No person shall place or maintain upon the ground in any public place any stone, concrete or other impervious material or substance in such manner as may obstruct the tree access of air and water upon the roots of any tree upon any public place without first obtaining a written permit from the City to do so. Unless otherwise provided for in such permit there shall be maintained about the base of the trunk of each tree at least nine (9) square feet of open ground for a tree three (3) inches in diameter and for every two (2) inches of increase of such diameter there shall be an increase of at least one (1) square foot of open ground.
(1943 R.O., Ch. II, Art. J.)