Hello there i would like to share with you my forest rendering. I needed something for my doors to cover them so i rendered an 6339x9961px image, with Full Sample render just to give it a try. Now I know, it could be done with much less samples. general render samples value was 300. Firstly i rendered all daylight animation, and choose this one to rendered full scale. There is only one tree model (sapling addon), terrain mesh (ANT Landscape generator addon), and one grass model (10cm radius of grass). Tree material is fully procedural, and quite nice generated. The color vary betwen tree location, but also, depends distance from tree center. Later if there is interest i will post the materials, and scene.
Here is also full size render if anyone like to print it somewhere (please, let me know or sent me the photo of the print :D) Full Size Render
There is also an animation:
Ok then. I used ANT Landscape generator addon for terrain, for the shadow variery for animation.
Always usefull is Sun Position Addon, which works perfectly.
For the leaves color variation I used this material:
This “From Dupli” checkbox is quite important. When checked it uses texture space from particle base mesh. When unchecked it uses texture space only from the object.
Now I know, it could be done with much less samples. general render samples value was 300. Firstly i rendered all daylight animation, and choose this one to rendered full scale. 
the animation looks really cool