1st pic: i'm wondering if the picture will leave a stronger impression if the tree is right smack in the middle? (yeah, break the 'old thirds rule'... someone else just clued me in on that, i'm only passing on the message)
2nd pic: nice moody atmosphere, but probably you can crop the foreground and let more sky into the picture. try using wide angle lens to sort of dwarf the buildings in the background, cos as it is they're stealing attention away from the tree.