Russ, the left side of your picture I find extraordinary. The excellent detailed trees, exspecially the two on top of the hill, lead our eyes down into the valley, across the lake, to the mountains, and finally, that sky kicks in and dominates.
Tootles, it's all fake. There are about 4 million instances (what Terragen 2 calls trees or any other object) in the shot. When the the program is told to render an image, the 'trees' are all 'grown' together to create a seamless ecology. The plants can crowd each other very closely, depending on how you've spaced them, but don't overlap like in Bryce, leaving obvious intersections between branches, leaves, etc. Another very cool thing about Terragen 2 is it's crop function. Small pieces can be re-rendered as a patch for the original area, that way additional complexity can be added to the picture without having to re-render the entire image, which is very time consuming. I used that feature about six or seven times in this picture.
That Terragen 2 is really amazing Russ. I keep looking at your beautiful work, and....I'm gettin closer and closer to having to buy it. Amazing Work my Friend.