I see two problems that should be resolved to make it look more convincing, the roots and and the tree's shadow.
You can see the shadow from your hand that the actual light source caused, it makes the outter fingers and part of your left palm a few shades darker as a normal shadow would. The tree's shadow however is just black, as if its shadow is somehow consuming all light, which is just not realistic. It needs to be represented with the same values as the current shadow that the light source is making. Take a ball and put it in your hand near a similar light course, the ball will not have a black shadow, it will be similar to the shadows represented in the original photo.
Second, the roots. The will need to have the appearance of being on your fingers not hovering above them, you can do this by again using the shadows and light already cast on the fingers. It is safe to assume that the roots would have close to the same shadowing and in the same areas due to the nature of dirt. To make it more convincing you will need to shape the roots around that look giving them the same curves/bumps as your fingers, then adding some volume is places that roots would be flowing through.
There are other problems but they are minor IMO to the two that I pointed out, and I feel fixing the two problems will improve this 100%.
Keep going with it, gl!
This post was edited by Tetu_880 on Aug 11 2012 04:43am