A buffer of not less than forty (40) feet in width shall be provided along any side or rear yard adjacent to a residential use or district. A buffer of not less than fifteen (15) feet in width shall be provided along any side or rear yard adjacent to a nonresidential district. Evergreen plant materials at least six (6) feet in height, so as to provide a year-round effective visual screen when viewed from the residential zone, or other suitable screen so approved by the Planning Board, shall be placed within the required buffer. If the required planting screen or other materials are set back from the industrial-residential boundary, then the portion between the residential district and the required screen shall be landscaped and maintained.