Comment posted Jan.9th, 2013, viewed 19 times
Your darks and background are not solid enough. I suspect they might look dark in reality but there are so many light patches and holes that make the background appear to look a lot lighter. The darks in this represent the extreme background shade, where no light is filtering into the dark wood, and what's principally missing are any areas of pure flat dark tone.
My suggestion was to leave patches of unrecognisable organic shapes in the background and then shade them so heavily they almost disappear. The eye will read them as unidentified background foliage and that will increase the perceived depth. But that only works if you have a sufficient plain black background to give them enough contrast to work. You can also cut those shapes later with a point of Blu-Tack.
As those mysterious organic shapes are meant to be read as distant foliage, it makes sense for them to only appear in the top half. In a dark forest, you'd expect the bottom half to be in very deep shade with virtually nothing showing at all. Just think "forest" and it all makes sense :o)
Your foreground and midground trees suffer a lot from having very soft and wooly edges. Soft edges belong to background elements. They eye expects to see sharp edges in the foreground and those sharp edges help it to understand that are in the foreground. If you strengthen the background darks, sharpen edges and adjust the midground tree, this will work much better for you. I think you'll be surprised how dark you can make those midground trees without them disappearing. Pushing them back into the shade will add even more mystery.
In response to image: