Nature is personified throughout this book and essentially becomes a character in its own right. Often metaphor and hyperbole are employed to much the same effect. Below are some examples.
I must have walked a mile into the woods until I found a stream. It was a clear athletic stream that rushed and ran and jumped and splashed.
In this first quotation, the stream is personified as "athletic," running and jumping like an excitable child. When the author personifies nature, in this example and others, she does so to reflect the mood of the narrator. It is, after all, a projection of the boy's own emotions that he imagines in the nature around him.
I must say this about that first fire. It was magic.... It cracked and snapped and smoked and filled the woods with brightness. It lighted the trees and made them warm and friendly. It stood tall and bright and held back the night.
In this second quotation, we have an example of hyperbole in the phrase "It...filled the woods with brightness." This is exaggeration because of course the light from the campfire cannot literally have illuminated the entire woods. There is also, in the final sentence, another example of personification. The fire is described as standing tall and "[holding] back the night." The fire is personified in this instance to show how the boy perceives it as a kind of guard or protector, looking after him and keeping him safe.
September blazed a trail into the mountains.
This third quotation is an example of a metaphor. The month of September does not literally set a trail of fire through the mountains, but describing its advance with this metaphor conveys the impression of the vibrant reds and oranges that the autumn brings, and also of the rapid movement of the squirrels and the chipmunks and the twittering birds.
Never, never have I seen such trees. They were giants—old, old giants. They must have begun when the world began.
In this fourth quotation, nature is again personified, this time as "old giants." This particular example of personification highlights how huge and also magical (giants usually exist, after all, in the realms of myths, legends, and fairy tales) nature seems from the perspective of the boy.