After putting in the three largest trees first, I then added some grasses and growies to the base of them and created some rolling ground.
With a pencil, I lightly sketched in some smaller trees into the background with a few slightly larger ones and a number of smaller trees.

Next I inked in the larger background trees first.
Again I added in some grasses and growies to the base of the trees creating a small hill in the background.
I will post this drawing at a later date once more of the background trees have been completed.