Within the inland sector established by section 460z-2 of this title the Secretary may acquire the following classes of property only with the consent of the owner:

(a) improved property as hereinafter defined;

(b) property used for commercial or industrial purposes if such commercial or industrial purposes are the same such purposes for which the property was being used on December 31, 1970, or such commercial or industrial purposes have been certified by the Secretary or his designee as compatible with or furthering the purposes of this subchapter;

(c) timberlands under sustained yield management so long as the Secretary determines that such management is being conducted in accordance with standards for timber production, including but not limited to harvesting reforestation, and debris cleanup, not less stringent than management standards imposed by the Secretary on comparable national forest lands: Provided, That the Secretary may acquire such lands or interests therein without the consent of the owner if he determines that such lands or interests are essential for recreation use or for access to or protection of recreation developments within the purposes of this subchapter. In any acquisition of such lands or interests the Secretary shall, to the extent practicable, minimize the impact of such acquisition on access to or the reasonable economic use for sustained yield forestry of adjoining lands not acquired; and

(d) property used on December 31, 1970, primarily for private, noncommercial recreational purposes if any improvements made to such property after said date are certified by the Secretary of Agriculture or his designee as compatible with the purposes of this subchapter.