For all developments on zoning lots immediately adjacent to the Staten Island Rapid Transit right-of-way, a building setback of at least 20 feet in depth, unobstructed from its lowest level to the sky, except as permitted herein, shall be provided along the lot line immediately adjacent to the right-of-way of such railroad. Such building setback shall be measured perpendicular to such lot line, as indicated on the District Map. Within such building setback area, unless the area is within a street or is waived according to the planting waiver provisions of paragraph (c) of Section 107-483 (Planting and screening for parking areas), there shall be provided one tree of three-inch caliper or more, pre-existing or newly planted, for each 400 square feet of such open area. Tree species shall be selected in accordance with Section 107-32 (Tree Requirements).