No person, firm or corporation shall interfere, cause, authorize or procure any interference with the Director of Public Properties, or any of his or her employees, agents or servants, while they are engaged in and about the planting, cultivating, mulching, pruning, spraying or removing of any tree in any public highway within the City, or in removing any device attached to a tree or in such removing of stone, cement, sidewalk or other material or substance as may be necessary for the protection and care of any such tree in accordance with the requirements set forth in Section 509.06, as to the area of open ground to be maintained about the base of the trunk of each shade tree in the public highways of the City.