Very nice, very realistic.
I only think that this rich, fertile kind of dirt you are reproducing here consists of a lot of things when you get close to it, fragments of plants,living roots, little amounts of sand, Insects if you want...
it won´t stay "clean" for a long time, something will start to grow in it sooner or later.
When you get that diversity, you got it!
Whatever mesocyclone used as dead trees
here
http://forums.planetside.co.uk/index.php?topic=5731.0would make some great roots, if you made it tiny and pale.
I am looking forward to what comes of this,
Best regards,
Jan