No person, firm or corporation shall hereafter, without written permit from the Director of Public Works, place or maintain upon the ground in any public right-of-way of the City stone, cement or other material without leaving an open space of ground around the trunk of any tree, in accordance with standard specifications approved by the Director of Public Works; and whenever there is no such open space around any existing trees in any public right-of-way of the City, the Director of Public Works may make such open space or cause the same to be made. (Ord. 1205 § 2, 1969; prior code § 27.814).