The Planning Board, as a condition of granting subdivision approval, shall require, unless good cause is shown for omission of same, the developer to encumber the larger tracts (the noncluster lots) by deed restrictions, conservation or agricultural easements, or other mechanism satisfactory to the Planning Board, to ensure that such parcels shall remain permanently as open space or agricultural land. For this purpose, land shall still be considered open space or agricultural land if used for the purposes set forth in § 270-26, Subsections A, B, C, D, E, H (provided the same are passive recreational areas), I and L.