Lands which may be acquired under this chapter shall be such as by reason of quality, location, or condition are better adapted to public conservation, forestry, recreation, experimental, and demonstration purposes than for continued private ownership and development. Such acquisition shall be limited in total within the state to 2 percent of the total land area of the state, and shall be further limited in each town or city to an amount of land, the assessed valuation of which on April 1 of the preceding year was 5 percent of the total assessed valuation on such date of all the real estate in such town or city. The provisions of this chapter shall not limit the authority of the United States to acquire lands for the White Mountain National Forest within the boundaries established by proclamation of the president of the United States, dated October 26, 1929; and the limitations as to area and valuation contained in this section shall not apply to acquisitions within the boundaries of the existing White Mountain National Forest Purchase Unit, or any new national forest purchase units that may be recommended by the land use board and approved by the governor and council; nor shall such acquisitions be included in computing such limitations.