Section 7. A person who without license willfully cuts down, carries away, girdles or otherwise destroys trees, timber, wood or underwood on the land of another shall be liable to the owner in tort for three times the amount of the damages assessed therefor; but if it is found that the defendant had good reason to believe that the land on which the trespass was committed was his own or that he was otherwise lawfully authorized to do the acts complained of, he shall be liable for single damages only.