For all types of digging operations, cleanly cut exposed or severed roots to promote rapid wound closure. Vibratory plows and chain trenchers leave cleaner cuts than bulldozers and backhoes. When working inside the dripline, use only hand tools. Instead of trenching, tunnel under the root system when it is necessary to work inside the dripline. Minimize the impact of root severing by avoiding construction during hot, dry weather, keeping trees well watered before and after digging and covering exposed roots with soil or mulch as soon as possible.
Smothered roots have their oxygen supply cut off.
The most common method of smothering roots is through changing the grade, that is, adding more topsoil or fill dirt to the existing contour of the area. This cuts off the water supply, too. For some tree species, like red oak, only a few inches of fill is enough to do serious damage. If the tree is already showing symptoms of advanced decline, it probably cannot be saved. If it appears mostly healthy and there is more than ten inches of fill anywhere inside the dripline, restore the area to its original contour by removal of all the fill.