If upon trial of such action it shall appear that the trespass was casual or involuntary, or that the defendant had probable cause to believe that the land on which such trespass was committed was his or her own, or that of the person in whose service or by whose direction the act was done, or that such tree or timber was taken from uninclosed [unenclosed] woodlands, for the purpose of repairing any public highway or bridge upon the land or adjoining it, judgment shall only be given for single damages.