Was just gonns sugest some thing like that, do a google for some ground images and use this as the base, then on the layers of vegitation (leaf's etc) use bump maps coupled with transparancy maps with these planes slightly higher than the ground (base plane), this should give it some depth.

Keep each of hte planes the same with some slight undulations (made using the artisan tool or sculpt poly tool)

YOu might suffer at render time but it will save you loads of polys.


Or if your not going too close to the floor, a simply image with the desaturated image as the bump might do it for you.