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. Construct a sturdy fence at least at the outer dripline of the tree or trees to be saved and allow zero activity within this area. The larger the area of zero activity around the tree, the less damage. The more this zone is violated by construction activities, the more the tree may be damaged.