Sure thing Diamond:
All of this is done in Photoshop, so if you have gimp or something hopefully you can figure out how to convert it =D
3 layers are used, 2 with textures one a color augmenter.
1. Top layer is a fill color of 6f8463 Put on the layers blend mode to Hard light
2. Middle Layer is the actual Forest Texture of it all, use the Forest Texture Image (the darker green one Image #2). put a layer style on it with these clicked on Shadow Drop, Size & Distance 2 and opacity 100%. Bevel and Emboss 150 depth, size 4, highlight mode Soft Light 100% opacity, Shadow mode Overylay 100% opacity. a Contour, just left default, also a Texture using one of photoshops own patterns called Granite, I set scale to 30, depth +100% (that might be default...) And lastly a Color Overlay with a color of 3cb878 blend mode set to Color 80% opacity. Now set the layer blend mode to hard light
3. Bottom Layer, I use a texture called Ground Dry Moss I think Genetica produced it. Anyways I uploaded it here, called Under Forest, (Image #1) Now apply a layer style again, and this time just a Pattern Overlay blend mode Color Burn, opacity 50% and use the Granite Pattern again, set scale to 30%. Now set layers blend mode to soft light 80%
That should do it as for whats really needed. I use layer masks to create the middle layer, and just do a selection and go and color the same selection of the forest layer mask to the other 2 layers (above and below it) so in reality I'm just coloring on one layer mask and coping that same layer mask over to the other 2 layers.
As for how I actually "painted" them on, I used some old grundge brushes that are around 300px size, they were I think once called a "Dust Grundge Brush" cause its a very low pressure brush (meaning its a very low opacity brush as it is, with spotted 100% opacity areas in the brush)
Edit: I added an example of the kind of brush, heck can just use that brush. (its in a .psd file, all you have to do is add it to a brush preset) and added the granite texture