Raising the Grade. A treeUs roots extend diameterically from the main trunk and are equal to or one-half times more in length than the height of the tree. To function properly, roots must have an adequate supply of air and water. Earth fills placed over the root zone often upset this delicate balance causing injury or even death to a tree. It is difficult to ascertain how much fill soil a tree can tolerate before injury occurs.
Tolerance depends upon the tree species and the porosity of the fill soil.
Oak, sugar maple, beech, and hackberry are very susceptible to by heavy fills. Usually, when more than six inches of fill is placed over the root zone, it is advisable to construct a dry well around the truck of the tree. The well should be place far enough from the trunk to permit the tree to increase in diameter as it ages. For young tree, the well should be placed at least two feet or more from the trunk. Special precautionary measures will be necessary if the tree roots are to be covered by a deep fill 2 feet or more or a shallow fill of heavy soil which becomes compacted.