No person shall do any excavating within two (2) feet of any tree or shrub on any street without the written permission of the Department of Public Works, and a permit from the State Department of Forests and Parks. Where in an authorized excavation it becomes necessary to expose or cut roots more than one (1) inch in diameter of a tree on any street, it shall be the duty of the contractor to protect such roots, under advice from the Department of Public Works. The contractor shall obtain a permit from the Department of Public Works, and obtain a permit from the State Department of Forests and Parks.