Minimum open space. A land area equal to a minimum of 20% of the gross tract of land area proposed for a mixed planned residential development shall not be included in lots or other required improvements and shall be set aside for open space. Open space shall be so planned within the development that a close visual and physical relationship between the open space and as many dwelling units as is reasonably possible is created. Open space areas should weave between dwelling units generally respecting a minimum width of 50 feet and periodical widening out into significant and usable recreation areas. The configuration of the open space areas should be arranged so that connections can be made to existing or future adjacent open spaces and other community facilities. Land designated as open spaces shall include, wherever feasible, natural features such as streams, brooks, wooded areas, steep slopes and other natural features of scenic or conservation value. The developer may be required to plant trees or other similar landscaping improvements. Said improvements may include removal of dead or diseased trees, thinning of trees or other growth to encourage more desirable growth; removal of trees in areas planned for ponds, lakes or active recreational facilities; grading and seeding, and improvement or protection of the natural drainage system by the use of protective structures, stabilization measures and similar improvements. Portions of the open space should be developed to afford both passive and active recreational opportunities. Passive recreational activities may include but are not limited to pedestrian paths, sitting areas and naturally preserved areas. Active recreational areas may include but are not limited to such facilities as swimming pools, tennis courts, bicycle paths, and play fields. The size, location and type of all such recreational facilities shall be as approved by the reviewing board. The reviewing board shall provide opportunity for the Recreation Commission to review and comment upon all proposals for recreation areas and facilities prior to approving the same. Development of open space and recreational facilities shall proceed at the same rate as development of the dwelling units. To assure compliance with this requirement, the Building Inspector shall from time to time following the approval of a mixed planned residential development review building permits and shall make an inspection of open space and recreational facilities to examine work taking place on the site. If he shall determine that open space and recreational facilities are not being developed at the same rate as dwelling units, he shall report the same to the reviewing board, which body may recommend such action as it deems appropriate to the Township Council. Land under permanent bodies or flowing streams of water and preexisting tract development shall not be used in computing common open space. In any event, any area in a floodplain as designated by Federal, state or local authorities may be used only to 1/2 of its area in computing common open space. At least 10% of the gross area must be common open space other than floodplain. At least 5% of the gross area shall be common open space free of structures or other improvements.