Section 25. The commissioners may, subject to appropriation, acquire by eminent domain, or by purchase or otherwise, the fee or other lesser interest in such real property within their respective counties as may be necessary to maintain, improve, protect, limit the future use of or otherwise conserve and properly utilize open spaces, and may control and manage the same; provided that such acquisition has been approved by the department of environmental management and the conservation committee of the city or town within which such land lies, or if such city or town has no conservation committee by a two thirds vote of the city council in the case of a city and by a two thirds vote of the board of selectmen in the case of a town. Land used for farming or agriculture, as defined in section one A of chapter one hundred and twenty-eight, shall not be taken by eminent domain under the authority of this section.