So the landowner is 86 but nothing has stopped him from cutting timber every 10 to 20 years so why worry about an 81 year old guy living on the land. He is causing no hard, make him the game warden for the property and leave him alone.
Actually, if the squatter has been cutting his own firewood, it’s like from trees on the property he didn’t own.
In that event, since the landowner was harvesting trees as income from the property, then the squatter was actually taking some of his potential profits.