Quantity of landscaping. A minimum of one planting unit shall be provided for every 2,500 square feet, or portion thereof, of nonresidential building coverage proposed after the effective date of this section. A minimum of one planting unit shall be provided for every residential dwelling unit (excluding single-family detached dwellings) proposed after the effective date of this section. These quantities shall be in addition to any other plantings required in other sections of this chapter.