What motivates Ulrich's change of heart, and does this change reflect internal or external conflict in "The Interlopers"?

Ulrich von Gradwitz's change of heart is motivated initially by his struggle against nature, which is an external conflict, and then by his conflict of conscience, an internal struggle.

While von Gradwitz is patrolling his coveted strip of woodland in search of the "poacher" Georg Znaeym, whose family has never accepted the court ruling that this land no longer belongs to them, Ulrich suddenly comes face-to-face with his mortal enemy. In that brief moment of civilized hesitation before shooting each other, a force of Nature creates an external conflict for the men when lightning strikes the huge beech tree under which they stand. Suddenly, they are pinioned beneath large, heavy branches.
While they lie victim to the force of the storm, each hurls curses at the other. Eventually, though, "[b]oth had now given up the useless struggle to free themselves from the mass of wood that held them down."

Ulrich struggles to free one arm enough to pull a flask of wine from his outer coat pocket. He decides to offer some of this wine to his foe, adding, "Let us drink, even if tonight one of us dies." Georg Znaeym refuses this offer. Nevertheless, Ulrich von Gradwitz further engages in his internal conflict as he places the feud into perspective with their life-and-death struggle in the coveted woods.

An idea was slowing forming in his brain. . . In the pain and languor that Ulrich himself was feeling, the old fierce hatred seemed to be dying down.

Finally, Ulrich von Gradwitz tells Georg Znaeym that he has been lying there thinking about their dispute, and he now realizes they both have been rather foolish because there are much better goals in life than to win a boundary dispute. He proposes,

"Neighbor, if you will help me to bury the old quarrel, I—I will ask you to be my friend."

After a long silence in which Znaeym ponders this proposal, Georg agrees, chuckling at how the people in the region would stare if the two men should ride into the market together after all the years of their animosity. Thus, their internal conflicts are resolved. Unfortunately, the external one with the forces of nature is lost when, rather than either of their hunting parties arriving, their shouts have beckoned other "interlopers": roaming wolves.