The colours are really good. I like the sharp line between the ground and the sky on the left and in the middle.
However, the purple-ish haze in the bakground behind the trees breaks it up, and is quite distracting. I say either spread that hazyness out all the way to the top (maybe letting it intrude just a bit into the bright left), and put in more trees as to make it appear more as a dark, dense forest (maybe only letting the orange light break through as a couple of rays).
Consider the proportions of the leftmost branch in relation to the trunk. It's quite hefty, almost as thick as the trunk. Yet it appears to be very short, as it's suddenly cut off by a rather small cluster of leaves. Realistically, such a branch would go farther than the point were the leaves at the left currently end, I think.
I hope I'm making sense.
