In "The Interlopers," the natural setting is everything because the entire conflict upon which the story is built is based on the rightful ownership of a feud between the von Gradwitz and Znaeym families.
The feud between the two families had been going on for generations, and it is therefore only natural that Ulrich and Georg hate each other. Hoping that the feud could end in a one-on-one altercation on the stormy night in question, von Gradwitz breaks away from the group he has come out with. As he had hoped, he soon comes across Znaeym, who is also alone.
Before either man can get the gumption to shoot, lightning strikes the tree above them and it falls, pinning both men to the ground. The fallen tree therefore plays a significant role in the story, because if it had not fallen, the conflict between the two men would have had an entirely different outcome.
As things stand, however, both are trapped and completely unable to move. Neither is seriously injured, and the two continue to bicker, both trying to convince the other that their party will be the first to arrive on the scene and rescue them.
As time goes on, however, being trapped under the fallen tree allows the men a chance to put their differences behind them, and they wind up becoming friends.
While the story does not have a happy ending, the natural setting and the fallen tree allow two lifelong enemies to set aside their differences.