Looking at the image, the parent material is grayish, which is what is exposed on the trail. The soil is browny with a reddish (oxide tone). You won't see much of the former exposed, while the veg will be underlain by the latter.
The understory could be done with a scattering of coarse foam over a base fine foam cover. If you want static grass, it looks very grassy with occasional bushes. Supertrees fragments with leaf flock make decent low bushes with good texture.
The trees are more challenging, but with so many trunks you could install a lot of these with only a few with actual canopy to give the dense look. These deciduous trees (and most trees) don't look like Super Trees stems, but they might do. A mixed forest like this will have a lot of snags (dead trees).
The pines? Looks like a white pine to me but all long needle pines kind of look similar. I would start with a wire form to get the main branche shapes and flock it with appropriate coarse foam. There was also a technique for these that goes back decades in MR using I *think* trimmed golden rod seed pod stems. It looked great in the pictures, might be OK here as a background pine.
Just some suggestions. Looks a lot like any sub-mature eastern mixed forest.
