If increasing the grade where trees are present is absolutely necessary, the approach to minimizing the impact of the fill on the trees varies, depending on the depth of fill applied. No More Than Four Inches Deep. Few species will tolerate fill of even a few inches placed against the main trunk. Besides reducing air exchange, such fill creates an environment conducive to the development of diseases such as the crown rots. Where there is a question about the likelihood of a tree tolerating a planned fill, a certified arborist should certainly be consulted before the grading begins.
Several practices can minimize the impact of shallow fill.
Whenever possible, fill should be coarser textured than the existing soil to facilitate water and air movement into and through the soil. Fill should be kept several feet away from the main stem of the tree and graded out to the desired depth. Under no circumstance should fill be placed against the trunk of the tree. And finally, grading within the tree's dripline area should drain away from the tree, or drainage should be directed away from the main stem by a berm. Few trees can confidently be predicted to thrive or even survive if more than four inches of fill are placed directly over their roots.