Depending on the scene, Vulcan, you can use primitve objects for simple trees as well. These objects are merely spikes on a terrain poking through another, landmass terrain. Random placement, nearly. But you can control their height (distance from the top edge of the "trees" terrain and the top edge of the "land" terrain). You can also control where they start vertically with both the scale and the clipping bracket in the Terrain Editor, which lops off the bottom so they start higher "up" on the land-terrain... Just some ideas for you!