Trees or shrubs bordering on any street on public or private property shall be trimmed to a sufficient height to allow free passage of pedestrians and vehicular travel, and so as not to obstruct or shade the street lights, the vision of traffic signs or the view of any street intersection. The minimum clearance of any overhanging portion of such trees or shrubs shall be nine (9) feet over sidewalks and fifteen (15) feet over all streets. When the Forester finds it necessary to order obstructing trees or shrubs on private property to be trimmed, the Forester shall cause a written notice to be served on the property owner requiring such trees or shrubs to be trimmed to the minimum height set out in this section within thirty (30) days after receipt thereof. Such notice shall be served by mailing a copy thereof by certified mail to the last known address of the property owner. If the Forester is unable to secure such notice on the property owner, it may be served on the occupant or person in charge of the property in the same manner. When the person to whom the notice is directed fails to comply therewith within the specified time, the Forester shall trim or cause to be trimmed such trees or shrubs. The exact cost of such work, plus an administrative fee, shall be certified by the Clerk to the County Treasurer for collection with and in the same manner as general property taxes. When the Forester finds it necessary to trim or cause to be trimmed trees and shrubs on public property, such trees and shrubs shall be trimmed to the minimum height set out in this section.