I've started working on a wallpaper for the Linux distro I run and I've hit a bit of a roadblock. I'm happy with the sky, the pond looks amazing... but the grass still looks video game-y and I haven't even touched the tree yet. I'm posting it in the hopes somebody can give me some ideas on how to proceed. I'd like to get as close to photorealistic as I can. But I want to avoid using textures or custom brushes.
I do have a method I think will work for the leaves of the tree. I've used it before with some success and I think I can improve it with some tweaking. But the bark has me drawing a blank. I don't want to simply cut&paste a texture into the general shape I have already.
The grass looks okay except that it's still a bit too 8-bit for my liking. And I'd like to add a decent looking treeline at the horizon rather than simply having the grass run up to the edge.
There are other details yet to be worked in. I need to add the tree's reflection in the pond and possibly a faint shadow on the ground. And there's always the option of adding something to the sky for further visual interest. The empty space to the left is deliberate... that keeps icons from being crowded out by wallpaper detail.
Anyhow, I'd be grateful if somebody could point me towards tutorials, filters, scripts, or whatever may help me finish this piece. I'm also keen to hear what I may have missed or not thought of yet. I'm sure there's room for improvement in what I've already done.

_________________
Just a short while ago I was a complete idiot when it comes to GIMP. Today, after many hours of practice, reading, and watching tutorials, I am proud to say I am an incomplete idiot.