I'm sure there are no trespassing laws in Wisconsin and after a few of them got caught, I'm sure they would learn the meaning of private property. If more police are needed in these areas to police the woods, so be it.
You know your other problem is you don't do enough research. Vang had already been arrested while hunting in Wisconin for trespassing. Yes there are trespassing laws and the shooter in this case was one who was arrested for trespassing.