The resolution of the main conflict that leads to the story's ending has to do with man versus nature. Specifically, the climax of the novel occurs when, after many adventures, each a bit more dangerous than the next, Billy and his dogs take on their most dangerous, and ultimately their last journey together and it is resolved when the treed mountain lion nearly kills Billy. Little Ann comes through with only a non-fatal wound to her shoulder, but Old Dan cannot be saved; the theme of the love of a boy and his dogs is demonstrated in the most poignant way, as Old Dan essentially gives his life to save Billy.
Although the two novels are very different in many ways, the final journey of Billy and his dogs always reminds me a little of Scout and Jem's journey home at the end of "To Kill A Mockingbird". In "Mockingbird," of course, the antagonist is a drunk townsperson, rather than a wild animal (although readers of "Mockingbird" might argue that Bob Ewell was not far from being a wild animal himself). However, Scout and Jem's adventures through the summers lead the the climactic encounter with Bob, and Scout's ultimate coming of age as she discovers the truth about Boo Radley, much as Billy's coming of age occurs as he deals with the loss of his dog and experiences comfort through the red fern.