The service to be performed under this Division shall be the maintenance of all publicly-owned greenbelt areas and all landscaped areas within publicly owned greenbelt areas and all landscaped areas within public rights of way; provided, that the City shall not be required to provide any service which exceeds in cost the funds collected from Skyline Service District No. 1 in any one fiscal year, and the City shall not be relieved of its obligation to perform services to the district which are normal and customary in other residential areas of the City. The term “maintenance” as used in this Section shall include planting, replanting, trimming and removal of trees and shrubs; watering, spraying and fertilization; cost of labor, plants and materials used; removal of trash and refuse; repair of decorative and retaining walls; cost of City equipment operation; cost of maintaining a water system to landscaped areas; and all other costs reasonable or necessary to carry out the maintenance of greenbelt and landscaped areas.