It is possible that someone could walk up to a tree you have been contemplating for hours on end, plant himself over your shoulder and take a photograph that is as "meaningful" as the one you happen to snap at that moment. Possible, but not probable. The more you study your subject, the more aware you become of its subtleties, which can influence your resulting photograph in many ways.
Furthermore, contemplation of "trees" (if that is your subject, or fences, mountains, rocks, etc.) can give you insight into how that subject speaks to you, and how that subject can speak through your lens. You needn't consider a particular tree, nor even actually be present to consider it. You can let your mind explore the trees you have known and/or imagined. You can contemplate what draws you to the subject, what you find appealing, what you hope to catch in your lens. This can give you insight into how to approach your subject when you encounter it, camera in hand.
Before you dismiss this as just so much hooey, consider that unless you are one of those fortunate persons who can take a flawless photograph by chance, understanding your subject is a vital step towards knowing how to photograph it.