Symbolism, Imagery, Allegory
Old Ben might have been shot many times by many hunters, but he's managed to stay alive. His foot might be mangled, but he still evades the encroachment of civilization... er, we mean, the hunters. You guessed it, Old Ben is symbolic of the wilderness itself, which has been under attack by the plantation owners and hunters in the area.
Remember that time when Isaac wants to have a little date with Old Ben? He's already shot his first buck, been initiated into manhood by Sam Fathers and is getting to know his way around the wilderness. But he still doesn't get to meet Old Ben until he leaves behind everything that "taints" him:
He had already relinquished, of his will, because of his need, in humility and peace and without regret yet apparently that had not been enough, the leaving of the gun was not enough. He stood for a moment—a child, alien and lost in the green and soaring gloom of the markless wilderness. Then he relinquished completely to it. it was the watch and the compass. He was still tainted. He removed the linked chain of the one and the looped thong of the other from his overalls and hung them on a bush and leaned the stick beside them and entered it. (5.1.39)
Only in a pure and primitive state can a person truly experience the wilderness. One can't have an authentic encounter with several pounds of gear on, can one?
When Old Ben finally dies, the hunters seem to lose their spirit. Major de Spain ends up selling his land to the timber logging company, which then decimates the forest where the men have been hunting. Like Old Ben, the wilderness manages to hold out for a while, but finally, inevitably, it succumbs.