Thanks Dune there were a lot of first in this scene; first time using L3DT to make a heightfield, first time using an external heightfield in Terragen, first time to get a population to work and go where I tried to put it, and the first time actually using color shaders to color the terrain and rock, up until now I had been creating image map shaders using textures I made in TextureMaker 3 using photographs of real rocks, grass, bark etc..
I will give your suggestion a try when I get home from work. I had a hard time getting the pops to take when I first opened the heightfield in T4 Beta. It may have been because the terrain was kind of a happy accident. I made a terraced terrain in L3DT and tried to make Butes, Mesas, and Plateaus, but when I opened it in T4 the features were almost non existent and it had a huge upward curve like a giant mound. Erode did not give me the effect I wanted as it actually erased the features I was trying to highlight. I saw the Heightfield Curve Vertical operator, never used it before, and gave it a try with the alternative curve checked and went pretty heavy on the glaciation and the Top of Curve set to 5000 and this was the result. I saved a .ter file, started a new project and did a heightfield load and the grass clump pop worked.
I checked out your web page, wow! You have some serious skills in many art disciplines, awesome work.