One of the more interesting comments I've received from my writers group lately is about the horror novel I'm working on, set in Civil War Missouri. The critiquer said, "If you want the landscape to be a character, then you need to describe it in more detail."
He's right, and until he said it I hadn't realized that my landscape is a major character. Missouri's Civil War was very different than most other regions'. The Union quickly conquered the state, but spent the rest of the war fighting bloody and determined bands of guerrillas. One of my main characters is a guerrilla leader, the other is a Union captain trying to hunt him down. They see Missouri's thick woodland in very different ways. The guerrilla lives in the woods. Its dense underbrush and hidden paths keep him safe. The captain, like the real Union troops from the real war, hates it. He can see barely fifty feet into it, and every time he tries to make it to the next town he's liable to receive a volley of gunfire erupting from the thick foliage crowding in on the road.
So I need to describe the forest and its creatures in as much detail as my human characters. This is something to keep in mind with all fiction, and a great deal of nonfiction as well. How does the terrain affect the story? How does it make the characters feel? How does it affect the way they act? What kind of atmosphere does it lend to the story? As writers, we have to remember that not all our characters are human.