Root Trenching/Cutting

Roots may be lost directly when the soil surface near trees is lowered, or when trenches are dug for underground utilities, or for the construction of curbs, sidewalks, foundations, etc. (Figure 1) The roots that are left after trenching may be insufficient to supply the crown with nutrients and water. A tree so affected will be more subject to drought, have poor growth (shoot extension) and leaves may be smaller than usual and may be chlorotic. Eventually, the loss of root mass may be balanced by crown dieback and the tree may die prematurely. The loss of a substantial proportion of the root system may also affect the stability of the tree. Remember that there may be only between five and 10 major roots attached to the tree at the root collar. If one of these is severed, all roots beyond that point will be lost representing 10 to 20% of the root system.

Figure 2 shows the effects of excavation on tree roots. A tree's root system may extend two to three times beyond the width of the crown. Such unobstructed conditions are seldom achieved in the urban environment, so the extent of the perimeter of the crown (the drip-line) as a conservative estimate of the extent of the root system.