Section 3. The commissioner may, from time to time within the limits of appropriations made therefor, acquire for the commonwealth, by eminent domain under chapter seventy-nine or by purchase, lease or otherwise, any lands suitable for purposes of conservation or recreation lying outside of the urban parks district, and may lay out and maintain such lands for such purposes and erect and maintain such structures and other facilities thereon as may be necessary to render such lands reasonably available and accessible therefor; provided, however, that no land held in trust for public use shall be taken by eminent domain. The commissioner may, with the approval of the governor and council, sell or exchange any land acquired under this section which in his judgment can no longer be advantageously used for purposes of recreation or held for purposes of conservation. He may, with like approval, authorize the construction and maintenance, on any land under control of the department and outside the urban parks district, of towers, poles, wires, pipes, and structures necessary for the purpose of transmitting electric power or intelligence by electricity, and may grant an easement over such land for such purposes. He may, at any time, sell such wood, timber or other product of the lands controlled by the division as the economical management of said lands may require.