The Secretary of Agriculture, in conformity with regulations prescribed by him, may permit the use and occupancy of national-forest lands in Alaska for purposes of residence, recreation, public convenience, education, industry, agriculture, and commerce, not incompatible with the best use and management of the national forests, for such periods as may be warranted but not exceeding thirty years and of such areas as may be necessary but not exceeding eighty acres, and after such permits have been issued and so long as they continue in full force and effect the lands therein described shall not be subject to location, entry, or appropriation, under the public land laws or mining laws, or to disposition under the mineral leasing laws: , That nothing contained in this section shall prevent the said Secretary from canceling, revoking, or otherwise terminating a permit so issued upon proof of a breach of its terms and conditions or for other just cause.Provided