The owner or agent of the abutting property shall keep the trees overhanging any public right-of-way trimmed so that all branches will be at least 15 feet above the surface of the street and eight feet above the sidewalks. If the abutting property owner fails to trim the trees as required in this chapter, the City will cause to have the trees trimmed and the costs will be assessed against the property as provided for in Section 155.07.