What type of conflict occurs when the wolves are spotted approaching the two trapped men?
This confrontation between the men and the wolves is a life and death conflict. But in literary analysis, this would be called a conflict of Man (humans) versus Nature.
Initially, this story centers upon a conflict of Man versus Man. George and Ulrich fight over a piece of land. This feud has been passed on to them through previous generations of their respective families. Ulrich's family technically owns it but Georg continues to raid/hunt on this piece of land. When the men meet in the woods, neither can bring himself to kill the other. The code of civilized humanity prevents them. But Nature is indifferent:
And before the moment of hesitation had given way to action, a deed of Nature’s own violence overwhelmed them both. A fierce shriek of the storm had been answered by a splitting crash over their heads, and ere they could leap aside, a mass of falling beech tree had thundered down on them.
A random act of nature pins them underneath the tree. During this imprisonment, the two men put the old feud to rest and thus, the conflict of man versus man is resolved. But they are still pinned, so the conflict of man/men versus nature continues. When the wolves appear, this conflict intensifies. The wolves represent nature just as the lightning and the tree do. Ulrich and Georg had fighting over land. Their initial 'man versus man' conflict seems even more trivial and pointless when they are faced against the indifference of nature itself.