Although many other states have put adverse possession into their statutes, New Hampshire has not, and it is in case law – which is as authoritative and binding as statutory law - that you will find most of the elements that must be proven in court.
The elements of adverse possession are:
the use must be adverse (without permission and hostile to the owner’s interests);
it must be notorious (the owner has had notice of the use);
it must be continuous and uninterrupted; it must be exclusive (not in common with neighbors, or others),
and it must be for a period of at least 20 years as defined in the statute of limitations for the recovery of real property (see RSA 508:2, I).
Adverse possession applies only to private property, not to public lands, waters, highways or transmission lines
I read in another story that the hermit and the present owner’s father had made a deal so the hermit could live on the land for as long as he wanted. What the deal was, was never specified. The son was using the property as a retirement nest by selling lumber harvested from it. Everything was going well until the city stepped in and told the son that the hermit’s place had to have a septic system installed because it was so close to the river. They tried to tell the city it was a hunting and fishing camp, but that didn’t work. The son didn’t want to pay the cost to install the system, so the city started putting pressure on him. That’s when everything started going south. Had the city not poked their nose into this thing, the son would’ve just kept on with the way things were going. That’s what I got out of the story anyway. Could be wrong.