There are 3 construction activities that kill most trees. Builders cut roots when they trench or dig near the dripline of a tree. Digging cellar holes, septic systems or even grading a lot will cut roots and kill trees. When roots are eliminated, the tree is not able to draw the water and nutrients it needs. The tree becomes dehydrated and starts to die at the top of the tree crown. (From Preserving Trees During Construction)