The land area which would otherwise be required for house lots, but which is not so used under the permitted lot size reduction provisions of this subsection, shall be devoted instead to contiguous common open space. The Township Committee may, at any time, upon the recommendation of the Township Planning Board or Board of Adjustment and Township Planner, accept the dedication of such open space or any interest therein for public use and maintenance, but such dedication shall not be required as a condition of the approval of the development.