Natural vegetation, groundcover, stands of trees or shrubs existing prior to development of the site may be acceptable to meet the landscaping requirement. Areas which have been cleared of vegetation or groundcover prior to or during construction, and which are not otherwise developed, shall be landscaped with trees, shrubs and suitable groundcover. Suitable materials for groundcover are those which permit rainwater infiltration of the soil and may include sod, ivy, bark, noncompacted gravel and the like.