Changing grade influences tree growth because roots position themselves where moisture and aeration conditions are best. Any change that affects air movement in and out of the soil will ultimately affect the root system. For example, both flooding the ground for a prolonged period and compacting the soil restrict air movement and roots suffocate and die. Also, trees with damaged root systems are more susceptible to diseases and insect pests which hasten the decline process. Borers, other insect pests, and root rot move in and become established within a short time.
Builders sometimes stockpile soil on tree roots when digging a foundation.
Oxygen cannot diffuse to the roots a the new depth and the roots suffocate. Chemicals toxic to roots build up under such conditions. And, excessive fill disturbs the balance of soil microorganisms which help tree roots pick-up soil nutrients. Some trees, such as elms, willows, sycamores, and some of the oaks, can survive this abuse for a couple of months before declining, whereas species like maples, dogwoods, pines, tulip poplars, and beeches are unable to withstand any excess fill. However, most trees will tolerate some fill because the roots will gradually grow toward the surface.