A buffer as applied in this article is an area set aside for the purpose of reducing the impact of commercial, industrial or parking activities on residential areas. A buffer shall consist of hedges, shrubs, trees, fencing and other landscape materials alone or in combination. Plant materials in the buffer area shall be of a type which provides a year-round visual screen at least six feet high at planting. Staggered rows of shrubs may be used, where appropriate, to achieve the desired effect. Suitable plant materials include but are not limited to evergreens such as white pine, Austrian pine, Canadian hemlock, arborvitae, upright yews, California privet, tall hedge, buckthorn or dark American arborvitae. All plant materials shall be of nursery quality, balled and burlapped. Buffer areas shall not be used for building, parking or storage of any kind and shall be suitably maintained.