Here are some notes I've made on the procedure image map use in EcoSystem. For the life of me, I couldn't get my Function Editor to look like the interface in the tutorial but I was able to get the same results. Here's some quick pointers to help ward off possible frustration when trying to follow the tutorials.
Everytime you make changes to any value regarding your Eco System, always hit the Populate key to effect the changes. Some changes require a render to see their effect.
Even though the color white is the highest value to populate plants, if your plant scale size is too high, a narrow white band will be devoid of growth. (In other words you can't force a giant redwood tree into a two foot strip :))
The tutorial suggests adding Mixed Materials after the EcoSystem. I add multiple materials before then add the EcoSystem. It's easier for me to see how the materials are effected by the image maps and I won't lose the EcoSystem settings.
Instead of using the same image map for each EcoSystem feature, I opted to use isolation maps based on the original map to target specific areas. This is more of a test on my part, but I was having one heck of time keying in the right filters to control the base image map. Using the isolation map has saved me some time.
Here's the images used to orient and color (their actual sizes are 1024x1024)
The map on the right helped to isolate the specific areas I wanted to affect. This saved me allot of time wrangling with the Function Editor. For the The level of grays you use in the isolation map really affects the outcome. That's when it's good to use the Function Editor to tweak the results to your liking.
Results using the base image map as described in the Tutorial
I can now isolate and define which trees are which colors in specific areas. Theoreticaly I could create batches of black and dark gray spots within the Isolation Map to further control color changes. The cool part is this using only one tree type. I could add another tree type to a different material and create a new EcoSystem.
EDIT: Use of Gausian Blur on the isolation map helps soften the rough edges in the circle. See image below.
My next tests will be on Density and Scaling and Orientation.