For the background. Create a terrain (or duplicate an existing terrain). It should be at 2048x2048 size. Create the basic terrain that you want if you dont have one already, and duplicate it (you've already done this if you had one to begin with). At this stage, you should have two terrains that are the same shape and position. Choose one and move it 0.2 bryce units up so that it is slightly above the one below it. Select the lower terrain and enter the terraine editor. Drag the "spikes" button slightly to get some small spikes. Then drag the "basic noise" slider to get quite a bit of noise. Apply a green or grassy material to this terrain, and you should see grass poking out of the top terrain. To vary the density of the grass, move the terrains closer together or futher apart. Tada! For the closer grass, use bantam or some other meshes.