Landscaping. All portions of every multiple-family development which are not used for locations of buildings, structures, parking, circulation roadways, sidewalks, preserve areas or similar purposes shall be suitably landscaped and permanently maintained with plantings of trees and shrubbery, as approved by the Planning Board as part of the site plan, so as to minimize erosion and stormwater runoff and harmoniously blend such uses with the residential character of the development and neighborhood.