Here is the final. I'll probably render it bigger at some point in the future, but right now I want to move onto other projects. Overall, I'm pleased with how it all turned out. Thank you all for your comments along the way.
Tim, it's good to see another person from the PNW on here, cheers. The tree distribution is entirely doable in the free version of Terragen. The placement of the tree populations is controlled by a Surface layer shader which is limited by both slope, so the rock will show up, and altitude, so there are not tree sticking out of the water. The "tricky part" is setting fractal breakup fort he surface layer to something that looks reasonable, but that just requires some time messing with the fractal scale and a generous helping of hitting the random seed button. I'd be happy to give you a hand, just send me a PM and I'll do what I can to help.