Here’s a tidbit from an interview he once gave:
I know it [nature] isn’t kind. As Matthew Arnold [a British poet] said: “Nature is cruel. It’s man that’s sick of blood.” And it doesn’t seem very sick of it. Nature is always more or less cruel. Shall I tell you what happened on the porch of a professor – minister he was, too? The war was going on, a beautiful moonlit night. He was there with some boys, talking about the horrors of war – how cruel men were to each other and how kind nature was, what a beautiful country this was spread beneath us, you know – moonlight on it. And just as he talked that way, spreading his arms over it, a bird began to shriek down in the woods – something had got into its nest. Nature was being cruel. The woods are killing each other anyway. That’s where the expression came from “a place in the sun.” A tree wanting a place in the sun it can’t get. The other trees won’t give it to it.