Along any adjacent properties, landscape planting of trees and shrubs shall be provided for a depth of at least 15 feet. The amount, density of planting, and types of plant materials uses shall be dependent upon existing conditions, proximity to existing dwellings, compatibility of adjacent uses, and any other pertinent considerations. Where adjacent property has been developed in such a manner that privacy from the development is desirable, the planting shall be of sufficient density and contain sufficient evergreen material to provide an effective visual screen. In other areas, particularly where vegetation already exists, the planting area must be left in its natural state or supplemented as necessary.