Section 25. Except as provided in section twenty-four, every forest warden shall have sole charge of the extinguishment of forest fires in his city or town. He shall investigate the causes and extent of forest fires and the injury done thereby, and shall report thereon to the forester at such times and in such form as he requires. Every forest warden shall also post in suitable places in the town such warnings against the setting of forest fires and statements of law relating thereto as may be supplied to him by the forester. The engineers or other officers in charge of fire departments in cities, towns and fire districts which have so voted shall perform the duties and exercise the powers of forest wardens with respect to forest fires.