When the public interests will be benefited thereby, the Secretary of the Interior is authorized, in his discretion, to accept, on behalf of the United States, title to any land within exterior boundaries of Lassen Volcanic National Park which, in the opinion of the Director of the National Park Service, are chiefly valuable for forest or recreational and national-park purposes, and in exchange therefor may patent not to exceed an equal value of such national-park land within the exterior boundaries of said national park; or the Secretary of the Interior may authorize the grantor to cut and remove an equal value of timber in exchange therefor from certain designated areas within the exterior boundaries of said national park: , That such timber shall be cut and removed from such designated area in a manner that will not injure the national park for recreational purposes and under such forestry regulations as shall be stipulated, the values in each case to be determined by the Secretary of the Interior. Lands conveyed to the United States under this section shall, upon acceptance of title, become a part of Lassen Volcanic National Park.Provided