Make a new layer above all the other layers and title it “bark”.

Using a size 18 brush set to 44% opacity draw multiple thin lines running vertically up and down the trunks. By using a light hand and making shaky, wavy lines that occasionally touch or cross over will give the impression of tree bark.

Now make a new layer beneath the “bark” and “outline” layers, and title it “trunk detail”.

Highlight the bark with color #895522 and a size 86 pixel brush set to 44% opacity (hard edged).

Make a new layer above all the other layers, and title it “root grass”.
This layer is going to incorporate the trees into the grass.

Make the impression of short grass growing around the base of the trees and their roots with color #32590D, and a size 25 pixel opaque brush.
(You may want to use a size 11 pixel brush for the grass around the base of the “beech” tree.)

Highlight the grass with color #588FOA and the same brush as before.

And you are done with the foreground! The last part to complete is the characters, animals, and optional detailing.