Also remember to up the scale of the foreground terrain. Another useful trick is to duplicate the foreground terrain, move it down in the y axis a little, change the texture to a contrasting one, edit the terrain and add a load of basic noise. The noise peaks will poke through the original terrain, looking like a load of pebbles or gravel. In this image, the pebbles are using this technique and have a matching texture to the stones that have been added as rocks....

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Toolset: Blender, GIMP, Indigo Render, LuxRender, TopMod, Knotplot, Ivy Gen, Plant Studio.