I'm spending a good deal of time with Carlson's Guide to Landscape Painting by John F. Carlson. It's probably one of the most eye-opening and thought-provoking books in my library.
From Chapter 9. Trees:
"Know your trees, their nature, their growth, their movement; understand that they are conscious, living things, with tribulations and desires not wholly disassociated from your own. Emerson has beautifully named trees, "rooted men." In many ways they excel man."
"Every tree is a "personality," and possesses, within the limits of its species, a tremendous latitude of expression. Its branches do not, could not, and should not, stick into its sides in a brittle way, as though a hole had previously been bored to let them in. A tree is a highly organized entity, which, when functioning within its realm, becomes beautiful."