Open space: A minimum of 40% of the gross tract acreage shall be in vegetative open space, which may include the required front yard planting area. A portion of this open space, in an amount deemed appropriate by the Borough Council, shall be designated and developed for recreation purposes usable by the anticipated residents, including but not limited to playgrounds and tot-lots. The open space also shall be designed, where appropriate, to incorporate and preserve significant natural features, such as tree stands, specimen trees or stream valleys.