Raising or lowering the grade of the root zone during construction injures plants. Lowering the grade removes part of the root system. Raising the grade decreases the movement of air and water into and out of the root zone. Piling soil deeply around the aboveground portions of the trunk can lead to rots.
The main symptom of a grade change is gradual decline and dieback. Dieback can occur quickly or take several years, depending on the severity of the root injury or altered root environment. At first only scattered dead branches are visible in the tree crown. These become more numerous each year until the tree finally dies. Other symptoms are poor growth, smaller than normal leaves and early fall color displays.
Little can be done to overcome the deleterious effects of grade changes. Whether a particular grade change will be injurious depends on the tree species involved and the type of fill. A few inches of clay fill is very harmful to oak, beech or dogwood.