These soils are often shallow with little soil depth and often consist of subsoil material covered with less than 6 inches of top soil. Root growth will often be slowed by soil layers which are significantly different than the soil above or below. For example, a sandy surface soil on top of a compacted clay layer, may be excessively wet at times because of poor drainage and droughty during dry periods because of poor root penetration. These small roots are the primary water and nutrient absorbers. They are functional for only 1 to 3 years, and then either die or become part of the large root system.
Most trees replace at least one third of their feeder roots each year.
Tree roots do not penetrate soils to great depths. Most roots will concentrate in the top 6 to 18 inches of topsoil. Tree roots occupy a larger area than previously believed. They will often extend out from the trunk in an irregular area which is 4 to 7 times larger than the area of their crown. The surest method of minimizing damage to a root system or soil during construction is to do nothing around, in, or on top of a tree's root system.