tree roots are extensive and are located in the upper few inches of soil. Broadcast fertilizers are very much available to the tree roots as are herbicides and other chemicals.
Soil compaction is one of the biggest problems a tree root can have.
Water and oxygen become unavailable when the pore spaces are closed. Avoid large grade changes during construction, both filling and removal. Avoid the use of plastic as a mulch or under mulches, use weed barriers that breathe. Many tree problems are accidental, by understanding more about the tree root system, these problems can be avoided. 1992 issue, pp.