Your Low-Poly Trees are nice and very useful.
The first picture looks very nice and sunny. There is friendly positive mood in it.
But in the seconde rendering the grass looks mutch to dark and "flat".
I recommend you for publictiy to make pictures with mutch more friendly, sunny and positive colors (no so mutch dark tones ! else it looks like warscenes from 3d-shooter games or an apocalypsescene).
Make the Grass green and give it some reflection (specular) and some sss to make it looks fresh and juicy
I hope I didn't offend you. I just wanna help you to improve things
Kind regards
Alain
Intel Pentium 2.8 GHz 2 Cores, 8 GB RAM, GeForce GTX Titan 8GB, Blender 2.72b, Win 7 64 Bit